// SPDX-License-Identifier: MIT

pragma solidity 0.8.7;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

/**
 * @title SymbiosisTokenVesting
 *
 * @dev A token holder contract that can release its token balance gradually like a
 * typical vesting scheme, with a cliff and vesting period.
 * There are 3 types of vesting schedule: CONTINUOUS, MONTHLY (every 30 days), QUARTERLY (every 90 days).
 */
contract SymbiosisTokenVesting is Ownable {
    // The vesting schedule is time-based (i.e. using block timestamps as opposed to e.g. block numbers), and is
    // therefore sensitive to timestamp manipulation (which is something miners can do, to a certain degree). Therefore,
    // it is recommended to avoid using short time durations (less than a minute). Typical vesting schemes, with a
    // cliff period of a year and a duration of four years, are safe to use.
    // solhint-disable not-rely-on-time

    using SafeERC20 for IERC20;

    event ReservedAdded(address indexed beneficiary, uint256 reserved);
    event TokensReleased(
        address indexed beneficiary,
        address indexed transferredTo,
        uint256 amount
    );
    event TokensWithdrawnByOwner(address indexed token, uint256 amount);

    // 100% in basis points
    uint256 public constant MAX_BPS = 10000;

    // private VestingSchedule time constants
    uint256 private constant MONTHLY_TIME = 30 days;
    uint256 private constant QUARTERLY_TIME = 90 days;

    // SymbiosisTokenVesting name
    string public name;

    // ERC20 token which is being vested
    IERC20 public token;

    // staking contract address
    address public stakingAddress;

    // Durations and timestamps are expressed in UNIX time, the same units as block.timestamp.
    uint256 public cliff; // the cliff time of the token vesting
    uint256 public start; // the start time of the token vesting
    uint256 public duration; // the duration of the token vesting

    // type of the token vesting
    enum VestingSchedule {
        CONTINUOUS,
        MONTHLY,
        QUARTERLY
    }
    VestingSchedule public immutable schedule;

    // basis points of the initial unlock – after the start and before the end of the cliff period
    uint256 public immutable cliffUnlockedBP;

    // total reserved tokens for beneficiaries
    uint256 public reserved;

    // reserved tokens to beneficiary
    mapping(address => uint256) public reservedForBeneficiary;

    // frozen amount for staking
    mapping(address => uint256) public frozenForStakeAmount;

    // total released (transferred) tokens
    uint256 public released;

    // released (transferred) tokens to beneficiary
    mapping(address => uint256) public releasedToBeneficiary;

    // array of beneficiaries for getters
    address[] internal beneficiaries;

    /**
     * @dev Creates a vesting contract that vests its balance of specific ERC20 token to the
     * beneficiaries, gradually in a linear fashion until start + duration. By then all
     * of the balance will have vested.
     * @param _token ERC20 token which is being vested
     * @param _cliffDuration duration in seconds of the cliff in which tokens will begin to vest
     * @param _cliffUnlockedBP basis points of initial unlock – after the start and before the end of the cliff period
     * @param _start the time (as Unix time) at which point vesting starts
     * @param _duration duration in seconds of the period in which the tokens will vest
     * @param _schedule type of the token vesting: CONTINUOUS, MONTHLY, QUARTERLY
     * @param _name SymbiosisTokenVesting name
     */
    constructor(
        IERC20 _token,
        uint256 _start,
        uint256 _cliffDuration,
        uint256 _cliffUnlockedBP,
        uint256 _duration,
        VestingSchedule _schedule,
        string memory _name
    ) {
        require(
            address(_token) != address(0),
            "SymbiosisTokenVesting: token is the zero address"
        );
        require(_duration > 0, "SymbiosisTokenVesting: duration is 0");

        require(
            _cliffDuration <= _duration,
            "SymbiosisTokenVesting: cliff is longer than duration"
        );

        require(
            _start + _duration > block.timestamp,
            "SymbiosisTokenVesting: final time is before current time"
        );

        require(
            _cliffUnlockedBP <= MAX_BPS,
            "SymbiosisTokenVesting: invalid cliff unlocked BP"
        );

        token = _token;
        duration = _duration;
        cliff = _start + _cliffDuration;
        start = _start;
        schedule = _schedule;
        name = _name;

        cliffUnlockedBP = _cliffUnlockedBP;
    }

    modifier onlyStaking() {
        require(
            msg.sender == stakingAddress,
            "SymbiosisTokenVesting: caller is not the staking address"
        );
        _;
    }

    function setStakingAddress(address _stakingAddress) external onlyOwner {
        stakingAddress = _stakingAddress;
    }

    /**
     * @notice Calculates the total amount of vested tokens.
     */
    function totalVested() public view returns (uint256) {
        uint256 currentBalance = token.balanceOf(address(this));
        return currentBalance + released;
    }

    /**
     * @notice Calculates the amount that has already vested but hasn't been released yet.
     * @param _beneficiary Address of vested tokens beneficiary
     */
    function releasableAmount(address _beneficiary)
        public
        view
        returns (uint256)
    {
        uint256 releasable = _vestedAmount(_beneficiary) - releasedToBeneficiary[_beneficiary];
        uint256 frozen = frozenForStakeAmount[_beneficiary];
        return (releasable > frozen) ? (releasable - frozen) : 0;
    }

    /**
     * @notice Get a beneficiary address with current index.
     */
    function getBeneficiary(uint256 index) external view returns (address) {
        return beneficiaries[index];
    }

    /**
     * @notice Get an array of beneficiary addresses.
     */
    function getBeneficiaries() external view returns (address[] memory) {
        return beneficiaries;
    }

