// 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/access/Ownable.sol



pragma solidity ^0.8.0;

/**
 * @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



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/utils/structs/EnumerableSet.sol



pragma solidity ^0.8.0;

/**
 * @dev Library for managing
 * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
 * types.
 *
 * Sets have the following properties:
 *
 * - Elements are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Elements are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableSet for EnumerableSet.AddressSet;
 *
 *     // Declare a set state variable
 *     EnumerableSet.AddressSet private mySet;
 * }
 * ```
 *
 * As of v3.3.0, sets of type `bytes32` (`Bytes32Set`), `address` (`AddressSet`)
 * and `uint256` (`UintSet`) are supported.
 */
library EnumerableSet {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Set type with
    // bytes32 values.
    // The Set implementation uses private functions, and user-facing
    // implementations (such as AddressSet) are just wrappers around the
    // underlying Set.
    // This means that we can only create new EnumerableSets for types that fit
    // in bytes32.

    struct Set {
        // Storage of set values
        bytes32[] _values;
        // Position of the value in the `values` array, plus 1 because index 0
        // means a value is not in the set.
        mapping(bytes32 => uint256) _indexes;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            // The value is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        // We read and store the value's index to prevent multiple reads from the same storage slot
        uint256 valueIndex = set._indexes[value];

        if (valueIndex != 0) {
            // Equivalent to contains(set, value)
            // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
            // the array, and then remove the last element (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;

            if (lastIndex != toDeleteIndex) {
                bytes32 lastvalue = set._values[lastIndex];

                // Move the last value to the index where the value to delete is
                set._values[toDeleteIndex] = lastvalue;
                // Update the index for the moved value
                set._indexes[lastvalue] = valueIndex; // Replace lastvalue's index to valueIndex
            }

            // Delete the slot where the moved value was stored
            set._values.pop();

            // Delete the index for the deleted slot
            delete set._indexes[value];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }

    /**
     * @dev Returns the value stored at position `index` in the set. O(1).
     *
     * Note that there are no guarantees on the ordering of values inside the
     * array, and it may change when more values are added or removed.
     *
     * Requirements:
     *
     * - `index` must be strictly less than {length}.
     */
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        return set._values[index];
    }

    // Bytes32Set

    struct Bytes32Set {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _add(set._inner, value);
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _remove(set._inner, value);
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(Bytes32Set storage set, bytes32 value) internal view returns (bool) {
        return _contains(set._inner, value);
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(Bytes32Set storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

    /**
     * @dev Returns the value stored at position `index` in the set. O(1).
     *
     * Note that there are no guarantees on the ordering of values inside the
     * array, and it may change when more values are added or removed.
     *
     * Requirements:
     *
     * - `index` must be strictly less than {length}.
     */
    function at(Bytes32Set storage set, uint256 index) internal view returns (bytes32) {
        return _at(set._inner, index);
    }

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

    /**
     * @dev Returns the value stored at position `index` in the set. O(1).
     *
     * Note that there are no guarantees on the ordering of values inside the
     * array, and it may change when more values are added or removed.
     *
     * Requirements:
     *
     * - `index` must be strictly less than {length}.
     */
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint160(uint256(_at(set._inner, index))));
    }

    // UintSet

    struct UintSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

    /**
     * @dev Returns the value stored at position `index` in the set. O(1).
     *
     * Note that there are no guarantees on the ordering of values inside the
     * array, and it may change when more values are added or removed.
     *
     * Requirements:
     *
     * - `index` must be strictly less than {length}.
     */
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



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



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);
            }
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol



pragma solidity ^0.8.0;

/**
 * @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: @openzeppelin/contracts/utils/introspection/IERC165.sol



pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol



pragma solidity ^0.8.0;

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
     */
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
     */
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
     */
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /**
     * @dev Returns the number of tokens in ``owner``'s account.
     */
    function balanceOf(address owner) external view returns (uint256 balance);

    /**
     * @dev Returns the owner of the `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function ownerOf(uint256 tokenId) external view returns (address owner);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId
    ) external;

    /**
     * @dev Transfers `tokenId` token from `from` to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) external;

    /**
     * @dev Gives permission to `to` to transfer `tokenId` token to another account.
     * The approval is cleared when the token is transferred.
