arrange erc721 && erc1155

contracts/external/utils/Address.sol

@@ -0,0 +1,190 @@
+// This is a file copied from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Address.sol
+// SPDX-License-Identifier: MIT
+
+pragma solidity 0.6.9;
+
+/**
+ * @dev Collection of functions related to the address type
+ */
+library Address {
+    /**
+     * @dev Returns true if `account` is a contract.
+     *
+     * [IMPORTANT]
+     * ====
+     * It is unsafe to assume that an address for which this function returns
+     * false is an externally-owned account (EOA) and not a contract.
+     *
+     * Among others, `isContract` will return false for the following
+     * types of addresses:
+     *
+     *  - an externally-owned account
+     *  - a contract in construction
+     *  - an address where a contract will be created
+     *  - an address where a contract lived, but was destroyed
+     * ====
+     */
+    function isContract(address account) internal view returns (bool) {
+        // This method relies on extcodesize, which returns 0 for contracts in
+        // construction, since the code is only stored at the end of the
+        // constructor execution.
+
+        uint256 size;
+        // solhint-disable-next-line no-inline-assembly
+        assembly { size := extcodesize(account) }
+        return size > 0;
+    }
+
+    /**
+     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
+     * `recipient`, forwarding all available gas and reverting on errors.
+     *
+     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
+     * of certain opcodes, possibly making contracts go over the 2300 gas limit
+     * imposed by `transfer`, making them unable to receive funds via
+     * `transfer`. {sendValue} removes this limitation.
+     *
+     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
+     *
+     * IMPORTANT: because control is transferred to `recipient`, care must be
+     * taken to not create reentrancy vulnerabilities. Consider using
+     * {ReentrancyGuard} or the
+     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
+     */
+    function sendValue(address payable recipient, uint256 amount) internal {
+        require(address(this).balance >= amount, "Address: insufficient balance");
+
+        // 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");
+        require(isContract(target), "Address: call to non-contract");
+
+        // solhint-disable-next-line avoid-low-level-calls
+        (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");
+
+        // solhint-disable-next-line avoid-low-level-calls
+        (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");
+
+        // solhint-disable-next-line avoid-low-level-calls
+        (bool success, bytes memory returndata) = target.delegatecall(data);
+        return _verifyCallResult(success, returndata, errorMessage);
+    }
+
+    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
+        if (success) {
+            return returndata;
+        } else {
+            // Look for revert reason and bubble it up if present
+            if (returndata.length > 0) {
+                // The easiest way to bubble the revert reason is using memory via assembly
+
+                // solhint-disable-next-line no-inline-assembly
+                assembly {
+                    let returndata_size := mload(returndata)
+                    revert(add(32, returndata), returndata_size)
+                }
+            } else {
+                revert(errorMessage);
+            }
+        }
+    }
+}

contracts/external/utils/Context.sol

@@ -0,0 +1,25 @@
+// This is a file copied from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Context.sol
+// SPDX-License-Identifier: MIT
+
+pragma solidity 0.6.9;
+
+/*
+ * @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) {
+        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
+        return msg.data;
+    }
+}

contracts/external/utils/ERC165.sol

@@ -0,0 +1,29 @@
+// This is a file copied from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/introspection/ERC165.sol
+// SPDX-License-Identifier: MIT
+
+pragma solidity 0.6.9;
+
+import "./IERC165.sol";
+
+/**
+ * @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;
+    }
+}

contracts/external/utils/IERC165.sol

@@ -0,0 +1,25 @@
+// This is a file copied from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.6/contracts/introspection/IERC165.sol
+// SPDX-License-Identifier: MIT
+
+pragma solidity 0.6.9;
+
+/**
+ * @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);
+}

contracts/external/utils/Strings.sol

@@ -0,0 +1,68 @@
+// This is a file copied from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Strings.sol
+// SPDX-License-Identifier: MIT
+
+pragma solidity 0.6.9;
+
+/**
+ * @dev String operations.
+ */
+library Strings {
+    bytes16 private constant alphabet = "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] = alphabet[value & 0xf];
+            value >>= 4;
+        }
+        require(value == 0, "Strings: hex length insufficient");
+        return string(buffer);
+    }
+
+}