Contract Source Code:

// contracts/TokenVesting.sol
// SPDX-License-Identifier: Apache-2.0
pragma solidity 0.8.18;

import { IERC20Metadata } from "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";
import { SafeERC20 } from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import { ReentrancyGuard } from "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import { Ownable } from "@openzeppelin/contracts/access/Ownable.sol";
import { Pausable } from "@openzeppelin/contracts/security/Pausable.sol";

/// @title TokenVesting - On-Chain vesting scheme enabled by smart contracts.
/// The TokenVesting contract can release its token balance gradually like a
/// typical vesting scheme, with a cliff and vesting period. The contract owner
/// can create vesting schedules for different users, even multiple for the same person.
/// Vesting schedules are optionally revokable by the owner. Additionally the
/// smart contract functions as an ERC20 compatible non-transferable virtual
/// token which can be used e.g. for governance.
/// This work is based on the TokenVesting contract by Abdelhamid Bakhta
/// (https://github.com/abdelhamidbakhta/token-vesting-contracts)
/// and was extended with the virtual token functionality and partially rewritten.
/// @author Schmackofant - schmackofant@protonmail.com

contract TokenVesting is IERC20Metadata, Ownable, ReentrancyGuard, Pausable {
    using SafeERC20 for IERC20Metadata;

    /// @notice The ERC20 name of the virtual token
    string public override name;

    /// @notice The ERC20 symbol of the virtual token
    string public override symbol;

    /// @notice The ERC20 number of decimals of the virtual token
    /// @dev This contract only supports native tokens with 18 decimals
    uint8 public constant override decimals = 18;

    enum Status {
        INITIALIZED, //0
        REVOKED
    }

    /**
     * @dev vesting schedule struct
     * @param cliff cliff period in seconds
     * @param start start time of the vesting period
     * @param duration duration of the vesting period in seconds
     * @param slicePeriodSeconds duration of a slice period for the vesting in seconds
     * @param amountTotal total amount of tokens to be released at the end of the vesting
     * @param released amount of tokens released so far
     * @param status schedule status (initialized, revoked)
     * @param beneficiary address of beneficiary of the vesting schedule
     * @param revokable whether or not the vesting is revokable
     */
    struct VestingSchedule {
        uint256 cliff;
        uint256 start;
        uint256 duration;
        uint256 slicePeriodSeconds;
        uint256 amountTotal;
        uint256 released;
        Status status;
        address beneficiary;
        bool revokable;
    }

    /// @notice address of the ERC20 native token
    IERC20Metadata public immutable nativeToken;

    /// @dev This mapping is used to keep track of the vesting schedule ids
    bytes32[] public vestingSchedulesIds;

    /// @dev This mapping is used to keep track of the vesting schedules
    mapping(bytes32 => VestingSchedule) private vestingSchedules;

    /// @notice total amount of native tokens in all vesting schedules
    uint256 public vestingSchedulesTotalAmount;

    /// @notice This mapping is used to keep track of the number of vesting schedules for each beneficiary
    mapping(address => uint256) public holdersVestingScheduleCount;

    /// @dev This mapping is used to keep track of the total amount of vested tokens for each beneficiary
    mapping(address => uint256) private holdersVestedAmount;

    event ScheduleCreated(
        bytes32 indexed scheduleId,
        address indexed beneficiary,
        uint256 amount,
        uint256 start,
        uint256 cliff,
        uint256 duration,
        uint256 slicePeriodSeconds,
        bool revokable
    );
    event TokensReleased(bytes32 indexed scheduleId, address indexed beneficiary, uint256 amount);
    event ScheduleRevoked(bytes32 indexed scheduleId);

    /**
     * @dev Reverts if the vesting schedule does not exist or has been revoked.
     */
    modifier onlyIfVestingScheduleNotRevoked(bytes32 vestingScheduleId) {
        // Check if schedule exists
        if (vestingSchedules[vestingScheduleId].duration == 0) revert InvalidSchedule();
        //slither-disable-next-line incorrect-equality
        if (vestingSchedules[vestingScheduleId].status == Status.REVOKED) revert ScheduleWasRevoked();
        _;
    }

