// File: contracts/FeeSplitter.sol



// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity 0.8.11;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

import "./interfaces/external/IWETH.sol";

/// @title Manage the fees between shareholders
/// @notice Receives fees collected by the NestedFactory, and splits the income among
/// shareholders (the NFT owners, Nested treasury and a NST buybacker contract).
contract FeeSplitter is Ownable, ReentrancyGuard {
    /* ------------------------------ EVENTS ------------------------------ */

    /// @dev Emitted when a payment is released
    /// @param to The address receiving the payment
    /// @param token The token transfered
    /// @param amount The amount paid
    event PaymentReleased(address to, address token, uint256 amount);

    /// @dev Emitted when a payment is received
    /// @param from The address sending the tokens
    /// @param token The token received
    /// @param amount The amount received
    event PaymentReceived(address from, address token, uint256 amount);

    /// @dev Emitted when the royalties weight is updated
    /// @param weight The new weight
    event RoyaltiesWeightUpdated(uint256 weight);

    /// @dev Emitted when a new shareholder is added
    /// @param account The new shareholder account
    /// @param weight The shareholder weight
    event ShareholdersAdded(address account, uint256 weight);

    /// @dev Emitted when a shareholder weight is updated
    /// @param account The shareholder address
    /// @param weight The new weight
    event ShareholderUpdated(address account, uint256 weight);

    /// @dev Emitted when royalties are claim released
    /// @param to The address claiming the royalties
    /// @param token The token received
    /// @param value The amount received
    event RoyaltiesReceived(address to, address token, uint256 value);

    /* ------------------------------ STRUCTS ------------------------------ */

    /// @dev Represent a shareholder
    /// @param account Shareholders address that can receive income
    /// @param weight Determines share allocation
    struct Shareholder {
        address account;
        uint96 weight;
    }

    /// @dev Registers shares and amount release for a specific token or ETH
    struct TokenRecords {
        uint256 totalShares;
        uint256 totalReleased;
        mapping(address => uint256) shares;
        mapping(address => uint256) released;
    }

    /* ----------------------------- VARIABLES ----------------------------- */

    /// @dev Map of tokens with the tokenRecords
    mapping(address => TokenRecords) private tokenRecords;

    /// @dev All the shareholders (array)
    Shareholder[] private shareholders;

    /// @dev Royalties part weights when applicable
    uint256 public royaltiesWeight;

    uint256 public totalWeights;

    address public immutable weth;

    /* ---------------------------- CONSTRUCTOR ---------------------------- */

    constructor(
        address[] memory _accounts,
        uint96[] memory _weights,
        uint256 _royaltiesWeight,
        address _weth
    ) {
        require(_weth != address(0), "FS: INVALID_ADDRESS");
        // Initial shareholders addresses and weights
        setShareholders(_accounts, _weights);
        setRoyaltiesWeight(_royaltiesWeight);
        weth = _weth;
    }

    /// @dev Receive ether after a WETH withdraw call
    receive() external payable {
        require(msg.sender == weth, "FS: ETH_SENDER_NOT_WETH");
    }

    /* -------------------------- OWNER FUNCTIONS -------------------------- */

    /// @notice Sets the weight assigned to the royalties part for the fee
    /// @param _weight The new royalties weight
    function setRoyaltiesWeight(uint256 _weight) public onlyOwner {
        require(_weight != 0, "FS: WEIGHT_ZERO");
        totalWeights = totalWeights + _weight - royaltiesWeight;
        royaltiesWeight = _weight;
        emit RoyaltiesWeightUpdated(_weight);
    }

    /// @notice Sets a new list of shareholders
    /// @param _accounts Shareholders accounts list
    /// @param _weights Weight for each shareholder. Determines part of the payment allocated to them
    function setShareholders(address[] memory _accounts, uint96[] memory _weights) public onlyOwner {
        delete shareholders;
        uint256 accountsLength = _accounts.length;
        require(accountsLength != 0, "FS: EMPTY_ARRAY");
        require(accountsLength == _weights.length, "FS: INPUTS_LENGTH_MUST_MATCH");
        totalWeights = royaltiesWeight;

        for (uint256 i = 0; i < accountsLength; i++) {
            _addShareholder(_accounts[i], _weights[i]);
        }
    }

