// File: node_modules\@openzeppelin\contracts\GSN\Context.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/*
 * @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 GSN 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 payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: node_modules\@openzeppelin\contracts\introspection\IERC165.sol

pragma solidity ^0.7.0;

/**
 * @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: node_modules\@openzeppelin\contracts\token\ERC721\IERC721.sol

pragma solidity ^0.7.0;


/**
 * @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: node_modules\@openzeppelin\contracts\token\ERC721\IERC721Metadata.sol

pragma solidity ^0.7.0;


/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Metadata is IERC721 {

    /**
     * @dev Returns the token collection name.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the token collection symbol.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the Uniform Resource Identifier (URI) for `tokenId` token.
     */
    function tokenURI(uint256 tokenId) external view returns (string memory);
}

// File: node_modules\@openzeppelin\contracts\token\ERC721\IERC721Enumerable.sol

pragma solidity ^0.7.0;


/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Enumerable is IERC721 {

    /**
     * @dev Returns the total amount of tokens stored by the contract.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns a token ID owned by `owner` at a given `index` of its token list.
     * Use along with {balanceOf} to enumerate all of ``owner``'s tokens.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) external view returns (uint256 tokenId);

    /**
     * @dev Returns a token ID at a given `index` of all the tokens stored by the contract.
     * Use along with {totalSupply} to enumerate all tokens.
     */
    function tokenByIndex(uint256 index) external view returns (uint256);
}

// File: node_modules\@openzeppelin\contracts\token\ERC721\IERC721Receiver.sol

pragma solidity ^0.7.0;

/**
 * @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: node_modules\@openzeppelin\contracts\introspection\ERC165.sol

pragma solidity ^0.7.0;


/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
abstract contract ERC165 is IERC165 {
    /*
     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
     */
    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;

    /**
     * @dev Mapping of interface ids to whether or not it's supported.
     */
    mapping(bytes4 => bool) private _supportedInterfaces;

    constructor () {
        // Derived contracts need only register support for their own interfaces,
        // we register support for ERC165 itself here
        _registerInterface(_INTERFACE_ID_ERC165);
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     *
     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
        return _supportedInterfaces[interfaceId];
    }

    /**
     * @dev Registers the contract as an implementer of the interface defined by
     * `interfaceId`. Support of the actual ERC165 interface is automatic and
     * registering its interface id is not required.
     *
     * See {IERC165-supportsInterface}.
     *
     * Requirements:
     *
     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
     */
    function _registerInterface(bytes4 interfaceId) internal virtual {
        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
        _supportedInterfaces[interfaceId] = true;
    }
}

// File: node_modules\@openzeppelin\contracts\math\SafeMath.sol

pragma solidity ^0.7.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: node_modules\@openzeppelin\contracts\utils\Address.sol

pragma solidity ^0.7.0;

/**
 * @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) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: node_modules\@openzeppelin\contracts\utils\EnumerableSet.sol

pragma solidity ^0.7.0;

/**
 * @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 v3.0.0, only sets of type `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;

            // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            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] = toDeleteIndex + 1; // All indexes are 1-based

            // 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) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[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(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(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(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(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: node_modules\@openzeppelin\contracts\utils\EnumerableMap.sol

pragma solidity ^0.7.0;