    /// @dev This error is fired when trying to perform an action that is not
    /// supported by the contract, like transfers and approvals. These actions
    /// will never be supported.
    error NotSupported();

    error DecimalsError();
    error InsufficientTokensInContract();
    error InsufficientReleasableTokens();
    error InvalidSchedule();
    error InvalidDuration();
    error InvalidAmount();
    error InvalidSlicePeriod();
    error InvalidStart();
    error DurationShorterThanCliff();
    error NotRevokable();
    error Unauthorized();
    error ScheduleWasRevoked();
    error TooManySchedulesForBeneficiary();

    /**
     * @notice Creates a vesting contract.
     * @param token_ address of the ERC20 native token contract
     * @param _name name of the virtual token
     * @param _symbol symbol of the virtual token
     */
    constructor(IERC20Metadata token_, string memory _name, string memory _symbol) {
        nativeToken = token_;
        if (nativeToken.decimals() != 18) revert DecimalsError();
        name = _name;
        symbol = _symbol;
    }

    /// @dev All types of transfers are permanently disabled.
    function transferFrom(address, address, uint256) public pure override returns (bool) {
        revert NotSupported();
    }

    /// @dev All types of transfers are permanently disabled.
    function transfer(address, uint256) public pure override returns (bool) {
        revert NotSupported();
    }

    /// @dev All types of approvals are permanently disabled to reduce code
    /// size.
    function approve(address, uint256) public pure override returns (bool) {
        revert NotSupported();
    }

    /// @dev Approvals cannot be set, so allowances are always zero.
    function allowance(address, address) public pure override returns (uint256) {
        return 0;
    }

    /// @notice Returns the amount of virtual tokens in existence
    function totalSupply() public view override returns (uint256) {
        return vestingSchedulesTotalAmount;
    }

    /// @notice Returns the sum of virtual tokens for a user
    /// @param user The user for whom the balance is calculated
    /// @return Balance of the user
    function balanceOf(address user) public view override returns (uint256) {
        return holdersVestedAmount[user];
    }

    /**
     * @notice Returns the vesting schedule information for a given holder and index.
     * @return the vesting schedule structure information
     */
    function getVestingScheduleByAddressAndIndex(address holder, uint256 index) external view returns (VestingSchedule memory) {
        return getVestingSchedule(computeVestingScheduleIdForAddressAndIndex(holder, index));
    }

    /**
     * @notice Public function for creating a vesting schedule (only callable by contract owner)
     * @param _beneficiary address of the beneficiary to whom vested tokens are transferred
     * @param _start start time of the vesting period
     * @param _cliff duration in seconds of the cliff in which tokens will begin to vest
     * @param _duration duration in seconds of the period in which the tokens will vest
     * @param _slicePeriodSeconds duration of a slice period for the vesting in seconds
     * @param _revokable whether the vesting is revokable or not
     * @param _amount total amount of tokens to be released at the end of the vesting
     */
    function createVestingSchedule(
        address _beneficiary,
        uint256 _start,
        uint256 _cliff,
        uint256 _duration,
        uint256 _slicePeriodSeconds,
        bool _revokable,
        uint256 _amount
    ) external onlyOwner {
        _createVestingSchedule(_beneficiary, _start, _cliff, _duration, _slicePeriodSeconds, _revokable, _amount);
    }

    /**
     * @notice Creates a new vesting schedule for a beneficiary.
     * @param _beneficiary address of the beneficiary to whom vested tokens are transferred
     * @param _start start time of the vesting period
     * @param _cliff duration in seconds of the cliff in which tokens will begin to vest
     * @param _duration duration in seconds of the period in which the tokens will vest
     * @param _slicePeriodSeconds duration of a slice period for the vesting in seconds
     * @param _revokable whether the vesting is revokable or not
     * @param _amount total amount of tokens to be released at the end of the vesting
     */
    function _createVestingSchedule(
        address _beneficiary,
        uint256 _start,
        uint256 _cliff,
        uint256 _duration,
        uint256 _slicePeriodSeconds,
        bool _revokable,
        uint256 _amount
    ) internal {
        if (getWithdrawableAmount() < _amount) revert InsufficientTokensInContract();

        // _start should be no further away than 30 weeks
        if (_start > block.timestamp + 30 weeks) revert InvalidStart();

