// File: contracts/tokenlock/HATTokenLock.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.6;

import "./TokenLock.sol";
import "../HATToken.sol";


contract HATTokenLock is TokenLock {

    bool public canDelegate;

    // Initializer
    function initialize(
        address _tokenLockOwner,
        address _beneficiary,
        HATToken _token,
        uint256 _managedAmount,
        uint256 _startTime,
        uint256 _endTime,
        uint256 _periods,
        uint256 _releaseStartTime,
        uint256 _vestingCliffTime,
        Revocability _revocable,
        bool _canDelegate
    ) external {
        _initialize(
            _tokenLockOwner,
            _beneficiary,
            address(_token),
            _managedAmount,
            _startTime,
            _endTime,
            _periods,
            _releaseStartTime,
            _vestingCliffTime,
            _revocable
        );
        if (_canDelegate) {
            _token.delegate(_beneficiary);
        }
        canDelegate = _canDelegate;
    }

    /// @dev delegate voting power
    /// @param _delegatee Address of delegatee
    function delegate(address _delegatee)
        external
        onlyBeneficiary
    {
        require(canDelegate, "delegate is disable");
        HATToken(address(token)).delegate(_delegatee);
    }
}

// File: contracts/tokenlock/TokenLock.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.8.6;

import "openzeppelin-solidity/contracts/utils/math/SafeMath.sol";
import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";
import "openzeppelin-solidity/contracts/token/ERC20/utils/SafeERC20.sol";

import "./OwnableInitializable.sol";
import "./MathUtils.sol";
import "./ITokenLock.sol";

// this contract is based on GraphTokenLock
// see https://github.com/graphprotocol/token-distribution/blob/main/contracts/GraphTokenLock.sol

/**
 * @title HatTokenLock
 * @notice Contract that manages an unlocking schedule of tokens.
 * @dev The contract lock manage a number of tokens deposited into the contract to ensure that
 * they can only be released under certain time conditions.
 *
 * This contract implements a release scheduled based on periods and tokens are released in steps
 * after each period ends. It can be configured with one period in which case it is like a plain TimeLock.
 * It also supports revocation to be used for vesting schedules.
 *
 * The contract supports receiving extra funds than the managed tokens ones that can be
 * withdrawn by the beneficiary at any time.
 *
 * A releaseStartTime parameter is included to override the default release schedule and
 * perform the first release on the configured time. After that it will continue with the
 * default schedule.
 */
// solhint-disable-next-line indent
abstract contract TokenLock is OwnableInitializable, ITokenLock {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    uint256 private constant MIN_PERIOD = 1;

    // -- State --

    IERC20 public token;
    address public beneficiary;

    // Configuration

    // Amount of tokens managed by the contract schedule
    uint256 public managedAmount;

    uint256 public startTime; // Start datetime (in unixtimestamp)
    uint256 public endTime; // Datetime after all funds are fully vested/unlocked (in unixtimestamp)
    uint256 public periods; // Number of vesting/release periods

    // First release date for tokens (in unixtimestamp)
    // If set, no tokens will be released before releaseStartTime ignoring
    // the amount to release each period
    uint256 public releaseStartTime;
    // A cliff set a date to which a beneficiary needs to get to vest
    // all preceding periods
    uint256 public vestingCliffTime;
    Revocability public revocable; // Whether to use vesting for locked funds

    // State

    bool public isRevoked;
    bool public isInitialized;
    bool public isAccepted;
    uint256 public releasedAmount;

    // -- Events --

    event TokensReleased(address indexed beneficiary, uint256 amount);
    event TokensWithdrawn(address indexed beneficiary, uint256 amount);
    event TokensRevoked(address indexed beneficiary, uint256 amount);
    event BeneficiaryChanged(address newBeneficiary);
    event LockAccepted();
    event LockCanceled();

    /**
     * @dev Only allow calls from the beneficiary of the contract
     */
    modifier onlyBeneficiary() {
        require(msg.sender == beneficiary, "!auth");
        _;
    }