/**
 * @dev Library for managing an enumerable variant of Solidity's
 * https://solidity.readthedocs.io/en/latest/types.html#mapping-types[`mapping`]
 * type.
 *
 * Maps have the following properties:
 *
 * - Entries are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Entries are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableMap for EnumerableMap.UintToAddressMap;
 *
 *     // Declare a set state variable
 *     EnumerableMap.UintToAddressMap private myMap;
 * }
 * ```
 *
 * As of v3.0.0, only maps of type `uint256 -> address` (`UintToAddressMap`) are
 * supported.
 */
library EnumerableMap {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Map type with
    // bytes32 keys and values.
    // The Map implementation uses private functions, and user-facing
    // implementations (such as Uint256ToAddressMap) are just wrappers around
    // the underlying Map.
    // This means that we can only create new EnumerableMaps for types that fit
    // in bytes32.

    struct MapEntry {
        bytes32 _key;
        bytes32 _value;
    }

    struct Map {
        // Storage of map keys and values
        MapEntry[] _entries;

        // Position of the entry defined by a key in the `entries` array, plus 1
        // because index 0 means a key is not in the map.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Adds a key-value pair to a map, or updates the value for an existing
     * key. O(1).
     *
     * Returns true if the key was added to the map, that is if it was not
     * already present.
     */
    function _set(Map storage map, bytes32 key, bytes32 value) private returns (bool) {
        // We read and store the key's index to prevent multiple reads from the same storage slot
        uint256 keyIndex = map._indexes[key];

        if (keyIndex == 0) { // Equivalent to !contains(map, key)
            map._entries.push(MapEntry({ _key: key, _value: value }));
            // The entry is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            map._indexes[key] = map._entries.length;
            return true;
        } else {
            map._entries[keyIndex - 1]._value = value;
            return false;
        }
    }

    /**
     * @dev Removes a key-value pair from a map. O(1).
     *
     * Returns true if the key was removed from the map, that is if it was present.
     */
    function _remove(Map storage map, bytes32 key) private returns (bool) {
        // We read and store the key's index to prevent multiple reads from the same storage slot
        uint256 keyIndex = map._indexes[key];

        if (keyIndex != 0) { // Equivalent to contains(map, key)
            // To delete a key-value pair from the _entries array in O(1), we swap the entry to delete with the last one
            // in the array, and then remove the last entry (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = keyIndex - 1;
            uint256 lastIndex = map._entries.length - 1;

            // When the entry to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            MapEntry storage lastEntry = map._entries[lastIndex];

            // Move the last entry to the index where the entry to delete is
            map._entries[toDeleteIndex] = lastEntry;
            // Update the index for the moved entry
            map._indexes[lastEntry._key] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved entry was stored
            map._entries.pop();

            // Delete the index for the deleted slot
            delete map._indexes[key];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the key is in the map. O(1).
     */
    function _contains(Map storage map, bytes32 key) private view returns (bool) {
        return map._indexes[key] != 0;
    }

    /**
     * @dev Returns the number of key-value pairs in the map. O(1).
     */
    function _length(Map storage map) private view returns (uint256) {
        return map._entries.length;
    }

   /**
    * @dev Returns the key-value pair stored at position `index` in the map. O(1).
    *
    * Note that there are no guarantees on the ordering of entries inside the
    * array, and it may change when more entries are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Map storage map, uint256 index) private view returns (bytes32, bytes32) {
        require(map._entries.length > index, "EnumerableMap: index out of bounds");

        MapEntry storage entry = map._entries[index];
        return (entry._key, entry._value);
    }

    /**
     * @dev Returns the value associated with `key`.  O(1).
     *
     * Requirements:
     *
     * - `key` must be in the map.
     */
    function _get(Map storage map, bytes32 key) private view returns (bytes32) {
        return _get(map, key, "EnumerableMap: nonexistent key");
    }

    /**
     * @dev Same as {_get}, with a custom error message when `key` is not in the map.
     */
    function _get(Map storage map, bytes32 key, string memory errorMessage) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, errorMessage); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }

    // UintToAddressMap

    struct UintToAddressMap {
        Map _inner;
    }

    /**
     * @dev Adds a key-value pair to a map, or updates the value for an existing
     * key. O(1).
     *
     * Returns true if the key was added to the map, that is if it was not
     * already present.
     */
    function set(UintToAddressMap storage map, uint256 key, address value) internal returns (bool) {
        return _set(map._inner, bytes32(key), bytes32(uint256(value)));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the key was removed from the map, that is if it was present.
     */
    function remove(UintToAddressMap storage map, uint256 key) internal returns (bool) {
        return _remove(map._inner, bytes32(key));
    }

    /**
     * @dev Returns true if the key is in the map. O(1).
     */
    function contains(UintToAddressMap storage map, uint256 key) internal view returns (bool) {
        return _contains(map._inner, bytes32(key));
    }

    /**
     * @dev Returns the number of elements in the map. O(1).
     */
    function length(UintToAddressMap storage map) internal view returns (uint256) {
        return _length(map._inner);
    }

   /**
