Crypto stamp

/*
 * Crypto stamp 2
 * digital-physical collectible postage stamp
 *
 * Developed by Capacity Blockchain Solutions GmbH <capacity.at>
 * for Österreichische Post AG <post.at>
 */

// File: @openzeppelin/contracts/GSN/Context.sol

pragma solidity ^0.6.0;

/*
 * @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.
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }

    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: @openzeppelin/contracts/introspection/IERC165.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol

pragma solidity ^0.6.2;


/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transfered 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`, `to` cannot be zero.
     * - `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`, `to` cannot be zero.
     * - `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`, `to` cannot be zero.
      * - `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/IERC721Metadata.sol

pragma solidity ^0.6.2;


/**
 * @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/IERC721Enumerable.sol

pragma solidity ^0.6.2;


/**
 * @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: @openzeppelin/contracts/token/ERC721/IERC721Receiver.sol

pragma solidity ^0.6.0;

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
abstract contract IERC721Receiver {
    /**
     * @notice Handle the receipt of an NFT
     * @dev The ERC721 smart contract calls this function on the recipient
     * after a {IERC721-safeTransferFrom}. This function MUST return the function selector,
     * otherwise the caller will revert the transaction. The selector to be
     * returned can be obtained as `this.onERC721Received.selector`. This
     * function MAY throw to revert and reject the transfer.
     * Note: the ERC721 contract address is always the message sender.
     * @param operator The address which called `safeTransferFrom` function
     * @param from The address which previously owned the token
     * @param tokenId The NFT identifier which is being transferred
     * @param data Additional data with no specified format
     * @return bytes4 `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
     */
    function onERC721Received(address operator, address from, uint256 tokenId, bytes memory data)
    public virtual returns (bytes4);
}

// File: @openzeppelin/contracts/introspection/ERC165.sol

pragma solidity ^0.6.0;


/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
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 () internal {
        // 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: @openzeppelin/contracts/math/SafeMath.sol

pragma solidity ^0.6.0;

/**
 * @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) {
        // Solidity only automatically asserts when dividing by 0
        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: @openzeppelin/contracts/utils/Address.sol

pragma solidity ^0.6.2;

/**
 * @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");
    }
}

// File: @openzeppelin/contracts/utils/EnumerableSet.sol

pragma solidity ^0.6.0;

/**
 * @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: contracts/EnumerableRandomMapSimple.sol

pragma solidity ^0.6.0;

library EnumerableRandomMapSimple {
    // 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 Map {
        // Storage of map keys and values
        mapping(bytes32 => bytes32) _entries;
        uint256 _length;
    }

    /**
     * @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) {
        bool newVal;
        if (map._entries[key] == bytes32("")) { // add new entry
            map._length++;
            newVal = true;
        }
        else if (value == bytes32("")) { // remove entry
            map._length--;
            newVal = false;
        }
        else {
            newVal = false;
        }
        map._entries[key] = value;
        return newVal;
    }

    /**
     * @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 pure returns (bool) {
        revert("No removal supported");
    }

    /**
     * @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._entries[key] != bytes32("");
    }

    /**
     * @dev Returns the number of key-value pairs in the map. O(1).
     */
    function _length(Map storage map) private view returns (uint256) {
        return map._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) {
        bytes32 key = bytes32(index);
        require(_contains(map, key), "EnumerableMap: index out of bounds");
        return (key, map._entries[key]);
    }

    /**
     * @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) {
        require(_contains(map, key), errorMessage); // Equivalent to contains(map, key)
        return map._entries[key];
    }

    // 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 view 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: @openzeppelin/contracts/utils/Strings.sol

pragma solidity ^0.6.0;

/**
 * @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: contracts/OZ_Clone/ERC721_simplemaps.sol

pragma solidity ^0.6.0;

// Clone of OpenZeppelin 3.0.0 token/ERC721/ERC721.sol with just imports adapted and EnumerableMap exchanged for EnumerableMapSimple,
// and totalSupply() marked as virtual.












/**
 * @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 EnumerableRandomMapSimple for EnumerableRandomMapSimple.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
    EnumerableRandomMapSimple.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 ^ 0xe985e9c ^ 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;

    constructor (string memory name, string memory symbol) public {
        _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 Gets the balance of the specified address.
     * @param owner address to query the balance of
     * @return uint256 representing the amount owned by the passed address
     */
    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 Gets the owner of the specified token ID.
     * @param tokenId uint256 ID of the token to query the owner of
     * @return address currently marked as the owner of the given token ID
     */
    function ownerOf(uint256 tokenId) public view override returns (address) {
        return _tokenOwners.get(tokenId, "ERC721: owner query for nonexistent token");
    }

    /**
     * @dev Gets the token name.
     * @return string representing the token name
     */
    function name() public view override returns (string memory) {
        return _name;
    }

    /**
     * @dev Gets the token symbol.
     * @return string representing the token symbol
     */
    function symbol() public view override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the URI for a given token ID. May return an empty string.
     *
     * If a base URI is set (via {_setBaseURI}), it is added as a prefix to the
     * token's own URI (via {_setTokenURI}).
     *
     * If there is a base URI but no token URI, the token's ID will be used as
     * its URI when appending it to the base URI. This pattern for autogenerated
     * token URIs can lead to large gas savings.
     *
     * .Examples
     * |===
     * |`_setBaseURI()` |`_setTokenURI()` |`tokenURI()`
     * | ""
     * | ""
     * | ""
     * | ""
     * | "token.uri/123"
     * | "token.uri/123"
     * | "token.uri/"
     * | "123"
     * | "token.uri/123"
     * | "token.uri/"
     * | ""
     * | "token.uri/<tokenId>"
     * |===
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    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 Gets the token ID at a given index of the tokens list of the requested owner.
     * @param owner address owning the tokens list to be accessed
     * @param index uint256 representing the index to be accessed of the requested tokens list
     * @return uint256 token ID at the given index of the tokens list owned by the requested address
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) public view override returns (uint256) {
        return _holderTokens[owner].at(index);
    }