    /**
     * @notice Initializes the contract
     * @param _tokenLockOwner Address of the contract owner
     * @param _beneficiary Address of the beneficiary of locked tokens
     * @param _managedAmount Amount of tokens to be managed by the lock contract
     * @param _startTime Start time of the release schedule
     * @param _endTime End time of the release schedule
     * @param _periods Number of periods between start time and end time
     * @param _releaseStartTime Override time for when the releases start
     * @param _vestingCliffTime Override time for when the vesting start
     * @param _revocable Whether the contract is revocable
     */
    function _initialize(
        address _tokenLockOwner,
        address _beneficiary,
        address _token,
        uint256 _managedAmount,
        uint256 _startTime,
        uint256 _endTime,
        uint256 _periods,
        uint256 _releaseStartTime,
        uint256 _vestingCliffTime,
        Revocability _revocable
    ) internal {
        require(!isInitialized, "Already initialized");
        require(_tokenLockOwner != address(0), "Owner cannot be zero");
        require(_beneficiary != address(0), "Beneficiary cannot be zero");
        require(_token != address(0), "Token cannot be zero");
        require(_managedAmount > 0, "Managed tokens cannot be zero");
        require(_startTime != 0, "Start time must be set");
        require(_startTime < _endTime, "Start time > end time");
        require(_periods >= MIN_PERIOD, "Periods cannot be below minimum");
        require(_revocable != Revocability.NotSet, "Must set a revocability option");
        require(_releaseStartTime < _endTime, "Release start time must be before end time");
        require(_vestingCliffTime < _endTime, "Cliff time must be before end time");

        isInitialized = true;

        OwnableInitializable.initialize(_tokenLockOwner);
        beneficiary = _beneficiary;
        token = IERC20(_token);

        managedAmount = _managedAmount;

        startTime = _startTime;
        endTime = _endTime;
        periods = _periods;

        // Optionals
        releaseStartTime = _releaseStartTime;
        vestingCliffTime = _vestingCliffTime;
        revocable = _revocable;
    }

    /**
     * @notice Change the beneficiary of funds managed by the contract
     * @dev Can only be called by the beneficiary
     * @param _newBeneficiary Address of the new beneficiary address
     */
    function changeBeneficiary(address _newBeneficiary) external onlyBeneficiary {
        require(_newBeneficiary != address(0), "Empty beneficiary");
        beneficiary = _newBeneficiary;
        emit BeneficiaryChanged(_newBeneficiary);
    }

    /**
     * @notice Beneficiary accepts the lock, the owner cannot retrieve back the tokens
     * @dev Can only be called by the beneficiary
     */
    function acceptLock() external onlyBeneficiary {
        isAccepted = true;
        emit LockAccepted();
    }

    /**
     * @notice Owner cancel the lock and return the balance in the contract
     * @dev Can only be called by the owner
     */
    function cancelLock() external onlyOwner {
        require(isAccepted == false, "Cannot cancel accepted contract");

        token.safeTransfer(owner(), currentBalance());

        emit LockCanceled();
    }

    // -- Balances --

    /**
     * @notice Returns the amount of tokens currently held by the contract
     * @return Tokens held in the contract
     */
    function currentBalance() public override view returns (uint256) {
        return token.balanceOf(address(this));
    }

    // -- Time & Periods --

    /**
     * @notice Returns the current block timestamp
     * @return Current block timestamp
     */
    function currentTime() public override view returns (uint256) {
        // solhint-disable-next-line not-rely-on-time
        return block.timestamp;
    }

    /**
     * @notice Gets duration of contract from start to end in seconds
     * @return Amount of seconds from contract startTime to endTime
     */
    function duration() public override view returns (uint256) {
        return endTime.sub(startTime);
    }

    /**
     * @notice Gets time elapsed since the start of the contract
     * @dev Returns zero if called before conctract starTime
     * @return Seconds elapsed from contract startTime
     */
    function sinceStartTime() public override view returns (uint256) {
        uint256 current = currentTime();
        if (current <= startTime) {
            return 0;
        }
        return current.sub(startTime);
    }