    * @dev Returns the element 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(UintToAddressMap storage map, uint256 index) internal view returns (uint256, address) {
        (bytes32 key, bytes32 value) = _at(map._inner, index);
        return (uint256(key), address(uint256(value)));
    }

    /**
     * @dev Returns the value associated with `key`.  O(1).
     *
     * Requirements:
     *
     * - `key` must be in the map.
     */
    function get(UintToAddressMap storage map, uint256 key) internal view returns (address) {
        return address(uint256(_get(map._inner, bytes32(key))));
    }

    /**
     * @dev Same as {get}, with a custom error message when `key` is not in the map.
     */
    function get(UintToAddressMap storage map, uint256 key, string memory errorMessage) internal view returns (address) {
        return address(uint256(_get(map._inner, bytes32(key), errorMessage)));
    }
}

// File: node_modules\@openzeppelin\contracts\utils\Strings.sol

pragma solidity ^0.7.0;

/**
 * @dev String operations.
 */
library Strings {
    /**
     * @dev Converts a `uint256` to its ASCII `string` representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        uint256 index = digits - 1;
        temp = value;
        while (temp != 0) {
            buffer[index--] = byte(uint8(48 + temp % 10));
            temp /= 10;
        }
        return string(buffer);
    }
}

// File: @openzeppelin\contracts\token\ERC721\ERC721.sol

pragma solidity ^0.7.0;












/**
 * @title ERC721 Non-Fungible Token Standard basic implementation
 * @dev see https://eips.ethereum.org/EIPS/eip-721
 */
contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable {
    using SafeMath for uint256;
    using Address for address;
    using EnumerableSet for EnumerableSet.UintSet;
    using EnumerableMap for EnumerableMap.UintToAddressMap;
    using Strings for uint256;

    // Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
    // which can be also obtained as `IERC721Receiver(0).onERC721Received.selector`
    bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;

    // Mapping from holder address to their (enumerable) set of owned tokens
    mapping (address => EnumerableSet.UintSet) private _holderTokens;

    // Enumerable mapping from token ids to their owners
    EnumerableMap.UintToAddressMap private _tokenOwners;

    // Mapping from token ID to approved address
    mapping (uint256 => address) private _tokenApprovals;

    // Mapping from owner to operator approvals
    mapping (address => mapping (address => bool)) private _operatorApprovals;

    // Token name
    string private _name;

    // Token symbol
    string private _symbol;

    // Optional mapping for token URIs
    mapping (uint256 => string) private _tokenURIs;

    // Base URI
    string private _baseURI;

    /*
     *     bytes4(keccak256('balanceOf(address)')) == 0x70a08231
     *     bytes4(keccak256('ownerOf(uint256)')) == 0x6352211e
     *     bytes4(keccak256('approve(address,uint256)')) == 0x095ea7b3
     *     bytes4(keccak256('getApproved(uint256)')) == 0x081812fc
     *     bytes4(keccak256('setApprovalForAll(address,bool)')) == 0xa22cb465
     *     bytes4(keccak256('isApprovedForAll(address,address)')) == 0xe985e9c5
     *     bytes4(keccak256('transferFrom(address,address,uint256)')) == 0x23b872dd
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256)')) == 0x42842e0e
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)')) == 0xb88d4fde
     *
     *     => 0x70a08231 ^ 0x6352211e ^ 0x095ea7b3 ^ 0x081812fc ^
     *        0xa22cb465 ^ 0xe985e9c5 ^ 0x23b872dd ^ 0x42842e0e ^ 0xb88d4fde == 0x80ac58cd
     */
    bytes4 private constant _INTERFACE_ID_ERC721 = 0x80ac58cd;

    /*
     *     bytes4(keccak256('name()')) == 0x06fdde03
     *     bytes4(keccak256('symbol()')) == 0x95d89b41
     *     bytes4(keccak256('tokenURI(uint256)')) == 0xc87b56dd
     *
     *     => 0x06fdde03 ^ 0x95d89b41 ^ 0xc87b56dd == 0x5b5e139f
     */
    bytes4 private constant _INTERFACE_ID_ERC721_METADATA = 0x5b5e139f;

    /*
     *     bytes4(keccak256('totalSupply()')) == 0x18160ddd
     *     bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) == 0x2f745c59
     *     bytes4(keccak256('tokenByIndex(uint256)')) == 0x4f6ccce7
     *
     *     => 0x18160ddd ^ 0x2f745c59 ^ 0x4f6ccce7 == 0x780e9d63
     */
    bytes4 private constant _INTERFACE_ID_ERC721_ENUMERABLE = 0x780e9d63;

    /**
     * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
     */
    constructor (string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;

        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(_INTERFACE_ID_ERC721);
        _registerInterface(_INTERFACE_ID_ERC721_METADATA);
        _registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
    }

    /**
     * @dev See {IERC721-balanceOf}.
     */
    function balanceOf(address owner) public view override returns (uint256) {
        require(owner != address(0), "ERC721: balance query for the zero address");

        return _holderTokens[owner].length();
    }

    /**
     * @dev See {IERC721-ownerOf}.
     */
    function ownerOf(uint256 tokenId) public view override returns (address) {
        return _tokenOwners.get(tokenId, "ERC721: owner query for nonexistent token");
    }

    /**
     * @dev See {IERC721Metadata-name}.
     */
    function name() public view override returns (string memory) {
        return _name;
    }

    /**
     * @dev See {IERC721Metadata-symbol}.
     */
    function symbol() public view override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 tokenId) public view override returns (string memory) {
        require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");

        string memory _tokenURI = _tokenURIs[tokenId];

        // If there is no base URI, return the token URI.
        if (bytes(_baseURI).length == 0) {
            return _tokenURI;
        }
        // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
        if (bytes(_tokenURI).length > 0) {
            return string(abi.encodePacked(_baseURI, _tokenURI));
        }
        // If there is a baseURI but no tokenURI, concatenate the tokenID to the baseURI.
        return string(abi.encodePacked(_baseURI, tokenId.toString()));
    }

    /**
    * @dev Returns the base URI set via {_setBaseURI}. This will be
    * automatically added as a prefix in {tokenURI} to each token's URI, or