    /**
     * @dev Gets the total amount of tokens stored by the contract.
     * @return uint256 representing the total amount of tokens
     */
    function totalSupply() public view override virtual returns (uint256) {
        // _tokenOwners are indexed by tokenIds, so .length() returns the number of tokenIds
        return _tokenOwners.length();
    }

    /**
     * @dev Gets the token ID at a given index of all the tokens in this contract
     * Reverts if the index is greater or equal to the total number of tokens.
     * @param index uint256 representing the index to be accessed of the tokens list
     * @return uint256 token ID at the given index of the tokens list
     */
    function tokenByIndex(uint256 index) public view override returns (uint256) {
        (uint256 tokenId, ) = _tokenOwners.at(index);
        return tokenId;
    }

    /**
     * @dev Approves another address to transfer the given token ID
     * The zero address indicates there is no approved address.
     * There can only be one approved address per token at a given time.
     * Can only be called by the token owner or an approved operator.
     * @param to address to be approved for the given token ID
     * @param tokenId uint256 ID of the token to be approved
     */
    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 Gets the approved address for a token ID, or zero if no address set
     * Reverts if the token ID does not exist.
     * @param tokenId uint256 ID of the token to query the approval of
     * @return address currently approved for the given token ID
     */
    function getApproved(uint256 tokenId) public view override returns (address) {
        require(_exists(tokenId), "ERC721: approved query for nonexistent token");

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev Sets or unsets the approval of a given operator
     * An operator is allowed to transfer all tokens of the sender on their behalf.
     * @param operator operator address to set the approval
     * @param approved representing the status of the approval to be set
     */
    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 Tells whether an operator is approved by a given owner.
     * @param owner owner address which you want to query the approval of
     * @param operator operator address which you want to query the approval of
     * @return bool whether the given operator is approved by the given owner
     */
    function isApprovedForAll(address owner, address operator) public view override returns (bool) {
        return _operatorApprovals[owner][operator];
    }

    /**
     * @dev Transfers the ownership of a given token ID to another address.
     * Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     * Requires the msg.sender to be the owner, approved, or operator.
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     */
    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 Safely transfers the ownership of a given token ID to another address
     * If the target address is a contract, it must implement {IERC721Receiver-onERC721Received},
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * Requires the msg.sender to be the owner, approved, or operator
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     */
    function safeTransferFrom(address from, address to, uint256 tokenId) public virtual override {
        safeTransferFrom(from, to, tokenId, "");
    }

    /**
     * @dev Safely transfers the ownership of a given token ID to another address
     * If the target address is a contract, it must implement {IERC721Receiver-onERC721Received},
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * Requires the _msgSender() to be the owner, approved, or operator
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     * @param _data bytes data to send along with a safe transfer check
     */
    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 the ownership of a given token ID to another address
     * If the target address is a contract, it must implement `onERC721Received`,
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * Requires the msg.sender to be the owner, approved, or operator
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     * @param _data bytes data to send along with a safe transfer check
     */
    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 the specified token exists.
     * @param tokenId uint256 ID of the token to query the existence of
     * @return bool whether the token exists
     */
    function _exists(uint256 tokenId) internal view returns (bool) {
        return _tokenOwners.contains(tokenId);
    }

    /**
     * @dev Returns whether the given spender can transfer a given token ID.
     * @param spender address of the spender to query
     * @param tokenId uint256 ID of the token to be transferred
     * @return bool whether the msg.sender is approved for the given token ID,
     * is an operator of the owner, or is the owner of the token
     */
    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 Internal function to safely mint a new token.
     * Reverts if the given token ID already exists.
     * If the target address is a contract, it must implement `onERC721Received`,
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * @param to The address that will own the minted token
     * @param tokenId uint256 ID of the token to be minted
     */
    function _safeMint(address to, uint256 tokenId) internal virtual {
        _safeMint(to, tokenId, "");
    }

    /**
     * @dev Internal function to safely mint a new token.
     * Reverts if the given token ID already exists.
     * If the target address is a contract, it must implement `onERC721Received`,
     * which is called upon a safe transfer, and return the magic value
     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
     * the transfer is reverted.
     * @param to The address that will own the minted token
     * @param tokenId uint256 ID of the token to be minted
     * @param _data bytes data to send along with a safe transfer check
     */
    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 Internal function to mint a new token.
     * Reverts if the given token ID already exists.
     * @param to The address that will own the minted token
     * @param tokenId uint256 ID of the token to be minted
     */
    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 Internal function to burn a specific token.
     * Reverts if the token does not exist.
     * @param tokenId uint256 ID of the token being burned
     */
    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 Internal function to transfer ownership of a given token ID to another address.
     * As opposed to {transferFrom}, this imposes no restrictions on msg.sender.
     * @param from current owner of the token
     * @param to address to receive the ownership of the given token ID
     * @param tokenId uint256 ID of the token to be transferred
     */
    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 Internal function to set the token URI for a given token.
     *
     * Reverts if the token ID does not exist.
     *
     * TIP: If all token IDs share a prefix (for example, if your URIs look like
     * `https://api.myproject.com/token/<id>`), use {_setBaseURI} to store
     * it and save gas.
     */
    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;
        }
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = to.call(abi.encodeWithSelector(
            IERC721Receiver(to).onERC721Received.selector,
            _msgSender(),
            from,
            tokenId,
            _data
        ));
        if (!success) {
            if (returndata.length > 0) {
                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert("ERC721: transfer to non ERC721Receiver implementer");
            }
        } else {
            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` and `to` are never both zero.
     *
     * 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/ERC721SimpleMapsURI.sol

pragma solidity ^0.6.0;


