pragma solidity 0.4.24;

// File: contracts/lib/openzeppelin-solidity/contracts/introspection/IERC165.sol

/**
 * @title IERC165
 * @dev https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md
 */
interface IERC165 {

  /**
   * @notice Query if a contract implements an interface
   * @param interfaceId The interface identifier, as specified in ERC-165
   * @dev Interface identification is specified in ERC-165. This function
   * uses less than 30,000 gas.
   */
  function supportsInterface(bytes4 interfaceId)
    external
    view
    returns (bool);
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/IERC721.sol

/**
 * @title ERC721 Non-Fungible Token Standard basic interface
 * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract IERC721 is IERC165 {

  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 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;
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/IERC721Receiver.sol

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
contract IERC721Receiver {
  /**
   * @notice Handle the receipt of an NFT
   * @dev The ERC721 smart contract calls this function on the recipient
   * after a `safeTransfer`. 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(keccak256("onERC721Received(address,address,uint256,bytes)"))`
   */
  function onERC721Received(
    address operator,
    address from,
    uint256 tokenId,
    bytes data
  )
    public
    returns(bytes4);
}

// File: contracts/lib/openzeppelin-solidity/contracts/math/SafeMath.sol

/**
 * @title SafeMath
 * @dev Math operations with safety checks that revert on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, reverts on 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-solidity/pull/522
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;
    require(c / a == b);

    return c;
  }

  /**
  * @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
  */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b > 0); // Solidity only automatically asserts when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;
  }

  /**
  * @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a);
    uint256 c = a - b;

    return c;
  }

  /**
  * @dev Adds two numbers, reverts on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a);

    return c;
  }

  /**
  * @dev Divides two numbers and returns the remainder (unsigned integer modulo),
  * reverts when dividing by zero.
  */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0);
    return a % b;
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/utils/Address.sol

/**
 * Utility library of inline functions on addresses
 */
library Address {

  /**
   * Returns whether the target address is a contract
   * @dev This function will return false if invoked during the constructor of a contract,
   * as the code is not actually created until after the constructor finishes.
   * @param account address of the account to check
   * @return whether the target address is a contract
   */
  function isContract(address account) internal view returns (bool) {
    uint256 size;
    // XXX Currently there is no better way to check if there is a contract in an address
    // than to check the size of the code at that address.
    // See https://ethereum.stackexchange.com/a/14016/36603
    // for more details about how this works.
    // TODO Check this again before the Serenity release, because all addresses will be
    // contracts then.
    // solium-disable-next-line security/no-inline-assembly
    assembly { size := extcodesize(account) }
    return size > 0;
  }

}

// File: contracts/lib/openzeppelin-solidity/contracts/introspection/ERC165.sol

/**
 * @title ERC165
 * @author Matt Condon (@shrugs)
 * @dev Implements ERC165 using a lookup table.
 */
contract ERC165 is IERC165 {

  bytes4 private constant _InterfaceId_ERC165 = 0x01ffc9a7;
  /**
   * 0x01ffc9a7 ===
   *   bytes4(keccak256('supportsInterface(bytes4)'))
   */

  /**
   * @dev a mapping of interface id to whether or not it's supported
   */
  mapping(bytes4 => bool) internal _supportedInterfaces;

  /**
   * @dev A contract implementing SupportsInterfaceWithLookup
   * implement ERC165 itself
   */
  constructor()
    public
  {
    _registerInterface(_InterfaceId_ERC165);
  }

  /**
   * @dev implement supportsInterface(bytes4) using a lookup table
   */
  function supportsInterface(bytes4 interfaceId)
    external
    view
    returns (bool)
  {
    return _supportedInterfaces[interfaceId];
  }

  /**
   * @dev private method for registering an interface
   */
  function _registerInterface(bytes4 interfaceId)
    internal
  {
    require(interfaceId != 0xffffffff);
    _supportedInterfaces[interfaceId] = true;
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/ERC721.sol

/**
 * @title ERC721 Non-Fungible Token Standard basic implementation
 * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract ERC721 is ERC165, IERC721 {

  using SafeMath for uint256;
  using Address for address;

