// File: contracts/FeeSharingSystem.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import {AccessControl} from '@openzeppelin/contracts/access/AccessControl.sol';
import {IERC20, SafeERC20} from '@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol';
import {ReentrancyGuard} from '@openzeppelin/contracts/security/ReentrancyGuard.sol';

import {TokenDistributor} from './TokenDistributor.sol';
import {IStakeFor} from './IStakeFor.sol';

/**
 * @title FeeSharingSystem
 * @notice It handles the distribution of fees using
 * WETH along with the auto-compounding of X2Y2.
 */
contract FeeSharingSystem is ReentrancyGuard, AccessControl, IStakeFor {
    using SafeERC20 for IERC20;

    // for `depositFor` call
    bytes32 public constant DEPOSIT_ROLE = keccak256('DEPOSIT_ROLE');

    // for `updateRewards()`
    bytes32 public constant REWARD_UPDATE_ROLE = keccak256('REWARD_UPDATE_ROLE');

    struct UserInfo {
        uint256 shares; // shares of token staked
        uint256 userRewardPerTokenPaid; // user reward per token paid
        uint256 rewards; // pending rewards
    }

    // Precision factor for calculating rewards and exchange rate
    uint256 public constant PRECISION_FACTOR = 10**18;

    IERC20 public immutable x2y2Token;

    IERC20 public immutable rewardToken;

    TokenDistributor public immutable tokenDistributor;

    // Reward rate (block)
    uint256 public currentRewardPerBlock;

    // Last reward adjustment block number
    uint256 public lastRewardAdjustment;

    // Last update block for rewards
    uint256 public lastUpdateBlock;

    // Current end block for the current reward period
    uint256 public periodEndBlock;

    // Reward per token stored
    uint256 public rewardPerTokenStored;

    // Total existing shares
    uint256 public totalShares;

    mapping(address => UserInfo) public userInfo;

    event Deposit(address indexed user, uint256 amount, uint256 harvestedAmount);
    event Harvest(address indexed user, uint256 harvestedAmount);
    event NewRewardPeriod(uint256 numberBlocks, uint256 rewardPerBlock, uint256 reward);
    event Withdraw(address indexed user, uint256 amount, uint256 harvestedAmount);

    /**
     * @notice Constructor
     * @param _x2y2Token address of the token staked
     * @param _rewardToken address of the reward token
     * @param _tokenDistributor address of the token distributor contract
     */
    constructor(
        address _x2y2Token,
        address _rewardToken,
        address _tokenDistributor
    ) {
        rewardToken = IERC20(_rewardToken);
        x2y2Token = IERC20(_x2y2Token);
        tokenDistributor = TokenDistributor(_tokenDistributor);
        _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
    }

    /**
     * @notice deposit on behalf of `user`, must be called on fresh deposit only
     * @param user deposit user
     * @param amount amount to deposit
     */
    function depositFor(address user, uint256 amount)
        external
        override
        nonReentrant
        onlyRole(DEPOSIT_ROLE)
        returns (bool)
    {
        require(amount >= PRECISION_FACTOR, 'Deposit: Amount must be >= 1 X2Y2');

        // Auto compounds for everyone
        tokenDistributor.harvestAndCompound();

        // Update reward for user
        _updateReward(user);

        // Retrieve total amount staked by this contract
        (uint256 totalAmountStaked, ) = tokenDistributor.userInfo(address(this));

        // transfer stakingToken from **sender**
        x2y2Token.safeTransferFrom(msg.sender, address(this), amount);

        uint256 currentShares;

        // Calculate the number of shares to issue for the user
        if (totalShares != 0) {
            currentShares = (amount * totalShares) / totalAmountStaked;
            // This is a sanity check to prevent deposit for 0 shares
            require(currentShares != 0, 'Deposit: Fail');
        } else {
            currentShares = amount;
        }

        // Adjust internal shares
        userInfo[user].shares += currentShares;
        totalShares += currentShares;

        // Verify X2Y2 token allowance and adjust if necessary
        _checkAndAdjustX2Y2TokenAllowanceIfRequired(amount, address(tokenDistributor));