     *
     * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
     *
     * Requirements:
     *
     * - The caller must own the token or be an approved operator.
     * - `tokenId` must exist.
     *
     * Emits an {Approval} event.
     */
    function approve(address to, uint256 tokenId) external;

    /**
     * @dev Returns the account approved for `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function getApproved(uint256 tokenId) external view returns (address operator);

    /**
     * @dev Approve or remove `operator` as an operator for the caller.
     * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
     *
     * Requirements:
     *
     * - The `operator` cannot be the caller.
     *
     * Emits an {ApprovalForAll} event.
     */
    function setApprovalForAll(address operator, bool _approved) external;

    /**
     * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
     *
     * See {setApprovalForAll}
     */
    function isApprovedForAll(address owner, address operator) external view returns (bool);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes calldata data
    ) external;
}

// File: @openzeppelin/contracts/token/ERC721/IERC721Receiver.sol



pragma solidity ^0.8.0;

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
interface IERC721Receiver {
    /**
     * @dev Whenever an {IERC721} `tokenId` token is transferred to this contract via {IERC721-safeTransferFrom}
     * by `operator` from `from`, this function is called.
     *
     * It must return its Solidity selector to confirm the token transfer.
     * If any other value is returned or the interface is not implemented by the recipient, the transfer will be reverted.
     *
     * The selector can be obtained in Solidity with `IERC721.onERC721Received.selector`.
     */
    function onERC721Received(
        address operator,
        address from,
        uint256 tokenId,
        bytes calldata data
    ) external returns (bytes4);
}

// File: @openzeppelin/contracts/token/ERC721/utils/ERC721Holder.sol



pragma solidity ^0.8.0;

/**
 * @dev Implementation of the {IERC721Receiver} interface.
 *
 * Accepts all token transfers.
 * Make sure the contract is able to use its token with {IERC721-safeTransferFrom}, {IERC721-approve} or {IERC721-setApprovalForAll}.
 */
contract ERC721Holder is IERC721Receiver {
    /**
     * @dev See {IERC721Receiver-onERC721Received}.
     *
     * Always returns `IERC721Receiver.onERC721Received.selector`.
     */
    function onERC721Received(
        address,
        address,
        uint256,
        bytes memory
    ) public virtual override returns (bytes4) {
        return this.onERC721Received.selector;
    }
}

// File: contracts/interfaces/IWETH.sol

pragma solidity >=0.5.0;

interface IWETH {
    function deposit() external payable;

    function transfer(address to, uint256 value) external returns (bool);

    function withdraw(uint256) external;
}

// File: contracts/interfaces/ICollectionWhitelistChecker.sol


pragma solidity ^0.8.0;

interface ICollectionWhitelistChecker {
    function canList(uint256 _tokenId) external view returns (bool);
}

// File: contracts/ERC721NFTMarketV1.sol


pragma solidity ^0.8.0;
pragma abicoder v2;

contract ERC721NFTMarketV1 is ERC721Holder, Ownable, ReentrancyGuard {
    using EnumerableSet for EnumerableSet.AddressSet;
    using EnumerableSet for EnumerableSet.UintSet;

    using SafeERC20 for IERC20;

    enum CollectionStatus {
        Pending,
        Open,
        Close
    }

    address public immutable WETH;

    uint256 public constant TOTAL_MAX_FEE = 1000; // 10% of a sale

    address public adminAddress;
    address public treasuryAddress;

    uint256 public minimumAskPrice; // in wei
    uint256 public maximumAskPrice; // in wei

    mapping(address => uint256) public pendingRevenue; // For creator/treasury to claim

    EnumerableSet.AddressSet private _collectionAddressSet;

    mapping(address => mapping(uint256 => Ask)) private _askDetails; // Ask details (price + seller address) for a given collection and a tokenId
    mapping(address => EnumerableSet.UintSet) private _askTokenIds; // Set of tokenIds for a collection
    mapping(address => Collection) private _collections; // Details about the collections
    mapping(address => mapping(address => EnumerableSet.UintSet)) private _tokenIdsOfSellerForCollection;

    struct Ask {
        address seller; // address of the seller
        uint256 price; // price of the token
    }

    struct Collection {
