// File: contracts/pools/IlluviumCorePool.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.8.1;

import "./IlluviumPoolBase.sol";

/**
 * @title Illuvium Core Pool
 *
 * @notice Core pools represent permanent pools like ILV or ILV/ETH Pair pool,
 *      core pools allow staking for arbitrary periods of time up to 1 year
 *
 * @dev See IlluviumPoolBase for more details
 *
 * @author Pedro Bergamini, reviewed by Basil Gorin
 */
contract IlluviumCorePool is IlluviumPoolBase {
    /// @dev Flag indicating pool type, false means "core pool"
    bool public constant override isFlashPool = false;

    /// @dev Link to deployed IlluviumVault instance
    address public vault;

    /// @dev Used to calculate vault rewards
    /// @dev This value is different from "reward per token" used in locked pool
    /// @dev Note: stakes are different in duration and "weight" reflects that
    uint256 public vaultRewardsPerWeight;

    /// @dev Pool tokens value available in the pool;
    ///      pool token examples are ILV (ILV core pool) or ILV/ETH pair (LP core pool)
    /// @dev For LP core pool this value doesnt' count for ILV tokens received as Vault rewards
    ///      while for ILV core pool it does count for such tokens as well
    uint256 public poolTokenReserve;

    /**
     * @dev Fired in receiveVaultRewards()
     *
     * @param _by an address that sent the rewards, always a vault
     * @param amount amount of tokens received
     */
    event VaultRewardsReceived(address indexed _by, uint256 amount);

    /**
     * @dev Fired in _processVaultRewards() and dependent functions, like processRewards()
     *
     * @param _by an address which executed the function
     * @param _to an address which received a reward
     * @param amount amount of reward received
     */
    event VaultRewardsClaimed(address indexed _by, address indexed _to, uint256 amount);

    /**
     * @dev Fired in setVault()
     *
     * @param _by an address which executed the function, always a factory owner
     */
    event VaultUpdated(address indexed _by, address _fromVal, address _toVal);

    /**
     * @dev Creates/deploys an instance of the core pool
     *
     * @param _ilv ILV ERC20 Token IlluviumERC20 address
     * @param _silv sILV ERC20 Token EscrowedIlluviumERC20 address
     * @param _factory Pool factory IlluviumPoolFactory instance/address
     * @param _poolToken token the pool operates on, for example ILV or ILV/ETH pair
     * @param _initBlock initial block used to calculate the rewards
     * @param _weight number representing a weight of the pool, actual weight fraction
     *      is calculated as that number divided by the total pools weight and doesn't exceed one
     */
    constructor(
        address _ilv,
        address _silv,
        IlluviumPoolFactory _factory,
        address _poolToken,
        uint64 _initBlock,
        uint32 _weight
    ) IlluviumPoolBase(_ilv, _silv, _factory, _poolToken, _initBlock, _weight) {}

    /**
     * @notice Calculates current vault rewards value available for address specified
     *
     * @dev Performs calculations based on current smart contract state only,
     *      not taking into account any additional time/blocks which might have passed
     *
     * @param _staker an address to calculate vault rewards value for
     * @return pending calculated vault reward value for the given address
     */
    function pendingVaultRewards(address _staker) public view returns (uint256 pending) {
        User memory user = users[_staker];

        return weightToReward(user.totalWeight, vaultRewardsPerWeight) - user.subVaultRewards;
    }

    /**
     * @dev Executed only by the factory owner to Set the vault
     *
     * @param _vault an address of deployed IlluviumVault instance
     */
    function setVault(address _vault) external {
        // verify function is executed by the factory owner
        require(factory.owner() == msg.sender, "access denied");

        // verify input is set
        require(_vault != address(0), "zero input");

        // emit an event
        emit VaultUpdated(msg.sender, vault, _vault);

        // update vault address
        vault = _vault;
    }

    /**
     * @dev Executed by the vault to transfer vault rewards ILV from the vault
     *      into the pool
     *
     * @dev This function is executed only for ILV core pools
     *
     * @param _rewardsAmount amount of ILV rewards to transfer into the pool
     */
    function receiveVaultRewards(uint256 _rewardsAmount) external {
        require(msg.sender == vault, "access denied");
        // return silently if there is no reward to receive
        if (_rewardsAmount == 0) {
            return;
        }
        require(usersLockingWeight > 0, "zero locking weight");

        transferIlvFrom(msg.sender, address(this), _rewardsAmount);

        vaultRewardsPerWeight += rewardToWeight(_rewardsAmount, usersLockingWeight);

        // update `poolTokenReserve` only if this is a ILV Core Pool
        if (poolToken == ilv) {
            poolTokenReserve += _rewardsAmount;
        }

        emit VaultRewardsReceived(msg.sender, _rewardsAmount);
    }

    /**
     * @notice Service function to calculate and pay pending vault and yield rewards to the sender
     *
     * @dev Internally executes similar function `_processRewards` from the parent smart contract
     *      to calculate and pay yield rewards; adds vault rewards processing
     *
     * @dev Can be executed by anyone at any time, but has an effect only when
     *      executed by deposit holder and when at least one block passes from the
     *      previous reward processing
     * @dev Executed internally when "staking as a pool" (`stakeAsPool`)
     * @dev When timing conditions are not met (executed too frequently, or after factory
     *      end block), function doesn't throw and exits silently
     *
     * @dev _useSILV flag has a context of yield rewards only
     *
     * @param _useSILV flag indicating whether to mint sILV token as a reward or not;
     *      when set to true - sILV reward is minted immediately and sent to sender,
     *      when set to false - new ILV reward deposit gets created if pool is an ILV pool
     *      (poolToken is ILV token), or new pool deposit gets created together with sILV minted
     *      when pool is not an ILV pool (poolToken is not an ILV token)
     */
    function processRewards(bool _useSILV) external override {
        _processRewards(msg.sender, _useSILV, true);
    }

    /**
     * @dev Executed internally by the pool itself (from the parent `IlluviumPoolBase` smart contract)
     *      as part of yield rewards processing logic (`IlluviumPoolBase._processRewards` function)
     * @dev Executed when _useSILV is false and pool is not an ILV pool - see `IlluviumPoolBase._processRewards`
     *
     * @param _staker an address which stakes (the yield reward)
     * @param _amount amount to be staked (yield reward amount)
     */
    function stakeAsPool(address _staker, uint256 _amount) external {
        require(factory.poolExists(msg.sender), "access denied");
        _sync();
        User storage user = users[_staker];
        if (user.tokenAmount > 0) {
            _processRewards(_staker, true, false);
        }
        uint256 depositWeight = _amount * YEAR_STAKE_WEIGHT_MULTIPLIER;
        Deposit memory newDeposit =
            Deposit({
                tokenAmount: _amount,
                lockedFrom: uint64(now256()),
                lockedUntil: uint64(now256() + 365 days),
                weight: depositWeight,
                isYield: true
            });
        user.tokenAmount += _amount;
        user.totalWeight += depositWeight;
        user.deposits.push(newDeposit);

        usersLockingWeight += depositWeight;

        user.subYieldRewards = weightToReward(user.totalWeight, yieldRewardsPerWeight);
        user.subVaultRewards = weightToReward(user.totalWeight, vaultRewardsPerWeight);

        // update `poolTokenReserve` only if this is a LP Core Pool (stakeAsPool can be executed only for LP pool)
        poolTokenReserve += _amount;
    }

    /**
     * @inheritdoc IlluviumPoolBase
     *
     * @dev Additionally to the parent smart contract, updates vault rewards of the holder,
     *      and updates (increases) pool token reserve (pool tokens value available in the pool)
     */
    function _stake(
        address _staker,
        uint256 _amount,
        uint64 _lockedUntil,
        bool _useSILV,
        bool _isYield
    ) internal override {
        super._stake(_staker, _amount, _lockedUntil, _useSILV, _isYield);
        User storage user = users[_staker];
        user.subVaultRewards = weightToReward(user.totalWeight, vaultRewardsPerWeight);

        poolTokenReserve += _amount;
    }

    /**
     * @inheritdoc IlluviumPoolBase
     *
     * @dev Additionally to the parent smart contract, updates vault rewards of the holder,
     *      and updates (decreases) pool token reserve (pool tokens value available in the pool)
     */
    function _unstake(
        address _staker,
        uint256 _depositId,
        uint256 _amount,
        bool _useSILV
    ) internal override {
        User storage user = users[_staker];
        Deposit memory stakeDeposit = user.deposits[_depositId];
        require(stakeDeposit.lockedFrom == 0 || now256() > stakeDeposit.lockedUntil, "deposit not yet unlocked");
        poolTokenReserve -= _amount;
        super._unstake(_staker, _depositId, _amount, _useSILV);
        user.subVaultRewards = weightToReward(user.totalWeight, vaultRewardsPerWeight);
    }

    /**
     * @inheritdoc IlluviumPoolBase
     *
     * @dev Additionally to the parent smart contract, processes vault rewards of the holder,
     *      and for ILV pool updates (increases) pool token reserve (pool tokens value available in the pool)
     */
    function _processRewards(
        address _staker,
        bool _useSILV,
        bool _withUpdate
    ) internal override returns (uint256 pendingYield) {
        _processVaultRewards(_staker);
        pendingYield = super._processRewards(_staker, _useSILV, _withUpdate);

        // update `poolTokenReserve` only if this is a ILV Core Pool
        if (poolToken == ilv && !_useSILV) {
            poolTokenReserve += pendingYield;
        }
    }

    /**
     * @dev Used internally to process vault rewards for the staker
     *
     * @param _staker address of the user (staker) to process rewards for
     */
    function _processVaultRewards(address _staker) private {
        User storage user = users[_staker];
        uint256 pendingVaultClaim = pendingVaultRewards(_staker);
        if (pendingVaultClaim == 0) return;
        // read ILV token balance of the pool via standard ERC20 interface
        uint256 ilvBalance = IERC20(ilv).balanceOf(address(this));
        require(ilvBalance >= pendingVaultClaim, "contract ILV balance too low");

        // update `poolTokenReserve` only if this is a ILV Core Pool
        if (poolToken == ilv) {
            // protects against rounding errors
            poolTokenReserve -= pendingVaultClaim > poolTokenReserve ? poolTokenReserve : pendingVaultClaim;
        }

        user.subVaultRewards = weightToReward(user.totalWeight, vaultRewardsPerWeight);

        // transfer fails if pool ILV balance is not enough - which is a desired behavior
        transferIlv(_staker, pendingVaultClaim);

        emit VaultRewardsClaimed(msg.sender, _staker, pendingVaultClaim);
    }
}

// File: contracts/pools/IlluviumPoolBase.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

import "../interfaces/IPool.sol";
import "../interfaces/ICorePool.sol";
import "./ReentrancyGuard.sol";
import "./IlluviumPoolFactory.sol";
import "../utils/SafeERC20.sol";
import "../token/EscrowedIlluviumERC20.sol";

/**
 * @title Illuvium Pool Base
 *
 * @notice An abstract contract containing common logic for any pool,
 *      be it a flash pool (temporary pool like SNX) or a core pool (permanent pool like ILV/ETH or ILV pool)
 *
 * @dev Deployment and initialization.
 *      Any pool deployed must be bound to the deployed pool factory (IlluviumPoolFactory)
 *      Additionally, 3 token instance addresses must be defined on deployment:
 *          - ILV token address
 *          - sILV token address, used to mint sILV rewards
 *          - pool token address, it can be ILV token address, ILV/ETH pair address, and others
 *
 * @dev Pool weight defines the fraction of the yield current pool receives among the other pools,
 *      pool factory is responsible for the weight synchronization between the pools.
 * @dev The weight is logically 10% for ILV pool and 90% for ILV/ETH pool.
 *      Since Solidity doesn't support fractions the weight is defined by the division of
 *      pool weight by total pools weight (sum of all registered pools within the factory)
 * @dev For ILV Pool we use 100 as weight and for ILV/ETH pool - 900.
 *
 * @author Pedro Bergamini, reviewed by Basil Gorin
 */
abstract contract IlluviumPoolBase is IPool, IlluviumAware, ReentrancyGuard {
    /// @dev Data structure representing token holder using a pool
    struct User {
        // @dev Total staked amount
        uint256 tokenAmount;
        // @dev Total weight
        uint256 totalWeight;
        // @dev Auxiliary variable for yield calculation
        uint256 subYieldRewards;
        // @dev Auxiliary variable for vault rewards calculation
        uint256 subVaultRewards;
        // @dev An array of holder's deposits
        Deposit[] deposits;
    }

    /// @dev Token holder storage, maps token holder address to their data record
    mapping(address => User) public users;

    /// @dev Link to sILV ERC20 Token EscrowedIlluviumERC20 instance
    address public immutable override silv;

    /// @dev Link to the pool factory IlluviumPoolFactory instance
    IlluviumPoolFactory public immutable factory;

    /// @dev Link to the pool token instance, for example ILV or ILV/ETH pair
    address public immutable override poolToken;

    /// @dev Pool weight, 100 for ILV pool or 900 for ILV/ETH
    uint32 public override weight;

    /// @dev Block number of the last yield distribution event
    uint64 public override lastYieldDistribution;

    /// @dev Used to calculate yield rewards
    /// @dev This value is different from "reward per token" used in locked pool
    /// @dev Note: stakes are different in duration and "weight" reflects that
    uint256 public override yieldRewardsPerWeight;

    /// @dev Used to calculate yield rewards, keeps track of the tokens weight locked in staking
    uint256 public override usersLockingWeight;

    /**
     * @dev Stake weight is proportional to deposit amount and time locked, precisely
     *      "deposit amount wei multiplied by (fraction of the year locked plus one)"
     * @dev To avoid significant precision loss due to multiplication by "fraction of the year" [0, 1],
     *      weight is stored multiplied by 1e6 constant, as an integer
     * @dev Corner case 1: if time locked is zero, weight is deposit amount multiplied by 1e6
     * @dev Corner case 2: if time locked is one year, fraction of the year locked is one, and
     *      weight is a deposit amount multiplied by 2 * 1e6
     */
    uint256 internal constant WEIGHT_MULTIPLIER = 1e6;

    /**
     * @dev When we know beforehand that staking is done for a year, and fraction of the year locked is one,
     *      we use simplified calculation and use the following constant instead previos one
     */
    uint256 internal constant YEAR_STAKE_WEIGHT_MULTIPLIER = 2 * WEIGHT_MULTIPLIER;