    /// @notice Updates weight for a shareholder
    /// @param _accountIndex Account to change the weight of
    /// @param _weight The new weight
    function updateShareholder(uint256 _accountIndex, uint96 _weight) external onlyOwner {
        require(_weight != 0, "FS: INVALID_WEIGHT");
        require(_accountIndex < shareholders.length, "FS: INVALID_ACCOUNT_INDEX");
        Shareholder storage _shareholder = shareholders[_accountIndex];
        totalWeights = totalWeights + _weight - _shareholder.weight;
        require(totalWeights != 0, "FS: TOTAL_WEIGHTS_ZERO");
        _shareholder.weight = _weight;
        emit ShareholderUpdated(_shareholder.account, _weight);
    }

    /* -------------------------- USERS FUNCTIONS -------------------------- */

    /// @notice Release multiple tokens and handle ETH unwrapping
    /// @param _tokens ERC20 tokens to release
    function releaseTokens(IERC20[] calldata _tokens) external nonReentrant {
        uint256 amount;
        for (uint256 i = 0; i < _tokens.length; i++) {
            amount = _releaseToken(_msgSender(), _tokens[i]);
            if (address(_tokens[i]) == weth) {
                IWETH(weth).withdraw(amount);
                (bool success, ) = _msgSender().call{ value: amount }("");
                require(success, "FS: ETH_TRANFER_ERROR");
            } else {
                SafeERC20.safeTransfer(_tokens[i], _msgSender(), amount);
            }
            emit PaymentReleased(_msgSender(), address(_tokens[i]), amount);
        }
    }

    /// @notice Release multiple tokens without ETH unwrapping
    /// @param _tokens ERC20 tokens to release
    function releaseTokensNoETH(IERC20[] calldata _tokens) external nonReentrant {
        uint256 amount;
        for (uint256 i = 0; i < _tokens.length; i++) {
            amount = _releaseToken(_msgSender(), _tokens[i]);
            SafeERC20.safeTransfer(_tokens[i], _msgSender(), amount);
            emit PaymentReleased(_msgSender(), address(_tokens[i]), amount);
        }
    }

    /// @notice Sends a fee to this contract for splitting, as an ERC20 token. No royalties are expected.
    /// @param _token Currency for the fee as an ERC20 token
    /// @param _amount Amount of token as fee to be claimed by this contract
    function sendFees(IERC20 _token, uint256 _amount) external nonReentrant {
        uint256 weights;
        unchecked {
            weights = totalWeights - royaltiesWeight;
        }

        uint256 balanceBeforeTransfer = _token.balanceOf(address(this));
        SafeERC20.safeTransferFrom(_token, _msgSender(), address(this), _amount);

        _sendFees(_token, _token.balanceOf(address(this)) - balanceBeforeTransfer, weights);
    }

    /// @notice Sends a fee to this contract for splitting, as an ERC20 token
    /// @param _royaltiesTarget The account that can claim royalties
    /// @param _token Currency for the fee as an ERC20 token
    /// @param _amount Amount of token as fee to be claimed by this contract
    function sendFeesWithRoyalties(
        address _royaltiesTarget,
        IERC20 _token,
        uint256 _amount
    ) external nonReentrant {
        require(_royaltiesTarget != address(0), "FS: INVALID_ROYALTIES_TARGET");

        uint256 balanceBeforeTransfer = _token.balanceOf(address(this));
        SafeERC20.safeTransferFrom(_token, _msgSender(), address(this), _amount);
        uint256 amountReceived = _token.balanceOf(address(this)) - balanceBeforeTransfer;

        uint256 _totalWeights = totalWeights;
        uint256 royaltiesAmount = (amountReceived * royaltiesWeight) / _totalWeights;

        _sendFees(_token, amountReceived, _totalWeights);
        _addShares(_royaltiesTarget, royaltiesAmount, address(_token));

        emit RoyaltiesReceived(_royaltiesTarget, address(_token), royaltiesAmount);
    }

    /* ------------------------------- VIEWS ------------------------------- */

    /// @notice Returns the amount due to an account. Call releaseToken to withdraw the amount.
    /// @param _account Account address to check the amount due for
    /// @param _token ERC20 payment token address
    /// @return The total amount due for the requested currency
    function getAmountDue(address _account, IERC20 _token) public view returns (uint256) {
        TokenRecords storage _tokenRecords = tokenRecords[address(_token)];
        uint256 _totalShares = _tokenRecords.totalShares;
        if (_totalShares == 0) return 0;

        uint256 totalReceived = _tokenRecords.totalReleased + _token.balanceOf(address(this));
        return (totalReceived * _tokenRecords.shares[_account]) / _totalShares - _tokenRecords.released[_account];
    }