        CollectionStatus status; // status of the collection
        address creatorAddress; // address of the creator
        address whitelistChecker; // whitelist checker (if not set --> 0x00)
        uint256 tradingFee; // trading fee (100 = 1%, 500 = 5%, 5 = 0.05%)
        uint256 creatorFee; // creator fee (100 = 1%, 500 = 5%, 5 = 0.05%)
    }

    // Ask order is cancelled
    event AskCancel(address indexed collection, address indexed seller, uint256 indexed tokenId);

    // Ask order is created
    event AskNew(address indexed collection, address indexed seller, uint256 indexed tokenId, uint256 askPrice);

    // Ask order is updated
    event AskUpdate(address indexed collection, address indexed seller, uint256 indexed tokenId, uint256 askPrice);

    // Collection is closed for trading and new listings
    event CollectionClose(address indexed collection);

    // New collection is added
    event CollectionNew(
        address indexed collection,
        address indexed creator,
        address indexed whitelistChecker,
        uint256 tradingFee,
        uint256 creatorFee
    );

    // Existing collection is updated
    event CollectionUpdate(
        address indexed collection,
        address indexed creator,
        address indexed whitelistChecker,
        uint256 tradingFee,
        uint256 creatorFee
    );

    // Admin and Treasury Addresses are updated
    event NewAdminAndTreasuryAddresses(address indexed admin, address indexed treasury);

    // Minimum/maximum ask prices are updated
    event NewMinimumAndMaximumAskPrices(uint256 minimumAskPrice, uint256 maximumAskPrice);

    // Recover NFT tokens sent by accident
    event NonFungibleTokenRecovery(address indexed token, uint256 indexed tokenId);

    // Pending revenue is claimed
    event RevenueClaim(address indexed claimer, uint256 amount);

    // Recover ERC20 tokens sent by accident
    event TokenRecovery(address indexed token, uint256 amount);

    // Ask order is matched by a trade
    event Trade(
        address indexed collection,
        uint256 indexed tokenId,
        address indexed seller,
        address buyer,
        uint256 askPrice,
        uint256 netPrice,
        bool withETH
    );

    // Modifier for the admin
    modifier onlyAdmin() {
        require(msg.sender == adminAddress, "Management: Not admin");
        _;
    }

    /**
     * @notice Constructor
     * @param _adminAddress: address of the admin
     * @param _treasuryAddress: address of the treasury
     * @param _WETHAddress: WETH address
     * @param _minimumAskPrice: minimum ask price
     * @param _maximumAskPrice: maximum ask price
     */
    constructor(
        address _adminAddress,
        address _treasuryAddress,
        address _WETHAddress,
        uint256 _minimumAskPrice,
        uint256 _maximumAskPrice
    ) {
        require(_adminAddress != address(0), "Operations: Admin address cannot be zero");
        require(_treasuryAddress != address(0), "Operations: Treasury address cannot be zero");
        require(_WETHAddress != address(0), "Operations: WETH address cannot be zero");
        require(_minimumAskPrice > 0, "Operations: _minimumAskPrice must be > 0");
        require(_minimumAskPrice < _maximumAskPrice, "Operations: _minimumAskPrice < _maximumAskPrice");

        adminAddress = _adminAddress;
        treasuryAddress = _treasuryAddress;

        WETH = _WETHAddress;

        minimumAskPrice = _minimumAskPrice;
        maximumAskPrice = _maximumAskPrice;
    }

    /**
     * @notice Buy token with ETH by matching the price of an existing ask order
     * @param _collection: contract address of the NFT
     * @param _tokenId: tokenId of the NFT purchased
     */
    function buyTokenUsingETH(address _collection, uint256 _tokenId) external payable nonReentrant {
        // Wrap ETH
        IWETH(WETH).deposit{value: msg.value}();

        _buyToken(_collection, _tokenId, msg.value, true);
    }

    /**
     * @notice Buy token with WETH by matching the price of an existing ask order
     * @param _collection: contract address of the NFT
     * @param _tokenId: tokenId of the NFT purchased
     * @param _price: price (must be equal to the askPrice set by the seller)
     */
    function buyTokenUsingWETH(
        address _collection,
        uint256 _tokenId,
        uint256 _price
    ) external nonReentrant {
        IERC20(WETH).safeTransferFrom(address(msg.sender), address(this), _price);

        _buyToken(_collection, _tokenId, _price, false);
    }

    /**
     * @notice Cancel existing ask order