    * to the token ID if no specific URI is set for that token ID.
    */
    function baseURI() public view returns (string memory) {
        return _baseURI;
    }

    /**
     * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) public view override returns (uint256) {
        return _holderTokens[owner].at(index);
    }

    /**
     * @dev See {IERC721Enumerable-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        // _tokenOwners are indexed by tokenIds, so .length() returns the number of tokenIds
        return _tokenOwners.length();
    }

    /**
     * @dev See {IERC721Enumerable-tokenByIndex}.
     */
    function tokenByIndex(uint256 index) public view override returns (uint256) {
        (uint256 tokenId, ) = _tokenOwners.at(index);
        return tokenId;
    }

    /**
     * @dev See {IERC721-approve}.
     */
    function approve(address to, uint256 tokenId) public virtual override {
        address owner = ownerOf(tokenId);
        require(to != owner, "ERC721: approval to current owner");

        require(_msgSender() == owner || isApprovedForAll(owner, _msgSender()),
            "ERC721: approve caller is not owner nor approved for all"
        );

        _approve(to, tokenId);
    }

    /**
     * @dev See {IERC721-getApproved}.
     */
    function getApproved(uint256 tokenId) public view override returns (address) {
        require(_exists(tokenId), "ERC721: approved query for nonexistent token");

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev See {IERC721-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual override {
        require(operator != _msgSender(), "ERC721: approve to caller");

        _operatorApprovals[_msgSender()][operator] = approved;
        emit ApprovalForAll(_msgSender(), operator, approved);
    }

    /**
     * @dev See {IERC721-isApprovedForAll}.
     */
    function isApprovedForAll(address owner, address operator) public view override returns (bool) {
        return _operatorApprovals[owner][operator];
    }

    /**
     * @dev See {IERC721-transferFrom}.
     */
    function transferFrom(address from, address to, uint256 tokenId) public virtual override {
        //solhint-disable-next-line max-line-length
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");

        _transfer(from, to, tokenId);
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId) public virtual override {
        safeTransferFrom(from, to, tokenId, "");
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public virtual override {
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
        _safeTransfer(from, to, tokenId, _data);
    }

    /**
     * @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.
     *
     * `_data` is additional data, it has no specified format and it is sent in call to `to`.
     *
     * This internal function is equivalent to {safeTransferFrom}, and can be used to e.g.
     * implement alternative mechanisms to perform token transfer, such as signature-based.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function _safeTransfer(address from, address to, uint256 tokenId, bytes memory _data) internal virtual {
        _transfer(from, to, tokenId);
        require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }

    /**
     * @dev Returns whether `tokenId` exists.
     *
     * Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
     *
     * Tokens start existing when they are minted (`_mint`),
     * and stop existing when they are burned (`_burn`).
     */
    function _exists(uint256 tokenId) internal view returns (bool) {
        return _tokenOwners.contains(tokenId);
    }

    /**
     * @dev Returns whether `spender` is allowed to manage `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _isApprovedOrOwner(address spender, uint256 tokenId) internal view returns (bool) {
        require(_exists(tokenId), "ERC721: operator query for nonexistent token");
        address owner = ownerOf(tokenId);
        return (spender == owner || getApproved(tokenId) == spender || isApprovedForAll(owner, spender));
    }

    /**
     * @dev Safely mints `tokenId` and transfers it to `to`.
     *
     * Requirements:
     d*
     * - `tokenId` must not exist.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function _safeMint(address to, uint256 tokenId) internal virtual {
        _safeMint(to, tokenId, "");
    }

    /**
     * @dev Same as {xref-ERC721-_safeMint-address-uint256-}[`_safeMint`], with an additional `data` parameter which is
     * forwarded in {IERC721Receiver-onERC721Received} to contract recipients.
     */
    function _safeMint(address to, uint256 tokenId, bytes memory _data) internal virtual {
        _mint(to, tokenId);
        require(_checkOnERC721Received(address(0), to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }

    /**
     * @dev Mints `tokenId` and transfers it to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {_safeMint} whenever possible
     *
     * Requirements:
     *
     * - `tokenId` must not exist.
     * - `to` cannot be the zero address.
     *
     * Emits a {Transfer} event.
     */
    function _mint(address to, uint256 tokenId) internal virtual {
        require(to != address(0), "ERC721: mint to the zero address");
        require(!_exists(tokenId), "ERC721: token already minted");

        _beforeTokenTransfer(address(0), to, tokenId);

        _holderTokens[to].add(tokenId);

        _tokenOwners.set(tokenId, to);

        emit Transfer(address(0), to, tokenId);
    }

    /**
     * @dev Destroys `tokenId`.
     * The approval is cleared when the token is burned.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     *
     * Emits a {Transfer} event.
     */
    function _burn(uint256 tokenId) internal virtual {
        address owner = ownerOf(tokenId);

        _beforeTokenTransfer(owner, address(0), tokenId);

        // Clear approvals
        _approve(address(0), tokenId);

        // Clear metadata (if any)
        if (bytes(_tokenURIs[tokenId]).length != 0) {
            delete _tokenURIs[tokenId];
        }

        _holderTokens[owner].remove(tokenId);

        _tokenOwners.remove(tokenId);

        emit Transfer(owner, address(0), tokenId);
    }

    /**
     * @dev Transfers `tokenId` from `from` to `to`.