    /**
     * @dev Rewards per weight are stored multiplied by 1e12, as integers.
     */
    uint256 internal constant REWARD_PER_WEIGHT_MULTIPLIER = 1e12;

    /**
     * @dev Fired in _stake() and stake()
     *
     * @param _by an address which performed an operation, usually token holder
     * @param _from token holder address, the tokens will be returned to that address
     * @param amount amount of tokens staked
     */
    event Staked(address indexed _by, address indexed _from, uint256 amount);

    /**
     * @dev Fired in _updateStakeLock() and updateStakeLock()
     *
     * @param _by an address which performed an operation
     * @param depositId updated deposit ID
     * @param lockedFrom deposit locked from value
     * @param lockedUntil updated deposit locked until value
     */
    event StakeLockUpdated(address indexed _by, uint256 depositId, uint64 lockedFrom, uint64 lockedUntil);

    /**
     * @dev Fired in _unstake() and unstake()
     *
     * @param _by an address which performed an operation, usually token holder
     * @param _to an address which received the unstaked tokens, usually token holder
     * @param amount amount of tokens unstaked
     */
    event Unstaked(address indexed _by, address indexed _to, uint256 amount);

    /**
     * @dev Fired in _sync(), sync() and dependent functions (stake, unstake, etc.)
     *
     * @param _by an address which performed an operation
     * @param yieldRewardsPerWeight updated yield rewards per weight value
     * @param lastYieldDistribution usually, current block number
     */
    event Synchronized(address indexed _by, uint256 yieldRewardsPerWeight, uint64 lastYieldDistribution);

    /**
     * @dev Fired in _processRewards(), processRewards() and dependent functions (stake, unstake, etc.)
     *
     * @param _by an address which performed an operation
     * @param _to an address which claimed the yield reward
     * @param sIlv flag indicating if reward was paid (minted) in sILV
     * @param amount amount of yield paid
     */
    event YieldClaimed(address indexed _by, address indexed _to, bool sIlv, uint256 amount);

    /**
     * @dev Fired in setWeight()
     *
     * @param _by an address which performed an operation, always a factory
     * @param _fromVal old pool weight value
     * @param _toVal new pool weight value
     */
    event PoolWeightUpdated(address indexed _by, uint32 _fromVal, uint32 _toVal);

    /**
     * @dev Overridden in sub-contracts to construct the pool
     *
     * @param _ilv ILV ERC20 Token IlluviumERC20 address
     * @param _silv sILV ERC20 Token EscrowedIlluviumERC20 address
     * @param _factory Pool factory IlluviumPoolFactory instance/address
     * @param _poolToken token the pool operates on, for example ILV or ILV/ETH pair
     * @param _initBlock initial block used to calculate the rewards
     *      note: _initBlock can be set to the future effectively meaning _sync() calls will do nothing
     * @param _weight number representing a weight of the pool, actual weight fraction
     *      is calculated as that number divided by the total pools weight and doesn't exceed one
     */
    constructor(
        address _ilv,
        address _silv,
        IlluviumPoolFactory _factory,
        address _poolToken,
        uint64 _initBlock,
        uint32 _weight
    ) IlluviumAware(_ilv) {
        // verify the inputs are set
        require(_silv != address(0), "sILV address not set");
        require(address(_factory) != address(0), "ILV Pool fct address not set");
        require(_poolToken != address(0), "pool token address not set");
        require(_initBlock > 0, "init block not set");
        require(_weight > 0, "pool weight not set");

        // verify sILV instance supplied
        require(
            EscrowedIlluviumERC20(_silv).TOKEN_UID() ==
                0xac3051b8d4f50966afb632468a4f61483ae6a953b74e387a01ef94316d6b7d62,
            "unexpected sILV TOKEN_UID"
        );
        // verify IlluviumPoolFactory instance supplied
        require(
            _factory.FACTORY_UID() == 0xc5cfd88c6e4d7e5c8a03c255f03af23c0918d8e82cac196f57466af3fd4a5ec7,
            "unexpected FACTORY_UID"
        );

        // save the inputs into internal state variables
        silv = _silv;
        factory = _factory;
        poolToken = _poolToken;
        weight = _weight;

        // init the dependent internal state variables
        lastYieldDistribution = _initBlock;
    }

    /**
     * @notice Calculates current yield rewards value available for address specified
     *
     * @param _staker an address to calculate yield rewards value for
     * @return calculated yield reward value for the given address
     */
    function pendingYieldRewards(address _staker) external view override returns (uint256) {
        // `newYieldRewardsPerWeight` will store stored or recalculated value for `yieldRewardsPerWeight`
        uint256 newYieldRewardsPerWeight;

        // if smart contract state was not updated recently, `yieldRewardsPerWeight` value
        // is outdated and we need to recalculate it in order to calculate pending rewards correctly
        if (blockNumber() > lastYieldDistribution && usersLockingWeight != 0) {
            uint256 endBlock = factory.endBlock();
            uint256 multiplier =
                blockNumber() > endBlock ? endBlock - lastYieldDistribution : blockNumber() - lastYieldDistribution;
            uint256 ilvRewards = (multiplier * weight * factory.ilvPerBlock()) / factory.totalWeight();

            // recalculated value for `yieldRewardsPerWeight`
            newYieldRewardsPerWeight = rewardToWeight(ilvRewards, usersLockingWeight) + yieldRewardsPerWeight;
        } else {
            // if smart contract state is up to date, we don't recalculate
            newYieldRewardsPerWeight = yieldRewardsPerWeight;
        }

        // based on the rewards per weight value, calculate pending rewards;
        User memory user = users[_staker];
        uint256 pending = weightToReward(user.totalWeight, newYieldRewardsPerWeight) - user.subYieldRewards;

        return pending;
    }

    /**
     * @notice Returns total staked token balance for the given address
     *
     * @param _user an address to query balance for
     * @return total staked token balance
     */
    function balanceOf(address _user) external view override returns (uint256) {
        // read specified user token amount and return
        return users[_user].tokenAmount;
    }

    /**
     * @notice Returns information on the given deposit for the given address
     *
     * @dev See getDepositsLength
     *
     * @param _user an address to query deposit for
     * @param _depositId zero-indexed deposit ID for the address specified
     * @return deposit info as Deposit structure
     */
    function getDeposit(address _user, uint256 _depositId) external view override returns (Deposit memory) {
        // read deposit at specified index and return
        return users[_user].deposits[_depositId];
    }

    /**
     * @notice Returns number of deposits for the given address. Allows iteration over deposits.
     *
     * @dev See getDeposit
     *
     * @param _user an address to query deposit length for
     * @return number of deposits for the given address
     */
    function getDepositsLength(address _user) external view override returns (uint256) {
        // read deposits array length and return
        return users[_user].deposits.length;
    }

    /**
     * @notice Stakes specified amount of tokens for the specified amount of time,
     *      and pays pending yield rewards if any
     *
     * @dev Requires amount to stake to be greater than zero
     *
     * @param _amount amount of tokens to stake
     * @param _lockUntil stake period as unix timestamp; zero means no locking
     * @param _useSILV a flag indicating if previous reward to be paid as sILV
     */
    function stake(
        uint256 _amount,
        uint64 _lockUntil,
        bool _useSILV
    ) external override {
        // delegate call to an internal function
        _stake(msg.sender, _amount, _lockUntil, _useSILV, false);
    }

    /**
     * @notice Unstakes specified amount of tokens, and pays pending yield rewards if any
     *
     * @dev Requires amount to unstake to be greater than zero
     *
     * @param _depositId deposit ID to unstake from, zero-indexed
     * @param _amount amount of tokens to unstake
     * @param _useSILV a flag indicating if reward to be paid as sILV
     */
    function unstake(
        uint256 _depositId,
        uint256 _amount,
        bool _useSILV
    ) external override {
        // delegate call to an internal function
        _unstake(msg.sender, _depositId, _amount, _useSILV);
    }

    /**
     * @notice Extends locking period for a given deposit
     *
     * @dev Requires new lockedUntil value to be:
     *      higher than the current one, and
     *      in the future, but
     *      no more than 1 year in the future
     *
     * @param depositId updated deposit ID
     * @param lockedUntil updated deposit locked until value
     * @param useSILV used for _processRewards check if it should use ILV or sILV
     */
    function updateStakeLock(
        uint256 depositId,
        uint64 lockedUntil,
        bool useSILV
    ) external {
        // sync and call processRewards
        _sync();
        _processRewards(msg.sender, useSILV, false);
        // delegate call to an internal function
        _updateStakeLock(msg.sender, depositId, lockedUntil);
    }

    /**
     * @notice Service function to synchronize pool state with current time
     *
     * @dev Can be executed by anyone at any time, but has an effect only when
     *      at least one block passes between synchronizations
     * @dev Executed internally when staking, unstaking, processing rewards in order
     *      for calculations to be correct and to reflect state progress of the contract
     * @dev When timing conditions are not met (executed too frequently, or after factory
     *      end block), function doesn't throw and exits silently
     */
    function sync() external override {
        // delegate call to an internal function
        _sync();
    }

    /**
     * @notice Service function to calculate and pay pending yield rewards to the sender
     *
     * @dev Can be executed by anyone at any time, but has an effect only when
     *      executed by deposit holder and when at least one block passes from the
     *      previous reward processing
     * @dev Executed internally when staking and unstaking, executes sync() under the hood
     *      before making further calculations and payouts
     * @dev When timing conditions are not met (executed too frequently, or after factory
     *      end block), function doesn't throw and exits silently
     *
     * @param _useSILV flag indicating whether to mint sILV token as a reward or not;
     *      when set to true - sILV reward is minted immediately and sent to sender,
     *      when set to false - new ILV reward deposit gets created if pool is an ILV pool
     *      (poolToken is ILV token), or new pool deposit gets created together with sILV minted
     *      when pool is not an ILV pool (poolToken is not an ILV token)
     */
    function processRewards(bool _useSILV) external virtual override {
        // delegate call to an internal function
        _processRewards(msg.sender, _useSILV, true);
    }

    /**
     * @dev Executed by the factory to modify pool weight; the factory is expected
     *      to keep track of the total pools weight when updating
     *
     * @dev Set weight to zero to disable the pool
     *
     * @param _weight new weight to set for the pool
     */
    function setWeight(uint32 _weight) external override {
        // verify function is executed by the factory
        require(msg.sender == address(factory), "access denied");

        // emit an event logging old and new weight values
        emit PoolWeightUpdated(msg.sender, weight, _weight);

        // set the new weight value
        weight = _weight;
    }

    /**
     * @dev Similar to public pendingYieldRewards, but performs calculations based on
     *      current smart contract state only, not taking into account any additional
     *      time/blocks which might have passed
     *
     * @param _staker an address to calculate yield rewards value for
     * @return pending calculated yield reward value for the given address
     */
    function _pendingYieldRewards(address _staker) internal view returns (uint256 pending) {
        // read user data structure into memory
        User memory user = users[_staker];

        // and perform the calculation using the values read
        return weightToReward(user.totalWeight, yieldRewardsPerWeight) - user.subYieldRewards;
    }

    /**
     * @dev Used internally, mostly by children implementations, see stake()
     *
     * @param _staker an address which stakes tokens and which will receive them back
     * @param _amount amount of tokens to stake
     * @param _lockUntil stake period as unix timestamp; zero means no locking
     * @param _useSILV a flag indicating if previous reward to be paid as sILV
     * @param _isYield a flag indicating if that stake is created to store yield reward
     *      from the previously unstaked stake
     */
    function _stake(
        address _staker,
        uint256 _amount,
        uint64 _lockUntil,
        bool _useSILV,
        bool _isYield
    ) internal virtual {
        // validate the inputs
        require(_amount > 0, "zero amount");
        require(
            _lockUntil == 0 || (_lockUntil > now256() && _lockUntil - now256() <= 365 days),
            "invalid lock interval"
        );

        // update smart contract state
        _sync();

        // get a link to user data struct, we will write to it later
        User storage user = users[_staker];
        // process current pending rewards if any
        if (user.tokenAmount > 0) {
            _processRewards(_staker, _useSILV, false);
        }

        // in most of the cases added amount `addedAmount` is simply `_amount`
        // however for deflationary tokens this can be different

        // read the current balance
        uint256 previousBalance = IERC20(poolToken).balanceOf(address(this));
        // transfer `_amount`; note: some tokens may get burnt here
        transferPoolTokenFrom(address(msg.sender), address(this), _amount);
        // read new balance, usually this is just the difference `previousBalance - _amount`
        uint256 newBalance = IERC20(poolToken).balanceOf(address(this));
        // calculate real amount taking into account deflation
        uint256 addedAmount = newBalance - previousBalance;

        // set the `lockFrom` and `lockUntil` taking into account that
        // zero value for `_lockUntil` means "no locking" and leads to zero values
        // for both `lockFrom` and `lockUntil`
        uint64 lockFrom = _lockUntil > 0 ? uint64(now256()) : 0;
        uint64 lockUntil = _lockUntil;

        // stake weight formula rewards for locking
        uint256 stakeWeight =
            (((lockUntil - lockFrom) * WEIGHT_MULTIPLIER) / 365 days + WEIGHT_MULTIPLIER) * addedAmount;

        // makes sure stakeWeight is valid
        assert(stakeWeight > 0);

        // create and save the deposit (append it to deposits array)
        Deposit memory deposit =
            Deposit({
                tokenAmount: addedAmount,
                weight: stakeWeight,
                lockedFrom: lockFrom,
                lockedUntil: lockUntil,
                isYield: _isYield
            });
        // deposit ID is an index of the deposit in `deposits` array
        user.deposits.push(deposit);

        // update user record
        user.tokenAmount += addedAmount;
        user.totalWeight += stakeWeight;
        user.subYieldRewards = weightToReward(user.totalWeight, yieldRewardsPerWeight);

        // update global variable
        usersLockingWeight += stakeWeight;

        // emit an event
        emit Staked(msg.sender, _staker, _amount);
    }

    /**
     * @dev Used internally, mostly by children implementations, see unstake()
     *
     * @param _staker an address which unstakes tokens (which previously staked them)
     * @param _depositId deposit ID to unstake from, zero-indexed
     * @param _amount amount of tokens to unstake
     * @param _useSILV a flag indicating if reward to be paid as sILV
     */
    function _unstake(
        address _staker,
        uint256 _depositId,
        uint256 _amount,
        bool _useSILV
    ) internal virtual {
        // verify an amount is set
        require(_amount > 0, "zero amount");

