// File: contracts/ReserveManager.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "./interfaces/IComptroller.sol";
import "./interfaces/ICToken.sol";
import "./interfaces/ICTokenAdmin.sol";
import "./interfaces/IBurner.sol";
import "./interfaces/IWeth.sol";

contract ReserveManager is Ownable, ReentrancyGuard {
    using SafeERC20 for IERC20;

    uint public constant COOLDOWN_PERIOD = 1 days;
    address public constant ethAddress = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;

    /**
     * @notice comptroller contract
     */
    IComptroller public immutable comptroller;

    /**
     * @notice usdc burner contract
     */
    IBurner public immutable usdcBurner;

    /**
     * @notice weth contract
     */
    address public immutable wethAddress;

    /**
     * @notice usdc contract
     */
    address public immutable usdcAddress;

    /**
     * @notice the extraction ratio, scaled by 1e18
     */
    uint public ratio = 0.5e18;

    /**
     * @notice cToken admin to extract reserves
     */
    mapping(address => address) public cTokenAdmins;

    /**
     * @notice burner contracts to convert assets into a specific token
     */
    mapping(address => address) public burners;

    struct ReservesSnapshot {
        uint timestamp;
        uint totalReserves;
    }

    /**
     * @notice reserves snapshot that records every reserves update
     */
    mapping(address => ReservesSnapshot) public reservesSnapshot;

    /**
     * @notice return if a cToken market is blocked from reserves sharing
     */
    mapping(address => bool) public isBlocked;

    /**
     * @notice return if a cToken market should be burnt manually
     */
    mapping(address => bool) public manualBurn;

    /**
     * @notice a manual burner that reseives assets whose onchain liquidity are not deep enough
     */
    address public manualBurner;

    /**
     * @notice Emitted when reserves are dispatched
     */
    event Dispatch(
        address indexed token,
        uint indexed amount,
        address destination
    );

    /**
     * @notice Emitted when a cTokenAdmin is updated
     */
    event CTokenAdminUpdated(
        address cToken,
        address oldAdmin,
        address newAdmin
    );

    /**
     * @notice Emitted when a cToken's burner is updated
     */
    event BurnerUpdated(
        address cToken,
        address oldBurner,
        address newBurner
    );

    /**
     * @notice Emitted when the reserves extraction ratio is updated
     */
    event RatioUpdated(
        uint oldRatio,
        uint newRatio
    );

    /**
     * @notice Emitted when a token is seized
     */
    event TokenSeized(
        address token,
        uint amount
    );

    /**
     * @notice Emitted when a cToken market is blocked or unblocked from reserves sharing
     */
    event MarketBlocked(
        address cToken,
        bool wasBlocked,
        bool isBlocked
    );

    /**
     * @notice Emitted when a cToken market is determined to be manually burnt or not
     */
    event MarketManualBurn(
        address cToken,
        bool wasManual,
        bool isManual
    );

    /**
     * @notice Emitted when a manual burner is updated
     */
    event ManualBurnerUpdated(
        address oldManualBurner,
        address newManualBurner
    );

    constructor(
        address _owner,
        address _manualBurner,
        IComptroller _comptroller,
        IBurner _usdcBurner,
        address _wethAddress,
        address _usdcAddress
    ) {
        transferOwnership(_owner);
        manualBurner = _manualBurner;
        comptroller = _comptroller;
        usdcBurner = _usdcBurner;
        wethAddress = _wethAddress;
        usdcAddress = _usdcAddress;

        // Set default ratio to 50%.
        ratio = 0.5e18;
    }

    /**
     * @notice Get the current block timestamp
     * @return The current block timestamp
     */
    function getBlockTimestamp() public virtual view returns (uint) {
        return block.timestamp;
    }