  // 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 token ID to owner
  mapping (uint256 => address) private _tokenOwner;

  // Mapping from token ID to approved address
  mapping (uint256 => address) private _tokenApprovals;

  // Mapping from owner to number of owned token
  mapping (address => uint256) private _ownedTokensCount;

  // Mapping from owner to operator approvals
  mapping (address => mapping (address => bool)) private _operatorApprovals;

  bytes4 private constant _InterfaceId_ERC721 = 0x80ac58cd;
  /*
   * 0x80ac58cd ===
   *   bytes4(keccak256('balanceOf(address)')) ^
   *   bytes4(keccak256('ownerOf(uint256)')) ^
   *   bytes4(keccak256('approve(address,uint256)')) ^
   *   bytes4(keccak256('getApproved(uint256)')) ^
   *   bytes4(keccak256('setApprovalForAll(address,bool)')) ^
   *   bytes4(keccak256('isApprovedForAll(address,address)')) ^
   *   bytes4(keccak256('transferFrom(address,address,uint256)')) ^
   *   bytes4(keccak256('safeTransferFrom(address,address,uint256)')) ^
   *   bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)'))
   */

  constructor()
    public
  {
    // register the supported interfaces to conform to ERC721 via ERC165
    _registerInterface(_InterfaceId_ERC721);
  }

  /**
   * @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 returns (uint256) {
    require(owner != address(0));
    return _ownedTokensCount[owner];
  }

  /**
   * @dev Gets the owner of the specified token ID
   * @param tokenId uint256 ID of the token to query the owner of
   * @return owner address currently marked as the owner of the given token ID
   */
  function ownerOf(uint256 tokenId) public view returns (address) {
    address owner = _tokenOwner[tokenId];
    require(owner != address(0));
    return owner;
  }

  /**
   * @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 {
    address owner = ownerOf(tokenId);
    require(to != owner);
    require(msg.sender == owner || isApprovedForAll(owner, msg.sender));

    _tokenApprovals[tokenId] = to;
    emit Approval(owner, 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 returns (address) {
    require(_exists(tokenId));
    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 to operator address to set the approval
   * @param approved representing the status of the approval to be set
   */
  function setApprovalForAll(address to, bool approved) public {
    require(to != msg.sender);
    _operatorApprovals[msg.sender][to] = approved;
    emit ApprovalForAll(msg.sender, to, 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
    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
  {
    require(_isApprovedOrOwner(msg.sender, tokenId));
    require(to != address(0));

    _clearApproval(from, tokenId);
    _removeTokenFrom(from, tokenId);
    _addTokenTo(to, tokenId);

    emit 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 `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
  {
    // solium-disable-next-line arg-overflow
    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 `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 safeTransferFrom(
    address from,
    address to,
    uint256 tokenId,
    bytes _data
  )
    public
  {
    transferFrom(from, to, tokenId);
    // solium-disable-next-line arg-overflow
    require(_checkAndCallSafeTransfer(from, to, tokenId, _data));
  }

  /**
   * @dev Returns whether the specified token exists
   * @param tokenId uint256 ID of the token to query the existence of
   * @return whether the token exists
   */
  function _exists(uint256 tokenId) internal view returns (bool) {
    address owner = _tokenOwner[tokenId];
    return owner != address(0);
  }

  /**
   * @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)
  {
    address owner = ownerOf(tokenId);
    // Disable solium check because of
    // https://github.com/duaraghav8/Solium/issues/175
    // solium-disable-next-line operator-whitespace
    return (
      spender == owner ||
      getApproved(tokenId) == spender ||
      isApprovedForAll(owner, spender)
    );
  }

  /**
   * @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 by the msg.sender
   */
  function _mint(address to, uint256 tokenId) internal {
    require(to != address(0));
    _addTokenTo(to, tokenId);
    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 by the msg.sender
   */
  function _burn(address owner, uint256 tokenId) internal {
    _clearApproval(owner, tokenId);
    _removeTokenFrom(owner, tokenId);
    emit Transfer(owner, address(0), tokenId);
  }