     *  As opposed to {transferFrom}, this imposes no restrictions on msg.sender.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     *
     * Emits a {Transfer} event.
     */
    function _transfer(address from, address to, uint256 tokenId) internal virtual {
        require(ownerOf(tokenId) == from, "ERC721: transfer of token that is not own");
        require(to != address(0), "ERC721: transfer to the zero address");

        _beforeTokenTransfer(from, to, tokenId);

        // Clear approvals from the previous owner
        _approve(address(0), tokenId);

        _holderTokens[from].remove(tokenId);
        _holderTokens[to].add(tokenId);

        _tokenOwners.set(tokenId, to);

        emit Transfer(from, to, tokenId);
    }

    /**
     * @dev Sets `_tokenURI` as the tokenURI of `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _setTokenURI(uint256 tokenId, string memory _tokenURI) internal virtual {
        require(_exists(tokenId), "ERC721Metadata: URI set of nonexistent token");
        _tokenURIs[tokenId] = _tokenURI;
    }

    /**
     * @dev Internal function to set the base URI for all token IDs. It is
     * automatically added as a prefix to the value returned in {tokenURI},
     * or to the token ID if {tokenURI} is empty.
     */
    function _setBaseURI(string memory baseURI_) internal virtual {
        _baseURI = baseURI_;
    }

    /**
     * @dev Internal function to invoke {IERC721Receiver-onERC721Received} on a target address.
     * The call is not executed if the target address is not a contract.
     *
     * @param from address representing the previous owner of the given token ID
     * @param to target address that will receive the tokens
     * @param tokenId uint256 ID of the token to be transferred
     * @param _data bytes optional data to send along with the call
     * @return bool whether the call correctly returned the expected magic value
     */
    function _checkOnERC721Received(address from, address to, uint256 tokenId, bytes memory _data)
        private returns (bool)
    {
        if (!to.isContract()) {
            return true;
        }
        bytes memory returndata = to.functionCall(abi.encodeWithSelector(
            IERC721Receiver(to).onERC721Received.selector,
            _msgSender(),
            from,
            tokenId,
            _data
        ), "ERC721: transfer to non ERC721Receiver implementer");
        bytes4 retval = abi.decode(returndata, (bytes4));
        return (retval == _ERC721_RECEIVED);
    }

    function _approve(address to, uint256 tokenId) private {
        _tokenApprovals[tokenId] = to;
        emit Approval(ownerOf(tokenId), to, tokenId);
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning.
     *
     * Calling conditions:
     *
     * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
     * transferred to `to`.
     * - When `from` is zero, `tokenId` will be minted for `to`.
     * - When `to` is zero, ``from``'s `tokenId` will be burned.
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal virtual { }
}

// File: contracts\GFarmNFT.sol

pragma solidity 0.7.5;


contract GFarmNFT is ERC721{

	// Current supply for each leverage
	uint16[8] supply = [0, 0, 0, 0, 0, 0, 0, 0];
	// Get the corresponding leverage for each NFT minted
	mapping(uint => uint16) idToLeverage;
	// Only the GFARM smart contract can mint new NFTs
	address immutable public owner;

	constructor() ERC721("GFarmNFT", "GFARMNFT"){
		owner = msg.sender;
	}

	// Verify leverage value (75,100,125,150,175,200,225,250)
	modifier correctLeverage(uint16 _leverage){
		require(_leverage >= 75 && _leverage <= 250 && _leverage % 25 == 0, "Wrong leverage value");
		_;
	}
	// Get ID from leverage (for arrays)
	function leverageID(uint16 _leverage) public pure correctLeverage(_leverage) returns(uint16){
		return (_leverage-50)/25-1;
	}
	// Required credits for each leverage (constant)
	function requiredCreditsArray() public pure returns(uint24[8] memory){
		// (blocks) => 2, 5, 7, 10, 12, 15, 17, 30 (days)
		return [12800, 32000, 44800, 64000, 76800, 96000, 108800, 192000];
	}
	// Max supply for each leverage (constant)
	function maxSupplyArray() public pure returns(uint16[8] memory){
		return [1000, 500, 400, 300, 200, 150, 100, 50];
	}
	// Get required credits from leverage based on the constant array
	function requiredCredits(uint16 _leverage) public pure returns(uint24){
		return requiredCreditsArray()[leverageID(_leverage)];
	}
	// Get max supply from leverage based on the constant array
	function maxSupply(uint16 _leverage) public pure returns(uint16){
		return maxSupplyArray()[leverageID(_leverage)];
	}
	// Get current supply from leverage
	function currentSupply(uint16 _leverage) public view returns(uint16){
		return supply[leverageID(_leverage)];
	}

	// Mint a leverage NFT to a user (increases supply)
	function mint(uint16 _leverage, uint _userCredits, address _userAddress) external{
		require(msg.sender == owner, "Caller must be the GFarm smart contract.");
		require(_userCredits >= requiredCredits(_leverage), "Not enough NFT credits");
		require(currentSupply(_leverage) < maxSupply(_leverage), "Max supply reached for this leverage");

		uint nftID = totalSupply();
		_mint(_userAddress, nftID);

		idToLeverage[nftID] = _leverage;
		supply[leverageID(_leverage)] += 1;
	}

	// Useful external functions
	function getLeverageFromID(uint id) external view returns(uint16){
		return idToLeverage[id];
	}
	function currentSupplyArray() external view returns(uint16[8] memory){
		return supply;
	}
}

// File: contracts\GFarmTokenInterface.sol

pragma solidity 0.7.5;

interface GFarmTokenInterface{
	function balanceOf(address account) external view returns (uint256);
    function transferFrom(address from, address to, uint256 value) external returns (bool);
    function transfer(address to, uint256 value) external returns (bool);
    function approve(address spender, uint256 value) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function burn(address from, uint256 amount) external;
    function mint(address to, uint256 amount) external;
}

// File: @uniswap\v2-core\contracts\interfaces\IUniswapV2Pair.sol

pragma solidity >=0.5.0;

interface IUniswapV2Pair {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external pure returns (string memory);
    function symbol() external pure returns (string memory);