        // get a link to user data struct, we will write to it later
        User storage user = users[_staker];
        // get a link to the corresponding deposit, we may write to it later
        Deposit storage stakeDeposit = user.deposits[_depositId];
        // deposit structure may get deleted, so we save isYield flag to be able to use it
        bool isYield = stakeDeposit.isYield;

        // verify available balance
        // if staker address ot deposit doesn't exist this check will fail as well
        require(stakeDeposit.tokenAmount >= _amount, "amount exceeds stake");

        // update smart contract state
        _sync();
        // and process current pending rewards if any
        _processRewards(_staker, _useSILV, false);

        // recalculate deposit weight
        uint256 previousWeight = stakeDeposit.weight;
        uint256 newWeight =
            (((stakeDeposit.lockedUntil - stakeDeposit.lockedFrom) * WEIGHT_MULTIPLIER) /
                365 days +
                WEIGHT_MULTIPLIER) * (stakeDeposit.tokenAmount - _amount);

        // update the deposit, or delete it if its depleted
        if (stakeDeposit.tokenAmount - _amount == 0) {
            delete user.deposits[_depositId];
        } else {
            stakeDeposit.tokenAmount -= _amount;
            stakeDeposit.weight = newWeight;
        }

        // update user record
        user.tokenAmount -= _amount;
        user.totalWeight = user.totalWeight - previousWeight + newWeight;
        user.subYieldRewards = weightToReward(user.totalWeight, yieldRewardsPerWeight);

        // update global variable
        usersLockingWeight = usersLockingWeight - previousWeight + newWeight;

        // if the deposit was created by the pool itself as a yield reward
        if (isYield) {
            // mint the yield via the factory
            factory.mintYieldTo(msg.sender, _amount);
        } else {
            // otherwise just return tokens back to holder
            transferPoolToken(msg.sender, _amount);
        }

        // emit an event
        emit Unstaked(msg.sender, _staker, _amount);
    }

    /**
     * @dev Used internally, mostly by children implementations, see sync()
     *
     * @dev Updates smart contract state (`yieldRewardsPerWeight`, `lastYieldDistribution`),
     *      updates factory state via `updateILVPerBlock`
     */
    function _sync() internal virtual {
        // update ILV per block value in factory if required
        if (factory.shouldUpdateRatio()) {
            factory.updateILVPerBlock();
        }

        // check bound conditions and if these are not met -
        // exit silently, without emitting an event
        uint256 endBlock = factory.endBlock();
        if (lastYieldDistribution >= endBlock) {
            return;
        }
        if (blockNumber() <= lastYieldDistribution) {
            return;
        }
        // if locking weight is zero - update only `lastYieldDistribution` and exit
        if (usersLockingWeight == 0) {
            lastYieldDistribution = uint64(blockNumber());
            return;
        }

        // to calculate the reward we need to know how many blocks passed, and reward per block
        uint256 currentBlock = blockNumber() > endBlock ? endBlock : blockNumber();
        uint256 blocksPassed = currentBlock - lastYieldDistribution;
        uint256 ilvPerBlock = factory.ilvPerBlock();

        // calculate the reward
        uint256 ilvReward = (blocksPassed * ilvPerBlock * weight) / factory.totalWeight();

        // update rewards per weight and `lastYieldDistribution`
        yieldRewardsPerWeight += rewardToWeight(ilvReward, usersLockingWeight);
        lastYieldDistribution = uint64(currentBlock);

        // emit an event
        emit Synchronized(msg.sender, yieldRewardsPerWeight, lastYieldDistribution);
    }

    /**
     * @dev Used internally, mostly by children implementations, see processRewards()
     *
     * @param _staker an address which receives the reward (which has staked some tokens earlier)
     * @param _useSILV flag indicating whether to mint sILV token as a reward or not, see processRewards()
     * @param _withUpdate flag allowing to disable synchronization (see sync()) if set to false
     * @return pendingYield the rewards calculated and optionally re-staked
     */
    function _processRewards(
        address _staker,
        bool _useSILV,
        bool _withUpdate
    ) internal virtual returns (uint256 pendingYield) {
        // update smart contract state if required
        if (_withUpdate) {
            _sync();
        }

        // calculate pending yield rewards, this value will be returned
        pendingYield = _pendingYieldRewards(_staker);

        // if pending yield is zero - just return silently
        if (pendingYield == 0) return 0;

        // get link to a user data structure, we will write into it later
        User storage user = users[_staker];

        // if sILV is requested
        if (_useSILV) {
            // - mint sILV
            mintSIlv(_staker, pendingYield);
        } else if (poolToken == ilv) {
            // calculate pending yield weight,
            // 2e6 is the bonus weight when staking for 1 year
            uint256 depositWeight = pendingYield * YEAR_STAKE_WEIGHT_MULTIPLIER;

            // if the pool is ILV Pool - create new ILV deposit
            // and save it - push it into deposits array
            Deposit memory newDeposit =
                Deposit({
                    tokenAmount: pendingYield,
                    lockedFrom: uint64(now256()),
                    lockedUntil: uint64(now256() + 365 days), // staking yield for 1 year
                    weight: depositWeight,
                    isYield: true
                });
            user.deposits.push(newDeposit);

            // update user record
            user.tokenAmount += pendingYield;
            user.totalWeight += depositWeight;

            // update global variable
            usersLockingWeight += depositWeight;
        } else {
            // for other pools - stake as pool
            address ilvPool = factory.getPoolAddress(ilv);
            ICorePool(ilvPool).stakeAsPool(_staker, pendingYield);
        }

        // update users's record for `subYieldRewards` if requested
        if (_withUpdate) {
            user.subYieldRewards = weightToReward(user.totalWeight, yieldRewardsPerWeight);
        }

        // emit an event
        emit YieldClaimed(msg.sender, _staker, _useSILV, pendingYield);
    }

    /**
     * @dev See updateStakeLock()
     *
     * @param _staker an address to update stake lock
     * @param _depositId updated deposit ID
     * @param _lockedUntil updated deposit locked until value
     */
    function _updateStakeLock(
        address _staker,
        uint256 _depositId,
        uint64 _lockedUntil
    ) internal {
        // validate the input time
        require(_lockedUntil > now256(), "lock should be in the future");

        // get a link to user data struct, we will write to it later
        User storage user = users[_staker];
        // get a link to the corresponding deposit, we may write to it later
        Deposit storage stakeDeposit = user.deposits[_depositId];

        // validate the input against deposit structure
        require(_lockedUntil > stakeDeposit.lockedUntil, "invalid new lock");

        // verify locked from and locked until values
        if (stakeDeposit.lockedFrom == 0) {
            require(_lockedUntil - now256() <= 365 days, "max lock period is 365 days");
            stakeDeposit.lockedFrom = uint64(now256());
        } else {
            require(_lockedUntil - stakeDeposit.lockedFrom <= 365 days, "max lock period is 365 days");
        }

        // update locked until value, calculate new weight
        stakeDeposit.lockedUntil = _lockedUntil;
        uint256 newWeight =
            (((stakeDeposit.lockedUntil - stakeDeposit.lockedFrom) * WEIGHT_MULTIPLIER) /
                365 days +
                WEIGHT_MULTIPLIER) * stakeDeposit.tokenAmount;

        // save previous weight
        uint256 previousWeight = stakeDeposit.weight;
        // update weight
        stakeDeposit.weight = newWeight;

        // update user total weight and global locking weight
        user.totalWeight = user.totalWeight - previousWeight + newWeight;
        usersLockingWeight = usersLockingWeight - previousWeight + newWeight;

        // emit an event
        emit StakeLockUpdated(_staker, _depositId, stakeDeposit.lockedFrom, _lockedUntil);
    }

    /**
     * @dev Converts stake weight (not to be mixed with the pool weight) to
     *      ILV reward value, applying the 10^12 division on weight
     *
     * @param _weight stake weight
     * @param rewardPerWeight ILV reward per weight
     * @return reward value normalized to 10^12
     */
    function weightToReward(uint256 _weight, uint256 rewardPerWeight) public pure returns (uint256) {
        // apply the formula and return
        return (_weight * rewardPerWeight) / REWARD_PER_WEIGHT_MULTIPLIER;
    }

    /**
     * @dev Converts reward ILV value to stake weight (not to be mixed with the pool weight),
     *      applying the 10^12 multiplication on the reward
     *      - OR -
     * @dev Converts reward ILV value to reward/weight if stake weight is supplied as second
     *      function parameter instead of reward/weight
     *
     * @param reward yield reward
     * @param rewardPerWeight reward/weight (or stake weight)
     * @return stake weight (or reward/weight)
     */
    function rewardToWeight(uint256 reward, uint256 rewardPerWeight) public pure returns (uint256) {
        // apply the reverse formula and return
        return (reward * REWARD_PER_WEIGHT_MULTIPLIER) / rewardPerWeight;
    }

    /**
     * @dev Testing time-dependent functionality is difficult and the best way of
     *      doing it is to override block number in helper test smart contracts
     *
     * @return `block.number` in mainnet, custom values in testnets (if overridden)
     */
    function blockNumber() public view virtual returns (uint256) {
        // return current block number
        return block.number;
    }

    /**
     * @dev Testing time-dependent functionality is difficult and the best way of
     *      doing it is to override time in helper test smart contracts
     *
     * @return `block.timestamp` in mainnet, custom values in testnets (if overridden)
     */
    function now256() public view virtual returns (uint256) {
        // return current block timestamp
        return block.timestamp;
    }

    /**
     * @dev Executes EscrowedIlluviumERC20.mint(_to, _values)
     *      on the bound EscrowedIlluviumERC20 instance
     *
     * @dev Reentrancy safe due to the EscrowedIlluviumERC20 design
     */
    function mintSIlv(address _to, uint256 _value) private {
        // just delegate call to the target
        EscrowedIlluviumERC20(silv).mint(_to, _value);
    }

    /**
     * @dev Executes SafeERC20.safeTransfer on a pool token
     *
     * @dev Reentrancy safety enforced via `ReentrancyGuard.nonReentrant`
     */
    function transferPoolToken(address _to, uint256 _value) internal nonReentrant {
        // just delegate call to the target
        SafeERC20.safeTransfer(IERC20(poolToken), _to, _value);
    }

    /**
     * @dev Executes SafeERC20.safeTransferFrom on a pool token
     *
     * @dev Reentrancy safety enforced via `ReentrancyGuard.nonReentrant`
     */
    function transferPoolTokenFrom(
        address _from,
        address _to,
        uint256 _value
    ) internal nonReentrant {
        // just delegate call to the target
        SafeERC20.safeTransferFrom(IERC20(poolToken), _from, _to, _value);
    }
}

// File: contracts/interfaces/IPool.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

import "./ILinkedToILV.sol";

/**
 * @title Illuvium Pool
 *
 * @notice An abstraction representing a pool, see IlluviumPoolBase for details
 *
 * @author Pedro Bergamini, reviewed by Basil Gorin
 */
interface IPool is ILinkedToILV {
    /**
     * @dev Deposit is a key data structure used in staking,
     *      it represents a unit of stake with its amount, weight and term (time interval)
     */
    struct Deposit {
        // @dev token amount staked
        uint256 tokenAmount;
        // @dev stake weight
        uint256 weight;
        // @dev locking period - from
        uint64 lockedFrom;
        // @dev locking period - until
        uint64 lockedUntil;
        // @dev indicates if the stake was created as a yield reward
        bool isYield;
    }

    // for the rest of the functions see Soldoc in IlluviumPoolBase

    function silv() external view returns (address);

    function poolToken() external view returns (address);

    function isFlashPool() external view returns (bool);

    function weight() external view returns (uint32);

    function lastYieldDistribution() external view returns (uint64);

    function yieldRewardsPerWeight() external view returns (uint256);

    function usersLockingWeight() external view returns (uint256);

    function pendingYieldRewards(address _user) external view returns (uint256);

    function balanceOf(address _user) external view returns (uint256);

    function getDeposit(address _user, uint256 _depositId) external view returns (Deposit memory);

    function getDepositsLength(address _user) external view returns (uint256);

    function stake(
        uint256 _amount,
        uint64 _lockedUntil,
        bool useSILV
    ) external;

    function unstake(
        uint256 _depositId,
        uint256 _amount,
        bool useSILV
    ) external;

    function sync() external;

    function processRewards(bool useSILV) external;

    function setWeight(uint32 _weight) external;
}

// File: contracts/interfaces/ICorePool.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.8.1;

import "./IPool.sol";

interface ICorePool is IPool {
    function vaultRewardsPerToken() external view returns (uint256);

    function poolTokenReserve() external view returns (uint256);

    function stakeAsPool(address _staker, uint256 _amount) external;

    function receiveVaultRewards(uint256 _amount) external;
}

// File: contracts/pools/ReentrancyGuard.sol



// https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-contracts/master/contracts/security/ReentrancyGuard.sol
// #24a0bc23cfe3fbc76f8f2510b78af1e948ae6651

// SPDX-License-Identifier: MIT

pragma solidity 0.8.1;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
  // Booleans are more expensive than uint256 or any type that takes up a full
  // word because each write operation emits an extra SLOAD to first read the
  // slot's contents, replace the bits taken up by the boolean, and then write
  // back. This is the compiler's defense against contract upgrades and
  // pointer aliasing, and it cannot be disabled.