        // Deposit user amount in the token distributor contract
        tokenDistributor.deposit(amount);

        emit Deposit(user, amount, 0);

        return true;
    }

    /**
     * @notice Deposit staked tokens (and collect reward tokens if requested)
     * @param amount amount to deposit (in X2Y2)
     * @param claimRewardToken whether to claim reward tokens
     * @dev There is a limit of 1 X2Y2 per deposit to prevent potential manipulation of current shares
     */
    function deposit(uint256 amount, bool claimRewardToken) external nonReentrant {
        require(amount >= PRECISION_FACTOR, 'Deposit: Amount must be >= 1 X2Y2');

        // Auto compounds for everyone
        tokenDistributor.harvestAndCompound();

        // Update reward for user
        _updateReward(msg.sender);

        // Retrieve total amount staked by this contract
        (uint256 totalAmountStaked, ) = tokenDistributor.userInfo(address(this));

        // Transfer X2Y2 tokens to this address
        x2y2Token.safeTransferFrom(msg.sender, address(this), amount);

        uint256 currentShares;

        // Calculate the number of shares to issue for the user
        if (totalShares != 0) {
            currentShares = (amount * totalShares) / totalAmountStaked;
            // This is a sanity check to prevent deposit for 0 shares
            require(currentShares != 0, 'Deposit: Fail');
        } else {
            currentShares = amount;
        }

        // Adjust internal shares
        userInfo[msg.sender].shares += currentShares;
        totalShares += currentShares;

        uint256 pendingRewards;

        if (claimRewardToken) {
            // Fetch pending rewards
            pendingRewards = userInfo[msg.sender].rewards;

            if (pendingRewards > 0) {
                userInfo[msg.sender].rewards = 0;
                rewardToken.safeTransfer(msg.sender, pendingRewards);
            }
        }

        // Verify X2Y2 token allowance and adjust if necessary
        _checkAndAdjustX2Y2TokenAllowanceIfRequired(amount, address(tokenDistributor));

        // Deposit user amount in the token distributor contract
        tokenDistributor.deposit(amount);

        emit Deposit(msg.sender, amount, pendingRewards);
    }

    /**
     * @notice Harvest reward tokens that are pending
     */
    function harvest() external nonReentrant {
        // Auto compounds for everyone
        tokenDistributor.harvestAndCompound();

        // Update reward for user
        _updateReward(msg.sender);

        // Retrieve pending rewards
        uint256 pendingRewards = userInfo[msg.sender].rewards;

        // If pending rewards are null, revert
        require(pendingRewards > 0, 'Harvest: Pending rewards must be > 0');

        // Adjust user rewards and transfer
        userInfo[msg.sender].rewards = 0;

        // Transfer reward token to sender
        rewardToken.safeTransfer(msg.sender, pendingRewards);

        emit Harvest(msg.sender, pendingRewards);
    }

    /**
     * @notice Withdraw staked tokens (and collect reward tokens if requested)
     * @param shares shares to withdraw
     * @param claimRewardToken whether to claim reward tokens
     */
    function withdraw(uint256 shares, bool claimRewardToken) external nonReentrant {
        require(
            (shares > 0) && (shares <= userInfo[msg.sender].shares),
            'Withdraw: Shares equal to 0 or larger than user shares'
        );

        _withdraw(shares, claimRewardToken);
    }

    /**
     * @notice Withdraw all staked tokens (and collect reward tokens if requested)
     * @param claimRewardToken whether to claim reward tokens
     */
    function withdrawAll(bool claimRewardToken) external nonReentrant {
        _withdraw(userInfo[msg.sender].shares, claimRewardToken);
    }

    /**
     * @notice Update the reward per block (in rewardToken)
     * @dev Only callable by owner. Owner is meant to be another smart contract.
     */
    function updateRewards(uint256 reward, uint256 rewardDurationInBlocks)
        external
        onlyRole(REWARD_UPDATE_ROLE)
    {
        // Adjust the current reward per block
        if (block.number >= periodEndBlock) {
            currentRewardPerBlock = reward / rewardDurationInBlocks;
        } else {
            currentRewardPerBlock =
                (reward + ((periodEndBlock - block.number) * currentRewardPerBlock)) /
                rewardDurationInBlocks;
        }

        lastUpdateBlock = block.number;
        periodEndBlock = block.number + rewardDurationInBlocks;

        emit NewRewardPeriod(rewardDurationInBlocks, currentRewardPerBlock, reward);
    }