    function decimals() external pure returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
    function PERMIT_TYPEHASH() external pure returns (bytes32);
    function nonces(address owner) external view returns (uint);

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external;

    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
    event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint);
    function factory() external view returns (address);
    function token0() external view returns (address);
    function token1() external view returns (address);
    function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
    function price0CumulativeLast() external view returns (uint);
    function price1CumulativeLast() external view returns (uint);
    function kLast() external view returns (uint);

    function mint(address to) external returns (uint liquidity);
    function burn(address to) external returns (uint amount0, uint amount1);
    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external;
    function skim(address to) external;
    function sync() external;

    function initialize(address, address) external;
}

// File: contracts\GFarm.sol

pragma solidity 0.7.5;





contract GFarm {

	using SafeMath for uint;

	// Tokens
	GFarmTokenInterface public immutable token;
	GFarmNFT public immutable nft;
	IUniswapV2Pair public immutable lp;

    // POOL 1

	// Constants
	uint constant POOL1_MULTIPLIER_1 = 10;
	uint constant POOL1_MULTIPLIER_2 = 5;
	uint constant POOL1_MULTIPLIER_1_DURATION = 100000; // 2 weeks
	uint constant POOL1_MULTIPLIER_2_DURATION = 200000; // 4 weeks
	uint immutable POOL1_MULTIPLIER_1_END;
	uint immutable POOL1_MULTIPLIER_2_END;
	uint constant POOL1_REFERRAL_P = 5;
	uint constant POOL1_CREDITS_MIN_P = 1;

	// Storage variables
	uint public POOL1_lastRewardBlock;
	uint public POOL1_accTokensPerLP; // divide by 1e18 for real value

	// POOL 2

    // Constants
	uint public constant POOL2_DURATION = 100000; // 2 weeks
	uint public immutable POOL2_END;

	// Storage variables
	uint public POOL2_lastRewardBlock;
	uint public POOL2_accTokensPerETH; // divide by 1e18 for real value

	// POOL 1 & POOL 2: Constants
	uint public immutable POOLS_START;
	uint public constant POOLS_TOKENS_PER_BLOCK = 1; // 1 token per block
	uint public constant POOLS_START_DELAY = 51000; // 8 days => 27th of december

	// Useful Uniswap addresses (for TVL & APY)
	address constant WETH = 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2;
	IUniswapV2Pair constant ETH_USDC_PAIR = IUniswapV2Pair(0xB4e16d0168e52d35CaCD2c6185b44281Ec28C9Dc);

    // Dev fund
    address immutable DEV_FUND;
    uint constant DEV_FUND_PERCENTAGE = 10;

	// Info about each user
	struct User {
        uint POOL1_provided;
        uint POOL1_rewardDebt;
        address POOL1_referral;
        uint POOL1_referralReward;

        uint POOL2_provided;
        uint POOL2_rewardDebt;

        uint NFT_CREDITS_amount;
        uint NFT_CREDITS_lastUpdated;
        bool NFT_CREDITS_receiving;
    }
    mapping(address => User) public users;

    //uint public fakeBlockNumber; // REPLACE EVERYWHERE BY BLOCK.NUMBER

	constructor(
		GFarmTokenInterface _token,
        IUniswapV2Pair _lp){

		token = _token;
        lp = _lp;
		DEV_FUND = msg.sender;

		POOL1_MULTIPLIER_1_END = block.number.add(POOLS_START_DELAY).add(POOL1_MULTIPLIER_1_DURATION);
		POOL1_MULTIPLIER_2_END = block.number.add(POOLS_START_DELAY).add(POOL1_MULTIPLIER_1_DURATION).add(POOL1_MULTIPLIER_2_DURATION);
		POOL2_END = block.number.add(POOLS_START_DELAY).add(POOL2_DURATION);
		POOLS_START = block.number.add(POOLS_START_DELAY);

		nft = new GFarmNFT();

        //fakeBlockNumber = block.number;
	}

    /*function increaseBlock(uint b) external { fakeBlockNumber += b; }
    function decreaseBlock(uint b) external { fakeBlockNumber -= b; }*/

    // Get token reward between two blocks
    function POOL1_getReward(uint _from, uint _to) private view returns (uint){
    	uint blocksWithMultiplier;

        if(_from >= POOLS_START && _to >= POOLS_START){
        	// Multiplier 1
        	if(_from <= POOL1_MULTIPLIER_1_END && _to <= POOL1_MULTIPLIER_1_END){
        		blocksWithMultiplier = _to.sub(_from).mul(POOL1_MULTIPLIER_1);
        	// Between multiplier 1 and multiplier 2
        	} else if(_from <= POOL1_MULTIPLIER_1_END && _to > POOL1_MULTIPLIER_1_END && _to <= POOL1_MULTIPLIER_2_END){
        		blocksWithMultiplier = POOL1_MULTIPLIER_1_END.sub(_from).mul(POOL1_MULTIPLIER_1).add(
        			_to.sub(POOL1_MULTIPLIER_1_END).mul(POOL1_MULTIPLIER_2)
        		);
        	// Between multiplier 1 and no multiplier (pretty unlikely)
        	} else if(_from <= POOL1_MULTIPLIER_1_END && _to > POOL1_MULTIPLIER_2_END){
        		blocksWithMultiplier = POOL1_MULTIPLIER_1_END.sub(_from).mul(POOL1_MULTIPLIER_1).add(
        			POOL1_MULTIPLIER_2_END.sub(POOL1_MULTIPLIER_1_END).mul(POOL1_MULTIPLIER_2).add(
        				_to.sub(POOL1_MULTIPLIER_2_END)
        			)
        		);
        	// Multplier 2
        	}else if(_from > POOL1_MULTIPLIER_1_END && _from <= POOL1_MULTIPLIER_2_END && _to <= POOL1_MULTIPLIER_2_END){
        		blocksWithMultiplier = _to.sub(_from).mul(POOL1_MULTIPLIER_2);
        	// Between multiplier 2 and no multiplier
        	} else if(_from > POOL1_MULTIPLIER_1_END && _from <= POOL1_MULTIPLIER_2_END && _to > POOL1_MULTIPLIER_2_END){
        		blocksWithMultiplier = POOL1_MULTIPLIER_2_END.sub(_from).mul(POOL1_MULTIPLIER_2).add(
        			_to.sub(POOL1_MULTIPLIER_2_END)
        		);
        	// No multiplier
        	}else{
        		blocksWithMultiplier = _to.sub(_from);
        	}
        }

    	return blocksWithMultiplier.mul(POOLS_TOKENS_PER_BLOCK).mul(1e18);
    }
    function POOL2_getReward(uint _from, uint _to) private view returns (uint){
    	uint blocksWithMultiplier;

        if(_from >= POOLS_START && _to >= POOLS_START){
        	// Before pool 2 has ended
        	if(_from <= POOL2_END && _to <= POOL2_END){
        		blocksWithMultiplier = _to.sub(_from);
        	// Between before and after pool 2 has ended
        	}else if(_from <= POOL2_END && _to > POOL2_END){
        		blocksWithMultiplier = POOL2_END.sub(_from);
        	// After pool 2 has ended
        	}else if(_from > POOL2_END && _to > POOL2_END){