        // _duration should be at least 7 days and max 50 years
        if (_duration < 7 days || _duration > 50 * (365 days)) revert InvalidDuration();

        if (_amount == 0) revert InvalidAmount();

        // _slicePeriodSeconds should be at least 60 seconds
        if (_slicePeriodSeconds == 0 || _slicePeriodSeconds > 60) revert InvalidSlicePeriod();

        // _duration must be longer than _cliff
        if (_duration < _cliff) revert DurationShorterThanCliff();

        if (_amount > 2 ** 200) revert InvalidAmount();
        if (holdersVestingScheduleCount[_beneficiary] >= 100) revert TooManySchedulesForBeneficiary();

        bytes32 vestingScheduleId = computeVestingScheduleIdForAddressAndIndex(_beneficiary, holdersVestingScheduleCount[_beneficiary]);
        vestingSchedules[vestingScheduleId] =
            VestingSchedule(_start + _cliff, _start, _duration, _slicePeriodSeconds, _amount, 0, Status.INITIALIZED, _beneficiary, _revokable);
        vestingSchedulesTotalAmount = vestingSchedulesTotalAmount + _amount;
        vestingSchedulesIds.push(vestingScheduleId);
        ++holdersVestingScheduleCount[_beneficiary];
        holdersVestedAmount[_beneficiary] = holdersVestedAmount[_beneficiary] + _amount;
        emit ScheduleCreated(vestingScheduleId, _beneficiary, _amount, _start, _cliff, _duration, _slicePeriodSeconds, _revokable);
    }

    /**
     * @notice Revokes the vesting schedule for given identifier.
     * @param vestingScheduleId the vesting schedule identifier
     */
    function revoke(bytes32 vestingScheduleId) external onlyOwner onlyIfVestingScheduleNotRevoked(vestingScheduleId) {
        VestingSchedule storage vestingSchedule = vestingSchedules[vestingScheduleId];
        if (!vestingSchedule.revokable) revert NotRevokable();
        if (_computeReleasableAmount(vestingSchedule) > 0) {
            _release(vestingScheduleId, _computeReleasableAmount(vestingSchedule));
        }
        uint256 unreleased = vestingSchedule.amountTotal - vestingSchedule.released;
        vestingSchedulesTotalAmount = vestingSchedulesTotalAmount - unreleased;
        holdersVestedAmount[vestingSchedule.beneficiary] = holdersVestedAmount[vestingSchedule.beneficiary] - unreleased;
        vestingSchedule.status = Status.REVOKED;
        emit ScheduleRevoked(vestingScheduleId);
    }

    /**
     * @notice Pauses or unpauses the release of tokens and claiming of schedules
     * @param paused true if the release of tokens and claiming of schedules should be paused, false otherwise
     */
    function setPaused(bool paused) external onlyOwner {
        if (paused) {
            _pause();
        } else {
            _unpause();
        }
    }

    /**
     * @notice Withdraw the specified amount if possible.
     * @param amount the amount to withdraw
     */
    function withdraw(uint256 amount) external nonReentrant onlyOwner {
        if (amount > getWithdrawableAmount()) revert InsufficientTokensInContract();
        nativeToken.safeTransfer(owner(), amount);
    }

    /**
     * @notice Internal function for releasing vested amount of tokens.
     * @param vestingScheduleId the vesting schedule identifier
     * @param amount the amount to release
     */
    function _release(bytes32 vestingScheduleId, uint256 amount) internal {
        VestingSchedule storage vestingSchedule = vestingSchedules[vestingScheduleId];
        bool isBeneficiary = msg.sender == vestingSchedule.beneficiary;
        bool isOwner = msg.sender == owner();
        if (!isBeneficiary && !isOwner) revert Unauthorized();
        if (amount > _computeReleasableAmount(vestingSchedule)) revert InsufficientReleasableTokens();
        vestingSchedule.released = vestingSchedule.released + amount;
        vestingSchedulesTotalAmount = vestingSchedulesTotalAmount - amount;
        holdersVestedAmount[vestingSchedule.beneficiary] = holdersVestedAmount[vestingSchedule.beneficiary] - amount;
        emit TokensReleased(vestingScheduleId, vestingSchedule.beneficiary, amount);
        nativeToken.safeTransfer(vestingSchedule.beneficiary, amount);
    }

