pragma solidity ^0.4.24;



library ECRecovery {

  
  function recover(bytes32 hash, bytes sig)
    internal
    pure
    returns (address)
  {
    bytes32 r;
    bytes32 s;
    uint8 v;

   
    if (sig.length != 65) {
      return (address(0));
    }

   
   
   
   
    assembly {
      r := mload(add(sig, 32))
      s := mload(add(sig, 64))
      v := byte(0, mload(add(sig, 96)))
    }

   
    if (v < 27) {
      v += 27;
    }

   
    if (v != 27 && v != 28) {
      return (address(0));
    } else {
     
      return ecrecover(toEthSignedMessageHash(hash), v, r, s);
    }
  }

  
  function toEthSignedMessageHash(bytes32 hash)
    internal
    pure
    returns (bytes32)
  {
   
   
    return keccak256(
      abi.encodePacked("\x19Ethereum Signed Message:\n32", hash)
    );
  }
}


contract Ownable {
  address public owner;


  event OwnershipRenounced(address indexed previousOwner);
  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );


  
  constructor() public {
    owner = msg.sender;
  }

  
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  
  function renounceOwnership() public onlyOwner {
    emit OwnershipRenounced(owner);
    owner = address(0);
  }

  
  function transferOwnership(address _newOwner) public onlyOwner {
    _transferOwnership(_newOwner);
  }

  
  function _transferOwnership(address _newOwner) internal {
    require(_newOwner != address(0));
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
  }
}


interface ERC165 {

  
  function supportsInterface(bytes4 _interfaceId)
    external
    view
    returns (bool);
}


contract SupportsInterfaceWithLookup is ERC165 {
  bytes4 public constant InterfaceId_ERC165 = 0x01ffc9a7;
  

  
  mapping(bytes4 => bool) internal supportedInterfaces;

  
  constructor()
    public
  {
    _registerInterface(InterfaceId_ERC165);
  }

  
  function supportsInterface(bytes4 _interfaceId)
    external
    view
    returns (bool)
  {
    return supportedInterfaces[_interfaceId];
  }

  
  function _registerInterface(bytes4 _interfaceId)
    internal
  {
    require(_interfaceId != 0xffffffff);
    supportedInterfaces[_interfaceId] = true;
  }
}


contract ERC721Basic is ERC165 {
  event Transfer(
    address indexed _from,
    address indexed _to,
    uint256 indexed _tokenId
  );
  event Approval(
    address indexed _owner,
    address indexed _approved,
    uint256 indexed _tokenId
  );
  event ApprovalForAll(
    address indexed _owner,
    address indexed _operator,
    bool _approved
  );

  function balanceOf(address _owner) public view returns (uint256 _balance);
  function ownerOf(uint256 _tokenId) public view returns (address _owner);
  function exists(uint256 _tokenId) public view returns (bool _exists);

  function approve(address _to, uint256 _tokenId) public;
  function getApproved(uint256 _tokenId)
    public view returns (address _operator);

  function setApprovalForAll(address _operator, bool _approved) public;
  function isApprovedForAll(address _owner, address _operator)
    public view returns (bool);

  function transferFrom(address _from, address _to, uint256 _tokenId) public;
  function safeTransferFrom(address _from, address _to, uint256 _tokenId)
    public;

  function safeTransferFrom(
    address _from,
    address _to,
    uint256 _tokenId,
    bytes _data
  )
    public;
}


contract ERC721Enumerable is ERC721Basic {
  function totalSupply() public view returns (uint256);
  function tokenOfOwnerByIndex(
    address _owner,
    uint256 _index
  )
    public
    view
    returns (uint256 _tokenId);

  function tokenByIndex(uint256 _index) public view returns (uint256);
}



contract ERC721Metadata is ERC721Basic {
  function name() external view returns (string _name);
  function symbol() external view returns (string _symbol);
  function tokenURI(uint256 _tokenId) public view returns (string);
}



contract ERC721 is ERC721Basic, ERC721Enumerable, ERC721Metadata {
}


library AddressUtils {

  
  function isContract(address addr) internal view returns (bool) {
    uint256 size;
   
   
   
   
   
   
   
    assembly { size := extcodesize(addr) }
    return size > 0;
  }

}


library SafeMath {

  
  function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
   
   
   
    if (a == 0) {
      return 0;
    }

    c = a * b;
    assert(c / a == b);
    return c;
  }

  
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
   
   
   
    return a / b;
  }

  
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  
  function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
    c = a + b;
    assert(c >= a);
    return c;
  }
}


contract ERC721Receiver {
  
  bytes4 internal constant ERC721_RECEIVED = 0xf0b9e5ba;

  
  function onERC721Received(
    address _from,
    uint256 _tokenId,
    bytes _data
  )
    public
    returns(bytes4);
}


contract ERC721BasicToken is SupportsInterfaceWithLookup, ERC721Basic {

  bytes4 private constant InterfaceId_ERC721 = 0x80ac58cd;
  

  bytes4 private constant InterfaceId_ERC721Exists = 0x4f558e79;
  

  using SafeMath for uint256;
  using AddressUtils for address;