/**
 * @title ERC721 With a nicer simple token URI
 * @dev see https://eips.ethereum.org/EIPS/eip-721
 */
contract ERC721SimpleMapsURI is ERC721 {

    // Similar to ERC1155 URI() event, but without a token ID.
    event BaseURI(string value);

    constructor (string memory name, string memory symbol, string memory baseURI)
    ERC721(name, symbol)
    public
    {
        _setBaseURI(baseURI);
    }

    /**
     * @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}.
     */
    function _setBaseURI(string memory baseURI_) internal override virtual {
        super._setBaseURI(baseURI_);
        emit BaseURI(baseURI());
    }

}

// File: contracts/CS1ColorsI.sol

/*
Color store interface for Crypto stamp 1
*/
pragma solidity ^0.6.0;

interface CS1ColorsI {

    enum Colors {
        Black,
        Green,
        Blue,
        Yellow,
        Red
    }

    // Returns the color of a given token ID
    function getColor(uint256 tokenId) external view returns (Colors);

}

// File: contracts/CS2PropertiesI.sol

/*
Interface for CS2 properties.
*/
pragma solidity ^0.6.0;

interface CS2PropertiesI {

    enum AssetType {
        Honeybadger,
        Llama,
        Panda,
        Doge
    }

    enum Colors {
        Black,
        Green,
        Blue,
        Yellow,
        Red
    }

    function getType(uint256 tokenId) external view returns (AssetType);
    function getColor(uint256 tokenId) external view returns (Colors);

}

// File: contracts/ENSReverseRegistrarI.sol

/*
 * Interfaces for ENS Reverse Registrar
 * See https://github.com/ensdomains/ens/blob/master/contracts/ReverseRegistrar.sol for full impl
 * Also see https://github.com/wealdtech/wealdtech-solidity/blob/master/contracts/ens/ENSReverseRegister.sol
 *
 * Use this as follows (registryAddress is the address of the ENS registry to use):
 * -----
 * // This hex value is caclulated by namehash('addr.reverse')
 * bytes32 public constant ENS_ADDR_REVERSE_NODE = 0x91d1777781884d03a6757a803996e38de2a42967fb37eeaca72729271025a9e2;
 * function registerReverseENS(address registryAddress, string memory calldata) external {
 *     require(registryAddress != address(0), "need a valid registry");
 *     address reverseRegistrarAddress = ENSRegistryOwnerI(registryAddress).owner(ENS_ADDR_REVERSE_NODE)
 *     require(reverseRegistrarAddress != address(0), "need a valid reverse registrar");
 *     ENSReverseRegistrarI(reverseRegistrarAddress).setName(name);
 * }
 * -----
 * or
 * -----
 * function registerReverseENS(address reverseRegistrarAddress, string memory calldata) external {
 *    require(reverseRegistrarAddress != address(0), "need a valid reverse registrar");
 *     ENSReverseRegistrarI(reverseRegistrarAddress).setName(name);
 * }
 * -----
 * ENS deployments can be found at https://docs.ens.domains/ens-deployments
 * E.g. Etherscan can be used to look up that owner on those contracts.
 * namehash.hash("addr.reverse") == "0x91d1777781884d03a6757a803996e38de2a42967fb37eeaca72729271025a9e2"
 * Ropsten: ens.owner(namehash.hash("addr.reverse")) == "0x6F628b68b30Dc3c17f345c9dbBb1E483c2b7aE5c"
 * Mainnet: ens.owner(namehash.hash("addr.reverse")) == "0x084b1c3C81545d370f3634392De611CaaBFf8148"
 */
pragma solidity ^0.6.0;

interface ENSRegistryOwnerI {
    function owner(bytes32 node) external view returns (address);
}

interface ENSReverseRegistrarI {
    function setName(string calldata name) external returns (bytes32 node);
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: contracts/AchievementsUpgradingI.sol

/*
Interface for CS2 color upgrading support by achievements.
*/
pragma solidity ^0.6.0;



interface AchievementsUpgradingI is IERC165 {
    /*
     *     Calculate the interface ID for ERC 165:
     *
     *     bytes4(keccak256('onContractAdded(bool)')) == 0x58cac597
     */

    /**
     * @notice Notify about changing a CS2 color as done by the "upgrading" mechanism
     * @dev The Cryptostamp2 smart contract calls this function when changing the color of any asset,
     * esp. as the result of upgrading. This function MUST return the function selector,
     * otherwise the caller will revert the transaction. The selector to be
     * returned can be obtained as `this.onCS2ColorChanged.selector`. This
     * function MAY throw to revert and reject the transfer.
     * Note: the Collection contract address is always the message sender.
     * @param tokenId The token identifier which is being changed
     * @param previousColor The previous color held by the token
     * @param newColor The new color assigned to the token, which MUST match the current color at time of this call
     * @return bytes4 `bytes4(keccak256("onCS2ColorChanged(uint256,uint8,uint8)"))`
     */
    function onCS2ColorChanged(uint256 tokenId, CS2PropertiesI.Colors previousColor, CS2PropertiesI.Colors newColor)
    external returns (bytes4);

}

// File: @openzeppelin/contracts/cryptography/ECDSA.sol

pragma solidity ^0.6.0;