  /**
   * @dev Internal function to clear current approval of a given token ID
   * Reverts if the given address is not indeed the owner of the token
   * @param owner owner of the token
   * @param tokenId uint256 ID of the token to be transferred
   */
  function _clearApproval(address owner, uint256 tokenId) internal {
    require(ownerOf(tokenId) == owner);
    if (_tokenApprovals[tokenId] != address(0)) {
      _tokenApprovals[tokenId] = address(0);
    }
  }

  /**
   * @dev Internal function to add a token ID to the list of a given address
   * @param to address representing the new owner of the given token ID
   * @param tokenId uint256 ID of the token to be added to the tokens list of the given address
   */
  function _addTokenTo(address to, uint256 tokenId) internal {
    require(_tokenOwner[tokenId] == address(0));
    _tokenOwner[tokenId] = to;
    _ownedTokensCount[to] = _ownedTokensCount[to].add(1);
  }

  /**
   * @dev Internal function to remove a token ID from the list of a given address
   * @param from address representing the previous owner of the given token ID
   * @param tokenId uint256 ID of the token to be removed from the tokens list of the given address
   */
  function _removeTokenFrom(address from, uint256 tokenId) internal {
    require(ownerOf(tokenId) == from);
    _ownedTokensCount[from] = _ownedTokensCount[from].sub(1);
    _tokenOwner[tokenId] = address(0);
  }

  /**
   * @dev Internal function to invoke `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 whether the call correctly returned the expected magic value
   */
  function _checkAndCallSafeTransfer(
    address from,
    address to,
    uint256 tokenId,
    bytes _data
  )
    internal
    returns (bool)
  {
    if (!to.isContract()) {
      return true;
    }
    bytes4 retval = IERC721Receiver(to).onERC721Received(
      msg.sender, from, tokenId, _data);
    return (retval == _ERC721_RECEIVED);
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/IERC721Enumerable.sol

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract IERC721Enumerable is IERC721 {
  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);
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/ERC721Enumerable.sol

contract ERC721Enumerable is ERC165, ERC721, IERC721Enumerable {
  // Mapping from owner to list of owned token IDs
  mapping(address => uint256[]) private _ownedTokens;

  // Mapping from token ID to index of the owner tokens list
  mapping(uint256 => uint256) private _ownedTokensIndex;

  // Array with all token ids, used for enumeration
  uint256[] private _allTokens;

  // Mapping from token id to position in the allTokens array
  mapping(uint256 => uint256) private _allTokensIndex;

  bytes4 private constant _InterfaceId_ERC721Enumerable = 0x780e9d63;
  /**
   * 0x780e9d63 ===
   *   bytes4(keccak256('totalSupply()')) ^
   *   bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) ^
   *   bytes4(keccak256('tokenByIndex(uint256)'))
   */

  /**
   * @dev Constructor function
   */
  constructor() public {
    // register the supported interface to conform to ERC721 via ERC165
    _registerInterface(_InterfaceId_ERC721Enumerable);
  }

  /**
   * @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
    returns (uint256)
  {
    require(index < balanceOf(owner));
    return _ownedTokens[owner][index];
  }

  /**
   * @dev Gets the total amount of tokens stored by the contract
   * @return uint256 representing the total amount of tokens
   */
  function totalSupply() public view returns (uint256) {
    return _allTokens.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 returns (uint256) {
    require(index < totalSupply());
    return _allTokens[index];
  }

  /**
   * @dev Internal function to add a token ID to the list of a given address
   * @param to address representing the new owner of the given token ID
   * @param tokenId uint256 ID of the token to be added to the tokens list of the given address
   */
  function _addTokenTo(address to, uint256 tokenId) internal {
    super._addTokenTo(to, tokenId);
    uint256 length = _ownedTokens[to].length;
    _ownedTokens[to].push(tokenId);
    _ownedTokensIndex[tokenId] = length;
  }