    /**
     * @notice Adds beneficiaries to SymbiosisTokenVesting by owner.
     *
     * Requirements:
     * - can only be called by owner.
     *
     * @param _beneficiaries Addresses of beneficiaries
     * @param _amounts Amounts of tokens reserved for beneficiaries
     */
    function addBeneficiaries(
        address[] memory _beneficiaries,
        uint256[] memory _amounts
    ) external onlyOwner {
        uint256 len = _beneficiaries.length;
        require(len == _amounts.length, "SymbiosisTokenVesting: Array lengths do not match");

        uint256 amountToBeneficiaries = 0;
        for (uint256 i = 0; i < len; i++) {
            amountToBeneficiaries = amountToBeneficiaries + _amounts[i];

            // add new beneficiary to array
            if (reservedForBeneficiary[_beneficiaries[i]] == 0) {
                beneficiaries.push(_beneficiaries[i]);
            }

            reservedForBeneficiary[_beneficiaries[i]] =
                reservedForBeneficiary[_beneficiaries[i]] +
                _amounts[i];

            emit ReservedAdded(_beneficiaries[i], _amounts[i]);
        }

        reserved = reserved + amountToBeneficiaries;

        // check reserved condition
        require(
            reserved <= totalVested(),
            "SymbiosisTokenVesting: reserved exceeds totalVested"
        );
    }

    /**
     * @notice Withdraws ERC20 token funds by owner (except vested token).
     *
     * Requirements:
     * - can only be called by owner.
     *
     * @param _token Token address (except vested token)
     * @param _amount The amount of token to withdraw
     **/
    function withdrawFunds(IERC20 _token, uint256 _amount) external onlyOwner {
        require(
            _token != token,
            "SymbiosisTokenVesting: vested token is not available for withdrawal"
        );
        _token.safeTransfer(msg.sender, _amount);
        emit TokensWithdrawnByOwner(address(_token), _amount);
    }

    /**
     * @notice Withdraws ERC20 vested token by owner.
     *
     * Requirements:
     * - can only be called by owner.
     *
     * @param _amount The amount of token to withdraw
     **/
    function emergencyWithdraw(uint256 _amount) external onlyOwner {
        require(
            block.timestamp < start,
            "SymbiosisTokenVesting: vesting has already started"
        );
        token.safeTransfer(msg.sender, _amount);
        emit TokensWithdrawnByOwner(address(token), _amount);
    }

    /**
     * @notice Transfers vested tokens to beneficiary.
     * @param _beneficiary Address of vested tokens beneficiary
     */
    function release(address _beneficiary) external {
        _release(_beneficiary, _beneficiary);
    }

    /**
     * @notice Transfers vested tokens of sender to specified address.
     * @param _transferTo Address to which tokens are transferred
     */
    function releaseToAddress(address _transferTo) external {
        _release(msg.sender, _transferTo);
    }

    function allocateStake(address _beneficiary, uint256 _amount)
        external
        onlyStaking
        returns (bool)
    {
        require(
            reservedForBeneficiary[_beneficiary] - releasedToBeneficiary[_beneficiary] >= _amount,
            "SymbiosisTokenVesting: allocation amount exceeds balance"
        );
        frozenForStakeAmount[_beneficiary] += _amount;

        return true;
    }

    function unlockStake(address _beneficiary, uint256 _amount)
        external
        onlyStaking
        returns (bool)
    {
        require(
            _amount <= frozenForStakeAmount[_beneficiary],
            "SymbiosisTokenVesting: amount exceeds frozen amount for this beneficiary"
        );
        frozenForStakeAmount[_beneficiary] -= _amount;

        return true;
    }

    /**
     * @dev Calculates the amount that has already vested.
     * @param _beneficiary Address of vested tokens beneficiary
     */
    function _vestedAmount(address _beneficiary)
        private
        view
        returns (uint256)
    {
        uint256 curTimestamp = block.timestamp;

        if (curTimestamp < start) {
            return 0;
        } else if (curTimestamp < cliff) {
            return reservedForBeneficiary[_beneficiary] * cliffUnlockedBP / MAX_BPS;
        } else if (curTimestamp >= start + duration) {
            return reservedForBeneficiary[_beneficiary];
        } else {
            return
                reservedForBeneficiary[_beneficiary] * cliffUnlockedBP / MAX_BPS +
                reservedForBeneficiary[_beneficiary] * (MAX_BPS - cliffUnlockedBP) * _vestedPeriod() / (duration - (cliff - start)) / MAX_BPS;
        }
    }

    /**
     * @dev Calculates the duration of period that is already unlocked according to VestingSchedule type.
     */
    function _vestedPeriod() private view returns (uint256 period) {
        period = block.timestamp - cliff; // CONTINUOUS from cliff

        if (schedule == VestingSchedule.MONTHLY) {
            period = period - (period % MONTHLY_TIME);
        } else if (schedule == VestingSchedule.QUARTERLY) {
            period = period - (period % QUARTERLY_TIME);
        }
    }

    /**
     * @dev Transfers vested tokens.
     * @param _beneficiary Address of vested tokens beneficiary
     * @param _transferTo Address to which tokens are transferred
     */
    function _release(address _beneficiary, address _transferTo) private {
        uint256 unreleased = releasableAmount(_beneficiary);

        require(unreleased > 0, "SymbiosisTokenVesting: no tokens are due");

        releasedToBeneficiary[_beneficiary] =
            releasedToBeneficiary[_beneficiary] +
            unreleased;
        released = released + unreleased;

        token.safeTransfer(_transferTo, unreleased);

        emit TokensReleased(_beneficiary, _transferTo, unreleased);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../utils/Context.sol";

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

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _setOwner(_msgSender());
    }

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

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

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

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

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// 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'
        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");
        }
    }
}

// SPDX-License-Identifier: MIT

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;
    }
}

// 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);
}

// 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;
        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);
            }
        }
    }
}