/**
 * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.
 *
 * These functions can be used to verify that a message was signed by the holder
 * of the private keys of a given address.
 */
library ECDSA {
    /**
     * @dev Returns the address that signed a hashed message (`hash`) with
     * `signature`. This address can then be used for verification purposes.
     *
     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
     * this function rejects them by requiring the `s` value to be in the lower
     * half order, and the `v` value to be either 27 or 28.
     *
     * IMPORTANT: `hash` _must_ be the result of a hash operation for the
     * verification to be secure: it is possible to craft signatures that
     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
     * this is by receiving a hash of the original message (which may otherwise
     * be too long), and then calling {toEthSignedMessageHash} on it.
     */
    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
        // Check the signature length
        if (signature.length != 65) {
            revert("ECDSA: invalid signature length");
        }

        // Divide the signature in r, s and v variables
        bytes32 r;
        bytes32 s;
        uint8 v;

        // ecrecover takes the signature parameters, and the only way to get them
        // currently is to use assembly.
        // solhint-disable-next-line no-inline-assembly
        assembly {
            r := mload(add(signature, 0x20))
            s := mload(add(signature, 0x40))
            v := byte(0, mload(add(signature, 0x60)))
        }

        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
        // the valid range for s in (281): 0 < s < secp256k1n ÷ 2 + 1, and for v in (282): v ∈ {27, 28}. Most
        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
        //
        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
        // these malleable signatures as well.
        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
            revert("ECDSA: invalid signature 's' value");
        }

        if (v != 27 && v != 28) {
            revert("ECDSA: invalid signature 'v' value");
        }

        // If the signature is valid (and not malleable), return the signer address
        address signer = ecrecover(hash, v, r, s);
        require(signer != address(0), "ECDSA: invalid signature");

        return signer;
    }

    /**
     * @dev Returns an Ethereum Signed Message, created from a `hash`. This
     * replicates the behavior of the
     * https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign[`eth_sign`]
     * JSON-RPC method.
     *
     * See {recover}.
     */
    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
        // 32 is the length in bytes of hash,
        // enforced by the type signature above
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
    }
}

// File: @openzeppelin/contracts/cryptography/MerkleProof.sol

pragma solidity ^0.6.0;

/**
 * @dev These functions deal with verification of Merkle trees (hash trees),
 */
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) {
        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 = keccak256(abi.encodePacked(computedHash, proofElement));
            } else {
                // Hash(current element of the proof + current computed hash)
                computedHash = keccak256(abi.encodePacked(proofElement, computedHash));
            }
        }

        // Check if the computed hash (root) is equal to the provided root
        return computedHash == root;
    }
}

// File: contracts/Cryptostamp2.sol

/*
Implements ERC 721 Token standard: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
*/
pragma solidity ^0.6.0;









/* The inheritance is very much the same as OpenZeppelin's ERC721Full,
 * but using simplified (and cheaper) versions of ERC721Enumerable and ERC721Metadata */
contract Cryptostamp2 is ERC721SimpleMapsURI, CS2PropertiesI {
    using SafeMath for uint256;

    bytes4 private constant _INTERFACE_ID_ACHIEVEMENTS_UPGRADING = 0x58cac597;
    uint8 private constant COLORBITS = 4;
    uint8 private constant COLORMOD = uint8(2) ** COLORBITS;

    address public createControl;
    address public tokenAssignmentControl;
    address public CS1Address;
    address public CS1ColorsAddress;
    AchievementsUpgradingI public achievementsContract;

    uint256 immutable finalSupply;
    uint256 constant maxSupportedSupply = 2 ** 24;
    bool public allowPublicMinting = false;
    bytes32 public dataRoot;

    uint256 public upgradesDone = 0;
    uint256 public upgradeMaximum;

    uint8[maxSupportedSupply] private properties;
    uint256[5][4] public typeColorSupply; // Note that numbers are reversed in Solidity compared to other languages!
    mapping(uint256 => bool) public usedInUpgrade;
    mapping(uint256 => bool) public usedInUpgradeCS1;

    mapping(address => uint256) public signedTransferNonce;

    event CreateControlTransferred(address indexed previousCreateControl, address indexed newCreateControl);
    event TokenAssignmentControlTransferred(address indexed previousTokenAssignmentControl, address indexed newTokenAssignmentControl);
    event AchievementsContractSet(address indexed achievementsContractAddress);
    event UpgradeMaximumChanged(uint256 previousUpgradeMaximum, uint256 newUpgradeMaximum);
    event DataRootSet(bytes32 dataRoot);
    event PublicMintingEnabled();
    event PublicMintingDisabled();
    event MintedWithProof(address operator, uint256 indexed tokenId, address indexed owner, AssetType aType, Colors color);
    event SignedTransfer(address operator, address indexed from, address indexed to, uint256 indexed tokenId, uint256 signedTransferNonce);
    event StampUpgraded(uint256 indexed changedTokenId, Colors previousColor, Colors newColor, bool withJoker, uint256 usedTokedId1, uint256 usedTokenId2);
    // TestAchievementsUpgrading event - never emitted in this contract but helpful for running our tests.
    event SeenCS2ColorChanged(uint256 tokenId, Colors previousColor, Colors newColor);

