Contract Diff Checker

Contract Name:
SpolarRewardPool

Contract Source Code:

// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

import "IERC20.sol";
import "SafeERC20.sol";
import "SafeMath.sol";

// Note that this pool has no minter key of spolar (rewards).
// Instead, the governance will call spolar distributeReward method and send reward to this pool at the beginning.
contract SpolarRewardPool {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    // governance
    address public operator;

    // Info of each user.
    struct UserInfo {
        uint256 amount; // How many LP tokens the user has provided.
        uint256 rewardDebt; // Reward debt. See explanation below.
    }

    // Info of each pool.
    struct PoolInfo {
        IERC20 token; // Address of LP token contract.
        uint256 allocPoint; // How many allocation points assigned to this pool. spolars to distribute per block.
        uint256 lastRewardTime; // Last time that spolars distribution occurs.
        uint256 accSpolarPerShare; // Accumulated spolars per share, times 1e18. See below.
        bool isStarted; // if lastRewardTime has passed
    }

    IERC20 public spolar;

    // Info of each pool.
    PoolInfo[] public poolInfo;

    // Info of each user that stakes LP tokens.
    mapping(uint256 => mapping(address => UserInfo)) public userInfo;

    // Total allocation points. Must be the sum of all allocation points in all pools.
    uint256 public totalAllocPoint = 0;

    // The time when spolar mining starts.
    uint256 public poolStartTime;

    // The time when spolar mining ends.
    uint256 public poolEndTime;

    uint256 public spolarPerSecond = 0.0015817901e18; // 41000 spolar / (300 days * 24h * 60min * 60s)
    uint256 public runningTime = 300 days; // 300 days
    uint256 public constant TOTAL_REWARDS = 41000e18;

    event Deposit(address indexed user, uint256 indexed pid, uint256 amount);
    event Withdraw(address indexed user, uint256 indexed pid, uint256 amount);
    event EmergencyWithdraw(address indexed user, uint256 indexed pid, uint256 amount);
    event RewardPaid(address indexed user, uint256 amount);

    constructor(
        address _spolar,
        uint256 _poolStartTime
    ) public {
        require(block.timestamp < _poolStartTime, "late");
        if (_spolar != address(0)) spolar = IERC20(_spolar);
        poolStartTime = _poolStartTime;
        poolEndTime = poolStartTime + runningTime;
        operator = msg.sender;
    }

    modifier onlyOperator() {
        require(operator == msg.sender, "SpolarRewardPool: caller is not the operator");
        _;
    }

    function checkPoolDuplicate(IERC20 _token) internal view {
        uint256 length = poolInfo.length;
        for (uint256 pid = 0; pid < length; ++pid) {
            require(poolInfo[pid].token != _token, "SpolarRewardPool: existing pool?");
        }
    }

    // Add a new lp to the pool. Can only be called by the owner.
    function add(
        uint256 _allocPoint,
        IERC20 _token,
        bool _withUpdate,
        uint256 _lastRewardTime
    ) public onlyOperator {
        checkPoolDuplicate(_token);
        if (_withUpdate) {
            massUpdatePools();
        }
        if (block.timestamp < poolStartTime) {
            // chef is sleeping
            if (_lastRewardTime == 0) {
                _lastRewardTime = poolStartTime;
            } else {
                if (_lastRewardTime < poolStartTime) {
                    _lastRewardTime = poolStartTime;
                }
            }
        } else {
            // chef is cooking
            if (_lastRewardTime == 0 || _lastRewardTime < block.timestamp) {
                _lastRewardTime = block.timestamp;
            }
        }
        bool _isStarted =
        (_lastRewardTime <= poolStartTime) ||
        (_lastRewardTime <= block.timestamp);
        poolInfo.push(PoolInfo({
            token : _token,
            allocPoint : _allocPoint,
            lastRewardTime : _lastRewardTime,
            accSpolarPerShare : 0,
            isStarted : _isStarted
            }));
        if (_isStarted) {
            totalAllocPoint = totalAllocPoint.add(_allocPoint);
        }
    }

    // Update the given pool's spolar allocation point. Can only be called by the owner.
    function set(uint256 _pid, uint256 _allocPoint) public onlyOperator {
        massUpdatePools();
        PoolInfo storage pool = poolInfo[_pid];
        if (pool.isStarted) {
            totalAllocPoint = totalAllocPoint.sub(pool.allocPoint).add(
                _allocPoint
            );
        }
        pool.allocPoint = _allocPoint;
    }

    // Return accumulate rewards over the given _from to _to block.
    function getGeneratedReward(uint256 _fromTime, uint256 _toTime) public view returns (uint256) {
        if (_fromTime >= _toTime) return 0;
        if (_toTime >= poolEndTime) {
            if (_fromTime >= poolEndTime) return 0;
            if (_fromTime <= poolStartTime) return poolEndTime.sub(poolStartTime).mul(spolarPerSecond);
            return poolEndTime.sub(_fromTime).mul(spolarPerSecond);
        } else {
            if (_toTime <= poolStartTime) return 0;
            if (_fromTime <= poolStartTime) return _toTime.sub(poolStartTime).mul(spolarPerSecond);
            return _toTime.sub(_fromTime).mul(spolarPerSecond);
        }
    }