        		blocksWithMultiplier = 0;
        	}
        }

    	return blocksWithMultiplier.mul(POOLS_TOKENS_PER_BLOCK).mul(1e18);
    }

    // Updates the pool storage variables
	function POOL1_update() private {
		uint lpSupply = lp.balanceOf(address(this));

        if (POOL1_lastRewardBlock == 0 || lpSupply == 0) {
            POOL1_lastRewardBlock = block.number;
            return;
        }

		uint reward = POOL1_getReward(POOL1_lastRewardBlock, block.number);
        
    	token.mint(address(this), reward);
    	token.mint(DEV_FUND, reward.mul(DEV_FUND_PERCENTAGE).div(100));

    	POOL1_accTokensPerLP = POOL1_accTokensPerLP.add(reward.mul(1e18).div(lpSupply));
        POOL1_lastRewardBlock = block.number;
	}	
	function POOL2_update(uint ethJustStaked) private {
		// Here we retrieve the balance before the last transfer,
		// Because solidity updates the balance before the rest of the code is executed
		// (Unlike the first pool, where we transfer the lp tokens to the farm after POOL1_update is called)
		uint ethSupply = address(this).balance.sub(ethJustStaked);

		if (POOL2_lastRewardBlock == 0 || ethSupply == 0) {
            POOL2_lastRewardBlock = block.number;
            return;
        }

		uint reward = POOL2_getReward(POOL2_lastRewardBlock, block.number);
        
    	token.mint(address(this), reward);
    	token.mint(DEV_FUND, reward.mul(DEV_FUND_PERCENTAGE).div(100));

    	POOL2_accTokensPerETH = POOL2_accTokensPerETH.add(reward.mul(1e18).div(ethSupply));
        POOL2_lastRewardBlock = block.number;
	}

	// Pending reward
	function POOL1_pendingReward() external view returns(uint){
		return _POOL1_pendingReward(users[msg.sender]);
	}
	function POOL2_pendingReward() external view returns(uint){
		return _POOL2_pendingReward(users[msg.sender], 0);
	}
	function _POOL1_pendingReward(User memory u) private view returns(uint){
		uint _POOL1_accTokensPerLP = POOL1_accTokensPerLP;
		uint lpSupply = lp.balanceOf(address(this));

		if (block.number > POOL1_lastRewardBlock && lpSupply != 0) {
			uint pendingReward = POOL1_getReward(POOL1_lastRewardBlock, block.number);
            _POOL1_accTokensPerLP = _POOL1_accTokensPerLP.add(pendingReward.mul(1e18).div(lpSupply));
        }

		return u.POOL1_provided.mul(_POOL1_accTokensPerLP).div(1e18).sub(u.POOL1_rewardDebt);
	}
	function _POOL2_pendingReward(User memory u, uint ethJustStaked) private view returns(uint){
		uint _POOL2_accTokensPerETH = POOL2_accTokensPerETH;
        // Here we retrieve the balance before the last transfer,
        // Because solidity updates the balance before the rest of the code is executed
        // (Unlike the first pool, where we transfer the lp tokens to the farm after POOL1_update is called)
		uint ethSupply = address(this).balance.sub(ethJustStaked);

		if (block.number > POOL2_lastRewardBlock && ethSupply != 0) {
            uint pendingReward = POOL2_getReward(POOL2_lastRewardBlock, block.number);
            _POOL2_accTokensPerETH = _POOL2_accTokensPerETH.add(pendingReward.mul(1e18).div(ethSupply));
        }

		return u.POOL2_provided.mul(_POOL2_accTokensPerETH).div(1e18).sub(u.POOL2_rewardDebt);
	}

	// Claim reward (harvest)
	function POOL1_harvest() external{
		_POOL1_harvest(msg.sender);
	}
	function POOL2_harvest() external{
		_POOL2_harvest(msg.sender, 0);
	}
	function _POOL1_harvest(address a) private{
		User storage u = users[a];
		uint pending = _POOL1_pendingReward(u);
		POOL1_update();

		if(pending > 0){
			if(u.POOL1_referral == address(0)){
				POOLS_safeTokenTransfer(a, pending);
				token.burn(a, pending.mul(POOL1_REFERRAL_P).div(100));
			}else{
				uint referralReward = pending.mul(POOL1_REFERRAL_P).div(100);
				uint userReward = pending.sub(referralReward);

				POOLS_safeTokenTransfer(a, userReward);
				POOLS_safeTokenTransfer(u.POOL1_referral, referralReward);

				User storage referralUser = users[u.POOL1_referral];
				referralUser.POOL1_referralReward = referralUser.POOL1_referralReward.add(referralReward);
			}
		}

		u.POOL1_rewardDebt = u.POOL1_provided.mul(POOL1_accTokensPerLP).div(1e18);
	}
	function _POOL2_harvest(address a, uint ethJustStaked) private{
		User storage u = users[a];
		uint pending = _POOL2_pendingReward(u, ethJustStaked);
		POOL2_update(ethJustStaked);

		if(pending > 0){
			POOLS_safeTokenTransfer(a, pending);
		}

		u.POOL2_rewardDebt = u.POOL2_provided.mul(POOL2_accTokensPerETH).div(1e18);
	}

	// Stake
	function POOL1_stake(uint amount, address referral) external{
		require(block.number >= POOLS_START, "Pool hasn't started yet.");
		require(amount > 0, "Staking 0 lp.");

        uint lpSupplyBefore = lp.balanceOf(address(this));

		_POOL1_harvest(msg.sender);
		lp.transferFrom(msg.sender, address(this), amount);

		User storage u = users[msg.sender];
		u.POOL1_provided = u.POOL1_provided.add(amount);
		u.POOL1_rewardDebt = u.POOL1_provided.mul(POOL1_accTokensPerLP).div(1e18);

		if(!u.NFT_CREDITS_receiving && u.POOL1_provided >= lpSupplyBefore.mul(POOL1_CREDITS_MIN_P).div(100)){
			u.NFT_CREDITS_receiving = true;
			u.NFT_CREDITS_lastUpdated = block.number;
		}

		if(u.POOL1_referral == address(0) && referral != address(0) && referral != msg.sender){
			u.POOL1_referral = referral;
		}
	}
	function POOL2_stake() payable external{
		require(block.number >= POOLS_START, "Pool hasn't started yet.");
		require(block.number <= POOL2_END, "Pool is finished, no more staking.");
		require(msg.value > 0, "Staking 0 ETH.");

		_POOL2_harvest(msg.sender, msg.value);

		User storage u = users[msg.sender];
		u.POOL2_provided = u.POOL2_provided.add(msg.value);
		u.POOL2_rewardDebt = u.POOL2_provided.mul(POOL2_accTokensPerETH).div(1e18);
	}

	// Unstake
	function POOL1_unstake(uint amount) external{
		User storage u = users[msg.sender];
		require(amount > 0, "Unstaking 0 lp.");
		require(u.POOL1_provided >= amount, "Unstaking more than currently staked.");

		_POOL1_harvest(msg.sender);
		lp.transfer(msg.sender, amount);

		u.POOL1_provided = u.POOL1_provided.sub(amount);
		u.POOL1_rewardDebt = u.POOL1_provided.mul(POOL1_accTokensPerLP).div(1e18);

		uint lpSupply = lp.balanceOf(address(this));

		if(u.NFT_CREDITS_receiving && u.POOL1_provided < lpSupply.mul(POOL1_CREDITS_MIN_P).div(100) || u.NFT_CREDITS_receiving && lpSupply == 0){
			u.NFT_CREDITS_amount = NFT_CREDITS_amount();