    /// @notice Getter for the total shares held by shareholders.
    /// @param _token Payment token address
    /// @return The total shares count
    function totalShares(address _token) external view returns (uint256) {
        return tokenRecords[_token].totalShares;
    }

    /// @notice Getter for the total amount of token already released.
    /// @param _token Payment token address
    /// @return The total amount release to shareholders
    function totalReleased(address _token) external view returns (uint256) {
        return tokenRecords[_token].totalReleased;
    }

    /// @notice Getter for the amount of shares held by an account.
    /// @param _account Account the shares belong to
    /// @param _token Payment token address
    /// @return The shares owned by the account
    function shares(address _account, address _token) external view returns (uint256) {
        return tokenRecords[_token].shares[_account];
    }

    /// @notice Getter for the amount of Ether already released to a shareholders.
    /// @param _account The target account for this request
    /// @param _token Payment token address
    /// @return The amount already released to this account
    function released(address _account, address _token) external view returns (uint256) {
        return tokenRecords[_token].released[_account];
    }

    /// @notice Finds a shareholder and return its index
    /// @param _account Account to find
    /// @return The shareholder index in the storage array
    function findShareholder(address _account) external view returns (uint256) {
        for (uint256 i = 0; i < shareholders.length; i++) {
            if (shareholders[i].account == _account) return i;
        }
        revert("FS: SHAREHOLDER_NOT_FOUND");
    }

    /* ------------------------- PRIVATE FUNCTIONS ------------------------- */

    /// @notice Transfers a fee to this contract
    /// @dev This method calculates the amount received, to support deflationary tokens
    /// @param _token Currency for the fee
    /// @param _amount Amount of token sent
    /// @param _totalWeights Total weights to determine the share count to allocate
    function _sendFees(
        IERC20 _token,
        uint256 _amount,
        uint256 _totalWeights
    ) private {
        Shareholder[] memory shareholdersCache = shareholders;
        for (uint256 i = 0; i < shareholdersCache.length; i++) {
            _addShares(
                shareholdersCache[i].account,
                (_amount * shareholdersCache[i].weight) / _totalWeights,
                address(_token)
            );
        }
        emit PaymentReceived(_msgSender(), address(_token), _amount);
    }

    /// @dev Increase the shares of a shareholder
    /// @param _account The shareholder address
    /// @param _shares The shares of the holder
    /// @param _token The updated token
    function _addShares(
        address _account,
        uint256 _shares,
        address _token
    ) private {
        TokenRecords storage _tokenRecords = tokenRecords[_token];
        _tokenRecords.shares[_account] += _shares;
        _tokenRecords.totalShares += _shares;
    }

    function _releaseToken(address _account, IERC20 _token) private returns (uint256) {
        uint256 amountToRelease = getAmountDue(_account, _token);
        require(amountToRelease != 0, "FS: NO_PAYMENT_DUE");

        TokenRecords storage _tokenRecords = tokenRecords[address(_token)];
        _tokenRecords.released[_account] += amountToRelease;
        _tokenRecords.totalReleased += amountToRelease;

        return amountToRelease;
    }

    function _addShareholder(address _account, uint96 _weight) private {
        require(_weight != 0, "FS: ZERO_WEIGHT");
        require(_account != address(0), "FS: INVALID_ADDRESS");
        for (uint256 i = 0; i < shareholders.length; i++) {
            require(shareholders[i].account != _account, "FS: ALREADY_SHAREHOLDER");
        }

        shareholders.push(Shareholder(_account, _weight));
        totalWeights += _weight;
        emit ShareholdersAdded(_account, _weight);
    }
}

// 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/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/external/IWETH.sol



// SPDX-License-Identifier: UNLICENSED

pragma solidity 0.8.11;

interface IWETH {
    function deposit() external payable;

    function withdraw(uint256) external;

    function totalSupply() external view returns (uint256);

    function transfer(address recipient, uint256 amount) external returns (bool);

    function allowance(address owner, address spender) external view returns (uint256);

    function approve(address spender, uint256 amount) external returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);

    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// 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/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);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

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