    /**
     * @notice Calculate pending rewards (WETH) for a user
     * @param user address of the user
     */
    function calculatePendingRewards(address user) external view returns (uint256) {
        return _calculatePendingRewards(user);
    }

    /**
     * @notice Calculate value of X2Y2 for a user given a number of shares owned
     * @param user address of the user
     */
    function calculateSharesValueInX2Y2(address user) external view returns (uint256) {
        // Retrieve amount staked
        (uint256 totalAmountStaked, ) = tokenDistributor.userInfo(address(this));

        // Adjust for pending rewards
        totalAmountStaked += tokenDistributor.calculatePendingRewards(address(this));

        // Return user pro-rata of total shares
        return
            userInfo[user].shares == 0
                ? 0
                : (totalAmountStaked * userInfo[user].shares) / totalShares;
    }

    /**
     * @notice Calculate price of one share (in X2Y2 token)
     * Share price is expressed times 1e18
     */
    function calculateSharePriceInX2Y2() external view returns (uint256) {
        (uint256 totalAmountStaked, ) = tokenDistributor.userInfo(address(this));

        // Adjust for pending rewards
        totalAmountStaked += tokenDistributor.calculatePendingRewards(address(this));

        return
            totalShares == 0
                ? PRECISION_FACTOR
                : (totalAmountStaked * PRECISION_FACTOR) / (totalShares);
    }

    /**
     * @notice Return last block where trading rewards were distributed
     */
    function lastRewardBlock() external view returns (uint256) {
        return _lastRewardBlock();
    }

    /**
     * @notice Calculate pending rewards for a user
     * @param user address of the user
     */
    function _calculatePendingRewards(address user) internal view returns (uint256) {
        return
            ((userInfo[user].shares *
                (_rewardPerToken() - (userInfo[user].userRewardPerTokenPaid))) / PRECISION_FACTOR) +
            userInfo[user].rewards;
    }

    /**
     * @notice Check current allowance and adjust if necessary
     * @param _amount amount to transfer
     * @param _to token to transfer
     */
    function _checkAndAdjustX2Y2TokenAllowanceIfRequired(uint256 _amount, address _to) internal {
        if (x2y2Token.allowance(address(this), _to) < _amount) {
            x2y2Token.approve(_to, type(uint256).max);
        }
    }

    /**
     * @notice Return last block where rewards must be distributed
     */
    function _lastRewardBlock() internal view returns (uint256) {
        return block.number < periodEndBlock ? block.number : periodEndBlock;
    }

    /**
     * @notice Return reward per token
     */
    function _rewardPerToken() internal view returns (uint256) {
        if (totalShares == 0) {
            return rewardPerTokenStored;
        }

        return
            rewardPerTokenStored +
            ((_lastRewardBlock() - lastUpdateBlock) * (currentRewardPerBlock * PRECISION_FACTOR)) /
            totalShares;
    }

    /**
     * @notice Update reward for a user account
     * @param _user address of the user
     */
    function _updateReward(address _user) internal {
        if (block.number != lastUpdateBlock) {
            rewardPerTokenStored = _rewardPerToken();
            lastUpdateBlock = _lastRewardBlock();
        }

        userInfo[_user].rewards = _calculatePendingRewards(_user);
        userInfo[_user].userRewardPerTokenPaid = rewardPerTokenStored;
    }

    /**
     * @notice Withdraw staked tokens (and collect reward tokens if requested)
     * @param shares shares to withdraw
     * @param claimRewardToken whether to claim reward tokens
     */
    function _withdraw(uint256 shares, bool claimRewardToken) internal {
        // Auto compounds for everyone
        tokenDistributor.harvestAndCompound();

        // Update reward for user
        _updateReward(msg.sender);

        // Retrieve total amount staked and calculated current amount (in X2Y2)
        (uint256 totalAmountStaked, ) = tokenDistributor.userInfo(address(this));
        uint256 currentAmount = (totalAmountStaked * shares) / totalShares;

        userInfo[msg.sender].shares -= shares;
        totalShares -= shares;

        // Withdraw amount equivalent in shares
        tokenDistributor.withdraw(currentAmount);

        uint256 pendingRewards;

        if (claimRewardToken) {
            // Fetch pending rewards
            pendingRewards = userInfo[msg.sender].rewards;

            if (pendingRewards > 0) {
                userInfo[msg.sender].rewards = 0;
                rewardToken.safeTransfer(msg.sender, pendingRewards);
            }
        }

