// File: @openzeppelin/contracts/utils/cryptography/MerkleProof.sol


// OpenZeppelin Contracts (last updated v4.5.0) (utils/cryptography/MerkleProof.sol)

pragma solidity ^0.8.0;

/**
 * @dev These functions deal with verification of Merkle Trees proofs.
 *
 * The proofs can be generated using the JavaScript library
 * https://github.com/miguelmota/merkletreejs[merkletreejs].
 * Note: the hashing algorithm should be keccak256 and pair sorting should be enabled.
 *
 * See `test/utils/cryptography/MerkleProof.test.js` for some examples.
 */
library MerkleProof {
    /**
     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
     * defined by `root`. For this, a `proof` must be provided, containing
     * sibling hashes on the branch from the leaf to the root of the tree. Each
     * pair of leaves and each pair of pre-images are assumed to be sorted.
     */
    function verify(
        bytes32[] memory proof,
        bytes32 root,
        bytes32 leaf
    ) internal pure returns (bool) {
        return processProof(proof, leaf) == root;
    }

    /**
     * @dev Returns the rebuilt hash obtained by traversing a Merklee tree up
     * from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
     * hash matches the root of the tree. When processing the proof, the pairs
     * of leafs & pre-images are assumed to be sorted.
     *
     * _Available since v4.4._
     */
    function processProof(bytes32[] memory proof, bytes32 leaf) internal pure returns (bytes32) {
        bytes32 computedHash = leaf;
        for (uint256 i = 0; i < proof.length; i++) {
            bytes32 proofElement = proof[i];
            if (computedHash <= proofElement) {
                // Hash(current computed hash + current element of the proof)
                computedHash = _efficientHash(computedHash, proofElement);
            } else {
                // Hash(current element of the proof + current computed hash)
                computedHash = _efficientHash(proofElement, computedHash);
            }
        }
        return computedHash;
    }

    function _efficientHash(bytes32 a, bytes32 b) private pure returns (bytes32 value) {
        assembly {
            mstore(0x00, a)
            mstore(0x20, b)
            value := keccak256(0x00, 0x40)
        }
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol


// OpenZeppelin Contracts v4.4.1 (utils/Strings.sol)

pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal 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);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }
}

// File: @openzeppelin/contracts/utils/Context.sol


// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

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


// OpenZeppelin Contracts v4.4.1 (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() {
        _transferOwnership(_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 {
        _transferOwnership(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");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// File: @openzeppelin/contracts/utils/Address.sol


// OpenZeppelin Contracts (last updated v4.5.0) (utils/Address.sol)

pragma solidity ^0.8.1;

/**
 * @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
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain `call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/token/ERC721/IERC721Receiver.sol


// OpenZeppelin Contracts v4.4.1 (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/utils/introspection/IERC165.sol


// OpenZeppelin Contracts v4.4.1 (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/utils/introspection/ERC165.sol


// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)

pragma solidity ^0.8.0;


/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
 * for the additional interface id that will be supported. For example:
 *
 * ```solidity
 * function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
 *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
 * }
 * ```
 *
 * Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
 */
abstract contract ERC165 is IERC165 {
    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IERC165).interfaceId;
    }
}

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol


// OpenZeppelin Contracts v4.4.1 (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/extensions/IERC721Metadata.sol


// OpenZeppelin Contracts v4.4.1 (token/ERC721/extensions/IERC721Metadata.sol)

pragma solidity ^0.8.0;


/**
 * @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: @openzeppelin/contracts/token/ERC721/extensions/IERC721Enumerable.sol


// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC721/extensions/IERC721Enumerable.sol)

pragma solidity ^0.8.0;


/**
 * @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);

    /**
     * @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: contracts/ERC721.sol



pragma solidity ^0.8.0;









/**
 * @dev Implementation of https://eips.ethereum.org/EIPS/eip-721[ERC721] Non-Fungible Token Standard, including
 * the Metadata and Enumerable extensions
 */
contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable {
  using Address for address;
  using Strings for uint256;

  string private _name;
  string private _symbol;