    /**
     * @notice Execute reduce reserve and burn on multiple cTokens
     * @param cTokens The token address list
     */
    function dispatchMultiple(address[] memory cTokens) external nonReentrant {
        for (uint i = 0; i < cTokens.length; i++) {
            dispatch(cTokens[i], true);
        }
        IBurner(usdcBurner).burn(usdcAddress);
    }

    receive() external payable {}

    /* Admin functions */

    /**
     * @notice Seize the accidentally deposited tokens
     * @param token The token
     * @param amount The amount
     */
    function seize(address token, uint amount) external onlyOwner {
        if (token == ethAddress) {
            payable(owner()).transfer(amount);
        } else {
            IERC20(token).safeTransfer(owner(), amount);
        }
        emit TokenSeized(token, amount);
    }

    /**
     * @notice Block or unblock a cToken from reserves sharing
     * @param cTokens The cToken address list
     * @param blocked Block from reserves sharing or not
     */
    function setBlocked(address[] memory cTokens, bool[] memory blocked) external onlyOwner {
        require(cTokens.length == blocked.length, "invalid data");

        for (uint i = 0; i < cTokens.length; i++) {
            bool wasBlocked = isBlocked[cTokens[i]];
            isBlocked[cTokens[i]] = blocked[i];

            emit MarketBlocked(cTokens[i], wasBlocked, blocked[i]);
        }
    }

    /**
     * @notice Set the admins of a list of cTokens
     * @param cTokens The cToken address list
     * @param newCTokenAdmins The admin address list
     */
    function setCTokenAdmins(address[] memory cTokens, address[] memory newCTokenAdmins) external onlyOwner {
        require(cTokens.length == newCTokenAdmins.length, "invalid data");

        for (uint i = 0; i < cTokens.length; i++) {
            require(comptroller.isMarketListed(cTokens[i]), "market not listed");
            require(ICToken(cTokens[i]).admin() == newCTokenAdmins[i], "mismatch cToken admin");

            address oldAdmin = cTokenAdmins[cTokens[i]];
            cTokenAdmins[cTokens[i]] = newCTokenAdmins[i];

            emit CTokenAdminUpdated(cTokens[i], oldAdmin, newCTokenAdmins[i]);
        }
    }

    /**
     * @notice Set the burners of a list of tokens
     * @param cTokens The cToken address list
     * @param newBurners The burner address list
     */
    function setBurners(address[] memory cTokens, address[] memory newBurners) external onlyOwner {
        require(cTokens.length == newBurners.length, "invalid data");

        for (uint i = 0; i < cTokens.length; i++) {
            address oldBurner = burners[cTokens[i]];
            burners[cTokens[i]] = newBurners[i];

            emit BurnerUpdated(cTokens[i], oldBurner, newBurners[i]);
        }
    }

    /**
     * @notice Determine a market should be burnt manually or not
     * @param cTokens The cToken address list
     * @param manual The list of markets which should be burnt manually or not
     */
    function setManualBurn(address[] memory cTokens, bool[] memory manual) external onlyOwner {
        require(cTokens.length == manual.length, "invalid data");

        for (uint i = 0; i < cTokens.length; i++) {
            bool wasManual = manualBurn[cTokens[i]];
            manualBurn[cTokens[i]] = manual[i];

            emit MarketManualBurn(cTokens[i], wasManual, manual[i]);
        }
    }

    /**
     * @notice Set new manual burner
     * @param newManualBurner The new manual burner
     */
    function setManualBurner(address newManualBurner) external onlyOwner {
        require(newManualBurner != address(0), "invalid new manual burner");

        address oldManualBurner = manualBurner;
        manualBurner = newManualBurner;

        emit ManualBurnerUpdated(oldManualBurner, newManualBurner);
    }

    /**
     * @notice Adjust the extraction ratio
     * @param newRatio The new extraction ratio
     */
    function adjustRatio(uint newRatio) external onlyOwner {
        require(newRatio <= 1e18, "invalid ratio");

        uint oldRatio = ratio;
        ratio = newRatio;
        emit RatioUpdated(oldRatio, newRatio);
    }