  // The values being non-zero value makes deployment a bit more expensive,
  // but in exchange the refund on every call to nonReentrant will be lower in
  // amount. Since refunds are capped to a percentage of the total
  // transaction's gas, it is best to keep them low in cases like this one, to
  // increase the likelihood of the full refund coming into effect.
  uint256 private constant _NOT_ENTERED = 1;
  uint256 private constant _ENTERED = 2;

  uint256 private _status;

  constructor () {
    _status = _NOT_ENTERED;
  }

  /**
   * @dev Prevents a contract from calling itself, directly or indirectly.
   * Calling a `nonReentrant` function from another `nonReentrant`
   * function is not supported. It is possible to prevent this from happening
   * by making the `nonReentrant` function external, and make it call a
   * `private` function that does the actual work.
   */
  modifier nonReentrant() {
    // On the first call to nonReentrant, _notEntered will be true
    require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

    // Any calls to nonReentrant after this point will fail
    _status = _ENTERED;

    _;

    // By storing the original value once again, a refund is triggered (see
    // https://eips.ethereum.org/EIPS/eip-2200)
    _status = _NOT_ENTERED;
  }
}

// File: contracts/pools/IlluviumPoolFactory.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

import "../interfaces/IPool.sol";
import "./IlluviumAware.sol";
import "./IlluviumCorePool.sol";
import "../token/EscrowedIlluviumERC20.sol";
import "../utils/Ownable.sol";

/**
 * @title Illuvium Pool Factory
 *
 * @notice ILV Pool Factory manages Illuvium Yield farming pools, provides a single
 *      public interface to access the pools, provides an interface for the pools
 *      to mint yield rewards, access pool-related info, update weights, etc.
 *
 * @notice The factory is authorized (via its owner) to register new pools, change weights
 *      of the existing pools, removing the pools (by changing their weights to zero)
 *
 * @dev The factory requires ROLE_TOKEN_CREATOR permission on the ILV token to mint yield
 *      (see `mintYieldTo` function)
 *
 * @author Pedro Bergamini, reviewed by Basil Gorin
 */
contract IlluviumPoolFactory is Ownable, IlluviumAware {
    /**
     * @dev Smart contract unique identifier, a random number
     * @dev Should be regenerated each time smart contact source code is changed
     *      and changes smart contract itself is to be redeployed
     * @dev Generated using https://www.random.org/bytes/
     */
    uint256 public constant FACTORY_UID = 0xc5cfd88c6e4d7e5c8a03c255f03af23c0918d8e82cac196f57466af3fd4a5ec7;

    /// @dev Auxiliary data structure used only in getPoolData() view function
    struct PoolData {
        // @dev pool token address (like ILV)
        address poolToken;
        // @dev pool address (like deployed core pool instance)
        address poolAddress;
        // @dev pool weight (200 for ILV pools, 800 for ILV/ETH pools - set during deployment)
        uint32 weight;
        // @dev flash pool flag
        bool isFlashPool;
    }

    /**
     * @dev ILV/block determines yield farming reward base
     *      used by the yield pools controlled by the factory
     */
    uint192 public ilvPerBlock;

    /**
     * @dev The yield is distributed proportionally to pool weights;
     *      total weight is here to help in determining the proportion
     */
    uint32 public totalWeight;

    /**
     * @dev ILV/block decreases by 3% every blocks/update (set to 91252 blocks during deployment);
     *      an update is triggered by executing `updateILVPerBlock` public function
     */
    uint32 public immutable blocksPerUpdate;

    /**
     * @dev End block is the last block when ILV/block can be decreased;
     *      it is implied that yield farming stops after that block
     */
    uint32 public endBlock;

    /**
     * @dev Each time the ILV/block ratio gets updated, the block number
     *      when the operation has occurred gets recorded into `lastRatioUpdate`
     * @dev This block number is then used to check if blocks/update `blocksPerUpdate`
     *      has passed when decreasing yield reward by 3%
     */
    uint32 public lastRatioUpdate;

    /// @dev sILV token address is used to create ILV core pool(s)
    address public immutable silv;

    /// @dev Maps pool token address (like ILV) -> pool address (like core pool instance)
    mapping(address => address) public pools;

    /// @dev Keeps track of registered pool addresses, maps pool address -> exists flag
    mapping(address => bool) public poolExists;

    /**
     * @dev Fired in createPool() and registerPool()
     *
     * @param _by an address which executed an action
     * @param poolToken pool token address (like ILV)
     * @param poolAddress deployed pool instance address
     * @param weight pool weight
     * @param isFlashPool flag indicating if pool is a flash pool
     */
    event PoolRegistered(
        address indexed _by,
        address indexed poolToken,
        address indexed poolAddress,
        uint64 weight,
        bool isFlashPool
    );

    /**
     * @dev Fired in changePoolWeight()
     *
     * @param _by an address which executed an action
     * @param poolAddress deployed pool instance address
     * @param weight new pool weight
     */
    event WeightUpdated(address indexed _by, address indexed poolAddress, uint32 weight);

    /**
     * @dev Fired in updateILVPerBlock()
     *
     * @param _by an address which executed an action
     * @param newIlvPerBlock new ILV/block value
     */
    event IlvRatioUpdated(address indexed _by, uint256 newIlvPerBlock);

    /**
     * @dev Creates/deploys a factory instance
     *
     * @param _ilv ILV ERC20 token address
     * @param _silv sILV ERC20 token address
     * @param _ilvPerBlock initial ILV/block value for rewards
     * @param _blocksPerUpdate how frequently the rewards gets updated (decreased by 3%), blocks
     * @param _initBlock block number to measure _blocksPerUpdate from
     * @param _endBlock block number when farming stops and rewards cannot be updated anymore
     */
    constructor(
        address _ilv,
        address _silv,
        uint192 _ilvPerBlock,
        uint32 _blocksPerUpdate,
        uint32 _initBlock,
        uint32 _endBlock
    ) IlluviumAware(_ilv) {
        // verify the inputs are set
        require(_silv != address(0), "sILV address not set");
        require(_ilvPerBlock > 0, "ILV/block not set");
        require(_blocksPerUpdate > 0, "blocks/update not set");
        require(_initBlock > 0, "init block not set");
        require(_endBlock > _initBlock, "invalid end block: must be greater than init block");

        // verify sILV instance supplied
        require(
            EscrowedIlluviumERC20(_silv).TOKEN_UID() ==
                0xac3051b8d4f50966afb632468a4f61483ae6a953b74e387a01ef94316d6b7d62,
            "unexpected sILV TOKEN_UID"
        );

        // save the inputs into internal state variables
        silv = _silv;
        ilvPerBlock = _ilvPerBlock;
        blocksPerUpdate = _blocksPerUpdate;
        lastRatioUpdate = _initBlock;
        endBlock = _endBlock;
    }

    /**
     * @notice Given a pool token retrieves corresponding pool address
     *
     * @dev A shortcut for `pools` mapping
     *
     * @param poolToken pool token address (like ILV) to query pool address for
     * @return pool address for the token specified
     */
    function getPoolAddress(address poolToken) external view returns (address) {
        // read the mapping and return
        return pools[poolToken];
    }

    /**
     * @notice Reads pool information for the pool defined by its pool token address,
     *      designed to simplify integration with the front ends
     *
     * @param _poolToken pool token address to query pool information for
     * @return pool information packed in a PoolData struct
     */
    function getPoolData(address _poolToken) public view returns (PoolData memory) {
        // get the pool address from the mapping
        address poolAddr = pools[_poolToken];

        // throw if there is no pool registered for the token specified
        require(poolAddr != address(0), "pool not found");

        // read pool information from the pool smart contract
        // via the pool interface (IPool)
        address poolToken = IPool(poolAddr).poolToken();
        bool isFlashPool = IPool(poolAddr).isFlashPool();
        uint32 weight = IPool(poolAddr).weight();

        // create the in-memory structure and return it
        return PoolData({ poolToken: poolToken, poolAddress: poolAddr, weight: weight, isFlashPool: isFlashPool });
    }

    /**
     * @dev Verifies if `blocksPerUpdate` has passed since last ILV/block
     *      ratio update and if ILV/block reward can be decreased by 3%
     *
     * @return true if enough time has passed and `updateILVPerBlock` can be executed
     */
    function shouldUpdateRatio() public view returns (bool) {
        // if yield farming period has ended
        if (blockNumber() > endBlock) {
            // ILV/block reward cannot be updated anymore
            return false;
        }

        // check if blocks/update (91252 blocks) have passed since last update
        return blockNumber() >= lastRatioUpdate + blocksPerUpdate;
    }

    /**
     * @dev Creates a core pool (IlluviumCorePool) and registers it within the factory
     *
     * @dev Can be executed by the pool factory owner only
     *
     * @param poolToken pool token address (like ILV, or ILV/ETH pair)
     * @param initBlock init block to be used for the pool created
     * @param weight weight of the pool to be created
     */
    function createPool(
        address poolToken,
        uint64 initBlock,
        uint32 weight
    ) external virtual onlyOwner {
        // create/deploy new core pool instance
        IPool pool = new IlluviumCorePool(ilv, silv, this, poolToken, initBlock, weight);

        // register it within a factory
        registerPool(address(pool));
    }

    /**
     * @dev Registers an already deployed pool instance within the factory
     *
     * @dev Can be executed by the pool factory owner only
     *
     * @param poolAddr address of the already deployed pool instance
     */
    function registerPool(address poolAddr) public onlyOwner {
        // read pool information from the pool smart contract
        // via the pool interface (IPool)
        address poolToken = IPool(poolAddr).poolToken();
        bool isFlashPool = IPool(poolAddr).isFlashPool();
        uint32 weight = IPool(poolAddr).weight();

        // ensure that the pool is not already registered within the factory
        require(pools[poolToken] == address(0), "this pool is already registered");

        // create pool structure, register it within the factory
        pools[poolToken] = poolAddr;
        poolExists[poolAddr] = true;
        // update total pool weight of the factory
        totalWeight += weight;

        // emit an event
        emit PoolRegistered(msg.sender, poolToken, poolAddr, weight, isFlashPool);
    }

    /**
     * @notice Decreases ILV/block reward by 3%, can be executed
     *      no more than once per `blocksPerUpdate` blocks
     */
    function updateILVPerBlock() external {
        // checks if ratio can be updated i.e. if blocks/update (91252 blocks) have passed
        require(shouldUpdateRatio(), "too frequent");

        // decreases ILV/block reward by 3%
        ilvPerBlock = (ilvPerBlock * 97) / 100;

        // set current block as the last ratio update block
        lastRatioUpdate = uint32(blockNumber());

        // emit an event
        emit IlvRatioUpdated(msg.sender, ilvPerBlock);
    }

    /**
     * @dev Mints ILV tokens; executed by ILV Pool only
     *
     * @dev Requires factory to have ROLE_TOKEN_CREATOR permission
     *      on the ILV ERC20 token instance
     *
     * @param _to an address to mint tokens to
     * @param _amount amount of ILV tokens to mint
     */
    function mintYieldTo(address _to, uint256 _amount) external {
        // verify that sender is a pool registered withing the factory
        require(poolExists[msg.sender], "access denied");

        // mint ILV tokens as required
        mintIlv(_to, _amount);
    }

    /**
     * @dev Changes the weight of the pool;
     *      executed by the pool itself or by the factory owner
     *
     * @param poolAddr address of the pool to change weight for
     * @param weight new weight value to set to
     */
    function changePoolWeight(address poolAddr, uint32 weight) external {
        // verify function is executed either by factory owner or by the pool itself
        require(msg.sender == owner() || poolExists[msg.sender]);

        // recalculate total weight
        totalWeight = totalWeight + weight - IPool(poolAddr).weight();

        // set the new pool weight
        IPool(poolAddr).setWeight(weight);

        // emit an event
        emit WeightUpdated(msg.sender, poolAddr, weight);
    }

    /**
     * @dev Testing time-dependent functionality is difficult and the best way of
     *      doing it is to override block number in helper test smart contracts
     *
     * @return `block.number` in mainnet, custom values in testnets (if overridden)
     */
    function blockNumber() public view virtual returns (uint256) {
        // return current block number
        return block.number;
    }
}

// File: contracts/utils/SafeERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

import "../interfaces/IERC20.sol";
import "./Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using Address for address;

    function safeTransfer(
        IERC20 token,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(
        IERC20 token,
        address from,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        uint256 newAllowance = token.allowance(address(this), spender) + value;
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        uint256 newAllowance = token.allowance(address(this), spender) - value;
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) {
            // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: contracts/token/EscrowedIlluviumERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

import "../utils/ERC20.sol";
import "../utils/AccessControl.sol";

contract EscrowedIlluviumERC20 is ERC20("Escrowed Illuvium", "sILV"), AccessControl {
  /**
   * @dev Smart contract unique identifier, a random number
   * @dev Should be regenerated each time smart contact source code is changed
   *      and changes smart contract itself is to be redeployed
   * @dev Generated using https://www.random.org/bytes/
   */
  uint256 public constant TOKEN_UID = 0xac3051b8d4f50966afb632468a4f61483ae6a953b74e387a01ef94316d6b7d62;

  /**
   * @notice Must be called by ROLE_TOKEN_CREATOR addresses.
   *
   * @param recipient address to receive the tokens.
   * @param amount number of tokens to be minted.
   */
  function mint(address recipient, uint256 amount) external {
    require(isSenderInRole(ROLE_TOKEN_CREATOR), "insufficient privileges (ROLE_TOKEN_CREATOR required)");
    _mint(recipient, amount);
  }

  /**
   * @param amount number of tokens to be burned.
   */
  function burn(uint256 amount) external {
    _burn(msg.sender, amount);
  }
}

// File: contracts/interfaces/ILinkedToILV.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

/**
 * @title Linked to ILV Marker Interface
 *
 * @notice Marks smart contracts which are linked to IlluviumERC20 token instance upon construction,
 *      all these smart contracts share a common ilv() address getter
 *
 * @notice Implementing smart contracts MUST verify that they get linked to real IlluviumERC20 instance
 *      and that ilv() getter returns this very same instance address
 *
 * @author Basil Gorin
 */
interface ILinkedToILV {
  /**
   * @notice Getter for a verified IlluviumERC20 instance address
   *
   * @return IlluviumERC20 token instance address smart contract is linked to
   */
  function ilv() external view returns (address);
}

// File: contracts/pools/IlluviumAware.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

import "../token/IlluviumERC20.sol";
import "../interfaces/ILinkedToILV.sol";

/**
 * @title Illuvium Aware
 *
 * @notice Helper smart contract to be inherited by other smart contracts requiring to
 *      be linked to verified IlluviumERC20 instance and performing some basic tasks on it
 *
 * @author Basil Gorin
 */
abstract contract IlluviumAware is ILinkedToILV {
  /// @dev Link to ILV ERC20 Token IlluviumERC20 instance
  address public immutable override ilv;

  /**
   * @dev Creates IlluviumAware instance, requiring to supply deployed IlluviumERC20 instance address
   *
   * @param _ilv deployed IlluviumERC20 instance address
   */
  constructor(address _ilv) {
    // verify ILV address is set and is correct
    require(_ilv != address(0), "ILV address not set");
    require(IlluviumERC20(_ilv).TOKEN_UID() == 0x83ecb176af7c4f35a45ff0018282e3a05a1018065da866182df12285866f5a2c, "unexpected TOKEN_UID");