  // nft ownership + burns data
  address[] public owners;
  uint public burnedTokens;

  function totalSupply() public override view returns (uint256) {
    return owners.length - burnedTokens;
  }

  function tokenByIndex(uint256 id) public override pure returns (uint256) {
    return id;
  }
  function tokenOfOwnerByIndex(address user, uint256 id) public override view returns (uint256) {
    uint256 ownedCount = 0;
    for(uint i = 0; i < owners.length; i++) {
      if(owners[i] == user) {
        if(ownedCount == id) {
          return i;
        } else {
          ownedCount++;
        }
      }
    }

    revert("ID_TOO_HIGH");
  }

  // 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;

  /**
  * @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_;
  }

  /**
  * @dev See {IERC165-supportsInterface}.
  */
  function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool) {
    return
    interfaceId == type(IERC721).interfaceId ||
      interfaceId == type(IERC721Metadata).interfaceId ||
      super.supportsInterface(interfaceId);
  }

  /**
  * @dev See {IERC721-balanceOf}.
  */
  function balanceOf(address owner) public view virtual override returns (uint256) {
    require(owner != address(0), "ERC721: balance query for the zero address");
    uint count;
    for(uint i = 0; i < owners.length; i++) {
      if(owner == owners[i]) {
        count++;
      }
    }
    return count;
  }

  /**
  * @dev See {IERC721-ownerOf}.
  */
  function ownerOf(uint256 tokenId) public view virtual override returns (address) {
    require(tokenId < owners.length, "ERC721: owner query for nonexistent token");
    address owner = owners[tokenId];
    return owner;
  }

  /**
  * @dev See {IERC721Metadata-name}.
  */
  function name() public view virtual override returns (string memory) {
    return _name;
  }

  /**
  * @dev See {IERC721Metadata-symbol}.
  */
  function symbol() public view virtual override returns (string memory) {
    return _symbol;
  }

  /**
  * @dev See {IERC721Metadata-tokenURI}.
  */
  function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
    require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");

    string memory baseURI = _baseURI();
    return bytes(baseURI).length > 0 ? string(abi.encodePacked(baseURI, tokenId.toString())) : "";
  }

  /**
  * @dev Base URI for computing {tokenURI}. If set, the resulting URI for each
  * token will be the concatenation of the `baseURI` and the `tokenId`. Empty
  * by default, can be overriden in child contracts.
    */
  function _baseURI() internal view virtual returns (string memory) {
    return "";
  }

  /**
  * @dev See {IERC721-approve}.
  */
  function approve(address to, uint256 tokenId) public virtual override {
    address owner = ERC721.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 virtual 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 virtual 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 virtual returns (bool) {
    return owners.length > tokenId && owners[tokenId] != address(0);
  }

  /**
  * @dev Returns whether `spender` is allowed to manage `tokenId`.
  *
    * Requirements:
    *
    * - `tokenId` must exist.
    */
  function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual returns (bool) {
    require(_exists(tokenId), "ERC721: operator query for nonexistent token");
    address owner = ERC721.ownerOf(tokenId);
    return (spender == owner || getApproved(tokenId) == spender || isApprovedForAll(owner, spender));
  }

  /**
  * @dev Safely mints `tokenId` and transfers it to `to`.
  *
    * Requirements:
    *
    * - `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), "ALREADY_MINTED");

    owners.push(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 = ERC721.ownerOf(tokenId);

    require(
      _msgSender() == owner || isApprovedForAll(owner, _msgSender()),
      "ERC721: approve caller is not owner nor approved for all"
    );

    // Clear approvals
    _approve(address(0), tokenId);

    // delete owners[tokenId];
    owners[tokenId] = address(0);
    burnedTokens++;

    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(ERC721.ownerOf(tokenId) == from, "ERC721: transfer of token that is not own");
    require(to != address(0), "ERC721: transfer to the zero address");

    // Clear approvals from the previous owner
    _approve(address(0), tokenId);

    owners[tokenId] = to;

    emit Transfer(from, to, tokenId);
  }

  /**
  * @dev Approve `to` to operate on `tokenId`
  *
    * Emits a {Approval} event.
    */
  function _approve(address to, uint256 tokenId) internal virtual {
    _tokenApprovals[tokenId] = to;
    emit Approval(ERC721.ownerOf(tokenId), to, tokenId);
  }