        // Transfer X2Y2 tokens to sender
        x2y2Token.safeTransfer(msg.sender, currentAmount);

        emit Withdraw(msg.sender, currentAmount, pendingRewards);
    }
}

// File: @openzeppelin/contracts/access/AccessControl.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/AccessControl.sol)

pragma solidity ^0.8.0;

import "./IAccessControl.sol";
import "../utils/Context.sol";
import "../utils/Strings.sol";
import "../utils/introspection/ERC165.sol";

/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms. This is a lightweight version that doesn't allow enumerating role
 * members except through off-chain means by accessing the contract event logs. Some
 * applications may benefit from on-chain enumerability, for those cases see
 * {AccessControlEnumerable}.
 *
 * Roles are referred to by their `bytes32` identifier. These should be exposed
 * in the external API and be unique. The best way to achieve this is by
 * using `public constant` hash digests:
 *
 * ```
 * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
 * ```
 *
 * Roles can be used to represent a set of permissions. To restrict access to a
 * function call, use {hasRole}:
 *
 * ```
 * function foo() public {
 *     require(hasRole(MY_ROLE, msg.sender));
 *     ...
 * }
 * ```
 *
 * Roles can be granted and revoked dynamically via the {grantRole} and
 * {revokeRole} functions. Each role has an associated admin role, and only
 * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
 *
 * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
 * that only accounts with this role will be able to grant or revoke other
 * roles. More complex role relationships can be created by using
 * {_setRoleAdmin}.
 *
 * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
 * grant and revoke this role. Extra precautions should be taken to secure
 * accounts that have been granted it.
 */
abstract contract AccessControl is Context, IAccessControl, ERC165 {
    struct RoleData {
        mapping(address => bool) members;
        bytes32 adminRole;
    }

    mapping(bytes32 => RoleData) private _roles;

    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

    /**
     * @dev Modifier that checks that an account has a specific role. Reverts
     * with a standardized message including the required role.
     *
     * The format of the revert reason is given by the following regular expression:
     *
     *  /^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/
     *
     * _Available since v4.1._
     */
    modifier onlyRole(bytes32 role) {
        _checkRole(role, _msgSender());
        _;
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IAccessControl).interfaceId || super.supportsInterface(interfaceId);
    }

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) public view override returns (bool) {
        return _roles[role].members[account];
    }

    /**
     * @dev Revert with a standard message if `account` is missing `role`.
     *
     * The format of the revert reason is given by the following regular expression:
     *
     *  /^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/
     */
    function _checkRole(bytes32 role, address account) internal view {
        if (!hasRole(role, account)) {
            revert(
                string(
                    abi.encodePacked(
                        "AccessControl: account ",
                        Strings.toHexString(uint160(account), 20),
                        " is missing role ",
                        Strings.toHexString(uint256(role), 32)
                    )
                )
            );
        }
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) public view override returns (bytes32) {
        return _roles[role].adminRole;
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) public virtual override onlyRole(getRoleAdmin(role)) {
        _grantRole(role, account);
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) public virtual override onlyRole(getRoleAdmin(role)) {
        _revokeRole(role, account);
    }

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been revoked `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) public virtual override {
        require(account == _msgSender(), "AccessControl: can only renounce roles for self");

        _revokeRole(role, account);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event. Note that unlike {grantRole}, this function doesn't perform any
     * checks on the calling account.
     *
     * [WARNING]
     * ====
     * This function should only be called from the constructor when setting
     * up the initial roles for the system.
     *
     * Using this function in any other way is effectively circumventing the admin
     * system imposed by {AccessControl}.
     * ====
     *
     * NOTE: This function is deprecated in favor of {_grantRole}.
     */
    function _setupRole(bytes32 role, address account) internal virtual {
        _grantRole(role, account);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.
     *
     * Emits a {RoleAdminChanged} event.
     */
    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
        bytes32 previousAdminRole = getRoleAdmin(role);
        _roles[role].adminRole = adminRole;
        emit RoleAdminChanged(role, previousAdminRole, adminRole);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * Internal function without access restriction.
     */
    function _grantRole(bytes32 role, address account) internal virtual {
        if (!hasRole(role, account)) {
            _roles[role].members[account] = true;
            emit RoleGranted(role, account, _msgSender());
        }
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * Internal function without access restriction.
     */
    function _revokeRole(bytes32 role, address account) internal virtual {
        if (hasRole(role, account)) {
            _roles[role].members[account] = false;
            emit RoleRevoked(role, account, _msgSender());
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/utils/SafeERC20.sol)