    /* Internal functions */

    /**
     * @notice Compare whether the two strings are the same
     * @param a The first string
     * @param b The second string
     * @return Two strings are the same or not
     */
    function compareStrings(string memory a, string memory b) internal pure returns (bool) {
        return (keccak256(abi.encodePacked((a))) == keccak256(abi.encodePacked((b))));
    }

    /**
     * @notice Execute reduce reserve for cToken
     * @param cToken The cToken to dispatch reduce reserve operation
     * @param batchJob indicate whether this function call is within a multiple cToken batch job
     */
    function dispatch(address cToken, bool batchJob) internal {
        require(!isBlocked[cToken], "market is blocked from reserves sharing");
        require(comptroller.isMarketListed(cToken), "market not listed");

        uint totalReserves = ICToken(cToken).totalReserves();
        ReservesSnapshot memory snapshot = reservesSnapshot[cToken];
        if (snapshot.timestamp > 0 && snapshot.totalReserves < totalReserves) {
            address cTokenAdmin = cTokenAdmins[cToken];
            require(cTokenAdmin == ICToken(cToken).admin(), "mismatch cToken admin");
            require(snapshot.timestamp + COOLDOWN_PERIOD <= getBlockTimestamp(), "still in the cooldown period");

            // Extract reserves through cTokenAdmin.
            uint reduceAmount = (totalReserves - snapshot.totalReserves) * ratio / 1e18;
            ICTokenAdmin(cTokenAdmin).extractReserves(cToken, reduceAmount);

            // After the extraction, the reserves in cToken should decrease.
            // Instead of getting reserves from cToken again, we subtract `totalReserves` with `reduceAmount` to save gas.
            totalReserves = totalReserves - reduceAmount;

            // Get the cToken underlying.
            address underlying;
            if (compareStrings(ICToken(cToken).symbol(), "crETH")) {
                IWeth(wethAddress).deposit{value: reduceAmount}();
                underlying = wethAddress;
            } else {
                underlying = ICToken(cToken).underlying();
            }

            // In case someone transfers tokens in directly, which will cause the dispatch reverted,
            // we burn all the tokens in the contract here.
            uint burnAmount = IERC20(underlying).balanceOf(address(this));

            address burner = burners[cToken];
            if (manualBurn[cToken]) {
                // Send the underlying to the manual burner.
                burner = manualBurner;
                IERC20(underlying).safeTransfer(manualBurner, burnAmount);
            } else {
                // Allow the corresponding burner to pull the assets to burn.
                require(burner != address(0), "burner not set");
                IERC20(underlying).safeIncreaseAllowance(burner, burnAmount);
                require(IBurner(burner).burn(underlying), "Burner failed to burn the underlying token");
            }

            emit Dispatch(underlying, burnAmount, burner);
        }

        // Update the reserve snapshot.
        reservesSnapshot[cToken] = ReservesSnapshot({
            timestamp: getBlockTimestamp(),
            totalReserves: totalReserves
        });

        // A standalone reduce-reserve operation followed by a final USDC burn
        if (!batchJob){
            IBurner(usdcBurner).burn(usdcAddress);
        }
    }
}

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



// 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);
    }
}

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



// SPDX-License-Identifier: MIT

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 make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

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

        _;

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

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../../../utils/Address.sol";

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

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

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

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

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

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

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

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

// File: contracts/interfaces/IComptroller.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface IComptroller {
    function isMarketListed(address cTokenAddress) external view returns (bool);
}

// File: contracts/interfaces/ICToken.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface ICToken {
    function admin() external view returns (address);
    function symbol() external view returns (string memory);
    function underlying() external view returns (address);
    function totalReserves() external view returns (uint);
}

// File: contracts/interfaces/ICTokenAdmin.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface ICTokenAdmin {
    function extractReserves(address cToken, uint reduceAmount) external;
}

// File: contracts/interfaces/IBurner.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface IBurner {
    function burn(address coin) external returns (bool);
}

// File: contracts/interfaces/IWeth.sol




// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

interface IWeth {
    function deposit() external payable;
}

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



// 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;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

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

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

        uint256 size;
        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);
    }

    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

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