    /**
     * @notice Returns amount available to be released after each period according to schedule
     * @return Amount of tokens available after each period
     */
    function amountPerPeriod() public override view returns (uint256) {
        return managedAmount.div(periods);
    }

    /**
     * @notice Returns the duration of each period in seconds
     * @return Duration of each period in seconds
     */
    function periodDuration() public override view returns (uint256) {
        return duration().div(periods);
    }

    /**
     * @notice Gets the current period based on the schedule
     * @return A number that represents the current period
     */
    function currentPeriod() public override view returns (uint256) {
        return sinceStartTime().div(periodDuration()).add(MIN_PERIOD);
    }

    /**
     * @notice Gets the number of periods that passed since the first period
     * @return A number of periods that passed since the schedule started
     */
    function passedPeriods() public override view returns (uint256) {
        return currentPeriod().sub(MIN_PERIOD);
    }

    // -- Locking & Release Schedule --

    /**
     * @notice Gets the currently available token according to the schedule
     * @dev Implements the step-by-step schedule based on periods for available tokens
     * @return Amount of tokens available according to the schedule
     */
    function availableAmount() public override view returns (uint256) {
        uint256 current = currentTime();

        // Before contract start no funds are available
        if (current < startTime) {
            return 0;
        }

        // After contract ended all funds are available
        if (current > endTime) {
            return managedAmount;
        }

        // Get available amount based on period
        return passedPeriods().mul(amountPerPeriod());
    }

    /**
     * @notice Gets the amount of currently vested tokens
     * @dev Similar to available amount, but is fully vested when contract is non-revocable
     * @return Amount of tokens already vested
     */
    function vestedAmount() public override view returns (uint256) {
        // If non-revocable it is fully vested
        if (revocable == Revocability.Disabled) {
            return managedAmount;
        }

        // Vesting cliff is activated and it has not passed means nothing is vested yet
        if (vestingCliffTime > 0 && currentTime() < vestingCliffTime) {
            return 0;
        }

        return availableAmount();
    }

    /**
     * @notice Gets tokens currently available for release
     * @dev Considers the schedule and takes into account already released tokens
     * @return Amount of tokens ready to be released
     */
    function releasableAmount() public override view returns (uint256) {
        // If a release start time is set no tokens are available for release before this date
        // If not set it follows the default schedule and tokens are available on
        // the first period passed
        if (releaseStartTime > 0 && currentTime() < releaseStartTime) {
            return 0;
        }

        // Vesting cliff is activated and it has not passed means nothing is vested yet
        // so funds cannot be released
        if (revocable == Revocability.Enabled && vestingCliffTime > 0 && currentTime() < vestingCliffTime) {
            return 0;
        }

        // A beneficiary can never have more releasable tokens than the contract balance
        uint256 releasable = availableAmount().sub(releasedAmount);
        return MathUtils.min(currentBalance(), releasable);
    }

    /**
     * @notice Gets the outstanding amount yet to be released based on the whole contract lifetime
     * @dev Does not consider schedule but just global amounts tracked
     * @return Amount of outstanding tokens for the lifetime of the contract
     */
    function totalOutstandingAmount() public override view returns (uint256) {
        return managedAmount.sub(releasedAmount);
    }

    /**
     * @notice Gets surplus amount in the contract based on outstanding amount to release
     * @dev All funds over outstanding amount is considered surplus that can be withdrawn by beneficiary
     * @return Amount of tokens considered as surplus
     */
    function surplusAmount() public override view returns (uint256) {
        uint256 balance = currentBalance();
        uint256 outstandingAmount = totalOutstandingAmount();
        if (balance > outstandingAmount) {
            return balance.sub(outstandingAmount);
        }
        return 0;
    }