    // write ILV address
    ilv = _ilv;
  }

  /**
   * @dev Executes IlluviumERC20.safeTransferFrom(address(this), _to, _value, "")
   *      on the bound IlluviumERC20 instance
   *
   * @dev Reentrancy safe due to the IlluviumERC20 design
   */
  function transferIlv(address _to, uint256 _value) internal {
    // just delegate call to the target
    transferIlvFrom(address(this), _to, _value);
  }

  /**
   * @dev Executes IlluviumERC20.transferFrom(_from, _to, _value)
   *      on the bound IlluviumERC20 instance
   *
   * @dev Reentrancy safe due to the IlluviumERC20 design
   */
  function transferIlvFrom(address _from, address _to, uint256 _value) internal {
    // just delegate call to the target
    IlluviumERC20(ilv).transferFrom(_from, _to, _value);
  }

  /**
   * @dev Executes IlluviumERC20.mint(_to, _values)
   *      on the bound IlluviumERC20 instance
   *
   * @dev Reentrancy safe due to the IlluviumERC20 design
   */
  function mintIlv(address _to, uint256 _value) internal {
    // just delegate call to the target
    IlluviumERC20(ilv).mint(_to, _value);
  }

}

// File: contracts/utils/Ownable.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        address msgSender = msg.sender;
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == msg.sender, "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: contracts/token/IlluviumERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

import "../utils/AddressUtils.sol";
import "../utils/AccessControl.sol";
import "./ERC20Receiver.sol";

/**
 * @title Illuvium (ILV) ERC20 token
 *
 * @notice Illuvium is a core ERC20 token powering the game.
 *      It serves as an in-game currency, is tradable on exchanges,
 *      it powers up the governance protocol (Illuvium DAO) and participates in Yield Farming.
 *
 * @dev Token Summary:
 *      - Symbol: ILV
 *      - Name: Illuvium
 *      - Decimals: 18
 *      - Initial token supply: 7,000,000 ILV
 *      - Maximum final token supply: 10,000,000 ILV
 *          - Up to 3,000,000 ILV may get minted in 3 years period via yield farming
 *      - Mintable: total supply may increase
 *      - Burnable: total supply may decrease
 *
 * @dev Token balances and total supply are effectively 192 bits long, meaning that maximum
 *      possible total supply smart contract is able to track is 2^192 (close to 10^40 tokens)
 *
 * @dev Smart contract doesn't use safe math. All arithmetic operations are overflow/underflow safe.
 *      Additionally, Solidity 0.8.1 enforces overflow/underflow safety.
 *
 * @dev ERC20: reviewed according to https://eips.ethereum.org/EIPS/eip-20
 *
 * @dev ERC20: contract has passed OpenZeppelin ERC20 tests,
 *      see https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/test/token/ERC20/ERC20.behavior.js
 *      see https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/test/token/ERC20/ERC20.test.js
 *      see adopted copies of these tests in the `test` folder
 *
 * @dev ERC223/ERC777: not supported;
 *      send tokens via `safeTransferFrom` and implement `ERC20Receiver.onERC20Received` on the receiver instead
 *
 * @dev Multiple Withdrawal Attack on ERC20 Tokens (ISBN:978-1-7281-3027-9) - resolved
 *      Related events and functions are marked with "ISBN:978-1-7281-3027-9" tag:
 *        - event Transferred(address indexed _by, address indexed _from, address indexed _to, uint256 _value)
 *        - event Approved(address indexed _owner, address indexed _spender, uint256 _oldValue, uint256 _value)
 *        - function increaseAllowance(address _spender, uint256 _value) public returns (bool)
 *        - function decreaseAllowance(address _spender, uint256 _value) public returns (bool)
 *      See: https://ieeexplore.ieee.org/document/8802438
 *      See: https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
 *
 * @author Basil Gorin
 */
contract IlluviumERC20 is AccessControl {
  /**
   * @dev Smart contract unique identifier, a random number
   * @dev Should be regenerated each time smart contact source code is changed
   *      and changes smart contract itself is to be redeployed
   * @dev Generated using https://www.random.org/bytes/
   */
  uint256 public constant TOKEN_UID = 0x83ecb176af7c4f35a45ff0018282e3a05a1018065da866182df12285866f5a2c;

  /**
   * @notice Name of the token: Illuvium
   *
   * @notice ERC20 name of the token (long name)
   *
   * @dev ERC20 `function name() public view returns (string)`
   *
   * @dev Field is declared public: getter name() is created when compiled,
   *      it returns the name of the token.
   */
  string public constant name = "Illuvium";

  /**
   * @notice Symbol of the token: ILV
   *
   * @notice ERC20 symbol of that token (short name)
   *
   * @dev ERC20 `function symbol() public view returns (string)`
   *
   * @dev Field is declared public: getter symbol() is created when compiled,
   *      it returns the symbol of the token
   */
  string public constant symbol = "ILV";

  /**
   * @notice Decimals of the token: 18
   *
   * @dev ERC20 `function decimals() public view returns (uint8)`
   *
   * @dev Field is declared public: getter decimals() is created when compiled,
   *      it returns the number of decimals used to get its user representation.
   *      For example, if `decimals` equals `6`, a balance of `1,500,000` tokens should
   *      be displayed to a user as `1,5` (`1,500,000 / 10 ** 6`).
   *
   * @dev NOTE: This information is only used for _display_ purposes: it in
   *      no way affects any of the arithmetic of the contract, including balanceOf() and transfer().
   */
  uint8 public constant decimals = 18;

  /**
   * @notice Total supply of the token: initially 7,000,000,
   *      with the potential to grow up to 10,000,000 during yield farming period (3 years)
   *
   * @dev ERC20 `function totalSupply() public view returns (uint256)`
   *
   * @dev Field is declared public: getter totalSupply() is created when compiled,
   *      it returns the amount of tokens in existence.
   */
  uint256 public totalSupply; // is set to 7 million * 10^18 in the constructor

  /**
   * @dev A record of all the token balances
   * @dev This mapping keeps record of all token owners:
   *      owner => balance
   */
  mapping(address => uint256) public tokenBalances;

  /**
   * @notice A record of each account's voting delegate
   *
   * @dev Auxiliary data structure used to sum up an account's voting power
   *
   * @dev This mapping keeps record of all voting power delegations:
   *      voting delegator (token owner) => voting delegate
   */
  mapping(address => address) public votingDelegates;

  /**
   * @notice A voting power record binds voting power of a delegate to a particular
   *      block when the voting power delegation change happened
   */
  struct VotingPowerRecord {
    /*
     * @dev block.number when delegation has changed; starting from
     *      that block voting power value is in effect
     */
    uint64 blockNumber;

    /*
     * @dev cumulative voting power a delegate has obtained starting
     *      from the block stored in blockNumber
     */
    uint192 votingPower;
  }

  /**
   * @notice A record of each account's voting power
   *
   * @dev Primarily data structure to store voting power for each account.
   *      Voting power sums up from the account's token balance and delegated
   *      balances.
   *
   * @dev Stores current value and entire history of its changes.
   *      The changes are stored as an array of checkpoints.
   *      Checkpoint is an auxiliary data structure containing voting
   *      power (number of votes) and block number when the checkpoint is saved
   *
   * @dev Maps voting delegate => voting power record
   */
  mapping(address => VotingPowerRecord[]) public votingPowerHistory;

  /**
   * @dev A record of nonces for signing/validating signatures in `delegateWithSig`
   *      for every delegate, increases after successful validation
   *
   * @dev Maps delegate address => delegate nonce
   */
  mapping(address => uint256) public nonces;

  /**
   * @notice A record of all the allowances to spend tokens on behalf
   * @dev Maps token owner address to an address approved to spend
   *      some tokens on behalf, maps approved address to that amount
   * @dev owner => spender => value
   */
  mapping(address => mapping(address => uint256)) public transferAllowances;

  /**
   * @notice Enables ERC20 transfers of the tokens
   *      (transfer by the token owner himself)
   * @dev Feature FEATURE_TRANSFERS must be enabled in order for
   *      `transfer()` function to succeed
   */
  uint32 public constant FEATURE_TRANSFERS = 0x0000_0001;

  /**
   * @notice Enables ERC20 transfers on behalf
   *      (transfer by someone else on behalf of token owner)
   * @dev Feature FEATURE_TRANSFERS_ON_BEHALF must be enabled in order for
   *      `transferFrom()` function to succeed
   * @dev Token owner must call `approve()` first to authorize
   *      the transfer on behalf
   */
  uint32 public constant FEATURE_TRANSFERS_ON_BEHALF = 0x0000_0002;

  /**
   * @dev Defines if the default behavior of `transfer` and `transferFrom`
   *      checks if the receiver smart contract supports ERC20 tokens
   * @dev When feature FEATURE_UNSAFE_TRANSFERS is enabled the transfers do not
   *      check if the receiver smart contract supports ERC20 tokens,
   *      i.e. `transfer` and `transferFrom` behave like `unsafeTransferFrom`
   * @dev When feature FEATURE_UNSAFE_TRANSFERS is disabled (default) the transfers
   *      check if the receiver smart contract supports ERC20 tokens,
   *      i.e. `transfer` and `transferFrom` behave like `safeTransferFrom`
   */
  uint32 public constant FEATURE_UNSAFE_TRANSFERS = 0x0000_0004;

  /**
   * @notice Enables token owners to burn their own tokens,
   *      including locked tokens which are burnt first
   * @dev Feature FEATURE_OWN_BURNS must be enabled in order for
   *      `burn()` function to succeed when called by token owner
   */
  uint32 public constant FEATURE_OWN_BURNS = 0x0000_0008;

  /**
   * @notice Enables approved operators to burn tokens on behalf of their owners,
   *      including locked tokens which are burnt first
   * @dev Feature FEATURE_OWN_BURNS must be enabled in order for
   *      `burn()` function to succeed when called by approved operator
   */
  uint32 public constant FEATURE_BURNS_ON_BEHALF = 0x0000_0010;

  /**
   * @notice Enables delegators to elect delegates
   * @dev Feature FEATURE_DELEGATIONS must be enabled in order for
   *      `delegate()` function to succeed
   */
  uint32 public constant FEATURE_DELEGATIONS = 0x0000_0020;

  /**
   * @notice Enables delegators to elect delegates on behalf
   *      (via an EIP712 signature)
   * @dev Feature FEATURE_DELEGATIONS must be enabled in order for
   *      `delegateWithSig()` function to succeed
   */
  uint32 public constant FEATURE_DELEGATIONS_ON_BEHALF = 0x0000_0040;

  /**
   * @notice Token creator is responsible for creating (minting)
   *      tokens to an arbitrary address
   * @dev Role ROLE_TOKEN_CREATOR allows minting tokens
   *      (calling `mint` function)
   */
  uint32 public constant ROLE_TOKEN_CREATOR = 0x0001_0000;

  /**
   * @notice Token destroyer is responsible for destroying (burning)
   *      tokens owned by an arbitrary address
   * @dev Role ROLE_TOKEN_DESTROYER allows burning tokens
   *      (calling `burn` function)
   */
  uint32 public constant ROLE_TOKEN_DESTROYER = 0x0002_0000;

  /**
   * @notice ERC20 receivers are allowed to receive tokens without ERC20 safety checks,
   *      which may be useful to simplify tokens transfers into "legacy" smart contracts
   * @dev When `FEATURE_UNSAFE_TRANSFERS` is not enabled addresses having
   *      `ROLE_ERC20_RECEIVER` permission are allowed to receive tokens
   *      via `transfer` and `transferFrom` functions in the same way they
   *      would via `unsafeTransferFrom` function
   * @dev When `FEATURE_UNSAFE_TRANSFERS` is enabled `ROLE_ERC20_RECEIVER` permission
   *      doesn't affect the transfer behaviour since
   *      `transfer` and `transferFrom` behave like `unsafeTransferFrom` for any receiver
   * @dev ROLE_ERC20_RECEIVER is a shortening for ROLE_UNSAFE_ERC20_RECEIVER
   */
  uint32 public constant ROLE_ERC20_RECEIVER = 0x0004_0000;

  /**
   * @notice ERC20 senders are allowed to send tokens without ERC20 safety checks,
   *      which may be useful to simplify tokens transfers into "legacy" smart contracts
   * @dev When `FEATURE_UNSAFE_TRANSFERS` is not enabled senders having
   *      `ROLE_ERC20_SENDER` permission are allowed to send tokens
   *      via `transfer` and `transferFrom` functions in the same way they
   *      would via `unsafeTransferFrom` function
   * @dev When `FEATURE_UNSAFE_TRANSFERS` is enabled `ROLE_ERC20_SENDER` permission
   *      doesn't affect the transfer behaviour since
   *      `transfer` and `transferFrom` behave like `unsafeTransferFrom` for any receiver
   * @dev ROLE_ERC20_SENDER is a shortening for ROLE_UNSAFE_ERC20_SENDER
   */
  uint32 public constant ROLE_ERC20_SENDER = 0x0008_0000;

  /**
   * @dev Magic value to be returned by ERC20Receiver upon successful reception of token(s)
   * @dev Equal to `bytes4(keccak256("onERC20Received(address,address,uint256,bytes)"))`,
   *      which can be also obtained as `ERC20Receiver(address(0)).onERC20Received.selector`
   */
  bytes4 private constant ERC20_RECEIVED = 0x4fc35859;

  /**
   * @notice EIP-712 contract's domain typeHash, see https://eips.ethereum.org/EIPS/eip-712#rationale-for-typehash
   */
  bytes32 public constant DOMAIN_TYPEHASH = keccak256("EIP712Domain(string name,uint256 chainId,address verifyingContract)");

  /**
   * @notice EIP-712 delegation struct typeHash, see https://eips.ethereum.org/EIPS/eip-712#rationale-for-typehash
   */
  bytes32 public constant DELEGATION_TYPEHASH = keccak256("Delegation(address delegate,uint256 nonce,uint256 expiry)");

  /**
   * @dev Fired in transfer(), transferFrom() and some other (non-ERC20) functions
   *
   * @dev ERC20 `event Transfer(address indexed _from, address indexed _to, uint256 _value)`
   *
   * @param _from an address tokens were consumed from
   * @param _to an address tokens were sent to
   * @param _value number of tokens transferred
   */
  event Transfer(address indexed _from, address indexed _to, uint256 _value);