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'
        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
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: @openzeppelin/contracts/security/ReentrancyGuard.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (security/ReentrancyGuard.sol)

pragma solidity ^0.8.0;

/**
 * @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 making 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/TokenDistributor.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import {ReentrancyGuard} from '@openzeppelin/contracts/security/ReentrancyGuard.sol';
import {IERC20, SafeERC20} from '@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol';

import {IMintableERC20} from './IMintableERC20.sol';

/**
 * @title TokenDistributor
 * @notice It handles the distribution of X2Y2 token.
 * It auto-adjusts block rewards over a set number of periods.
 */
contract TokenDistributor is ReentrancyGuard {
    using SafeERC20 for IERC20;
    using SafeERC20 for IMintableERC20;

    struct StakingPeriod {
        uint256 rewardPerBlockForStaking;
        uint256 rewardPerBlockForOthers;
        uint256 periodLengthInBlock;
    }

    struct UserInfo {
        uint256 amount; // Amount of staked tokens provided by user
        uint256 rewardDebt; // Reward debt
    }

    // Precision factor for calculating rewards
    uint256 public constant PRECISION_FACTOR = 10**12;

    IMintableERC20 public immutable x2y2Token;

    address public immutable tokenSplitter;

    // Number of reward periods
    uint256 public immutable NUMBER_PERIODS;

    // Block number when rewards start
    uint256 public immutable START_BLOCK;

    // Accumulated tokens per share
    uint256 public accTokenPerShare;

    // Current phase for rewards
    uint256 public currentPhase;

    // Block number when rewards end
    uint256 public endBlock;

    // Block number of the last update
    uint256 public lastRewardBlock;

    // Tokens distributed per block for other purposes (team + treasury + trading rewards)
    uint256 public rewardPerBlockForOthers;

    // Tokens distributed per block for staking
    uint256 public rewardPerBlockForStaking;

    // Total amount staked
    uint256 public totalAmountStaked;

    mapping(uint256 => StakingPeriod) public stakingPeriod;

    mapping(address => UserInfo) public userInfo;

    event Compound(address indexed user, uint256 harvestedAmount);
    event Deposit(address indexed user, uint256 amount, uint256 harvestedAmount);
    event NewRewardsPerBlock(
        uint256 indexed currentPhase,
        uint256 startBlock,
        uint256 rewardPerBlockForStaking,
        uint256 rewardPerBlockForOthers
    );
    event Withdraw(address indexed user, uint256 amount, uint256 harvestedAmount);

    /**
     * @notice Constructor
     * @param _x2y2Token token address
     * @param _tokenSplitter token splitter contract address (for team and trading rewards)
     * @param _startBlock start block for reward program
     * @param _rewardsPerBlockForStaking array of rewards per block for staking
     * @param _rewardsPerBlockForOthers array of rewards per block for other purposes (team + treasury + trading rewards)
     * @param _periodLengthesInBlocks array of period lengthes
     * @param _numberPeriods number of periods with different rewards/lengthes (e.g., if 3 changes --> 4 periods)
     */
    constructor(
        address _x2y2Token,
        address _tokenSplitter,
        uint256 _startBlock,
        uint256[] memory _rewardsPerBlockForStaking,
        uint256[] memory _rewardsPerBlockForOthers,
        uint256[] memory _periodLengthesInBlocks,
        uint256 _numberPeriods
    ) {
        require(
            (_periodLengthesInBlocks.length == _numberPeriods) &&
                (_rewardsPerBlockForStaking.length == _numberPeriods) &&
                (_rewardsPerBlockForStaking.length == _numberPeriods),
            'Distributor: Lengthes must match numberPeriods'
        );