  /**
   * @dev Internal function to remove a token ID from the list of a given address
   * @param from address representing the previous owner of the given token ID
   * @param tokenId uint256 ID of the token to be removed from the tokens list of the given address
   */
  function _removeTokenFrom(address from, uint256 tokenId) internal {
    super._removeTokenFrom(from, tokenId);

    // To prevent a gap in the array, we store the last token in the index of the token to delete, and
    // then delete the last slot.
    uint256 tokenIndex = _ownedTokensIndex[tokenId];
    uint256 lastTokenIndex = _ownedTokens[from].length.sub(1);
    uint256 lastToken = _ownedTokens[from][lastTokenIndex];

    _ownedTokens[from][tokenIndex] = lastToken;
    // This also deletes the contents at the last position of the array
    _ownedTokens[from].length--;

    // Note that this will handle single-element arrays. In that case, both tokenIndex and lastTokenIndex are going to
    // be zero. Then we can make sure that we will remove tokenId from the ownedTokens list since we are first swapping
    // the lastToken to the first position, and then dropping the element placed in the last position of the list

    _ownedTokensIndex[tokenId] = 0;
    _ownedTokensIndex[lastToken] = tokenIndex;
  }

  /**
   * @dev Internal function to mint a new token
   * Reverts if the given token ID already exists
   * @param to address the beneficiary that will own the minted token
   * @param tokenId uint256 ID of the token to be minted by the msg.sender
   */
  function _mint(address to, uint256 tokenId) internal {
    super._mint(to, tokenId);

    _allTokensIndex[tokenId] = _allTokens.length;
    _allTokens.push(tokenId);
  }

  /**
   * @dev Internal function to burn a specific token
   * Reverts if the token does not exist
   * @param owner owner of the token to burn
   * @param tokenId uint256 ID of the token being burned by the msg.sender
   */
  function _burn(address owner, uint256 tokenId) internal {
    super._burn(owner, tokenId);

    // Reorg all tokens array
    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;
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/IERC721Metadata.sol

/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract IERC721Metadata is IERC721 {
  function name() external view returns (string);
  function symbol() external view returns (string);
  function tokenURI(uint256 tokenId) public view returns (string);
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/ERC721Metadata.sol

contract ERC721Metadata is ERC165, ERC721, IERC721Metadata {
  // Token name
  string internal _name;

  // Token symbol
  string internal _symbol;

  // Optional mapping for token URIs
  mapping(uint256 => string) private _tokenURIs;

  bytes4 private constant InterfaceId_ERC721Metadata = 0x5b5e139f;
  /**
   * 0x5b5e139f ===
   *   bytes4(keccak256('name()')) ^
   *   bytes4(keccak256('symbol()')) ^
   *   bytes4(keccak256('tokenURI(uint256)'))
   */

  /**
   * @dev Constructor function
   */
  constructor(string name, string symbol) public {
    _name = name;
    _symbol = symbol;

    // register the supported interfaces to conform to ERC721 via ERC165
    _registerInterface(InterfaceId_ERC721Metadata);
  }

  /**
   * @dev Gets the token name
   * @return string representing the token name
   */
  function name() external view returns (string) {
    return _name;
  }

  /**
   * @dev Gets the token symbol
   * @return string representing the token symbol
   */
  function symbol() external view returns (string) {
    return _symbol;
  }

  /**
   * @dev Returns an URI for a given token ID
   * Throws if the token ID does not exist. May return an empty string.
   * @param tokenId uint256 ID of the token to query
   */
  function tokenURI(uint256 tokenId) public view returns (string) {
    require(_exists(tokenId));
    return _tokenURIs[tokenId];
  }

  /**
   * @dev Internal function to set the token URI for a given token
   * Reverts if the token ID does not exist
   * @param tokenId uint256 ID of the token to set its URI
   * @param uri string URI to assign
   */
  function _setTokenURI(uint256 tokenId, string uri) internal {
    require(_exists(tokenId));
    _tokenURIs[tokenId] = uri;
  }