  /**
  * @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()) {
      try IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data) returns (bytes4 retval) {
        return retval == IERC721Receiver.onERC721Received.selector;
      } catch (bytes memory reason) {
        if (reason.length == 0) {
          revert("ERC721: transfer to non ERC721Receiver implementer");
        } else {
          assembly {
            revert(add(32, reason), mload(reason))
          }
        }
      }
    } else {
      return true;
    }
  }
}


// File: contracts/FroyoKittens.sol


pragma solidity ^0.8.6;





contract FroyoKittens is ERC721, Ownable {

  //---------------------------------------------------------------
  //  CONSTANTS
  //---------------------------------------------------------------
  uint256 public constant MAX_SUPPLY = 10000;
  uint256 public constant NFT_PRICE = 0.1 ether;
  uint256 public constant WHITELIST_PRICE = 0.1 ether;
  uint256 public mintStartTime;
  bool    public isRevealed;

  //---------------------------------------------------------------
  //  METADATA
  //---------------------------------------------------------------
  string public baseURI;
  string public coverURI;

  function tokenURI(uint256 id) public view virtual override returns (string memory) {
    require(_exists(id), "ERC721Metadata: URI query for nonexistent token");
    if(!isRevealed) {
      return coverURI;
    }

    return string(abi.encodePacked(baseURI, Strings.toString(id), ".json"));
  }

  //---------------------------------------------------------------
  //  CONSTRUCTOR
  //---------------------------------------------------------------

  constructor(string memory _coverURI) ERC721("FroyoKittens", "FroyoKitten") {
    coverURI = _coverURI;
    // Sunday, 10 April 2022 at 00:00 UTC
    mintStartTime = 1649563200;
  }

  function mint(uint256 amount) public payable {
    require(msg.value == (amount * NFT_PRICE), "WRONG_ETH_AMOUNT");
    require(owners.length + amount <= MAX_SUPPLY, "MAX_SUPPLY");
    require(block.timestamp >= mintStartTime, "NOT_LIVE");

    minters[msg.sender] += amount;
    require(minters[msg.sender] < 3, "ADDRESS_MAX_REACHED");
    for(uint256 i = 0; i < amount; i++) {
      _safeMint(msg.sender, owners.length);
    }
  }

  mapping (address => uint256) public minters;

  function burn(uint256 id) public {
    _burn(id);
  }

  //----------------------------------------------------------------
  //  WHITELISTS
  //----------------------------------------------------------------

  /// @dev - Merkle Tree root hash
  bytes32 public root;

  function setMerkleRoot(bytes32 merkleroot) public onlyOwner {
    root = merkleroot;
  }

  function premint(uint256 amount, bytes32[] calldata proof)
  external
  payable
  {
    address account = msg.sender;
    require(_verify(_leaf(account), proof), "INVALID_MERKLE_PROOF");
    require(msg.value == (amount * WHITELIST_PRICE), "WRONG_ETH_AMOUNT");
    require(owners.length + amount <= MAX_SUPPLY, "MAX_SUPPLY");

    minters[msg.sender] += amount;
    require(minters[account] < 3, "ADDRESS_MAX_REACHED");

    for(uint256 i = 0; i < amount; i++) {
      _safeMint(account, owners.length);
    }
  }

  function _leaf(address account)
  internal pure returns (bytes32)
  {
    return keccak256(abi.encodePacked(account));
  }

  function _verify(bytes32 leaf, bytes32[] memory proof)
  internal view returns (bool)
  {
    return MerkleProof.verify(proof, root, leaf);
  }

  //----------------------------------------------------------------
  //  ADMIN FUNCTIONS
  //----------------------------------------------------------------

  function setCoverURI(string memory uri) public onlyOwner {
    coverURI = uri;
  }
  function setBaseURI(string memory uri) public onlyOwner {
    baseURI = uri;
  }
  function setMintStartTime(uint256 _startTime) public onlyOwner {
    mintStartTime = _startTime;
  }
  function setIsRevealed(bool _isRevealed) public onlyOwner {
    isRevealed = _isRevealed;
  }

  //---------------------------------------------------------------
  // WITHDRAWAL
  //---------------------------------------------------------------

  function withdraw(address to, uint256 amount) public onlyOwner {
    (bool success,) = payable(to).call{ value: amount }("");
    require(success, "WITHDRAWAL_FAILED");
  }
}