        // 1. Operational checks for supply
        uint256 nonCirculatingSupply = IMintableERC20(_x2y2Token).SUPPLY_CAP() -
            IMintableERC20(_x2y2Token).totalSupply();

        uint256 amountTokensToBeMinted;

        for (uint256 i = 0; i < _numberPeriods; i++) {
            amountTokensToBeMinted +=
                (_rewardsPerBlockForStaking[i] * _periodLengthesInBlocks[i]) +
                (_rewardsPerBlockForOthers[i] * _periodLengthesInBlocks[i]);

            stakingPeriod[i] = StakingPeriod({
                rewardPerBlockForStaking: _rewardsPerBlockForStaking[i],
                rewardPerBlockForOthers: _rewardsPerBlockForOthers[i],
                periodLengthInBlock: _periodLengthesInBlocks[i]
            });
        }

        require(
            amountTokensToBeMinted == nonCirculatingSupply,
            'Distributor: Wrong reward parameters'
        );

        // 2. Store values
        x2y2Token = IMintableERC20(_x2y2Token);
        tokenSplitter = _tokenSplitter;
        rewardPerBlockForStaking = _rewardsPerBlockForStaking[0];
        rewardPerBlockForOthers = _rewardsPerBlockForOthers[0];

        START_BLOCK = _startBlock;
        endBlock = _startBlock + _periodLengthesInBlocks[0];

        NUMBER_PERIODS = _numberPeriods;

        // Set the lastRewardBlock as the startBlock
        lastRewardBlock = _startBlock;
    }

    /**
     * @notice Deposit staked tokens and compounds pending rewards
     * @param amount amount to deposit (in X2Y2)
     */
    function deposit(uint256 amount) external nonReentrant {
        require(amount > 0, 'Deposit: Amount must be > 0');
        require(block.number >= START_BLOCK, 'Deposit: Not started yet');

        // Update pool information
        _updatePool();

        // Transfer X2Y2 tokens to this contract
        x2y2Token.safeTransferFrom(msg.sender, address(this), amount);

        uint256 pendingRewards;

        // If not new deposit, calculate pending rewards (for auto-compounding)
        if (userInfo[msg.sender].amount > 0) {
            pendingRewards =
                ((userInfo[msg.sender].amount * accTokenPerShare) / PRECISION_FACTOR) -
                userInfo[msg.sender].rewardDebt;
        }

        // Adjust user information
        userInfo[msg.sender].amount += (amount + pendingRewards);
        userInfo[msg.sender].rewardDebt =
            (userInfo[msg.sender].amount * accTokenPerShare) /
            PRECISION_FACTOR;

        // Increase totalAmountStaked
        totalAmountStaked += (amount + pendingRewards);

        emit Deposit(msg.sender, amount, pendingRewards);
    }

    /**
     * @notice Compound based on pending rewards
     */
    function harvestAndCompound() external nonReentrant {
        // Update pool information
        _updatePool();

        // Calculate pending rewards
        uint256 pendingRewards = ((userInfo[msg.sender].amount * accTokenPerShare) /
            PRECISION_FACTOR) - userInfo[msg.sender].rewardDebt;

        // Return if no pending rewards
        if (pendingRewards == 0) {
            // It doesn't throw revertion (to help with the fee-sharing auto-compounding contract)
            return;
        }

        // Adjust user amount for pending rewards
        userInfo[msg.sender].amount += pendingRewards;

        // Adjust totalAmountStaked
        totalAmountStaked += pendingRewards;

        // Recalculate reward debt based on new user amount
        userInfo[msg.sender].rewardDebt =
            (userInfo[msg.sender].amount * accTokenPerShare) /
            PRECISION_FACTOR;

        emit Compound(msg.sender, pendingRewards);
    }

    /**
     * @notice Update pool rewards
     */
    function updatePool() external nonReentrant {
        _updatePool();
    }

    /**
     * @notice Withdraw staked tokens and compound pending rewards
     * @param amount amount to withdraw
     */
    function withdraw(uint256 amount) external nonReentrant {
        require(
            (userInfo[msg.sender].amount >= amount) && (amount > 0),
            'Withdraw: Amount must be > 0 or lower than user balance'
        );

        // Update pool
        _updatePool();

        // Calculate pending rewards
        uint256 pendingRewards = ((userInfo[msg.sender].amount * accTokenPerShare) /
            PRECISION_FACTOR) - userInfo[msg.sender].rewardDebt;