     * @param _collection: contract address of the NFT
     * @param _tokenId: tokenId of the NFT
     */
    function cancelAskOrder(address _collection, uint256 _tokenId) external nonReentrant {
        // Verify the sender has listed it
        require(_tokenIdsOfSellerForCollection[msg.sender][_collection].contains(_tokenId), "Order: Token not listed");

        // Adjust the information
        _tokenIdsOfSellerForCollection[msg.sender][_collection].remove(_tokenId);
        delete _askDetails[_collection][_tokenId];
        _askTokenIds[_collection].remove(_tokenId);

        // Transfer the NFT back to the user
        IERC721(_collection).transferFrom(address(this), address(msg.sender), _tokenId);

        // Emit event
        emit AskCancel(_collection, msg.sender, _tokenId);
    }

    /**
     * @notice Claim pending revenue (treasury or creators)
     */
    function claimPendingRevenue() external nonReentrant {
        uint256 revenueToClaim = pendingRevenue[msg.sender];
        require(revenueToClaim != 0, "Claim: Nothing to claim");
        pendingRevenue[msg.sender] = 0;

        IERC20(WETH).safeTransfer(address(msg.sender), revenueToClaim);

        emit RevenueClaim(msg.sender, revenueToClaim);
    }

    /**
     * @notice Create ask order
     * @param _collection: contract address of the NFT
     * @param _tokenId: tokenId of the NFT
     * @param _askPrice: price for listing (in wei)
     */
    function createAskOrder(
        address _collection,
        uint256 _tokenId,
        uint256 _askPrice
    ) external nonReentrant {
        // Verify price is not too low/high
        require(_askPrice >= minimumAskPrice && _askPrice <= maximumAskPrice, "Order: Price not within range");

        // Verify collection is accepted
        require(_collections[_collection].status == CollectionStatus.Open, "Collection: Not for listing");

        // Verify token has restriction
        require(_canTokenBeListed(_collection, _tokenId), "Order: tokenId not eligible");

        // Transfer NFT to this contract
        IERC721(_collection).safeTransferFrom(address(msg.sender), address(this), _tokenId);

        // Adjust the information
        _tokenIdsOfSellerForCollection[msg.sender][_collection].add(_tokenId);
        _askDetails[_collection][_tokenId] = Ask({seller: msg.sender, price: _askPrice});

        // Add tokenId to the askTokenIds set
        _askTokenIds[_collection].add(_tokenId);

        // Emit event
        emit AskNew(_collection, msg.sender, _tokenId, _askPrice);
    }

    /**
     * @notice Modify existing ask order
     * @param _collection: contract address of the NFT
     * @param _tokenId: tokenId of the NFT
     * @param _newPrice: new price for listing (in wei)
     */
    function modifyAskOrder(
        address _collection,
        uint256 _tokenId,
        uint256 _newPrice
    ) external nonReentrant {
        // Verify new price is not too low/high
        require(_newPrice >= minimumAskPrice && _newPrice <= maximumAskPrice, "Order: Price not within range");

        // Verify collection is accepted
        require(_collections[_collection].status == CollectionStatus.Open, "Collection: Not for listing");

        // Verify the sender has listed it
        require(_tokenIdsOfSellerForCollection[msg.sender][_collection].contains(_tokenId), "Order: Token not listed");

        // Adjust the information
        _askDetails[_collection][_tokenId].price = _newPrice;

        // Emit event
        emit AskUpdate(_collection, msg.sender, _tokenId, _newPrice);
    }

    /**
     * @notice Add a new collection
     * @param _collection: collection address
     * @param _creator: creator address (must be 0x00 if none)
     * @param _whitelistChecker: whitelist checker (for additional restrictions, must be 0x00 if none)
     * @param _tradingFee: trading fee (100 = 1%, 500 = 5%, 5 = 0.05%)
     * @param _creatorFee: creator fee (100 = 1%, 500 = 5%, 5 = 0.05%, 0 if creator is 0x00)
     * @dev Callable by admin
     */
    function addCollection(
        address _collection,
        address _creator,
        address _whitelistChecker,
        uint256 _tradingFee,
        uint256 _creatorFee
    ) external onlyAdmin {
        require(!_collectionAddressSet.contains(_collection), "Operations: Collection already listed");
        require(IERC721(_collection).supportsInterface(0x80ac58cd), "Operations: Not ERC721");

        require(
            (_creatorFee == 0 && _creator == address(0)) || (_creatorFee != 0 && _creator != address(0)),