    /**
     * @notice Release vested amount of tokens.
     * @param vestingScheduleId the vesting schedule identifier
     * @param amount the amount to release
     */
    function release(bytes32 vestingScheduleId, uint256 amount) external nonReentrant onlyIfVestingScheduleNotRevoked(vestingScheduleId) {
        _release(vestingScheduleId, amount);
    }

    /**
     * @notice Release all available tokens for holder address
     * @param holder address of the holder & beneficiary
     */
    function releaseAvailableTokensForHolder(address holder) external nonReentrant {
        if (msg.sender != holder && msg.sender != owner()) revert Unauthorized();
        uint256 vestingScheduleCount = holdersVestingScheduleCount[holder];
        for (uint256 i = 0; i < vestingScheduleCount; i++) {
            bytes32 vestingScheduleId = computeVestingScheduleIdForAddressAndIndex(holder, i);
            uint256 releasable = computeReleasableAmount(vestingScheduleId);
            if (releasable > 0) {
                _release(vestingScheduleId, releasable);
            }
        }
    }

    /**
     * @notice Returns the array of vesting schedule ids
     * @return vestingSchedulesIds
     */
    function getVestingSchedulesIds() external view returns (bytes32[] memory) {
        return vestingSchedulesIds;
    }

    /**
     * @notice Computes the vested amount of tokens for the given vesting schedule identifier.
     * @return the vested amount
     */
    function computeReleasableAmount(bytes32 vestingScheduleId) public view onlyIfVestingScheduleNotRevoked(vestingScheduleId) returns (uint256) {
        return _computeReleasableAmount(vestingSchedules[vestingScheduleId]);
    }

    /**
     * @notice Returns the vesting schedule information for a given identifier.
     * @return the vesting schedule structure information
     */
    function getVestingSchedule(bytes32 vestingScheduleId) public view returns (VestingSchedule memory) {
        return vestingSchedules[vestingScheduleId];
    }

    /**
     * @notice Returns the amount of native tokens that can be withdrawn by the owner.
     * @return the amount of tokens
     */
    function getWithdrawableAmount() public view returns (uint256) {
        return nativeToken.balanceOf(address(this)) - vestingSchedulesTotalAmount;
    }

    /**
     * @notice Computes the vesting schedule identifier for an address and an index.
     */
    function computeVestingScheduleIdForAddressAndIndex(address holder, uint256 index) public pure returns (bytes32) {
        return keccak256(abi.encodePacked(holder, index));
    }

    /**
     * @dev Computes the releasable amount of tokens for a vesting schedule.
     * @return the amount of releasable tokens
     */
    function _computeReleasableAmount(VestingSchedule storage vestingSchedule) internal view returns (uint256) {
        uint256 currentTime = block.timestamp;
        //slither-disable-next-line incorrect-equality
        if (currentTime < vestingSchedule.cliff || vestingSchedule.status == Status.REVOKED) {
            return 0;
        } else if (currentTime >= vestingSchedule.start + vestingSchedule.duration) {
            return vestingSchedule.amountTotal - vestingSchedule.released;
        } else {
            uint256 timeFromStart = currentTime - vestingSchedule.start;
            uint256 secondsPerSlice = vestingSchedule.slicePeriodSeconds;
            uint256 vestedSlicePeriods = timeFromStart / secondsPerSlice;
            // Disable warning: duration and token amounts are checked in schedule creation and prevent underflow/overflow
            //slither-disable-next-line divide-before-multiply
            uint256 vestedSeconds = vestedSlicePeriods * secondsPerSlice;
            // Disable warning: duration and token amounts are checked in schedule creation and prevent underflow/overflow
            //slither-disable-next-line divide-before-multiply
            uint256 vestedAmount = vestingSchedule.amountTotal * vestedSeconds / vestingSchedule.duration;
            return vestedAmount - vestingSchedule.released;
        }
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (access/Ownable.sol)

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() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

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

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        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 {
        _transferOwnership(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");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (security/Pausable.sol)

pragma solidity ^0.8.0;