        // Adjust user information
        userInfo[msg.sender].amount = userInfo[msg.sender].amount + pendingRewards - amount;
        userInfo[msg.sender].rewardDebt =
            (userInfo[msg.sender].amount * accTokenPerShare) /
            PRECISION_FACTOR;

        // Adjust total amount staked
        totalAmountStaked = totalAmountStaked + pendingRewards - amount;

        // Transfer X2Y2 tokens to the sender
        x2y2Token.safeTransfer(msg.sender, amount);

        emit Withdraw(msg.sender, amount, pendingRewards);
    }

    /**
     * @notice Withdraw all staked tokens and collect tokens
     */
    function withdrawAll() external nonReentrant {
        require(userInfo[msg.sender].amount > 0, 'Withdraw: Amount must be > 0');

        // Update pool
        _updatePool();

        // Calculate pending rewards and amount to transfer (to the sender)
        uint256 pendingRewards = ((userInfo[msg.sender].amount * accTokenPerShare) /
            PRECISION_FACTOR) - userInfo[msg.sender].rewardDebt;

        uint256 amountToTransfer = userInfo[msg.sender].amount + pendingRewards;

        // Adjust total amount staked
        totalAmountStaked = totalAmountStaked - userInfo[msg.sender].amount;

        // Adjust user information
        userInfo[msg.sender].amount = 0;
        userInfo[msg.sender].rewardDebt = 0;

        // Transfer X2Y2 tokens to the sender
        x2y2Token.safeTransfer(msg.sender, amountToTransfer);

        emit Withdraw(msg.sender, amountToTransfer, pendingRewards);
    }

    /**
     * @notice Calculate pending rewards for a user
     * @param user address of the user
     * @return Pending rewards
     */
    function calculatePendingRewards(address user) external view returns (uint256) {
        if ((block.number > lastRewardBlock) && (totalAmountStaked != 0)) {
            uint256 multiplier = _getMultiplier(lastRewardBlock, block.number);

            uint256 tokenRewardForStaking = multiplier * rewardPerBlockForStaking;

            uint256 adjustedEndBlock = endBlock;
            uint256 adjustedCurrentPhase = currentPhase;

            // Check whether to adjust multipliers and reward per block
            while (
                (block.number > adjustedEndBlock) && (adjustedCurrentPhase < (NUMBER_PERIODS - 1))
            ) {
                // Update current phase
                adjustedCurrentPhase++;

                // Update rewards per block
                uint256 adjustedRewardPerBlockForStaking = stakingPeriod[adjustedCurrentPhase]
                    .rewardPerBlockForStaking;

                // Calculate adjusted block number
                uint256 previousEndBlock = adjustedEndBlock;

                // Update end block
                adjustedEndBlock =
                    previousEndBlock +
                    stakingPeriod[adjustedCurrentPhase].periodLengthInBlock;

                // Calculate new multiplier
                uint256 newMultiplier = (block.number <= adjustedEndBlock)
                    ? (block.number - previousEndBlock)
                    : stakingPeriod[adjustedCurrentPhase].periodLengthInBlock;

                // Adjust token rewards for staking
                tokenRewardForStaking += (newMultiplier * adjustedRewardPerBlockForStaking);
            }

            uint256 adjustedTokenPerShare = accTokenPerShare +
                (tokenRewardForStaking * PRECISION_FACTOR) /
                totalAmountStaked;

            return
                (userInfo[user].amount * adjustedTokenPerShare) /
                PRECISION_FACTOR -
                userInfo[user].rewardDebt;
        } else {
            return
                (userInfo[user].amount * accTokenPerShare) /
                PRECISION_FACTOR -
                userInfo[user].rewardDebt;
        }
    }

    /**
     * @notice Update reward variables of the pool
     */
    function _updatePool() internal {
        if (block.number <= lastRewardBlock) {
            return;
        }

        if (totalAmountStaked == 0) {
            lastRewardBlock = block.number;
            return;
        }

        // Calculate multiplier
        uint256 multiplier = _getMultiplier(lastRewardBlock, block.number);

        // Calculate rewards for staking and others
        uint256 tokenRewardForStaking = multiplier * rewardPerBlockForStaking;
        uint256 tokenRewardForOthers = multiplier * rewardPerBlockForOthers;