            "Operations: Creator parameters incorrect"
        );

        require(_tradingFee + _creatorFee <= TOTAL_MAX_FEE, "Operations: Sum of fee must inferior to TOTAL_MAX_FEE");

        _collectionAddressSet.add(_collection);

        _collections[_collection] = Collection({
            status: CollectionStatus.Open,
            creatorAddress: _creator,
            whitelistChecker: _whitelistChecker,
            tradingFee: _tradingFee,
            creatorFee: _creatorFee
        });

        emit CollectionNew(_collection, _creator, _whitelistChecker, _tradingFee, _creatorFee);
    }

    /**
     * @notice Allows the admin to close collection for trading and new listing
     * @param _collection: collection address
     * @dev Callable by admin
     */
    function closeCollectionForTradingAndListing(address _collection) external onlyAdmin {
        require(_collectionAddressSet.contains(_collection), "Operations: Collection not listed");

        _collections[_collection].status = CollectionStatus.Close;
        _collectionAddressSet.remove(_collection);

        emit CollectionClose(_collection);
    }

    /**
     * @notice Modify collection characteristics
     * @param _collection: collection address
     * @param _creator: creator address (must be 0x00 if none)
     * @param _whitelistChecker: whitelist checker (for additional restrictions, must be 0x00 if none)
     * @param _tradingFee: trading fee (100 = 1%, 500 = 5%, 5 = 0.05%)
     * @param _creatorFee: creator fee (100 = 1%, 500 = 5%, 5 = 0.05%, 0 if creator is 0x00)
     * @dev Callable by admin
     */
    function modifyCollection(
        address _collection,
        address _creator,
        address _whitelistChecker,
        uint256 _tradingFee,
        uint256 _creatorFee
    ) external onlyAdmin {
        require(_collectionAddressSet.contains(_collection), "Operations: Collection not listed");

        require(
            (_creatorFee == 0 && _creator == address(0)) || (_creatorFee != 0 && _creator != address(0)),
            "Operations: Creator parameters incorrect"
        );

        require(_tradingFee + _creatorFee <= TOTAL_MAX_FEE, "Operations: Sum of fee must inferior to TOTAL_MAX_FEE");

        _collections[_collection] = Collection({
            status: CollectionStatus.Open,
            creatorAddress: _creator,
            whitelistChecker: _whitelistChecker,
            tradingFee: _tradingFee,
            creatorFee: _creatorFee
        });

        emit CollectionUpdate(_collection, _creator, _whitelistChecker, _tradingFee, _creatorFee);
    }

    /**
     * @notice Allows the admin to update minimum and maximum prices for a token (in wei)
     * @param _minimumAskPrice: minimum ask price
     * @param _maximumAskPrice: maximum ask price
     * @dev Callable by admin
     */
    function updateMinimumAndMaximumPrices(uint256 _minimumAskPrice, uint256 _maximumAskPrice) external onlyAdmin {
        require(_minimumAskPrice < _maximumAskPrice, "Operations: _minimumAskPrice < _maximumAskPrice");

        minimumAskPrice = _minimumAskPrice;
        maximumAskPrice = _maximumAskPrice;

        emit NewMinimumAndMaximumAskPrices(_minimumAskPrice, _maximumAskPrice);
    }

    /**
     * @notice Allows the owner to recover tokens sent to the contract by mistake
     * @param _token: token address
     * @dev Callable by owner
     */
    function recoverFungibleTokens(address _token) external onlyOwner {
        require(_token != WETH, "Operations: Cannot recover WETH");
        uint256 amountToRecover = IERC20(_token).balanceOf(address(this));
        require(amountToRecover != 0, "Operations: No token to recover");

        IERC20(_token).safeTransfer(address(msg.sender), amountToRecover);

        emit TokenRecovery(_token, amountToRecover);
    }

    /**
     * @notice Allows the owner to recover NFTs sent to the contract by mistake
     * @param _token: NFT token address
     * @param _tokenId: tokenId
     * @dev Callable by owner
     */
    function recoverNonFungibleToken(address _token, uint256 _tokenId) external onlyOwner nonReentrant {
        require(!_askTokenIds[_token].contains(_tokenId), "Operations: NFT not recoverable");
        IERC721(_token).safeTransferFrom(address(this), address(msg.sender), _tokenId);

        emit NonFungibleTokenRecovery(_token, _tokenId);
    }

    /**
     * @notice Set admin address
     * @dev Only callable by owner
     * @param _adminAddress: address of the admin
     * @param _treasuryAddress: address of the treasury
     */