    constructor(address _createControl, address _tokenAssignmentControl, address _CS1Address, address _CS1ColorsAddress, uint256 _finalSupply, uint256 _upgradeMaximum)
    ERC721SimpleMapsURI("Crypto stamp Edition 2", "CS2", "https://test.crypto.post.at/CS2/meta/")
    public
    {
        createControl = _createControl;
        require(address(createControl) != address(0x0), "You need to provide an actual createControl address.");
        tokenAssignmentControl = _tokenAssignmentControl;
        require(address(tokenAssignmentControl) != address(0x0), "You need to provide an actual tokenAssignmentControl address.");
        CS1ColorsAddress = _CS1ColorsAddress;
        require(address(CS1ColorsAddress) != address(0x0), "You need to provide an actual CS1 colors address.");
        CS1Address = _CS1Address;
        require(address(CS1Address) != address(0x0), "You need to provide an actual CS1 address.");
        finalSupply = _finalSupply;
        require(_finalSupply <= maxSupportedSupply, "The final supply is too high.");
        upgradeMaximum = _upgradeMaximum;
    }

    modifier onlyCreateControl()
    {
        require(msg.sender == createControl, "createControl key required for this function.");
        _;
    }

    modifier onlyTokenAssignmentControl() {
        require(msg.sender == tokenAssignmentControl, "tokenAssignmentControl key required for this function.");
        _;
    }

    modifier requireMinting() {
        require(mintingFinished() == false, "This call only works when minting is not finished.");
        _;
    }

    /*** Enable adjusting variables after deployment ***/

    function transferTokenAssignmentControl(address _newTokenAssignmentControl)
    public
    onlyTokenAssignmentControl
    {
        require(_newTokenAssignmentControl != address(0), "tokenAssignmentControl cannot be the zero address.");
        emit TokenAssignmentControlTransferred(tokenAssignmentControl, _newTokenAssignmentControl);
        tokenAssignmentControl = _newTokenAssignmentControl;
    }

    function transferCreateControl(address _newCreateControl)
    public
    onlyCreateControl
    {
        require(_newCreateControl != address(0), "createControl cannot be the zero address.");
        emit CreateControlTransferred(createControl, _newCreateControl);
        createControl = _newCreateControl;
    }

    // Set an achievements contract.
    function setAchievementsContract(address _achievementsAddress)
    public
    onlyCreateControl
    {
        achievementsContract = AchievementsUpgradingI(_achievementsAddress);
        emit AchievementsContractSet(_achievementsAddress);
        if (_achievementsAddress != address(0)) {
            require(IERC165(achievementsContract).supportsInterface(_INTERFACE_ID_ACHIEVEMENTS_UPGRADING),
                    "Need to implement the achievements upgrading interface!");
        }
    }

    function setUpgradeMaximum(uint256 _newUpgradeMaximum)
    public
    onlyCreateControl
    {
        require(upgradesDone <= _newUpgradeMaximum, "Already more upgrades done than the requested limit.");
        emit UpgradeMaximumChanged(upgradeMaximum, _newUpgradeMaximum);
        upgradeMaximum = _newUpgradeMaximum;
    }

    function setDataRoot(bytes32 _newDataRoot)
    public
    onlyCreateControl
    {
        require(dataRoot == bytes32(""), "Can only set root once.");
        emit DataRootSet(_newDataRoot);
        dataRoot = _newDataRoot;
    }

    /*** Base functionality: minting, URI, property getters, etc. ***/

    // Override totalSupply() so it reports the target final supply.
    /**
     * @dev Gets the total amount of tokens stored by the contract.
     * @return uint256 representing the total amount of tokens
     */
    function totalSupply()
    public view override
    returns (uint256) {
        return finalSupply;
    }

    /**
     * @dev Gets the actually minted amount of tokens in the contract.
     * @return uint256 representing the minted amount of tokens
     */
    function mintedSupply()
    public view
    returns (uint256) {
        return super.totalSupply();
    }

    // Issue a new crypto stamp asset, giving it to a specific owner address.
    // As appending the ID into a URI in Solidity is complicated, generate both
    // externally and hand them over to the asset here.
    function create(uint256 _tokenId, address _owner, AssetType _type, Colors _color)
    public
    onlyCreateControl
    requireMinting
    {
        // _mint already ends up checking if owner != 0 and that tokenId doesn't exist yet.
        _mintWithProperties(_tokenId, _owner, _type, _color);
    }

    // Batch-issue multiple crypto stamps with adjacent IDs.
    function createMulti(uint256 _tokenIdStart, address[] memory _owners, AssetType[] memory _types, Colors[] memory _colors)
    public
    onlyCreateControl
    requireMinting
    {
        require(_owners.length == _types.length && _owners.length == _colors.length, "All given arrays need to be the same length.");
        uint256 addrcount = _owners.length;
        for (uint256 i = 0; i < addrcount; i++) {
            // Make sure this is in sync with what create() does.
            _mintWithProperties(_tokenIdStart + i, _owners[i], _types[i], _colors[i]);
        }
    }

    // Issue a crypto stamp with a merkle proof.
    function createWithProof(bytes32 tokenData, bytes32[] memory merkleProof)
    public
    requireMinting
    returns (uint256)
    {
        require(publicMintingAllowed(), "Public minting needs to be allowed.");
        (uint256 tokenId, address owner, AssetType aType, Colors color) = getDataFieldsFromProof(tokenData, merkleProof);
        require(!_exists(tokenId), "Token already exists.");
        emit MintedWithProof(msg.sender, tokenId, owner, aType, color);
        _mintWithProperties(tokenId, owner, aType, color);
        return tokenId;
    }

    /**
     * @dev Gets the token ID of the specified token ID
     * @param tokenData bytes32 token data : 11 bytes TokenId | 1 byte properties split in 4 bits + 4 bits | 20 bytes owner
     * @param merkleProof bytes32[] memory array of a storage proof
     * @return address currently marked as the owner of the given token ID, if manifested explicitly or if the proof matches
     */
    function getTokenIdFromProof(bytes32 tokenData, bytes32[] memory merkleProof)
    public view
    returns (uint256) {
        (uint256 tokenId, /*address owner*/, /*AssetType aType*/, /*Colors color*/) = getDataFieldsFromProof(tokenData, merkleProof);
        return tokenId;
    }