    // -- Value Transfer --

    /**
     * @notice Releases tokens based on the configured schedule
     * @dev All available releasable tokens are transferred to beneficiary
     */
    function release() external override onlyBeneficiary {
        uint256 amountToRelease = releasableAmount();
        require(amountToRelease > 0, "No available releasable amount");

        releasedAmount = releasedAmount.add(amountToRelease);

        token.safeTransfer(beneficiary, amountToRelease);

        emit TokensReleased(beneficiary, amountToRelease);
    }

    /**
     * @notice Withdraws surplus, unmanaged tokens from the contract
     * @dev Tokens in the contract over outstanding amount are considered as surplus
     * @param _amount Amount of tokens to withdraw
     */
    function withdrawSurplus(uint256 _amount) external override onlyBeneficiary {
        require(_amount > 0, "Amount cannot be zero");
        require(surplusAmount() >= _amount, "Amount requested > surplus available");

        token.safeTransfer(beneficiary, _amount);

        emit TokensWithdrawn(beneficiary, _amount);
    }

    /**
     * @notice Revokes a vesting schedule and return the unvested tokens to the owner
     * @dev Vesting schedule is always calculated based on managed tokens
     */
    function revoke() external override onlyOwner {
        require(revocable == Revocability.Enabled, "Contract is non-revocable");
        require(isRevoked == false, "Already revoked");

        uint256 unvestedAmount = managedAmount.sub(vestedAmount());
        require(unvestedAmount > 0, "No available unvested amount");

        isRevoked = true;

        token.safeTransfer(owner(), unvestedAmount);

        emit TokensRevoked(beneficiary, unvestedAmount);
    }
}

// File: contracts/HATToken.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.6;
import "openzeppelin-solidity/contracts/utils/math/SafeMath.sol";
import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";


contract HATToken is IERC20 {

    struct PendingMinter {
        uint256 seedAmount;
        uint256 setMinterPendingAt;
    }

    /// @notice A checkpoint for marking number of votes from a given block
    struct Checkpoint {
        uint32 fromBlock;
        uint96 votes;
    }

    /// @notice EIP-20 token name for this token
    // solhint-disable-next-line const-name-snakecase
    string public constant name = "hats.finance";

    /// @notice EIP-20 token symbol for this token
    // solhint-disable-next-line const-name-snakecase
    string public constant symbol = "HAT";

    /// @notice EIP-20 token decimals for this token
    // solhint-disable-next-line const-name-snakecase
    uint8 public constant decimals = 18;

    /// @notice Total number of tokens in circulation
    uint public override totalSupply;

    address public governance;
    address public governancePending;
    uint256 public setGovernancePendingAt;
    uint256 public immutable timeLockDelay;
    uint256 public constant CAP = 10000000e18;

    /// @notice Address which may mint new tokens
    /// minter -> minting seedAmount
    mapping (address => uint256) public minters;

    /// @notice Address which may mint new tokens
    /// minter -> minting seedAmount
    mapping (address => PendingMinter) public pendingMinters;

    // @notice Allowance amounts on behalf of others
    mapping (address => mapping (address => uint96)) internal allowances;

    // @notice Official record of token balances for each account
    mapping (address => uint96) internal balances;

    /// @notice A record of each accounts delegate
    mapping (address => address) public delegates;

    /// @notice A record of votes checkpoints for each account, by index
    mapping (address => mapping (uint32 => Checkpoint)) public checkpoints;

    /// @notice The number of checkpoints for each account
    mapping (address => uint32) public numCheckpoints;

    /// @notice A record of states for signing / validating signatures
    mapping (address => uint) public nonces;

    /// @notice The EIP-712 typehash for the contract's domain
    bytes32 public constant DOMAIN_TYPEHASH =
    keccak256("EIP712Domain(string name,uint256 chainId,address verifyingContract)");

    /// @notice The EIP-712 typehash for the delegation struct used by the contract
    bytes32 public constant DELEGATION_TYPEHASH =
    keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");

    /// @notice The EIP-712 typehash for the permit struct used by the contract
    bytes32 public constant PERMIT_TYPEHASH =
    keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");