    function setAdminAndTreasuryAddresses(address _adminAddress, address _treasuryAddress) external onlyOwner {
        require(_adminAddress != address(0), "Operations: Admin address cannot be zero");
        require(_treasuryAddress != address(0), "Operations: Treasury address cannot be zero");

        adminAddress = _adminAddress;
        treasuryAddress = _treasuryAddress;

        emit NewAdminAndTreasuryAddresses(_adminAddress, _treasuryAddress);
    }

    /**
     * @notice Check asks for an array of tokenIds in a collection
     * @param collection: address of the collection
     * @param tokenIds: array of tokenId
     */
    function viewAsksByCollectionAndTokenIds(address collection, uint256[] calldata tokenIds)
        external
        view
        returns (bool[] memory statuses, Ask[] memory askInfo)
    {
        uint256 length = tokenIds.length;

        statuses = new bool[](length);
        askInfo = new Ask[](length);

        for (uint256 i = 0; i < length; i++) {
            if (_askTokenIds[collection].contains(tokenIds[i])) {
                statuses[i] = true;
            } else {
                statuses[i] = false;
            }

            askInfo[i] = _askDetails[collection][tokenIds[i]];
        }

        return (statuses, askInfo);
    }

    /**
     * @notice View ask orders for a given collection across all sellers
     * @param collection: address of the collection
     * @param cursor: cursor
     * @param size: size of the response
     */
    function viewAsksByCollection(
        address collection,
        uint256 cursor,
        uint256 size
    )
        external
        view
        returns (
            uint256[] memory tokenIds,
            Ask[] memory askInfo,
            uint256
        )
    {
        uint256 length = size;

        if (length > _askTokenIds[collection].length() - cursor) {
            length = _askTokenIds[collection].length() - cursor;
        }

        tokenIds = new uint256[](length);
        askInfo = new Ask[](length);

        for (uint256 i = 0; i < length; i++) {
            tokenIds[i] = _askTokenIds[collection].at(cursor + i);
            askInfo[i] = _askDetails[collection][tokenIds[i]];
        }

        return (tokenIds, askInfo, cursor + length);
    }

    /**
     * @notice View ask orders for a given collection and a seller
     * @param collection: address of the collection
     * @param seller: address of the seller
     * @param cursor: cursor
     * @param size: size of the response
     */
    function viewAsksByCollectionAndSeller(
        address collection,
        address seller,
        uint256 cursor,
        uint256 size
    )
        external
        view
        returns (
            uint256[] memory tokenIds,
            Ask[] memory askInfo,
            uint256
        )
    {
        uint256 length = size;

        if (length > _tokenIdsOfSellerForCollection[seller][collection].length() - cursor) {
            length = _tokenIdsOfSellerForCollection[seller][collection].length() - cursor;
        }

        tokenIds = new uint256[](length);
        askInfo = new Ask[](length);

        for (uint256 i = 0; i < length; i++) {
            tokenIds[i] = _tokenIdsOfSellerForCollection[seller][collection].at(cursor + i);
            askInfo[i] = _askDetails[collection][tokenIds[i]];
        }

        return (tokenIds, askInfo, cursor + length);
    }

    /*
     * @notice View addresses and details for all the collections available for trading
     * @param cursor: cursor
     * @param size: size of the response
     */
    function viewCollections(uint256 cursor, uint256 size)
        external
        view
        returns (
            address[] memory collectionAddresses,
            Collection[] memory collectionDetails,
            uint256
        )
    {
        uint256 length = size;

        if (length > _collectionAddressSet.length() - cursor) {
            length = _collectionAddressSet.length() - cursor;
        }

        collectionAddresses = new address[](length);
        collectionDetails = new Collection[](length);

        for (uint256 i = 0; i < length; i++) {
            collectionAddresses[i] = _collectionAddressSet.at(cursor + i);
            collectionDetails[i] = _collections[collectionAddresses[i]];
        }

        return (collectionAddresses, collectionDetails, cursor + length);
    }

    /**
     * @notice Calculate price and associated fees for a collection
     * @param collection: address of the collection
     * @param price: listed price