    /**
     * @dev Gets the owner of the specified token ID
     * @param tokenData bytes32 token data : 11 bytes TokenId | 1 byte properties split in 4 bits + 4 bits | 20 bytes owner
     * @param merkleProof bytes32[] memory array of a storage proof
     * @return address currently marked as the owner of the given token ID, if manifested explicitly or if the proof matches
     */
    function getOwnerFromProof(bytes32 tokenData, bytes32[] memory merkleProof)
    public view
    returns (address) {
        (uint256 tokenId, address owner, /*AssetType aType*/, /*Colors color*/) = getDataFieldsFromProof(tokenData, merkleProof);
        if (_exists(tokenId)) return ownerOf(tokenId);
        return owner;
    }

    /**
     * @dev Gets the owner of the specified token ID
     * @param tokenData bytes32 token data : 11 bytes TokenId | 1 byte properties split in 4 bits + 4 bits | 20 bytes owner
     * @param merkleProof bytes32[] memory array of a storage proof
     * @return AssetType of the given token.
     */
    function getTypeFromProof(bytes32 tokenData, bytes32[] memory merkleProof)
    public view
    returns (AssetType) {
        (uint256 tokenId, /*address owner*/, AssetType aType, /*Colors color*/) = getDataFieldsFromProof(tokenData, merkleProof);
        if (_exists(tokenId)) return getType(tokenId);
        return aType;
    }

    /**
     * @dev Gets the color of the specified token ID even if not manifested yet.
     * @param tokenData bytes32 token data : 11 bytes TokenId | 1 byte properties split in 4 bits + 4 bits | 20 bytes owner
     * @param merkleProof  bytes32[] memory array of a storage proof
     * @return color of the given token.
     */
    function getColorFromProof(bytes32 tokenData, bytes32[] memory merkleProof)
    public view
    returns (Colors) {
        (uint256 tokenId, /*address owner*/, /*AssetType aType*/, Colors color) = getDataFieldsFromProof(tokenData, merkleProof);
        if (_exists(tokenId)) return getColor(tokenId);
        return color;
    }

    /**
     * @dev Gets the tokenId, owner, type and color from the specified token proof.
     * @param tokenData bytes32 token data : 11 bytes TokenId | 1 byte properties split in 4 bits + 4 bits | 20 bytes owner
     * @param merkleProof  bytes32[] memory array of a storage proof
     * @return tokenId, owner, type and color of the given token.
     */
    function getDataFieldsFromProof(bytes32 tokenData, bytes32[] memory merkleProof)
    public view
    returns (uint256, address, AssetType, Colors)
    {
        require(dataRoot != bytes32(""), "Root needs to be set.");
        require(MerkleProof.verify(merkleProof, dataRoot, tokenData), "Verification failed.");
        uint256 tokenId = uint256(tokenData >> 168); // shift by 20 bytes for address and 1 byte for properties
        AssetType aType = AssetType(uint8(tokenData[11]) >> COLORBITS);
        Colors color = Colors(uint8(tokenData[11]) % COLORMOD);
        address owner = address(uint256(tokenData)); // address() cuts off everything except the lower 160 bits
        require(owner != address(0), "tokenData needs to contain an owner.");
        return (tokenId, owner, aType, color);
    }

    // Actually issue a crypto stamp with its properties, or just check the properties if it already exists.
    function _mintWithProperties(uint256 _tokenId, address _owner, AssetType _type, Colors _color)
    internal
    {
        if (_exists(_tokenId)) {
            require(getType(_tokenId) == _type, "Type mismatch with existing token.");
            if (upgradesDone == 0) {
                // Once any upgrades have been done, we don't know if the minted color is still set necessarily.
                require(getColor(_tokenId) == _color, "Color mismatch with existing token.");
            }
        }
        else {
            _mint(_owner, _tokenId);
            // Store the type in the higher bits of the unit and the color in the lower bits.
            properties[_tokenId] = uint8(_type) * COLORMOD + uint8(_color);
            typeColorSupply[uint(_type)][uint(_color)] = typeColorSupply[uint(_type)][uint(_color)].add(1);
        }
    }

    // Determine if the creation/minting process is done.
    function mintingFinished()
    public view
    returns (bool)
    {
        return (super.totalSupply() >= finalSupply);
    }

    // Allow creation/minting by anyone who can show a valid merkle proof.
    function enablePublicMinting()
    public
    onlyCreateControl
    {
        require(dataRoot != bytes32(""), "Root needs to be set.");
        allowPublicMinting = true;
        emit PublicMintingEnabled();
    }

    // deactive public creation/minting.
    function disablePublicMinting()
    public
    onlyCreateControl
    {
        allowPublicMinting = false;
        emit PublicMintingDisabled();
    }

    // Determine if the creation/minting process is done.
    function publicMintingAllowed()
    public view
    returns (bool)
    {
        return (!mintingFinished() && allowPublicMinting);
    }

    // Set new base for the token URI.
    function setBaseURI(string memory _newBaseURI)
    public
    onlyCreateControl
    {
        super._setBaseURI(_newBaseURI);
    }

    // Get type of the given token.
    function getType(uint256 tokenId)
    public view override
    returns (AssetType) {
        require(_exists(tokenId), "Token ID needs to exist.");
        return AssetType(properties[tokenId] >> COLORBITS);
    }