    /// @notice An event thats emitted when a new minter address is pending
    event MinterPending(address indexed minter, uint256 seedAmount, uint256 at);
    /// @notice An event thats emitted when the minter address is changed
    event MinterChanged(address indexed minter, uint256 seedAmount);
    /// @notice An event thats emitted when a new governance address is pending
    event GovernancePending(address indexed oldGovernance, address indexed newGovernance, uint256 at);
    /// @notice An event thats emitted when a new governance address is set
    event GovernanceChanged(address indexed oldGovernance, address indexed newGovernance);
    /// @notice An event thats emitted when an account changes its delegate
    event DelegateChanged(address indexed delegator, address indexed fromDelegate, address indexed toDelegate);
    /// @notice An event thats emitted when a delegate account's vote balance changes
    event DelegateVotesChanged(address indexed delegate, uint previousBalance, uint newBalance);

    /**
     * @notice Construct a new HAT token
     */
    // solhint-disable-next-line func-visibility
    constructor(address _governance, uint256 _timeLockDelay) {
        governance = _governance;
        timeLockDelay = _timeLockDelay;
    }

    function setPendingGovernance(address _governance) external {
        require(msg.sender == governance, "HAT:!governance");
        require(_governance != address(0), "HAT:!_governance");
        governancePending = _governance;
        // solhint-disable-next-line not-rely-on-time
        setGovernancePendingAt = block.timestamp;
        emit GovernancePending(governance, _governance, setGovernancePendingAt);
    }

    function confirmGovernance() external {
        require(msg.sender == governance, "HAT:!governance");
        require(setGovernancePendingAt > 0, "HAT:!governancePending");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp - setGovernancePendingAt > timeLockDelay,
        "HAT: cannot confirm governance at this time");
        emit GovernanceChanged(governance, governancePending);
        governance = governancePending;
        setGovernancePendingAt = 0;
    }

    function setPendingMinter(address _minter, uint256 _cap) external {
        require(msg.sender == governance, "HAT::!governance");
        pendingMinters[_minter].seedAmount = _cap;
        // solhint-disable-next-line not-rely-on-time
        pendingMinters[_minter].setMinterPendingAt = block.timestamp;
        emit MinterPending(_minter, _cap, pendingMinters[_minter].setMinterPendingAt);
    }

    function confirmMinter(address _minter) external {
        require(msg.sender == governance, "HAT::mint: only the governance can confirm minter");
        require(pendingMinters[_minter].setMinterPendingAt > 0, "HAT:: no pending minter was set");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp - pendingMinters[_minter].setMinterPendingAt > timeLockDelay,
        "HATToken: cannot confirm at this time");
        minters[_minter] = pendingMinters[_minter].seedAmount;
        pendingMinters[_minter].setMinterPendingAt = 0;
        emit MinterChanged(_minter, pendingMinters[_minter].seedAmount);
    }

    function burn(uint256 _amount) external {
        return _burn(msg.sender, _amount);
    }

    function mint(address _account, uint _amount) external {
        require(minters[msg.sender] >= _amount, "HATToken: amount greater than limitation");
        minters[msg.sender] = SafeMath.sub(minters[msg.sender], _amount);
        _mint(_account, _amount);
    }

    /**
     * @notice Get the number of tokens `spender` is approved to spend on behalf of `account`
     * @param account The address of the account holding the funds
     * @param spender The address of the account spending the funds
     * @return The number of tokens approved
     */
    function allowance(address account, address spender) external override view returns (uint) {
        return allowances[account][spender];
    }

    /**
     * @notice Approve `spender` to transfer up to `amount` from `src`
     * @dev This will overwrite the approval amount for `spender`
     *  and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)
     * @param spender The address of the account which may transfer tokens
     * @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
     * @return Whether or not the approval succeeded
     */
    function approve(address spender, uint rawAmount) external override returns (bool) {
        uint96 amount;
        if (rawAmount == type(uint256).max) {
            amount = type(uint96).max;
        } else {
            amount = safe96(rawAmount, "HAT::approve: amount exceeds 96 bits");
        }

        allowances[msg.sender][spender] = amount;