  /**
   * @dev Fired in approve() and approveAtomic() functions
   *
   * @dev ERC20 `event Approval(address indexed _owner, address indexed _spender, uint256 _value)`
   *
   * @param _owner an address which granted a permission to transfer
   *      tokens on its behalf
   * @param _spender an address which received a permission to transfer
   *      tokens on behalf of the owner `_owner`
   * @param _value amount of tokens granted to transfer on behalf
   */
  event Approval(address indexed _owner, address indexed _spender, uint256 _value);

  /**
   * @dev Fired in mint() function
   *
   * @param _by an address which minted some tokens (transaction sender)
   * @param _to an address the tokens were minted to
   * @param _value an amount of tokens minted
   */
  event Minted(address indexed _by, address indexed _to, uint256 _value);

  /**
   * @dev Fired in burn() function
   *
   * @param _by an address which burned some tokens (transaction sender)
   * @param _from an address the tokens were burnt from
   * @param _value an amount of tokens burnt
   */
  event Burnt(address indexed _by, address indexed _from, uint256 _value);

  /**
   * @dev Resolution for the Multiple Withdrawal Attack on ERC20 Tokens (ISBN:978-1-7281-3027-9)
   *
   * @dev Similar to ERC20 Transfer event, but also logs an address which executed transfer
   *
   * @dev Fired in transfer(), transferFrom() and some other (non-ERC20) functions
   *
   * @param _by an address which performed the transfer
   * @param _from an address tokens were consumed from
   * @param _to an address tokens were sent to
   * @param _value number of tokens transferred
   */
  event Transferred(address indexed _by, address indexed _from, address indexed _to, uint256 _value);

  /**
   * @dev Resolution for the Multiple Withdrawal Attack on ERC20 Tokens (ISBN:978-1-7281-3027-9)
   *
   * @dev Similar to ERC20 Approve event, but also logs old approval value
   *
   * @dev Fired in approve() and approveAtomic() functions
   *
   * @param _owner an address which granted a permission to transfer
   *      tokens on its behalf
   * @param _spender an address which received a permission to transfer
   *      tokens on behalf of the owner `_owner`
   * @param _oldValue previously granted amount of tokens to transfer on behalf
   * @param _value new granted amount of tokens to transfer on behalf
   */
  event Approved(address indexed _owner, address indexed _spender, uint256 _oldValue, uint256 _value);

  /**
   * @dev Notifies that a key-value pair in `votingDelegates` mapping has changed,
   *      i.e. a delegator address has changed its delegate address
   *
   * @param _of delegator address, a token owner
   * @param _from old delegate, an address which delegate right is revoked
   * @param _to new delegate, an address which received the voting power
   */
  event DelegateChanged(address indexed _of, address indexed _from, address indexed _to);

  /**
   * @dev Notifies that a key-value pair in `votingPowerHistory` mapping has changed,
   *      i.e. a delegate's voting power has changed.
   *
   * @param _of delegate whose voting power has changed
   * @param _fromVal previous number of votes delegate had
   * @param _toVal new number of votes delegate has
   */
  event VotingPowerChanged(address indexed _of, uint256 _fromVal, uint256 _toVal);

  /**
   * @dev Deploys the token smart contract,
   *      assigns initial token supply to the address specified
   *
   * @param _initialHolder owner of the initial token supply
   */
  constructor(address _initialHolder) {
    // verify initial holder address non-zero (is set)
    require(_initialHolder != address(0), "_initialHolder not set (zero address)");

    // mint initial supply
    mint(_initialHolder, 7_000_000e18);
  }

  // ===== Start: ERC20/ERC223/ERC777 functions =====

  /**
   * @notice Gets the balance of a particular address
   *
   * @dev ERC20 `function balanceOf(address _owner) public view returns (uint256 balance)`
   *
   * @param _owner the address to query the the balance for
   * @return balance an amount of tokens owned by the address specified
   */
  function balanceOf(address _owner) public view returns (uint256 balance) {
    // read the balance and return
    return tokenBalances[_owner];
  }

  /**
   * @notice Transfers some tokens to an external address or a smart contract
   *
   * @dev ERC20 `function transfer(address _to, uint256 _value) public returns (bool success)`
   *
   * @dev Called by token owner (an address which has a
   *      positive token balance tracked by this smart contract)
   * @dev Throws on any error like
   *      * insufficient token balance or
   *      * incorrect `_to` address:
   *          * zero address or
   *          * self address or
   *          * smart contract which doesn't support ERC20
   *
   * @param _to an address to transfer tokens to,
   *      must be either an external address or a smart contract,
   *      compliant with the ERC20 standard
   * @param _value amount of tokens to be transferred, must
   *      be greater than zero
   * @return success true on success, throws otherwise
   */
  function transfer(address _to, uint256 _value) public returns (bool success) {
    // just delegate call to `transferFrom`,
    // `FEATURE_TRANSFERS` is verified inside it
    return transferFrom(msg.sender, _to, _value);
  }

  /**
   * @notice Transfers some tokens on behalf of address `_from' (token owner)
   *      to some other address `_to`
   *
   * @dev ERC20 `function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)`
   *
   * @dev Called by token owner on his own or approved address,
   *      an address approved earlier by token owner to
   *      transfer some amount of tokens on its behalf
   * @dev Throws on any error like
   *      * insufficient token balance or
   *      * incorrect `_to` address:
   *          * zero address or
   *          * same as `_from` address (self transfer)
   *          * smart contract which doesn't support ERC20
   *
   * @param _from token owner which approved caller (transaction sender)
   *      to transfer `_value` of tokens on its behalf
   * @param _to an address to transfer tokens to,
   *      must be either an external address or a smart contract,
   *      compliant with the ERC20 standard
   * @param _value amount of tokens to be transferred, must
   *      be greater than zero
   * @return success true on success, throws otherwise
   */
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
    // depending on `FEATURE_UNSAFE_TRANSFERS` we execute either safe (default)
    // or unsafe transfer
    // if `FEATURE_UNSAFE_TRANSFERS` is enabled
    // or receiver has `ROLE_ERC20_RECEIVER` permission
    // or sender has `ROLE_ERC20_SENDER` permission
    if(isFeatureEnabled(FEATURE_UNSAFE_TRANSFERS)
      || isOperatorInRole(_to, ROLE_ERC20_RECEIVER)
      || isSenderInRole(ROLE_ERC20_SENDER)) {
      // we execute unsafe transfer - delegate call to `unsafeTransferFrom`,
      // `FEATURE_TRANSFERS` is verified inside it
      unsafeTransferFrom(_from, _to, _value);
    }
    // otherwise - if `FEATURE_UNSAFE_TRANSFERS` is disabled
    // and receiver doesn't have `ROLE_ERC20_RECEIVER` permission
    else {
      // we execute safe transfer - delegate call to `safeTransferFrom`, passing empty `_data`,
      // `FEATURE_TRANSFERS` is verified inside it
      safeTransferFrom(_from, _to, _value, "");
    }

    // both `unsafeTransferFrom` and `safeTransferFrom` throw on any error, so
    // if we're here - it means operation successful,
    // just return true
    return true;
  }

  /**
   * @notice Transfers some tokens on behalf of address `_from' (token owner)
   *      to some other address `_to`
   *
   * @dev Inspired by ERC721 safeTransferFrom, this function allows to
   *      send arbitrary data to the receiver on successful token transfer
   * @dev Called by token owner on his own or approved address,
   *      an address approved earlier by token owner to
   *      transfer some amount of tokens on its behalf
   * @dev Throws on any error like
   *      * insufficient token balance or
   *      * incorrect `_to` address:
   *          * zero address or
   *          * same as `_from` address (self transfer)
   *          * smart contract which doesn't support ERC20Receiver interface
   * @dev Returns silently on success, throws otherwise
   *
   * @param _from token owner which approved caller (transaction sender)
   *      to transfer `_value` of tokens on its behalf
   * @param _to an address to transfer tokens to,
   *      must be either an external address or a smart contract,
   *      compliant with the ERC20 standard
   * @param _value amount of tokens to be transferred, must
   *      be greater than zero
   * @param _data [optional] additional data with no specified format,
   *      sent in onERC20Received call to `_to` in case if its a smart contract
   */
  function safeTransferFrom(address _from, address _to, uint256 _value, bytes memory _data) public {
    // first delegate call to `unsafeTransferFrom`
    // to perform the unsafe token(s) transfer
    unsafeTransferFrom(_from, _to, _value);

    // after the successful transfer - check if receiver supports
    // ERC20Receiver and execute a callback handler `onERC20Received`,
    // reverting whole transaction on any error:
    // check if receiver `_to` supports ERC20Receiver interface
    if(AddressUtils.isContract(_to)) {
      // if `_to` is a contract - execute onERC20Received
      bytes4 response = ERC20Receiver(_to).onERC20Received(msg.sender, _from, _value, _data);

      // expected response is ERC20_RECEIVED
      require(response == ERC20_RECEIVED, "invalid onERC20Received response");
    }
  }

  /**
   * @notice Transfers some tokens on behalf of address `_from' (token owner)
   *      to some other address `_to`
   *
   * @dev In contrast to `safeTransferFrom` doesn't check recipient
   *      smart contract to support ERC20 tokens (ERC20Receiver)
   * @dev Designed to be used by developers when the receiver is known
   *      to support ERC20 tokens but doesn't implement ERC20Receiver interface
   * @dev Called by token owner on his own or approved address,
   *      an address approved earlier by token owner to
   *      transfer some amount of tokens on its behalf
   * @dev Throws on any error like
   *      * insufficient token balance or
   *      * incorrect `_to` address:
   *          * zero address or
   *          * same as `_from` address (self transfer)
   * @dev Returns silently on success, throws otherwise
   *
   * @param _from token owner which approved caller (transaction sender)
   *      to transfer `_value` of tokens on its behalf
   * @param _to an address to transfer tokens to,
   *      must be either an external address or a smart contract,
   *      compliant with the ERC20 standard
   * @param _value amount of tokens to be transferred, must
   *      be greater than zero
   */
  function unsafeTransferFrom(address _from, address _to, uint256 _value) public {
    // if `_from` is equal to sender, require transfers feature to be enabled
    // otherwise require transfers on behalf feature to be enabled
    require(_from == msg.sender && isFeatureEnabled(FEATURE_TRANSFERS)
         || _from != msg.sender && isFeatureEnabled(FEATURE_TRANSFERS_ON_BEHALF),
            _from == msg.sender? "transfers are disabled": "transfers on behalf are disabled");

    // non-zero source address check - Zeppelin
    // obviously, zero source address is a client mistake
    // it's not part of ERC20 standard but it's reasonable to fail fast
    // since for zero value transfer transaction succeeds otherwise
    require(_from != address(0), "ERC20: transfer from the zero address"); // Zeppelin msg

    // non-zero recipient address check
    require(_to != address(0), "ERC20: transfer to the zero address"); // Zeppelin msg

    // sender and recipient cannot be the same
    require(_from != _to, "sender and recipient are the same (_from = _to)");

    // sending tokens to the token smart contract itself is a client mistake
    require(_to != address(this), "invalid recipient (transfer to the token smart contract itself)");

    // according to ERC-20 Token Standard, https://eips.ethereum.org/EIPS/eip-20
    // "Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event."
    if(_value == 0) {
      // emit an ERC20 transfer event
      emit Transfer(_from, _to, _value);

      // don't forget to return - we're done
      return;
    }

    // no need to make arithmetic overflow check on the _value - by design of mint()

    // in case of transfer on behalf
    if(_from != msg.sender) {
      // read allowance value - the amount of tokens allowed to transfer - into the stack
      uint256 _allowance = transferAllowances[_from][msg.sender];

      // verify sender has an allowance to transfer amount of tokens requested
      require(_allowance >= _value, "ERC20: transfer amount exceeds allowance"); // Zeppelin msg

      // update allowance value on the stack
      _allowance -= _value;

      // update the allowance value in storage
      transferAllowances[_from][msg.sender] = _allowance;

      // emit an improved atomic approve event
      emit Approved(_from, msg.sender, _allowance + _value, _allowance);

      // emit an ERC20 approval event to reflect the decrease
      emit Approval(_from, msg.sender, _allowance);
    }

    // verify sender has enough tokens to transfer on behalf
    require(tokenBalances[_from] >= _value, "ERC20: transfer amount exceeds balance"); // Zeppelin msg

    // perform the transfer:
    // decrease token owner (sender) balance
    tokenBalances[_from] -= _value;

    // increase `_to` address (receiver) balance
    tokenBalances[_to] += _value;

    // move voting power associated with the tokens transferred
    __moveVotingPower(votingDelegates[_from], votingDelegates[_to], _value);

    // emit an improved transfer event
    emit Transferred(msg.sender, _from, _to, _value);

    // emit an ERC20 transfer event
    emit Transfer(_from, _to, _value);
  }

  /**
   * @notice Approves address called `_spender` to transfer some amount
   *      of tokens on behalf of the owner
   *
   * @dev ERC20 `function approve(address _spender, uint256 _value) public returns (bool success)`
   *
   * @dev Caller must not necessarily own any tokens to grant the permission
   *
   * @param _spender an address approved by the caller (token owner)
   *      to spend some tokens on its behalf
   * @param _value an amount of tokens spender `_spender` is allowed to
   *      transfer on behalf of the token owner
   * @return success true on success, throws otherwise
   */
  function approve(address _spender, uint256 _value) public returns (bool success) {
    // non-zero spender address check - Zeppelin
    // obviously, zero spender address is a client mistake
    // it's not part of ERC20 standard but it's reasonable to fail fast
    require(_spender != address(0), "ERC20: approve to the zero address"); // Zeppelin msg

    // read old approval value to emmit an improved event (ISBN:978-1-7281-3027-9)
    uint256 _oldValue = transferAllowances[msg.sender][_spender];

    // perform an operation: write value requested into the storage
    transferAllowances[msg.sender][_spender] = _value;

    // emit an improved atomic approve event (ISBN:978-1-7281-3027-9)
    emit Approved(msg.sender, _spender, _oldValue, _value);

    // emit an ERC20 approval event
    emit Approval(msg.sender, _spender, _value);

    // operation successful, return true
    return true;
  }

  /**
   * @notice Returns the amount which _spender is still allowed to withdraw from _owner.
   *
   * @dev ERC20 `function allowance(address _owner, address _spender) public view returns (uint256 remaining)`
   *
   * @dev A function to check an amount of tokens owner approved
   *      to transfer on its behalf by some other address called "spender"
   *
   * @param _owner an address which approves transferring some tokens on its behalf
   * @param _spender an address approved to transfer some tokens on behalf
   * @return remaining an amount of tokens approved address `_spender` can transfer on behalf
   *      of token owner `_owner`
   */
  function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
    // read the value from storage and return
    return transferAllowances[_owner][_spender];
  }