    // Get color of the given token.
    function getColor(uint256 tokenId)
    public view override
    returns (Colors) {
        require(_exists(tokenId), "Token ID needs to exist.");
        return Colors(properties[tokenId] % COLORMOD);
    }

    // Returns whether the specified token exists
    function exists(uint256 tokenId)
    public view
    returns (bool) {
        return _exists(tokenId);
    }


    function typeSupply(AssetType _type)
    public view
    returns (uint256) {
        uint256 thisTypeSupply = 0;
        for (uint256 i = 0; i < typeColorSupply[uint(_type)].length; i++) {
          thisTypeSupply = thisTypeSupply.add(typeColorSupply[uint(_type)][i]);
        }
        return thisTypeSupply;
    }


    function colorSupply(Colors _color)
    public view
    returns (uint256) {
        uint256 thisColorSupply = 0;
        for (uint256 i = 0; i < typeColorSupply.length; i++) {
          thisColorSupply = thisColorSupply.add(typeColorSupply[i][uint(_color)]);
        }
        return thisColorSupply;
    }

    /*** Allows any user to initiate a transfer with the signature of the current stamp owner  ***/

    // Outward-facing function for signed transfer: assembles the expected data and then calls the internal function to do the rest.
    // Can called by anyone knowing about the right signature, but can only transfer to the given specific target.
    function signedTransfer(uint256 _tokenId, address _to, bytes memory _signature)
    public
    {
        address currentOwner = ownerOf(_tokenId);
        // The signed data contains the token ID, the transfer target and a nonce.
        bytes32 data = keccak256(abi.encodePacked(address(this), this.signedTransfer.selector, currentOwner, _to, _tokenId, signedTransferNonce[currentOwner]));
        _signedTransferInternal(currentOwner, data, _tokenId, _to, _signature);
    }

    // Outward-facing function for operator-driven signed transfer: assembles the expected data and then calls the internal function to do the rest.
    // Can transfer to any target, but only be called by the trusted operator contained in the signature.
    function signedTransferWithOperator(uint256 _tokenId, address _to, bytes memory _signature)
    public
    {
        address currentOwner = ownerOf(_tokenId);
        // The signed data contains the operator, the token ID, and a nonce. Note that we use the selector of the external function here!
        bytes32 data = keccak256(abi.encodePacked(address(this), this.signedTransferWithOperator.selector, msg.sender, currentOwner, _tokenId, signedTransferNonce[currentOwner]));
        _signedTransferInternal(currentOwner, data, _tokenId, _to, _signature);
    }

    // Actually check the signature and perform a signed transfer.
    function _signedTransferInternal(address _currentOwner, bytes32 _data, uint256 _tokenId, address _to, bytes memory _signature)
    internal
    {
        bytes32 hash = ECDSA.toEthSignedMessageHash(_data);
        address signer = ECDSA.recover(hash, _signature);
        require(signer == _currentOwner, "Signature needs to match parameters, nonce, and current owner.");
        // Now that we checked that the signature is correct, do the actual transfer and increase the nonce.
        emit SignedTransfer(msg.sender, _currentOwner, _to, _tokenId, signedTransferNonce[_currentOwner]);
        signedTransferNonce[_currentOwner] = signedTransferNonce[_currentOwner].add(1);
        _safeTransfer(_currentOwner, _to, _tokenId, "");
    }

    // Mint token and transfer it in the same transaction.
    // Can called by anyone knowing about the right signature (and proof), but can only transfer to the given specific target.
    function signedTransferWithMintProof(bytes32 tokenData, address _to, bytes calldata _signature, bytes32[] calldata merkleProof)
    external
    {
        uint256 tokenId = createWithProof(tokenData, merkleProof);
        signedTransfer(tokenId, _to, _signature);
    }

    // Mint token and transfer it in the same transaction.
    // Can transfer to any target, but only be called by the trusted operator contained in the signature.
    function signedTransferWithOperatorAndMintProof(bytes32 tokenData, address _to, bytes calldata _signature, bytes32[] calldata merkleProof)
    external
    {
        uint256 tokenId = createWithProof(tokenData, merkleProof);
        signedTransferWithOperator(tokenId, _to, _signature);
    }

    /*** Upgrading functionality: upgrade color of the stamp using other stamps of the same color ***/

    // Returns whether upgrading is possible at this time.
    function upgradesAllowed() public view returns (bool) {
        return (address(achievementsContract) != address(0) && upgradesDone < upgradeMaximum);
    }

    // Upgrade 1 CS2 stamp by "upgrading" with 2 other CS2 of same type and color.
    function upgradeStamp(uint256 _upgradeTokenId, uint256 _helperTokenId1, uint256 _helperTokenId2)
    public
    {
        require(address(achievementsContract) != address(0), "No achievements contract set");
        require(upgradesDone < upgradeMaximum, "Maximum upgrades reached");
        require(_upgradeTokenId != _helperTokenId1 &&
                _upgradeTokenId != _helperTokenId2 &&
                _helperTokenId1 != _helperTokenId2,
                "You actually need to use 3 different tokens to upgrade");
        require(msg.sender == ownerOf(_upgradeTokenId) &&
                msg.sender == ownerOf(_helperTokenId1) &&
                msg.sender == ownerOf(_helperTokenId2),
                "Caller has to be owner of all tokens.");
        require(usedInUpgrade[_upgradeTokenId] == false &&
                usedInUpgrade[_helperTokenId1] == false &&
                usedInUpgrade[_helperTokenId2] == false,
                "Cannot used stamps already used in a upgrade.");
        Colors previousColor = getColor(_upgradeTokenId);
        AssetType aType = getType(_upgradeTokenId);
        require(getType(_helperTokenId1) == aType && getColor(_helperTokenId1) == previousColor &&
                getType(_helperTokenId2) == aType && getColor(_helperTokenId2) == previousColor,
                "All tokens involved must have the same type and color");
        usedInUpgrade[_helperTokenId1] = true;
        usedInUpgrade[_helperTokenId2] = true;
        // Now, actually upgrade the color and notify the achievements contract.
        Colors newColor = _upgradeColor(_upgradeTokenId, aType, previousColor);
        emit StampUpgraded(_upgradeTokenId, previousColor, newColor, false, _helperTokenId1, _helperTokenId2);
    }