        emit Approval(msg.sender, spender, 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, uint addedValue) external virtual returns (bool) {
        require(spender != address(0), "HAT: increaseAllowance to the zero address");
        uint96 valueToAdd = safe96(addedValue, "HAT::increaseAllowance: addedValue exceeds 96 bits");
        allowances[msg.sender][spender] =
        add96(allowances[msg.sender][spender], valueToAdd, "HAT::increaseAllowance: overflows");
        emit Approval(msg.sender, spender, allowances[msg.sender][spender]);
        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, uint subtractedValue) external virtual returns (bool) {
        require(spender != address(0), "HAT: decreaseAllowance to the zero address");
        uint96 valueTosubtract = safe96(subtractedValue, "HAT::decreaseAllowance: subtractedValue exceeds 96 bits");
        allowances[msg.sender][spender] = sub96(allowances[msg.sender][spender], valueTosubtract,
        "HAT::decreaseAllowance: spender allowance is less than subtractedValue");
        emit Approval(msg.sender, spender, allowances[msg.sender][spender]);
        return true;
    }

    /**
     * @notice Triggers an approval from owner to spends
     * @param owner The address to approve from
     * @param spender The address to be approved
     * @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
     * @param deadline The time at which to expire the signature
     * @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 permit(address owner, address spender, uint rawAmount, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
        uint96 amount;
        if (rawAmount == type(uint256).max) {
            amount = type(uint96).max;
        } else {
            amount = safe96(rawAmount, "HAT::permit: amount exceeds 96 bits");
        }

        bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));
        bytes32 structHash = keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, rawAmount, nonces[owner]++, deadline));
        bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "HAT::permit: invalid signature");
        require(signatory == owner, "HAT::permit: unauthorized");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp <= deadline, "HAT::permit: signature expired");

        allowances[owner][spender] = amount;

        emit Approval(owner, spender, amount);
    }

    /**
     * @notice Get the number of tokens held by the `account`
     * @param account The address of the account to get the balance of
     * @return The number of tokens held
     */
    function balanceOf(address account) external view override returns (uint) {
        return balances[account];
    }

    /**
     * @notice Transfer `amount` tokens from `msg.sender` to `dst`
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function transfer(address dst, uint rawAmount) external override returns (bool) {
        uint96 amount = safe96(rawAmount, "HAT::transfer: amount exceeds 96 bits");
        _transferTokens(msg.sender, dst, amount);
        return true;
    }

    /**
     * @notice Transfer `amount` tokens from `src` to `dst`
     * @param src The address of the source account
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function transferFrom(address src, address dst, uint rawAmount) external override returns (bool) {
        address spender = msg.sender;
        uint96 spenderAllowance = allowances[src][spender];
        uint96 amount = safe96(rawAmount, "HAT::approve: amount exceeds 96 bits");

        if (spender != src && spenderAllowance != type(uint96).max) {
            uint96 newAllowance = sub96(spenderAllowance, amount,
            "HAT::transferFrom: transfer amount exceeds spender allowance");
            allowances[src][spender] = newAllowance;

            emit Approval(src, spender, newAllowance);
        }

        _transferTokens(src, dst, amount);
        return true;
    }

    /**
     * @notice Delegate votes from `msg.sender` to `delegatee`
     * @param delegatee The address to delegate votes to
     */
    function delegate(address delegatee) external {
        return _delegate(msg.sender, delegatee);
    }

    /**
     * @notice Delegates votes from signatory to `delegatee`
     * @param delegatee The address to delegate votes to
     * @param nonce The contract state required to match the signature
     * @param expiry The time at which to expire the signature
     * @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 delegateBySig(address delegatee, uint nonce, uint expiry, uint8 v, bytes32 r, bytes32 s) external {
        bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));
        bytes32 structHash = keccak256(abi.encode(DELEGATION_TYPEHASH, delegatee, nonce, expiry));
        bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "HAT::delegateBySig: invalid signature");
        require(nonce == nonces[signatory]++, "HAT::delegateBySig: invalid nonce");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp <= expiry, "HAT::delegateBySig: signature expired");
        return _delegate(signatory, delegatee);
    }

    /**
     * @notice Gets the current votes balance for `account`
     * @param account The address to get votes balance
     * @return The number of current votes for `account`
     */
    function getCurrentVotes(address account) external view returns (uint96) {
        uint32 nCheckpoints = numCheckpoints[account];
        return nCheckpoints > 0 ? checkpoints[account][nCheckpoints - 1].votes : 0;
    }