  // ===== End: ERC20/ERC223/ERC777 functions =====

  // ===== Start: Resolution for the Multiple Withdrawal Attack on ERC20 Tokens (ISBN:978-1-7281-3027-9) =====

  /**
   * @notice Increases the allowance granted to `spender` by the transaction sender
   *
   * @dev Resolution for the Multiple Withdrawal Attack on ERC20 Tokens (ISBN:978-1-7281-3027-9)
   *
   * @dev Throws if value to increase by is zero or too big and causes arithmetic overflow
   *
   * @param _spender an address approved by the caller (token owner)
   *      to spend some tokens on its behalf
   * @param _value an amount of tokens to increase by
   * @return success true on success, throws otherwise
   */
  function increaseAllowance(address _spender, uint256 _value) public virtual returns (bool) {
    // read current allowance value
    uint256 currentVal = transferAllowances[msg.sender][_spender];

    // non-zero _value and arithmetic overflow check on the allowance
    require(currentVal + _value > currentVal, "zero value approval increase or arithmetic overflow");

    // delegate call to `approve` with the new value
    return approve(_spender, currentVal + _value);
  }

  /**
   * @notice Decreases the allowance granted to `spender` by the caller.
   *
   * @dev Resolution for the Multiple Withdrawal Attack on ERC20 Tokens (ISBN:978-1-7281-3027-9)
   *
   * @dev Throws if value to decrease by is zero or is bigger than currently allowed value
   *
   * @param _spender an address approved by the caller (token owner)
   *      to spend some tokens on its behalf
   * @param _value an amount of tokens to decrease by
   * @return success true on success, throws otherwise
   */
  function decreaseAllowance(address _spender, uint256 _value) public virtual returns (bool) {
    // read current allowance value
    uint256 currentVal = transferAllowances[msg.sender][_spender];

    // non-zero _value check on the allowance
    require(_value > 0, "zero value approval decrease");

    // verify allowance decrease doesn't underflow
    require(currentVal >= _value, "ERC20: decreased allowance below zero");

    // delegate call to `approve` with the new value
    return approve(_spender, currentVal - _value);
  }

  // ===== End: Resolution for the Multiple Withdrawal Attack on ERC20 Tokens (ISBN:978-1-7281-3027-9) =====

  // ===== Start: Minting/burning extension =====

  /**
   * @dev Mints (creates) some tokens to address specified
   * @dev The value specified is treated as is without taking
   *      into account what `decimals` value is
   * @dev Behaves effectively as `mintTo` function, allowing
   *      to specify an address to mint tokens to
   * @dev Requires sender to have `ROLE_TOKEN_CREATOR` permission
   *
   * @dev Throws on overflow, if totalSupply + _value doesn't fit into uint256
   *
   * @param _to an address to mint tokens to
   * @param _value an amount of tokens to mint (create)
   */
  function mint(address _to, uint256 _value) public {
    // check if caller has sufficient permissions to mint tokens
    require(isSenderInRole(ROLE_TOKEN_CREATOR), "insufficient privileges (ROLE_TOKEN_CREATOR required)");

    // non-zero recipient address check
    require(_to != address(0), "ERC20: mint to the zero address"); // Zeppelin msg

    // non-zero _value and arithmetic overflow check on the total supply
    // this check automatically secures arithmetic overflow on the individual balance
    require(totalSupply + _value > totalSupply, "zero value mint or arithmetic overflow");

    // uint192 overflow check (required by voting delegation)
    require(totalSupply + _value <= type(uint192).max, "total supply overflow (uint192)");

    // perform mint:
    // increase total amount of tokens value
    totalSupply += _value;

    // increase `_to` address balance
    tokenBalances[_to] += _value;

    // create voting power associated with the tokens minted
    __moveVotingPower(address(0), votingDelegates[_to], _value);

    // fire a minted event
    emit Minted(msg.sender, _to, _value);

    // emit an improved transfer event
    emit Transferred(msg.sender, address(0), _to, _value);

    // fire ERC20 compliant transfer event
    emit Transfer(address(0), _to, _value);
  }

  /**
   * @dev Burns (destroys) some tokens from the address specified
   * @dev The value specified is treated as is without taking
   *      into account what `decimals` value is
   * @dev Behaves effectively as `burnFrom` function, allowing
   *      to specify an address to burn tokens from
   * @dev Requires sender to have `ROLE_TOKEN_DESTROYER` permission
   *
   * @param _from an address to burn some tokens from
   * @param _value an amount of tokens to burn (destroy)
   */
  function burn(address _from, uint256 _value) public {
    // check if caller has sufficient permissions to burn tokens
    // and if not - check for possibility to burn own tokens or to burn on behalf
    if(!isSenderInRole(ROLE_TOKEN_DESTROYER)) {
      // if `_from` is equal to sender, require own burns feature to be enabled
      // otherwise require burns on behalf feature to be enabled
      require(_from == msg.sender && isFeatureEnabled(FEATURE_OWN_BURNS)
           || _from != msg.sender && isFeatureEnabled(FEATURE_BURNS_ON_BEHALF),
              _from == msg.sender? "burns are disabled": "burns on behalf are disabled");

      // in case of burn on behalf
      if(_from != msg.sender) {
        // read allowance value - the amount of tokens allowed to be burnt - into the stack
        uint256 _allowance = transferAllowances[_from][msg.sender];

        // verify sender has an allowance to burn amount of tokens requested
        require(_allowance >= _value, "ERC20: burn amount exceeds allowance"); // Zeppelin msg

        // update allowance value on the stack
        _allowance -= _value;

        // update the allowance value in storage
        transferAllowances[_from][msg.sender] = _allowance;

        // emit an improved atomic approve event
        emit Approved(msg.sender, _from, _allowance + _value, _allowance);

        // emit an ERC20 approval event to reflect the decrease
        emit Approval(_from, msg.sender, _allowance);
      }
    }

    // at this point we know that either sender is ROLE_TOKEN_DESTROYER or
    // we burn own tokens or on behalf (in latest case we already checked and updated allowances)
    // we have left to execute balance checks and burning logic itself

    // non-zero burn value check
    require(_value != 0, "zero value burn");

    // non-zero source address check - Zeppelin
    require(_from != address(0), "ERC20: burn from the zero address"); // Zeppelin msg

    // verify `_from` address has enough tokens to destroy
    // (basically this is a arithmetic overflow check)
    require(tokenBalances[_from] >= _value, "ERC20: burn amount exceeds balance"); // Zeppelin msg

    // perform burn:
    // decrease `_from` address balance
    tokenBalances[_from] -= _value;

    // decrease total amount of tokens value
    totalSupply -= _value;

    // destroy voting power associated with the tokens burnt
    __moveVotingPower(votingDelegates[_from], address(0), _value);

    // fire a burnt event
    emit Burnt(msg.sender, _from, _value);

    // emit an improved transfer event
    emit Transferred(msg.sender, _from, address(0), _value);

    // fire ERC20 compliant transfer event
    emit Transfer(_from, address(0), _value);
  }

  // ===== End: Minting/burning extension =====

  // ===== Start: DAO Support (Compound-like voting delegation) =====

  /**
   * @notice Gets current voting power of the account `_of`
   * @param _of the address of account to get voting power of
   * @return current cumulative voting power of the account,
   *      sum of token balances of all its voting delegators
   */
  function getVotingPower(address _of) public view returns (uint256) {
    // get a link to an array of voting power history records for an address specified
    VotingPowerRecord[] storage history = votingPowerHistory[_of];

    // lookup the history and return latest element
    return history.length == 0? 0: history[history.length - 1].votingPower;
  }

  /**
   * @notice Gets past voting power of the account `_of` at some block `_blockNum`
   * @dev Throws if `_blockNum` is not in the past (not the finalized block)
   * @param _of the address of account to get voting power of
   * @param _blockNum block number to get the voting power at
   * @return past cumulative voting power of the account,
   *      sum of token balances of all its voting delegators at block number `_blockNum`
   */
  function getVotingPowerAt(address _of, uint256 _blockNum) public view returns (uint256) {
    // make sure block number is not in the past (not the finalized block)
    require(_blockNum < block.number, "not yet determined"); // Compound msg

    // get a link to an array of voting power history records for an address specified
    VotingPowerRecord[] storage history = votingPowerHistory[_of];

    // if voting power history for the account provided is empty
    if(history.length == 0) {
      // than voting power is zero - return the result
      return 0;
    }

    // check latest voting power history record block number:
    // if history was not updated after the block of interest
    if(history[history.length - 1].blockNumber <= _blockNum) {
      // we're done - return last voting power record
      return getVotingPower(_of);
    }

    // check first voting power history record block number:
    // if history was never updated before the block of interest
    if(history[0].blockNumber > _blockNum) {
      // we're done - voting power at the block num of interest was zero
      return 0;
    }

    // `votingPowerHistory[_of]` is an array ordered by `blockNumber`, ascending;
    // apply binary search on `votingPowerHistory[_of]` to find such an entry number `i`, that
    // `votingPowerHistory[_of][i].blockNumber <= _blockNum`, but in the same time
    // `votingPowerHistory[_of][i + 1].blockNumber > _blockNum`
    // return the result - voting power found at index `i`
    return history[__binaryLookup(_of, _blockNum)].votingPower;
  }

  /**
   * @dev Reads an entire voting power history array for the delegate specified
   *
   * @param _of delegate to query voting power history for
   * @return voting power history array for the delegate of interest
   */
  function getVotingPowerHistory(address _of) public view returns(VotingPowerRecord[] memory) {
    // return an entire array as memory
    return votingPowerHistory[_of];
  }

  /**
   * @dev Returns length of the voting power history array for the delegate specified;
   *      useful since reading an entire array just to get its length is expensive (gas cost)
   *
   * @param _of delegate to query voting power history length for
   * @return voting power history array length for the delegate of interest
   */
  function getVotingPowerHistoryLength(address _of) public view returns(uint256) {
    // read array length and return
    return votingPowerHistory[_of].length;
  }

  /**
   * @notice Delegates voting power of the delegator `msg.sender` to the delegate `_to`
   *
   * @dev Accepts zero value address to delegate voting power to, effectively
   *      removing the delegate in that case
   *
   * @param _to address to delegate voting power to
   */
  function delegate(address _to) public {
    // verify delegations are enabled
    require(isFeatureEnabled(FEATURE_DELEGATIONS), "delegations are disabled");
    // delegate call to `__delegate`
    __delegate(msg.sender, _to);
  }

  /**
   * @notice Delegates voting power of the delegator (represented by its signature) to the delegate `_to`
   *
   * @dev Accepts zero value address to delegate voting power to, effectively
   *      removing the delegate in that case
   *
   * @dev Compliant with EIP-712: Ethereum typed structured data hashing and signing,
   *      see https://eips.ethereum.org/EIPS/eip-712
   *
   * @param _to address to delegate voting power to
   * @param _nonce nonce used to construct the signature, and used to validate it;
   *      nonce is increased by one after successful signature validation and vote delegation
   * @param _exp signature expiration time
   * @param v the recovery byte of the signature
   * @param r half of the ECDSA signature pair
   * @param s half of the ECDSA signature pair
   */
  function delegateWithSig(address _to, uint256 _nonce, uint256 _exp, uint8 v, bytes32 r, bytes32 s) public {
    // verify delegations on behalf are enabled
    require(isFeatureEnabled(FEATURE_DELEGATIONS_ON_BEHALF), "delegations on behalf are disabled");

    // build the EIP-712 contract domain separator
    bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), block.chainid, address(this)));

    // build the EIP-712 hashStruct of the delegation message
    bytes32 hashStruct = keccak256(abi.encode(DELEGATION_TYPEHASH, _to, _nonce, _exp));

    // calculate the EIP-712 digest "\x19\x01" ‖ domainSeparator ‖ hashStruct(message)
    bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, hashStruct));

    // recover the address who signed the message with v, r, s
    address signer = ecrecover(digest, v, r, s);

    // perform message integrity and security validations
    require(signer != address(0), "invalid signature"); // Compound msg
    require(_nonce == nonces[signer], "invalid nonce"); // Compound msg
    require(block.timestamp < _exp, "signature expired"); // Compound msg

    // update the nonce for that particular signer to avoid replay attack
    nonces[signer]++;

    // delegate call to `__delegate` - execute the logic required
    __delegate(signer, _to);
  }

  /**
   * @dev Auxiliary function to delegate delegator's `_from` voting power to the delegate `_to`
   * @dev Writes to `votingDelegates` and `votingPowerHistory` mappings
   *
   * @param _from delegator who delegates his voting power
   * @param _to delegate who receives the voting power
   */
  function __delegate(address _from, address _to) private {
    // read current delegate to be replaced by a new one
    address _fromDelegate = votingDelegates[_from];

    // read current voting power (it is equal to token balance)
    uint256 _value = tokenBalances[_from];

    // reassign voting delegate to `_to`
    votingDelegates[_from] = _to;

    // update voting power for `_fromDelegate` and `_to`
    __moveVotingPower(_fromDelegate, _to, _value);

    // emit an event
    emit DelegateChanged(_from, _fromDelegate, _to);
  }

  /**
   * @dev Auxiliary function to move voting power `_value`
   *      from delegate `_from` to the delegate `_to`
   *
   * @dev Doesn't have any effect if `_from == _to`, or if `_value == 0`
   *
   * @param _from delegate to move voting power from
   * @param _to delegate to move voting power to
   * @param _value voting power to move from `_from` to `_to`
   */
  function __moveVotingPower(address _from, address _to, uint256 _value) private {
    // if there is no move (`_from == _to`) or there is nothing to move (`_value == 0`)
    if(_from == _to || _value == 0) {
      // return silently with no action
      return;
    }

    // if source address is not zero - decrease its voting power
    if(_from != address(0)) {
      // read current source address voting power
      uint256 _fromVal = getVotingPower(_from);

      // calculate decreased voting power
      // underflow is not possible by design:
      // voting power is limited by token balance which is checked by the callee
      uint256 _toVal = _fromVal - _value;

      // update source voting power from `_fromVal` to `_toVal`
      __updateVotingPower(_from, _fromVal, _toVal);
    }

    // if destination address is not zero - increase its voting power
    if(_to != address(0)) {
      // read current destination address voting power
      uint256 _fromVal = getVotingPower(_to);