    // View function to see pending spolars on frontend.
    function pendingShare(uint256 _pid, address _user) external view returns (uint256) {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][_user];
        uint256 accSpolarPerShare = pool.accSpolarPerShare;
        uint256 tokenSupply = pool.token.balanceOf(address(this));
        if (block.timestamp > pool.lastRewardTime && tokenSupply != 0) {
            uint256 _generatedReward = getGeneratedReward(pool.lastRewardTime, block.timestamp);
            uint256 _spolarReward = _generatedReward.mul(pool.allocPoint).div(totalAllocPoint);
            accSpolarPerShare = accSpolarPerShare.add(_spolarReward.mul(1e18).div(tokenSupply));
        }
        return user.amount.mul(accSpolarPerShare).div(1e18).sub(user.rewardDebt);
    }

    // Update reward variables for all pools. Be careful of gas spending!
    function massUpdatePools() public {
        uint256 length = poolInfo.length;
        for (uint256 pid = 0; pid < length; ++pid) {
            updatePool(pid);
        }
    }

    // Update reward variables of the given pool to be up-to-date.
    function updatePool(uint256 _pid) public {
        PoolInfo storage pool = poolInfo[_pid];
        if (block.timestamp <= pool.lastRewardTime) {
            return;
        }
        uint256 tokenSupply = pool.token.balanceOf(address(this));
        if (tokenSupply == 0) {
            pool.lastRewardTime = block.timestamp;
            return;
        }
        if (!pool.isStarted) {
            pool.isStarted = true;
            totalAllocPoint = totalAllocPoint.add(pool.allocPoint);
        }
        if (totalAllocPoint > 0) {
            uint256 _generatedReward = getGeneratedReward(pool.lastRewardTime, block.timestamp);
            uint256 _spolarReward = _generatedReward.mul(pool.allocPoint).div(totalAllocPoint);
            pool.accSpolarPerShare = pool.accSpolarPerShare.add(_spolarReward.mul(1e18).div(tokenSupply));
        }
        pool.lastRewardTime = block.timestamp;
    }

    // Deposit LP tokens.
    function deposit(uint256 _pid, uint256 _amount) public {
        address _sender = msg.sender;
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][_sender];
        updatePool(_pid);
        if (user.amount > 0) {
            uint256 _pending = user.amount.mul(pool.accSpolarPerShare).div(1e18).sub(user.rewardDebt);
            if (_pending > 0) {
                safeSpolarTransfer(_sender, _pending);
                emit RewardPaid(_sender, _pending);
            }
        }
        if (_amount > 0) {
            pool.token.safeTransferFrom(_sender, address(this), _amount);
            user.amount = user.amount.add(_amount);
        }
        user.rewardDebt = user.amount.mul(pool.accSpolarPerShare).div(1e18);
        emit Deposit(_sender, _pid, _amount);
    }

    // Withdraw LP tokens.
    function withdraw(uint256 _pid, uint256 _amount) public {
        address _sender = msg.sender;
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][_sender];
        require(user.amount >= _amount, "withdraw: not good");
        updatePool(_pid);
        uint256 _pending = user.amount.mul(pool.accSpolarPerShare).div(1e18).sub(user.rewardDebt);
        if (_pending > 0) {
            safeSpolarTransfer(_sender, _pending);
            emit RewardPaid(_sender, _pending);
        }
        if (_amount > 0) {
            user.amount = user.amount.sub(_amount);
            pool.token.safeTransfer(_sender, _amount);
        }
        user.rewardDebt = user.amount.mul(pool.accSpolarPerShare).div(1e18);
        emit Withdraw(_sender, _pid, _amount);
    }

    // Withdraw without caring about rewards. EMERGENCY ONLY.
    function emergencyWithdraw(uint256 _pid) public {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][msg.sender];
        uint256 _amount = user.amount;
        user.amount = 0;
        user.rewardDebt = 0;
        pool.token.safeTransfer(msg.sender, _amount);
        emit EmergencyWithdraw(msg.sender, _pid, _amount);
    }

    // Safe spolar transfer function, just in case if rounding error causes pool to not have enough spolars.
    function safeSpolarTransfer(address _to, uint256 _amount) internal {
        uint256 _spolarBal = spolar.balanceOf(address(this));
        if (_spolarBal > 0) {
            if (_amount > _spolarBal) {
                spolar.safeTransfer(_to, _spolarBal);
            } else {
                spolar.safeTransfer(_to, _amount);
            }
        }
    }

    function setOperator(address _operator) external onlyOperator {
        operator = _operator;
    }

    function governanceRecoverUnsupported(IERC20 _token, uint256 amount, address to) external onlyOperator {
        if (block.timestamp < poolEndTime + 90 days) {
            // do not allow to drain core token (spolar or lps) if less than 90 days after pool ends
            require(_token != spolar, "spolar");
            uint256 length = poolInfo.length;
            for (uint256 pid = 0; pid < length; ++pid) {
                PoolInfo storage pool = poolInfo[pid];
                require(_token != pool.token, "pool.token");
            }
        }
        _token.safeTransfer(to, amount);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <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 >=0.6.0 <0.8.0;

import "IERC20.sol";
import "SafeMath.sol";
import "Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

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

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

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

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

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

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

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

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

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

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

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

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

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

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

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) return 0;
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }

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

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

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

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

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

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

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

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

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

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

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

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

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

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

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

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

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

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

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

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

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

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

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