			u.NFT_CREDITS_receiving = false;
			u.NFT_CREDITS_lastUpdated = block.number;
		}
	}
	function POOL2_unstake(uint amount) external{
		User storage u = users[msg.sender];
		require(amount > 0, "Unstaking 0 ETH.");
		require(u.POOL2_provided >= amount, "Unstaking more than currently staked.");

		_POOL2_harvest(msg.sender, 0);
		msg.sender.transfer(amount);

		u.POOL2_provided = u.POOL2_provided.sub(amount);
		u.POOL2_rewardDebt = u.POOL2_provided.mul(POOL2_accTokensPerETH).div(1e18);
	}

	// NFTs
	function NFT_claim(uint16 _leverage) external{
		User storage u = users[msg.sender];
		nft.mint(_leverage, NFT_CREDITS_amount(), msg.sender);
		uint requiredCredits = nft.requiredCredits(_leverage);
		u.NFT_CREDITS_amount = NFT_CREDITS_amount().sub(requiredCredits);
		u.NFT_CREDITS_lastUpdated = block.number;
	}
	function NFT_CREDITS_amount() public view returns(uint){
    	User memory u = users[msg.sender];
    	if(u.NFT_CREDITS_receiving){
    		return u.NFT_CREDITS_amount.add(block.number.sub(u.NFT_CREDITS_lastUpdated));
    	}else{
    		return u.NFT_CREDITS_amount;
    	}
    }

	// Prevent rounding errors
	function POOLS_safeTokenTransfer(address _to, uint _amount) private {
        uint bal = token.balanceOf(address(this));
        if (_amount > bal) {
            token.transfer(_to, bal);
        } else {
            token.transfer(_to, _amount);
        }
    }

    // USEFUL PRICING FUNCTIONS (FOR TVL & APY)

    // divide by 1e5 for real value
    function getEthPrice() private view returns(uint){
        (uint112 reserves0, uint112 reserves1, ) = ETH_USDC_PAIR.getReserves();
        uint reserveUSDC;
        uint reserveETH;

        if(WETH == ETH_USDC_PAIR.token0()){
            reserveETH = reserves0;
            reserveUSDC = reserves1;
        }else{
            reserveUSDC = reserves0;
            reserveETH = reserves1;
        }
        // Divide number of USDC by number of ETH
        // we multiply by 1e12 because USDC only has 6 decimals
        return reserveUSDC.mul(1e12).mul(1e5).div(reserveETH);
    }
    // divide by 1e5 for real value
    function getGFarmPriceEth() private view returns(uint){
        (uint112 reserves0, uint112 reserves1, ) = lp.getReserves();

        uint reserveETH;
        uint reserveGFARM;

        if(WETH == lp.token0()){
            reserveETH = reserves0;
            reserveGFARM = reserves1;
        }else{
            reserveGFARM = reserves0;
            reserveETH = reserves1;
        }

        return reserveETH.mul(1e5).div(reserveGFARM);
    }

    // UI VIEW FUNCTIONS (READ-ONLY)
    
    function POOLS_blocksLeftUntilStart() external view returns(uint){
    	if(block.number > POOLS_START){ return 0; }
    	return POOLS_START.sub(block.number);
    }
	function POOL1_getMultiplier() public view returns (uint) {
		if(block.number < POOLS_START){
			return 0;
		}
        if(block.number <= POOL1_MULTIPLIER_1_END){
        	return POOL1_MULTIPLIER_1;
        }else if(block.number <= POOL1_MULTIPLIER_2_END){
        	return POOL1_MULTIPLIER_2;
        }
        return 1;
    }
	function POOL2_getMultiplier() public view returns (uint) {
		if(block.number < POOLS_START || block.number > POOL2_END){
			return 0;
		}
        return 1;
    }
    function POOL1_rewardPerBlock() external view returns(uint){
    	return POOL1_getMultiplier().mul(POOLS_TOKENS_PER_BLOCK).mul(1e18);
    }
    function POOL2_rewardPerBlock() external view returns(uint){
    	return POOL2_getMultiplier().mul(POOLS_TOKENS_PER_BLOCK).mul(1e18);
    }
    function POOL1_provided() external view returns(uint){
    	return users[msg.sender].POOL1_provided;
    }
    function POOL2_provided() external view returns(uint){
    	return users[msg.sender].POOL2_provided;
    }
    function POOL1_referralReward() external view returns(uint){
    	return users[msg.sender].POOL1_referralReward;
    }
    function POOL2_blocksLeft() external view returns(uint){
    	if(block.number > POOL2_END){
    		return 0;
    	}
    	return POOL2_END.sub(block.number);
    }
    function POOL1_referral() external view returns(address){
        return users[msg.sender].POOL1_referral;
    }
    function POOL1_minLpsNftCredits() external view returns(uint){
    	return lp.balanceOf(address(this)).mul(POOL1_CREDITS_MIN_P).div(100);
    }
    // divide by 1e5 for real value
    function POOL1_tvl() public view returns(uint){
    	if(lp.totalSupply() == 0){ return 0; }

    	(uint112 reserves0, uint112 reserves1, ) = lp.getReserves();
    	uint reserveEth;

    	if(WETH == lp.token0()){
    		reserveEth = reserves0;
    	}else{
			reserveEth = reserves1;
    	}

    	uint lpPriceEth = reserveEth.mul(1e5).mul(2).div(lp.totalSupply());
    	uint lpPriceUsd = lpPriceEth.mul(getEthPrice()).div(1e5);

    	return lp.balanceOf(address(this)).mul(lpPriceUsd).div(1e18);
    }
    // divide by 1e5 for real value
    function POOL2_tvl() public view returns(uint){
    	return address(this).balance.mul(getEthPrice()).div(1e18);
    }
    // divide by 1e5 for real value
    function POOLS_tvl() external view returns(uint){
    	return POOL1_tvl().add(POOL2_tvl());
    }
    // divide by 1e5 for real value
    function POOL1_apy() external view returns(uint){
    	if(POOL1_tvl() == 0){ return 0; }
    	return POOLS_TOKENS_PER_BLOCK.mul(POOL1_getMultiplier()).mul(2336000).mul(getGFarmPriceEth()).mul(getEthPrice()).mul(100).div(POOL1_tvl());
    }
    // divide by 1e5 for real value
    function POOL2_apy() external view returns(uint){
    	if(POOL2_tvl() == 0){ return 0; }
    	return POOLS_TOKENS_PER_BLOCK.mul(POOL2_getMultiplier()).mul(2336000).mul(getGFarmPriceEth()).mul(getEthPrice()).mul(100).div(POOL2_tvl());
    }
    function NFT_owned() external view returns(uint[8] memory nfts){
    	for(uint i = 0; i < nft.balanceOf(msg.sender); i++){
            uint id = nft.leverageID(nft.getLeverageFromID(nft.tokenOfOwnerByIndex(msg.sender, i)));
            nfts[id] = nfts[id].add(1);
        }
    }
    function NFT_requiredCreditsArray() external view returns(uint24[8] memory){
    	return nft.requiredCreditsArray();
    }
	function NFT_maxSupplyArray() external view returns(uint16[8] memory){
		return nft.maxSupplyArray();
	}
	function NFT_currentSupplyArray() external view returns(uint16[8] memory){
		return nft.currentSupplyArray();
	}
}