    /**
     * @notice Determine the prior number of votes for an account as of a block number
     * @dev Block number must be a finalized block or else this function will revert to prevent misinformation.
     * @param account The address of the account to check
     * @param blockNumber The block number to get the vote balance at
     * @return The number of votes the account had as of the given block
     */
    function getPriorVotes(address account, uint blockNumber) external view returns (uint96) {
        require(blockNumber < block.number, "HAT::getPriorVotes: not yet determined");

        uint32 nCheckpoints = numCheckpoints[account];
        if (nCheckpoints == 0) {
            return 0;
        }

        // First check most recent balance
        if (checkpoints[account][nCheckpoints - 1].fromBlock <= blockNumber) {
            return checkpoints[account][nCheckpoints - 1].votes;
        }

        // Next check implicit zero balance
        if (checkpoints[account][0].fromBlock > blockNumber) {
            return 0;
        }

        uint32 lower = 0;
        uint32 upper = nCheckpoints - 1;
        while (upper > lower) {
            uint32 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
            Checkpoint memory cp = checkpoints[account][center];
            if (cp.fromBlock == blockNumber) {
                return cp.votes;
            } else if (cp.fromBlock < blockNumber) {
                lower = center;
            } else {
                upper = center - 1;
            }
        }
        return checkpoints[account][lower].votes;
    }

    /**
     * @notice Mint new tokens
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to be minted
     */
    function _mint(address dst, uint rawAmount) internal {
        require(dst != address(0), "HAT::mint: cannot transfer to the zero address");
        require(SafeMath.add(totalSupply, rawAmount) <= CAP, "ERC20Capped: CAP exceeded");

        // mint the amount
        uint96 amount = safe96(rawAmount, "HAT::mint: amount exceeds 96 bits");
        totalSupply = safe96(SafeMath.add(totalSupply, amount), "HAT::mint: totalSupply exceeds 96 bits");

        // transfer the amount to the recipient
        balances[dst] = add96(balances[dst], amount, "HAT::mint: transfer amount overflows");
        emit Transfer(address(0), dst, amount);

        // move delegates
        _moveDelegates(address(0), delegates[dst], amount);
    }

    /**
     * Burn tokens
     * @param src The address of the source account
     * @param rawAmount The number of tokens to be burned
     */
    function _burn(address src, uint rawAmount) internal {
        require(src != address(0), "HAT::burn: cannot burn to the zero address");

        // burn the amount
        uint96 amount = safe96(rawAmount, "HAT::burn: amount exceeds 96 bits");
        totalSupply = safe96(SafeMath.sub(totalSupply, amount), "HAT::mint: totalSupply exceeds 96 bits");

        // reduce the amount from src address
        balances[src] = sub96(balances[src], amount, "HAT::burn: burn amount exceeds balance");
        emit Transfer(src, address(0), amount);

        // move delegates
        _moveDelegates(delegates[src], address(0), amount);
    }

    function _delegate(address delegator, address delegatee) internal {
        address currentDelegate = delegates[delegator];
        uint96 delegatorBalance = balances[delegator];
        delegates[delegator] = delegatee;

        emit DelegateChanged(delegator, currentDelegate, delegatee);

        _moveDelegates(currentDelegate, delegatee, delegatorBalance);
    }

    function _transferTokens(address src, address dst, uint96 amount) internal {
        require(src != address(0), "HAT::_transferTokens: cannot transfer from the zero address");
        require(dst != address(0), "HAT::_transferTokens: cannot transfer to the zero address");

        balances[src] = sub96(balances[src], amount, "HAT::_transferTokens: transfer amount exceeds balance");
        balances[dst] = add96(balances[dst], amount, "HAT::_transferTokens: transfer amount overflows");
        emit Transfer(src, dst, amount);