        // Check whether to adjust multipliers and reward per block
        while ((block.number > endBlock) && (currentPhase < (NUMBER_PERIODS - 1))) {
            // Update rewards per block
            _updateRewardsPerBlock(endBlock);

            uint256 previousEndBlock = endBlock;

            // Adjust the end block
            endBlock += stakingPeriod[currentPhase].periodLengthInBlock;

            // Adjust multiplier to cover the missing periods with other lower inflation schedule
            uint256 newMultiplier = _getMultiplier(previousEndBlock, block.number);

            // Adjust token rewards
            tokenRewardForStaking += (newMultiplier * rewardPerBlockForStaking);
            tokenRewardForOthers += (newMultiplier * rewardPerBlockForOthers);
        }

        // Mint tokens only if token rewards for staking are not null
        if (tokenRewardForStaking > 0) {
            // It allows protection against potential issues to prevent funds from being locked
            bool mintStatus = x2y2Token.mint(address(this), tokenRewardForStaking);
            if (mintStatus) {
                accTokenPerShare =
                    accTokenPerShare +
                    ((tokenRewardForStaking * PRECISION_FACTOR) / totalAmountStaked);
            }

            x2y2Token.mint(tokenSplitter, tokenRewardForOthers);
        }

        // Update last reward block only if it wasn't updated after or at the end block
        if (lastRewardBlock <= endBlock) {
            lastRewardBlock = block.number;
        }
    }

    /**
     * @notice Update rewards per block
     * @dev Rewards are halved by 2 (for staking + others)
     */
    function _updateRewardsPerBlock(uint256 _newStartBlock) internal {
        // Update current phase
        currentPhase++;

        // Update rewards per block
        rewardPerBlockForStaking = stakingPeriod[currentPhase].rewardPerBlockForStaking;
        rewardPerBlockForOthers = stakingPeriod[currentPhase].rewardPerBlockForOthers;

        emit NewRewardsPerBlock(
            currentPhase,
            _newStartBlock,
            rewardPerBlockForStaking,
            rewardPerBlockForOthers
        );
    }

    /**
     * @notice Return reward multiplier over the given "from" to "to" block.
     * @param from block to start calculating reward
     * @param to block to finish calculating reward
     * @return the multiplier for the period
     */
    function _getMultiplier(uint256 from, uint256 to) internal view returns (uint256) {
        if (to <= endBlock) {
            return to - from;
        } else if (from >= endBlock) {
            return 0;
        } else {
            return endBlock - from;
        }
    }
}

// File: contracts/IStakeFor.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IStakeFor {
    function depositFor(address user, uint256 amount) external returns (bool);
}

// File: @openzeppelin/contracts/access/IAccessControl.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/IAccessControl.sol)

pragma solidity ^0.8.0;

/**
 * @dev External interface of AccessControl declared to support ERC165 detection.
 */
interface IAccessControl {
    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
     *
     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call, an admin role
     * bearer except when using {AccessControl-_setupRole}.
     */
    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Emitted when `account` is revoked `role`.
     *
     * `sender` is the account that originated the contract call:
     *   - if using `revokeRole`, it is the admin role bearer
     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
     */
    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) external view returns (bool);

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {AccessControl-_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) external view returns (bytes32);

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) external;

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) external;

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) external;
}

// File: @openzeppelin/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Strings.sol)

pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }
}

// File: @openzeppelin/contracts/utils/introspection/ERC165.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)

pragma solidity ^0.8.0;

import "./IERC165.sol";

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
 * for the additional interface id that will be supported. For example:
 *
 * ```solidity
 * function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
 *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
 * }
 * ```
 *
 * Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
 */
abstract contract ERC165 is IERC165 {
    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IERC165).interfaceId;
    }
}

// File: @openzeppelin/contracts/utils/introspection/IERC165.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/introspection/IERC165.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/IERC20.sol)

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/contracts/utils/Address.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Address.sol)

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;
        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");

        (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");

        (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");

        (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");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal 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

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: contracts/IMintableERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import {IERC20} from '@openzeppelin/contracts/token/ERC20/IERC20.sol';

interface IMintableERC20 is IERC20 {
    function SUPPLY_CAP() external view returns (uint256);

    function mint(address account, uint256 amount) external returns (bool);
}