    // Upgrade 1 CS2 stamp by "upgrading" with 1 other CS2 of same type and color and 1 CS1 of same color (as a "joker").
    function upgradeStampWithJoker(uint256 _upgradeTokenId, uint256 _helperTokenId, uint256 _helperCS1TokenId)
    public
    {
        require(address(achievementsContract) != address(0), "No achievements contract set");
        require(upgradesDone < upgradeMaximum, "Maximum upgrades reached");
        require(_upgradeTokenId != _helperTokenId, "You actually need to use different tokens to upgrade");
        IERC721 CS1 = IERC721(CS1Address);
        CS1ColorsI CS1Colors = CS1ColorsI(CS1ColorsAddress);
        require(msg.sender == ownerOf(_upgradeTokenId) &&
                msg.sender == ownerOf(_helperTokenId) &&
                msg.sender == CS1.ownerOf(_helperCS1TokenId),
                "Caller has to be owner of all tokens.");
        require(usedInUpgrade[_upgradeTokenId] == false &&
                usedInUpgrade[_helperTokenId] == false &&
                usedInUpgradeCS1[_helperCS1TokenId] == false,
                "Cannot used stamps already used in a upgrade.");
        Colors previousColor = getColor(_upgradeTokenId);
        AssetType aType = getType(_upgradeTokenId);
        // Note: The second line below ONLY works because the Colors enums are the same on both contracts!
        require(getType(_helperTokenId) == aType && getColor(_helperTokenId) == previousColor &&
                CS1Colors.getColor(_helperCS1TokenId) == CS1ColorsI.Colors(uint8(previousColor)),
                "All tokens involved must have the same color, and all CS2 tokens the same type");
        usedInUpgrade[_helperTokenId] = true;
        usedInUpgradeCS1[_helperCS1TokenId] = true;
        // Now, actually upgrade the color and notify the achievements contract.
        Colors newColor = _upgradeColor(_upgradeTokenId, aType, previousColor);
        emit StampUpgraded(_upgradeTokenId, previousColor, newColor, true, _helperTokenId, _helperCS1TokenId);
    }

    function _upgradeColor(uint256 _upgradeTokenId, AssetType _assetType, Colors _previousColor)
    private
    returns(Colors)
    {
        Colors newColor = Colors(uint256(_previousColor).add(1));
        properties[_upgradeTokenId] = uint8(_assetType) * COLORMOD + uint8(newColor);
        typeColorSupply[uint(_assetType)][uint(_previousColor)] = typeColorSupply[uint(_assetType)][uint(_previousColor)].sub(1);
        typeColorSupply[uint(_assetType)][uint(newColor)] = typeColorSupply[uint(_assetType)][uint(newColor)].add(1);
        upgradesDone = upgradesDone.add(1);
        require(
            achievementsContract.onCS2ColorChanged(_upgradeTokenId, _previousColor, newColor) ==
                achievementsContract.onCS2ColorChanged.selector,
            "Achievements upgrading: got unknown value from onCS2ColorChanged"
        );
        return newColor;
    }

    /*** Enable reverse ENS registration ***/

    // Call this with the address of the reverse registrar for the respecitve network and the ENS name to register.
    // The reverse registrar can be found as the owner of 'addr.reverse' in the ENS system.
    // See https://docs.ens.domains/ens-deployments for address of ENS deployments, e.g. Etherscan can be used to look up that owner on those.
    // namehash.hash("addr.reverse") == "0x91d1777781884d03a6757a803996e38de2a42967fb37eeaca72729271025a9e2"
    // Ropsten: ens.owner(namehash.hash("addr.reverse")) == "0x6F628b68b30Dc3c17f345c9dbBb1E483c2b7aE5c"
    // Mainnet: ens.owner(namehash.hash("addr.reverse")) == "0x084b1c3C81545d370f3634392De611CaaBFf8148"
    function registerReverseENS(address _reverseRegistrarAddress, string calldata _name)
    external
    onlyTokenAssignmentControl
    {
       require(_reverseRegistrarAddress != address(0), "need a valid reverse registrar");
       ENSReverseRegistrarI(_reverseRegistrarAddress).setName(_name);
    }

    /*** Make sure currency doesn't get stranded in this contract ***/

    // If this contract gets a balance in some ERC20 contract after it's finished, then we can rescue it.
    function rescueToken(IERC20 _foreignToken, address _to)
    external
    onlyTokenAssignmentControl
    {
        _foreignToken.transfer(_to, _foreignToken.balanceOf(address(this)));
    }

    // If this contract gets a balance in some ERC721 contract after it's finished, then we can rescue it.
    function approveNFTrescue(IERC721 _foreignNFT, address _to)
    external
    onlyTokenAssignmentControl
    {
        _foreignNFT.setApprovalForAll(_to, true);
    }

    // Make sure this contract cannot receive ETH.
    receive()
    external payable
    {
        revert("The contract cannot receive ETH payments.");
    }
}

{
  "compilationTarget": {
    "Cryptostamp2.sol": "Cryptostamp2"
  },
  "evmVersion": "istanbul",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}