        _moveDelegates(delegates[src], delegates[dst], amount);
    }

    function _moveDelegates(address srcRep, address dstRep, uint96 amount) internal {
        if (srcRep != dstRep && amount > 0) {
            if (srcRep != address(0)) {
                uint32 srcRepNum = numCheckpoints[srcRep];
                uint96 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
                uint96 srcRepNew = sub96(srcRepOld, amount, "HAT::_moveVotes: vote amount underflows");
                _writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
            }

            if (dstRep != address(0)) {
                uint32 dstRepNum = numCheckpoints[dstRep];
                uint96 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
                uint96 dstRepNew = add96(dstRepOld, amount, "HAT::_moveVotes: vote amount overflows");
                _writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
            }
        }
    }

    function _writeCheckpoint(address delegatee, uint32 nCheckpoints, uint96 oldVotes, uint96 newVotes) internal {
        uint32 blockNumber = safe32(block.number, "HAT::_writeCheckpoint: block number exceeds 32 bits");

        if (nCheckpoints > 0 && checkpoints[delegatee][nCheckpoints - 1].fromBlock == blockNumber) {
            checkpoints[delegatee][nCheckpoints - 1].votes = newVotes;
        } else {
            checkpoints[delegatee][nCheckpoints] = Checkpoint(blockNumber, newVotes);
            numCheckpoints[delegatee] = nCheckpoints + 1;
        }

        emit DelegateVotesChanged(delegatee, oldVotes, newVotes);
    }

    function safe32(uint n, string memory errorMessage) internal pure returns (uint32) {
        require(n < 2**32, errorMessage);
        return uint32(n);
    }

    function safe96(uint n, string memory errorMessage) internal pure returns (uint96) {
        require(n < 2**96, errorMessage);
        return uint96(n);
    }

    function add96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
        uint96 c = a + b;
        require(c >= a, errorMessage);
        return c;
    }

    function sub96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
        require(b <= a, errorMessage);
        return a - b;
    }

    function getChainId() internal view returns (uint) {
        uint256 chainId;
        // solhint-disable-next-line no-inline-assembly
        assembly { chainId := chainid() }
        return chainId;
    }
}

// File: openzeppelin-solidity/contracts/utils/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is no longer needed starting with Solidity 0.8. The compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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: openzeppelin-solidity/contracts/token/ERC20/utils/SafeERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../../../utils/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 {
        unchecked {
            uint256 oldAllowance = token.allowance(address(this), spender);
            require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
            uint256 newAllowance = oldAllowance - 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/tokenlock/OwnableInitializable.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.8.6;


/**
 * @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.
 *
 * The owner account will be passed on initialization of 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.
 */
contract OwnableInitializable {
    address private _owner;

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

    /**
     * @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() external 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) external virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    function initialize(address initialOwner) internal {
        _owner = initialOwner;
        emit OwnershipTransferred(address(0), initialOwner);
    }
}

// File: contracts/tokenlock/MathUtils.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.8.6;

library MathUtils {
    function min(uint256 a, uint256 b) internal pure returns (uint256) {
        return a < b ? a : b;
    }
}

// File: contracts/tokenlock/ITokenLock.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.8.6;
pragma experimental ABIEncoderV2;

import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";

interface ITokenLock {
    enum Revocability { NotSet, Enabled, Disabled }

    // -- Balances --

    function currentBalance() external view returns (uint256);

    // -- Time & Periods --

    function currentTime() external view returns (uint256);

    function duration() external view returns (uint256);

    function sinceStartTime() external view returns (uint256);

    function amountPerPeriod() external view returns (uint256);

    function periodDuration() external view returns (uint256);

    function currentPeriod() external view returns (uint256);

    function passedPeriods() external view returns (uint256);

    // -- Locking & Release Schedule --

    function availableAmount() external view returns (uint256);

    function vestedAmount() external view returns (uint256);

    function releasableAmount() external view returns (uint256);

    function totalOutstandingAmount() external view returns (uint256);

    function surplusAmount() external view returns (uint256);

    // -- Value Transfer --

    function release() external;

    function withdrawSurplus(uint256 _amount) external;

    function revoke() external;
}

// File: openzeppelin-solidity/contracts/utils/Address.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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 v3.4._
     */
    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 v3.4._
     */
    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);
            }
        }
    }
}