 
 
  bytes4 private constant ERC721_RECEIVED = 0xf0b9e5ba;

 
  mapping (uint256 => address) internal tokenOwner;

 
  mapping (uint256 => address) internal tokenApprovals;

 
  mapping (address => uint256) internal ownedTokensCount;

 
  mapping (address => mapping (address => bool)) internal operatorApprovals;

  
  modifier onlyOwnerOf(uint256 _tokenId) {
    require(ownerOf(_tokenId) == msg.sender);
    _;
  }

  
  modifier canTransfer(uint256 _tokenId) {
    require(isApprovedOrOwner(msg.sender, _tokenId));
    _;
  }

  constructor()
    public
  {
   
    _registerInterface(InterfaceId_ERC721);
    _registerInterface(InterfaceId_ERC721Exists);
  }

  
  function balanceOf(address _owner) public view returns (uint256) {
    require(_owner != address(0));
    return ownedTokensCount[_owner];
  }

  
  function ownerOf(uint256 _tokenId) public view returns (address) {
    address owner = tokenOwner[_tokenId];
    require(owner != address(0));
    return owner;
  }

  
  function exists(uint256 _tokenId) public view returns (bool) {
    address owner = tokenOwner[_tokenId];
    return owner != address(0);
  }

  
  function approve(address _to, uint256 _tokenId) public {
    address owner = ownerOf(_tokenId);
    require(_to != owner);
    require(msg.sender == owner || isApprovedForAll(owner, msg.sender));

    tokenApprovals[_tokenId] = _to;
    emit Approval(owner, _to, _tokenId);
  }

  
  function getApproved(uint256 _tokenId) public view returns (address) {
    return tokenApprovals[_tokenId];
  }

  
  function setApprovalForAll(address _to, bool _approved) public {
    require(_to != msg.sender);
    operatorApprovals[msg.sender][_to] = _approved;
    emit ApprovalForAll(msg.sender, _to, _approved);
  }

  
  function isApprovedForAll(
    address _owner,
    address _operator
  )
    public
    view
    returns (bool)
  {
    return operatorApprovals[_owner][_operator];
  }

  
  function transferFrom(
    address _from,
    address _to,
    uint256 _tokenId
  )
    public
    canTransfer(_tokenId)
  {
    require(_from != address(0));
    require(_to != address(0));

    clearApproval(_from, _tokenId);
    removeTokenFrom(_from, _tokenId);
    addTokenTo(_to, _tokenId);

    emit Transfer(_from, _to, _tokenId);
  }

  
  function safeTransferFrom(
    address _from,
    address _to,
    uint256 _tokenId
  )
    public
    canTransfer(_tokenId)
  {
   
    safeTransferFrom(_from, _to, _tokenId, "");
  }

  
  function safeTransferFrom(
    address _from,
    address _to,
    uint256 _tokenId,
    bytes _data
  )
    public
    canTransfer(_tokenId)
  {
    transferFrom(_from, _to, _tokenId);
   
    require(checkAndCallSafeTransfer(_from, _to, _tokenId, _data));
  }

  
  function isApprovedOrOwner(
    address _spender,
    uint256 _tokenId
  )
    internal
    view
    returns (bool)
  {
    address owner = ownerOf(_tokenId);
   
   
   
    return (
      _spender == owner ||
      getApproved(_tokenId) == _spender ||
      isApprovedForAll(owner, _spender)
    );
  }

  
  function _mint(address _to, uint256 _tokenId) internal {
    require(_to != address(0));
    addTokenTo(_to, _tokenId);
    emit Transfer(address(0), _to, _tokenId);
  }

  
  function _burn(address _owner, uint256 _tokenId) internal {
    clearApproval(_owner, _tokenId);
    removeTokenFrom(_owner, _tokenId);
    emit Transfer(_owner, address(0), _tokenId);
  }

  
  function clearApproval(address _owner, uint256 _tokenId) internal {
    require(ownerOf(_tokenId) == _owner);
    if (tokenApprovals[_tokenId] != address(0)) {
      tokenApprovals[_tokenId] = address(0);
      emit Approval(_owner, address(0), _tokenId);
    }
  }

  
  function addTokenTo(address _to, uint256 _tokenId) internal {
    require(tokenOwner[_tokenId] == address(0));
    tokenOwner[_tokenId] = _to;
    ownedTokensCount[_to] = ownedTokensCount[_to].add(1);
  }

  
  function removeTokenFrom(address _from, uint256 _tokenId) internal {
    require(ownerOf(_tokenId) == _from);
    ownedTokensCount[_from] = ownedTokensCount[_from].sub(1);
    tokenOwner[_tokenId] = address(0);
  }