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

/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor() {
        _paused = false;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        _requireNotPaused();
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        _requirePaused();
        _;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Throws if the contract is paused.
     */
    function _requireNotPaused() internal view virtual {
        require(!paused(), "Pausable: paused");
    }

    /**
     * @dev Throws if the contract is not paused.
     */
    function _requirePaused() internal view virtual {
        require(paused(), "Pausable: not paused");
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.8.0) (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() {
        _nonReentrantBefore();
        _;
        _nonReentrantAfter();
    }

    function _nonReentrantBefore() private {
        // On the first call to nonReentrant, _status will be _NOT_ENTERED
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

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

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

    /**
     * @dev Returns true if the reentrancy guard is currently set to "entered", which indicates there is a
     * `nonReentrant` function in the call stack.
     */
    function _reentrancyGuardEntered() internal view returns (bool) {
        return _status == _ENTERED;
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @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);

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

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Permit.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in
 * https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].
 *
 * Adds the {permit} method, which can be used to change an account's ERC20 allowance (see {IERC20-allowance}) by
 * presenting a message signed by the account. By not relying on {IERC20-approve}, the token holder account doesn't
 * need to send a transaction, and thus is not required to hold Ether at all.
 */
interface IERC20Permit {
    /**
     * @dev Sets `value` as the allowance of `spender` over ``owner``'s tokens,
     * given ``owner``'s signed approval.
     *
     * IMPORTANT: The same issues {IERC20-approve} has related to transaction
     * ordering also apply here.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `deadline` must be a timestamp in the future.
     * - `v`, `r` and `s` must be a valid `secp256k1` signature from `owner`
     * over the EIP712-formatted function arguments.
     * - the signature must use ``owner``'s current nonce (see {nonces}).
     *
     * For more information on the signature format, see the
     * https://eips.ethereum.org/EIPS/eip-2612#specification[relevant EIP
     * section].
     */
    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    /**
     * @dev Returns the current nonce for `owner`. This value must be
     * included whenever a signature is generated for {permit}.
     *
     * Every successful call to {permit} increases ``owner``'s nonce by one. This
     * prevents a signature from being used multiple times.
     */
    function nonces(address owner) external view returns (uint256);

    /**
     * @dev Returns the domain separator used in the encoding of the signature for {permit}, as defined by {EIP712}.
     */
    // solhint-disable-next-line func-name-mixedcase
    function DOMAIN_SEPARATOR() external view returns (bytes32);
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.8.0) (token/ERC20/utils/SafeERC20.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../extensions/IERC20Permit.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));
        }
    }

    function safePermit(
        IERC20Permit token,
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal {
        uint256 nonceBefore = token.nonces(owner);
        token.permit(owner, spender, value, deadline, v, r, s);
        uint256 nonceAfter = token.nonces(owner);
        require(nonceAfter == nonceBefore + 1, "SafeERC20: permit did not succeed");
    }

    /**
     * @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
// OpenZeppelin Contracts (last updated v4.8.0) (utils/Address.sol)

pragma solidity ^0.8.1;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     *
     * Furthermore, `isContract` will also return true if the target contract within
     * the same transaction is already scheduled for destruction by `SELFDESTRUCT`,
     * which only has an effect at the end of a transaction.
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 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://consensys.net/diligence/blog/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 functionCallWithValue(target, data, 0, "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");
        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResultFromTarget(target, 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) {
        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResultFromTarget(target, 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) {
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verify that a low level call to smart-contract was successful, and revert (either by bubbling
     * the revert reason or using the provided one) in case of unsuccessful call or if target was not a contract.
     *
     * _Available since v4.8._
     */
    function verifyCallResultFromTarget(
        address target,
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        if (success) {
            if (returndata.length == 0) {
                // only check isContract if the call was successful and the return data is empty
                // otherwise we already know that it was a contract
                require(isContract(target), "Address: call to non-contract");
            }
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    /**
     * @dev Tool to verify that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason or 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 {
            _revert(returndata, errorMessage);
        }
    }

    function _revert(bytes memory returndata, string memory errorMessage) private pure {
        // 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
            /// @solidity memory-safe-assembly
            assembly {
                let returndata_size := mload(returndata)
                revert(add(32, returndata), returndata_size)
            }
        } else {
            revert(errorMessage);
        }
    }
}

// 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;
    }
}