  /**
   * @dev Internal function to burn a specific token
   * Reverts if the token does not exist
   * @param owner owner of the token to burn
   * @param tokenId uint256 ID of the token being burned by the msg.sender
   */
  function _burn(address owner, uint256 tokenId) internal {
    super._burn(owner, tokenId);

    // Clear metadata (if any)
    if (bytes(_tokenURIs[tokenId]).length != 0) {
      delete _tokenURIs[tokenId];
    }
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/ERC721Full.sol

/**
 * @title Full ERC721 Token
 * This implementation includes all the required and some optional functionality of the ERC721 standard
 * Moreover, it includes approve all functionality using operator terminology
 * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract ERC721Full is ERC721, ERC721Enumerable, ERC721Metadata {
  constructor(string name, string symbol) ERC721Metadata(name, symbol)
    public
  {
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/access/Roles.sol

/**
 * @title Roles
 * @dev Library for managing addresses assigned to a Role.
 */
library Roles {
  struct Role {
    mapping (address => bool) bearer;
  }

  /**
   * @dev give an account access to this role
   */
  function add(Role storage role, address account) internal {
    require(account != address(0));
    role.bearer[account] = true;
  }

  /**
   * @dev remove an account's access to this role
   */
  function remove(Role storage role, address account) internal {
    require(account != address(0));
    role.bearer[account] = false;
  }

  /**
   * @dev check if an account has this role
   * @return bool
   */
  function has(Role storage role, address account)
    internal
    view
    returns (bool)
  {
    require(account != address(0));
    return role.bearer[account];
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/access/roles/MinterRole.sol

contract MinterRole {
  using Roles for Roles.Role;

  event MinterAdded(address indexed account);
  event MinterRemoved(address indexed account);

  Roles.Role private minters;

  constructor() public {
    minters.add(msg.sender);
  }

  modifier onlyMinter() {
    require(isMinter(msg.sender));
    _;
  }

  function isMinter(address account) public view returns (bool) {
    return minters.has(account);
  }

  function addMinter(address account) public onlyMinter {
    minters.add(account);
    emit MinterAdded(account);
  }

  function renounceMinter() public {
    minters.remove(msg.sender);
  }

  function _removeMinter(address account) internal {
    minters.remove(account);
    emit MinterRemoved(account);
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/ERC721Mintable.sol

/**
 * @title ERC721Mintable
 * @dev ERC721 minting logic
 */
contract ERC721Mintable is ERC721Full, MinterRole {
  event MintingFinished();

  bool private _mintingFinished = false;

  modifier onlyBeforeMintingFinished() {
    require(!_mintingFinished);
    _;
  }

  /**
   * @return true if the minting is finished.
   */
  function mintingFinished() public view returns(bool) {
    return _mintingFinished;
  }

  /**
   * @dev Function to mint tokens
   * @param to The address that will receive the minted tokens.
   * @param tokenId The token id to mint.
   * @return A boolean that indicates if the operation was successful.
   */
  function mint(
    address to,
    uint256 tokenId
  )
    public
    onlyMinter
    onlyBeforeMintingFinished
    returns (bool)
  {
    _mint(to, tokenId);
    return true;
  }

  function mintWithTokenURI(
    address to,
    uint256 tokenId,
    string tokenURI
  )
    public
    onlyMinter
    onlyBeforeMintingFinished
    returns (bool)
  {
    mint(to, tokenId);
    _setTokenURI(tokenId, tokenURI);
    return true;
  }

  /**
   * @dev Function to stop minting new tokens.
   * @return True if the operation was successful.
   */
  function finishMinting()
    public
    onlyMinter
    onlyBeforeMintingFinished
    returns (bool)
  {
    _mintingFinished = true;
    emit MintingFinished();
    return true;
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/access/roles/PauserRole.sol

contract PauserRole {
  using Roles for Roles.Role;

  event PauserAdded(address indexed account);
  event PauserRemoved(address indexed account);