     */
    function calculatePriceAndFeesForCollection(address collection, uint256 price)
        external
        view
        returns (
            uint256 netPrice,
            uint256 tradingFee,
            uint256 creatorFee
        )
    {
        if (_collections[collection].status != CollectionStatus.Open) {
            return (0, 0, 0);
        }

        return (_calculatePriceAndFeesForCollection(collection, price));
    }

    /**
     * @notice Checks if an array of tokenIds can be listed
     * @param _collection: address of the collection
     * @param _tokenIds: array of tokenIds
     * @dev if collection is not for trading, it returns array of bool with false
     */
    function canTokensBeListed(address _collection, uint256[] calldata _tokenIds)
        external
        view
        returns (bool[] memory listingStatuses)
    {
        listingStatuses = new bool[](_tokenIds.length);

        if (_collections[_collection].status != CollectionStatus.Open) {
            return listingStatuses;
        }

        for (uint256 i = 0; i < _tokenIds.length; i++) {
            listingStatuses[i] = _canTokenBeListed(_collection, _tokenIds[i]);
        }

        return listingStatuses;
    }

    /**
     * @notice Buy token by matching the price of an existing ask order
     * @param _collection: contract address of the NFT
     * @param _tokenId: tokenId of the NFT purchased
     * @param _price: price (must match the askPrice from the seller)
     * @param _withETH: whether the token is bought with ETH (true) or WETH (false)
     */
    function _buyToken(
        address _collection,
        uint256 _tokenId,
        uint256 _price,
        bool _withETH
    ) internal {
        require(_collections[_collection].status == CollectionStatus.Open, "Collection: Not for trading");
        require(_askTokenIds[_collection].contains(_tokenId), "Buy: Not for sale");

        Ask memory askOrder = _askDetails[_collection][_tokenId];

        // Front-running protection
        require(_price == askOrder.price, "Buy: Incorrect price");
        require(msg.sender != askOrder.seller, "Buy: Buyer cannot be seller");

        // Calculate the net price (collected by seller), trading fee (collected by treasury), creator fee (collected by creator)
        (uint256 netPrice, uint256 tradingFee, uint256 creatorFee) = _calculatePriceAndFeesForCollection(
            _collection,
            _price
        );

        // Update storage information
        _tokenIdsOfSellerForCollection[askOrder.seller][_collection].remove(_tokenId);
        delete _askDetails[_collection][_tokenId];
        _askTokenIds[_collection].remove(_tokenId);

        // Transfer WETH
        IERC20(WETH).safeTransfer(askOrder.seller, netPrice);

        // Update pending revenues for treasury/creator (if any!)
        if (creatorFee != 0) {
            pendingRevenue[_collections[_collection].creatorAddress] += creatorFee;
        }

        // Update trading fee if not equal to 0
        if (tradingFee != 0) {
            pendingRevenue[treasuryAddress] += tradingFee;
        }

        // Transfer NFT to buyer
        IERC721(_collection).safeTransferFrom(address(this), address(msg.sender), _tokenId);

        // Emit event
        emit Trade(_collection, _tokenId, askOrder.seller, msg.sender, _price, netPrice, _withETH);
    }

    /**
     * @notice Calculate price and associated fees for a collection
     * @param _collection: address of the collection
     * @param _askPrice: listed price
     */
    function _calculatePriceAndFeesForCollection(address _collection, uint256 _askPrice)
        internal
        view
        returns (
            uint256 netPrice,
            uint256 tradingFee,
            uint256 creatorFee
        )
    {
        tradingFee = (_askPrice * _collections[_collection].tradingFee) / 10000;
        creatorFee = (_askPrice * _collections[_collection].creatorFee) / 10000;

        netPrice = _askPrice - tradingFee - creatorFee;

        return (netPrice, tradingFee, creatorFee);
    }

    /**
     * @notice Checks if a token can be listed
     * @param _collection: address of the collection
     * @param _tokenId: tokenId
     */
    function _canTokenBeListed(address _collection, uint256 _tokenId) internal view returns (bool) {
        address whitelistCheckerAddress = _collections[_collection].whitelistChecker;
        return
            (whitelistCheckerAddress == address(0)) ||
            ICollectionWhitelistChecker(whitelistCheckerAddress).canList(_tokenId);
    }
}