      // calculate increased voting power
      // overflow is not possible by design:
      // max token supply limits the cumulative voting power
      uint256 _toVal = _fromVal + _value;

      // update destination voting power from `_fromVal` to `_toVal`
      __updateVotingPower(_to, _fromVal, _toVal);
    }
  }

  /**
   * @dev Auxiliary function to update voting power of the delegate `_of`
   *      from value `_fromVal` to value `_toVal`
   *
   * @param _of delegate to update its voting power
   * @param _fromVal old voting power of the delegate
   * @param _toVal new voting power of the delegate
   */
  function __updateVotingPower(address _of, uint256 _fromVal, uint256 _toVal) private {
    // get a link to an array of voting power history records for an address specified
    VotingPowerRecord[] storage history = votingPowerHistory[_of];

    // if there is an existing voting power value stored for current block
    if(history.length != 0 && history[history.length - 1].blockNumber == block.number) {
      // update voting power which is already stored in the current block
      history[history.length - 1].votingPower = uint192(_toVal);
    }
    // otherwise - if there is no value stored for current block
    else {
      // add new element into array representing the value for current block
      history.push(VotingPowerRecord(uint64(block.number), uint192(_toVal)));
    }

    // emit an event
    emit VotingPowerChanged(_of, _fromVal, _toVal);
  }

  /**
   * @dev Auxiliary function to lookup an element in a sorted (asc) array of elements
   *
   * @dev This function finds the closest element in an array to the value
   *      of interest (not exceeding that value) and returns its index within an array
   *
   * @dev An array to search in is `votingPowerHistory[_to][i].blockNumber`,
   *      it is sorted in ascending order (blockNumber increases)
   *
   * @param _to an address of the delegate to get an array for
   * @param n value of interest to look for
   * @return an index of the closest element in an array to the value
   *      of interest (not exceeding that value)
   */
  function __binaryLookup(address _to, uint256 n) private view returns(uint256) {
    // get a link to an array of voting power history records for an address specified
    VotingPowerRecord[] storage history = votingPowerHistory[_to];

    // left bound of the search interval, originally start of the array
    uint256 i = 0;

    // right bound of the search interval, originally end of the array
    uint256 j = history.length - 1;

    // the iteration process narrows down the bounds by
    // splitting the interval in a half oce per each iteration
    while(j > i) {
      // get an index in the middle of the interval [i, j]
      uint256 k = j - (j - i) / 2;

      // read an element to compare it with the value of interest
      VotingPowerRecord memory cp = history[k];

      // if we've got a strict equal - we're lucky and done
      if(cp.blockNumber == n) {
        // just return the result - index `k`
        return k;
      }
      // if the value of interest is bigger - move left bound to the middle
      else if (cp.blockNumber < n) {
        // move left bound `i` to the middle position `k`
        i = k;
      }
      // otherwise, when the value of interest is smaller - move right bound to the middle
      else {
        // move right bound `j` to the middle position `k - 1`:
        // element at position `k` is bigger and cannot be the result
        j = k - 1;
      }
    }

    // reaching that point means no exact match found
    // since we're interested in the element which is not bigger than the
    // element of interest, we return the lower bound `i`
    return i;
  }
}

// ===== End: DAO Support (Compound-like voting delegation) =====

// File: contracts/utils/AddressUtils.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

/**
 * @title Address Utils
 *
 * @dev Utility library of inline functions on addresses
 *
 * @author Basil Gorin
 */
library AddressUtils {

  /**
   * @notice Checks if the target address is a contract
   * @dev This function will return false if invoked during the constructor of a contract,
   *      as the code is not actually created until after the constructor finishes.
   * @param addr address to check
   * @return whether the target address is a contract
   */
  function isContract(address addr) internal view returns (bool) {
    // a variable to load `extcodesize` to
    uint256 size = 0;

    // XXX Currently there is no better way to check if there is a contract in an address
    // than to check the size of the code at that address.
    // See https://ethereum.stackexchange.com/a/14016/36603 for more details about how this works.
    // TODO: Check this again before the Serenity release, because all addresses will be contracts.
    // solium-disable-next-line security/no-inline-assembly
    assembly {
      // retrieve the size of the code at address `addr`
      size := extcodesize(addr)
    }

    // positive size indicates a smart contract address
    return size > 0;
  }

}

// File: contracts/utils/AccessControl.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

/**
 * @title Access Control List
 *
 * @notice Access control smart contract provides an API to check
 *      if specific operation is permitted globally and/or
 *      if particular user has a permission to execute it.
 *
 * @notice It deals with two main entities: features and roles.
 *
 * @notice Features are designed to be used to enable/disable specific
 *      functions (public functions) of the smart contract for everyone.
 * @notice User roles are designed to restrict access to specific
 *      functions (restricted functions) of the smart contract to some users.
 *
 * @notice Terms "role", "permissions" and "set of permissions" have equal meaning
 *      in the documentation text and may be used interchangeably.
 * @notice Terms "permission", "single permission" implies only one permission bit set.
 *
 * @dev This smart contract is designed to be inherited by other
 *      smart contracts which require access control management capabilities.
 *
 * @author Basil Gorin
 */
contract AccessControl {
  /**
   * @notice Access manager is responsible for assigning the roles to users,
   *      enabling/disabling global features of the smart contract
   * @notice Access manager can add, remove and update user roles,
   *      remove and update global features
   *
   * @dev Role ROLE_ACCESS_MANAGER allows modifying user roles and global features
   * @dev Role ROLE_ACCESS_MANAGER has single bit at position 255 enabled
   */
  uint256 public constant ROLE_ACCESS_MANAGER = 0x8000000000000000000000000000000000000000000000000000000000000000;

  /**
   * @dev Bitmask representing all the possible permissions (super admin role)
   * @dev Has all the bits are enabled (2^256 - 1 value)
   */
  uint256 private constant FULL_PRIVILEGES_MASK = type(uint256).max; // before 0.8.0: uint256(-1) overflows to 0xFFFF...

  /**
   * @notice Privileged addresses with defined roles/permissions
   * @notice In the context of ERC20/ERC721 tokens these can be permissions to
   *      allow minting or burning tokens, transferring on behalf and so on
   *
   * @dev Maps user address to the permissions bitmask (role), where each bit
   *      represents a permission
   * @dev Bitmask 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
   *      represents all possible permissions
   * @dev Zero address mapping represents global features of the smart contract
   */
  mapping(address => uint256) public userRoles;

  /**
   * @dev Fired in updateRole() and updateFeatures()
   *
   * @param _by operator which called the function
   * @param _to address which was granted/revoked permissions
   * @param _requested permissions requested
   * @param _actual permissions effectively set
   */
  event RoleUpdated(address indexed _by, address indexed _to, uint256 _requested, uint256 _actual);

  /**
   * @notice Creates an access control instance,
   *      setting contract creator to have full privileges
   */
  constructor() {
    // contract creator has full privileges
    userRoles[msg.sender] = FULL_PRIVILEGES_MASK;
  }

  /**
   * @notice Retrieves globally set of features enabled
   *
   * @dev Auxiliary getter function to maintain compatibility with previous
   *      versions of the Access Control List smart contract, where
   *      features was a separate uint256 public field
   *
   * @return 256-bit bitmask of the features enabled
   */
  function features() public view returns(uint256) {
    // according to new design features are stored in zero address
    // mapping of `userRoles` structure
    return userRoles[address(0)];
  }

  /**
   * @notice Updates set of the globally enabled features (`features`),
   *      taking into account sender's permissions
   *
   * @dev Requires transaction sender to have `ROLE_ACCESS_MANAGER` permission
   * @dev Function is left for backward compatibility with older versions
   *
   * @param _mask bitmask representing a set of features to enable/disable
   */
  function updateFeatures(uint256 _mask) public {
    // delegate call to `updateRole`
    updateRole(address(0), _mask);
  }

  /**
   * @notice Updates set of permissions (role) for a given user,
   *      taking into account sender's permissions.
   *
   * @dev Setting role to zero is equivalent to removing an all permissions
   * @dev Setting role to `FULL_PRIVILEGES_MASK` is equivalent to
   *      copying senders' permissions (role) to the user
   * @dev Requires transaction sender to have `ROLE_ACCESS_MANAGER` permission
   *
   * @param operator address of a user to alter permissions for or zero
   *      to alter global features of the smart contract
   * @param role bitmask representing a set of permissions to
   *      enable/disable for a user specified
   */
  function updateRole(address operator, uint256 role) public {
    // caller must have a permission to update user roles
    require(isSenderInRole(ROLE_ACCESS_MANAGER), "insufficient privileges (ROLE_ACCESS_MANAGER required)");

    // evaluate the role and reassign it
    userRoles[operator] = evaluateBy(msg.sender, userRoles[operator], role);

    // fire an event
    emit RoleUpdated(msg.sender, operator, role, userRoles[operator]);
  }

  /**
   * @notice Determines the permission bitmask an operator can set on the
   *      target permission set
   * @notice Used to calculate the permission bitmask to be set when requested
   *     in `updateRole` and `updateFeatures` functions
   *
   * @dev Calculated based on:
   *      1) operator's own permission set read from userRoles[operator]
   *      2) target permission set - what is already set on the target
   *      3) desired permission set - what do we want set target to
   *
   * @dev Corner cases:
   *      1) Operator is super admin and its permission set is `FULL_PRIVILEGES_MASK`:
   *        `desired` bitset is returned regardless of the `target` permission set value
   *        (what operator sets is what they get)
   *      2) Operator with no permissions (zero bitset):
   *        `target` bitset is returned regardless of the `desired` value
   *        (operator has no authority and cannot modify anything)
   *
   * @dev Example:
   *      Consider an operator with the permissions bitmask     00001111
   *      is about to modify the target permission set          01010101
   *      Operator wants to set that permission set to          00110011
   *      Based on their role, an operator has the permissions
   *      to update only lowest 4 bits on the target, meaning that
   *      high 4 bits of the target set in this example is left
   *      unchanged and low 4 bits get changed as desired:      01010011
   *
   * @param operator address of the contract operator which is about to set the permissions
   * @param target input set of permissions to operator is going to modify
   * @param desired desired set of permissions operator would like to set
   * @return resulting set of permissions given operator will set
   */
  function evaluateBy(address operator, uint256 target, uint256 desired) public view returns(uint256) {
    // read operator's permissions
    uint256 p = userRoles[operator];

    // taking into account operator's permissions,
    // 1) enable the permissions desired on the `target`
    target |= p & desired;
    // 2) disable the permissions desired on the `target`
    target &= FULL_PRIVILEGES_MASK ^ (p & (FULL_PRIVILEGES_MASK ^ desired));

    // return calculated result
    return target;
  }

  /**
   * @notice Checks if requested set of features is enabled globally on the contract
   *
   * @param required set of features to check against
   * @return true if all the features requested are enabled, false otherwise
   */
  function isFeatureEnabled(uint256 required) public view returns(bool) {
    // delegate call to `__hasRole`, passing `features` property
    return __hasRole(features(), required);
  }

  /**
   * @notice Checks if transaction sender `msg.sender` has all the permissions required
   *
   * @param required set of permissions (role) to check against
   * @return true if all the permissions requested are enabled, false otherwise
   */
  function isSenderInRole(uint256 required) public view returns(bool) {
    // delegate call to `isOperatorInRole`, passing transaction sender
    return isOperatorInRole(msg.sender, required);
  }

  /**
   * @notice Checks if operator has all the permissions (role) required
   *
   * @param operator address of the user to check role for
   * @param required set of permissions (role) to check
   * @return true if all the permissions requested are enabled, false otherwise
   */
  function isOperatorInRole(address operator, uint256 required) public view returns(bool) {
    // delegate call to `__hasRole`, passing operator's permissions (role)
    return __hasRole(userRoles[operator], required);
  }

  /**
   * @dev Checks if role `actual` contains all the permissions required `required`
   *
   * @param actual existent role
   * @param required required role
   * @return true if actual has required role (all permissions), false otherwise
   */
  function __hasRole(uint256 actual, uint256 required) internal pure returns(bool) {
    // check the bitmask for the role required and return the result
    return actual & required == required;
  }
}

// File: contracts/token/ERC20Receiver.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

/**
 * @title ERC20 token receiver interface
 *
 * @dev Interface for any contract that wants to support safe transfers
 *      from ERC20 token smart contracts.
 * @dev Inspired by ERC721 and ERC223 token standards
 *
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 * @dev See https://github.com/ethereum/EIPs/issues/223
 *
 * @author Basil Gorin
 */
interface ERC20Receiver {
  /**
   * @notice Handle the receipt of a ERC20 token(s)
   * @dev The ERC20 smart contract calls this function on the recipient
   *      after a successful transfer (`safeTransferFrom`).
   *      This function MAY throw to revert and reject the transfer.
   *      Return of other than the magic value MUST result in the transaction being reverted.
   * @notice The contract address is always the message sender.
   *      A wallet/broker/auction application MUST implement the wallet interface
   *      if it will accept safe transfers.
   * @param _operator The address which called `safeTransferFrom` function
   * @param _from The address which previously owned the token
   * @param _value amount of tokens which is being transferred
   * @param _data additional data with no specified format
   * @return `bytes4(keccak256("onERC20Received(address,address,uint256,bytes)"))` unless throwing
   */
  function onERC20Received(address _operator, address _from, uint256 _value, bytes calldata _data) external returns(bytes4);
}

// File: contracts/utils/ERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

import "../interfaces/IERC20.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */

// Copied from Open Zeppelin

contract ERC20 is IERC20 {
    mapping(address => uint256) private _balances;

    mapping(address => mapping(address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @notice Token creator is responsible for creating (minting)
     *      tokens to an arbitrary address
     * @dev Role ROLE_TOKEN_CREATOR allows minting tokens
     *      (calling `mint` function)
     */
    uint32 public constant ROLE_TOKEN_CREATOR = 0x0001_0000;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, msg.sender, _allowances[sender][msg.sender] - amount);
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender] + addedValue);
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender] - subtractedValue);
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender] - amount;
        _balances[recipient] = _balances[recipient] + amount;
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply + amount;
        _balances[account] = _balances[account] + amount;
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account] - amount;
        _totalSupply = _totalSupply - amount;
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal virtual {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}
}

// File: contracts/interfaces/IERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: contracts/utils/Address.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.1;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            size := extcodesize(account)
        }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.3._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.3._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) private pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}