  
  function checkAndCallSafeTransfer(
    address _from,
    address _to,
    uint256 _tokenId,
    bytes _data
  )
    internal
    returns (bool)
  {
    if (!_to.isContract()) {
      return true;
    }
    bytes4 retval = ERC721Receiver(_to).onERC721Received(
      _from, _tokenId, _data);
    return (retval == ERC721_RECEIVED);
  }
}


contract ERC721Token is SupportsInterfaceWithLookup, ERC721BasicToken, ERC721 {

  bytes4 private constant InterfaceId_ERC721Enumerable = 0x780e9d63;
  

  bytes4 private constant InterfaceId_ERC721Metadata = 0x5b5e139f;
  

 
  string internal name_;

 
  string internal symbol_;

 
  mapping(address => uint256[]) internal ownedTokens;

 
  mapping(uint256 => uint256) internal ownedTokensIndex;

 
  uint256[] internal allTokens;

 
  mapping(uint256 => uint256) internal allTokensIndex;

 
  mapping(uint256 => string) internal tokenURIs;

  
  constructor(string _name, string _symbol) public {
    name_ = _name;
    symbol_ = _symbol;

   
    _registerInterface(InterfaceId_ERC721Enumerable);
    _registerInterface(InterfaceId_ERC721Metadata);
  }

  
  function name() external view returns (string) {
    return name_;
  }

  
  function symbol() external view returns (string) {
    return symbol_;
  }

  
  function tokenURI(uint256 _tokenId) public view returns (string) {
    require(exists(_tokenId));
    return tokenURIs[_tokenId];
  }

  
  function tokenOfOwnerByIndex(
    address _owner,
    uint256 _index
  )
    public
    view
    returns (uint256)
  {
    require(_index < balanceOf(_owner));
    return ownedTokens[_owner][_index];
  }

  
  function totalSupply() public view returns (uint256) {
    return allTokens.length;
  }

  
  function tokenByIndex(uint256 _index) public view returns (uint256) {
    require(_index < totalSupply());
    return allTokens[_index];
  }

  
  function _setTokenURI(uint256 _tokenId, string _uri) internal {
    require(exists(_tokenId));
    tokenURIs[_tokenId] = _uri;
  }

  
  function addTokenTo(address _to, uint256 _tokenId) internal {
    super.addTokenTo(_to, _tokenId);
    uint256 length = ownedTokens[_to].length;
    ownedTokens[_to].push(_tokenId);
    ownedTokensIndex[_tokenId] = length;
  }

  
  function removeTokenFrom(address _from, uint256 _tokenId) internal {
    super.removeTokenFrom(_from, _tokenId);

    uint256 tokenIndex = ownedTokensIndex[_tokenId];
    uint256 lastTokenIndex = ownedTokens[_from].length.sub(1);
    uint256 lastToken = ownedTokens[_from][lastTokenIndex];

    ownedTokens[_from][tokenIndex] = lastToken;
    ownedTokens[_from][lastTokenIndex] = 0;
   
   
   

    ownedTokens[_from].length--;
    ownedTokensIndex[_tokenId] = 0;
    ownedTokensIndex[lastToken] = tokenIndex;
  }

  
  function _mint(address _to, uint256 _tokenId) internal {
    super._mint(_to, _tokenId);

    allTokensIndex[_tokenId] = allTokens.length;
    allTokens.push(_tokenId);
  }

  
  function _burn(address _owner, uint256 _tokenId) internal {
    super._burn(_owner, _tokenId);

   
    if (bytes(tokenURIs[_tokenId]).length != 0) {
      delete tokenURIs[_tokenId];
    }

   
    uint256 tokenIndex = allTokensIndex[_tokenId];
    uint256 lastTokenIndex = allTokens.length.sub(1);
    uint256 lastToken = allTokens[lastTokenIndex];

    allTokens[tokenIndex] = lastToken;
    allTokens[lastTokenIndex] = 0;

    allTokens.length--;
    allTokensIndex[_tokenId] = 0;
    allTokensIndex[lastToken] = tokenIndex;
  }

}




contract ImpItem is ERC721Token, Ownable {
    using ECRecovery for bytes32;

    event TokenInformationUpdated(string _name, string _symbol);

    constructor(string _name, string _symbol) ERC721Token(_name, _symbol) public {

    }

    
    function setTokenInformation(string _newName, string _newSymbol) external onlyOwner {
        name_ = _newName;
        symbol_ = _newSymbol;

       
        emit TokenInformationUpdated(name_, symbol_);
    }

    
    function symbol() external view returns (string) {
        return symbol_;
    }

    
    function burn(uint _tokenId) external {
        _burn(msg.sender, _tokenId);
    }

    
    function mint(uint _tokenId, string _uri, bytes _signedData) external {
        bytes32 validatingHash = keccak256(
            abi.encodePacked(msg.sender, _tokenId, _uri)
        );

       
        address addressRecovered = validatingHash.recover(_signedData);

        require(addressRecovered == owner);

       
       
        _mint(msg.sender, _tokenId);

        _setTokenURI(_tokenId, _uri);
    }

}