  Roles.Role private pausers;

  constructor() public {
    pausers.add(msg.sender);
  }

  modifier onlyPauser() {
    require(isPauser(msg.sender));
    _;
  }

  function isPauser(address account) public view returns (bool) {
    return pausers.has(account);
  }

  function addPauser(address account) public onlyPauser {
    pausers.add(account);
    emit PauserAdded(account);
  }

  function renouncePauser() public {
    pausers.remove(msg.sender);
  }

  function _removePauser(address account) internal {
    pausers.remove(account);
    emit PauserRemoved(account);
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/lifecycle/Pausable.sol

/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is PauserRole {
  event Paused();
  event Unpaused();

  bool private _paused = false;


  /**
   * @return true if the contract is paused, false otherwise.
   */
  function paused() public view returns(bool) {
    return _paused;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {
    require(!_paused);
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {
    require(_paused);
    _;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() public onlyPauser whenNotPaused {
    _paused = true;
    emit Paused();
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() public onlyPauser whenPaused {
    _paused = false;
    emit Unpaused();
  }
}

// File: contracts/lib/openzeppelin-solidity/contracts/token/ERC721/ERC721Pausable.sol

/**
 * @title ERC721 Non-Fungible Pausable token
 * @dev ERC721 modified with pausable transfers.
 **/
contract ERC721Pausable is ERC721, Pausable {
  function approve(
    address to,
    uint256 tokenId
  )
    public
    whenNotPaused
  {
    super.approve(to, tokenId);
  }

  function setApprovalForAll(
    address to,
    bool approved
  )
    public
    whenNotPaused
  {
    super.setApprovalForAll(to, approved);
  }

  function transferFrom(
    address from,
    address to,
    uint256 tokenId
  )
    public
    whenNotPaused
  {
    super.transferFrom(from, to, tokenId);
  }
}

// File: contracts/HeroAsset.sol

contract HeroAsset is ERC721Mintable, ERC721Pausable {

    uint16 public constant HERO_TYPE_OFFSET = 10000;

    string public tokenURIPrefix = "https://www.mycryptoheroes.net/metadata/hero/";
    mapping(uint16 => uint16) private heroTypeToSupplyLimit;

    constructor() public ERC721Full("MyCryptoHeroes:Hero", "MCHH") {}

    function setSupplyLimit(uint16 _heroType, uint16 _supplyLimit) external onlyMinter {
        require(heroTypeToSupplyLimit[_heroType] == 0 || _supplyLimit < heroTypeToSupplyLimit[_heroType],
            "_supplyLimit is bigger");
        heroTypeToSupplyLimit[_heroType] = _supplyLimit;
    }

    function setTokenURIPrefix(string _tokenURIPrefix) external onlyMinter {
        tokenURIPrefix = _tokenURIPrefix;
    }

    function getSupplyLimit(uint16 _heroType) public view returns (uint16) {
        return heroTypeToSupplyLimit[_heroType];
    }

    function mintHeroAsset(address _owner, uint256 _tokenId) public onlyMinter {
        uint16 _heroType = uint16(_tokenId / HERO_TYPE_OFFSET);
        uint16 _heroTypeIndex = uint16(_tokenId % HERO_TYPE_OFFSET) - 1;
        require(_heroTypeIndex < heroTypeToSupplyLimit[_heroType], "supply over");
        _mint(_owner, _tokenId);
    }

    function tokenURI(uint256 tokenId) public view returns (string) {
        bytes32 tokenIdBytes;
        if (tokenId == 0) {
            tokenIdBytes = "0";
        } else {
            uint256 value = tokenId;
            while (value > 0) {
                tokenIdBytes = bytes32(uint256(tokenIdBytes) / (2 ** 8));
                tokenIdBytes |= bytes32(((value % 10) + 48) * 2 ** (8 * 31));
                value /= 10;
            }
        }

        bytes memory prefixBytes = bytes(tokenURIPrefix);
        bytes memory tokenURIBytes = new bytes(prefixBytes.length + tokenIdBytes.length);

        uint8 i;
        uint8 index = 0;
        
        for (i = 0; i < prefixBytes.length; i++) {
            tokenURIBytes[index] = prefixBytes[i];
            index++;
        }
        
        for (i = 0; i < tokenIdBytes.length; i++) {
            tokenURIBytes[index] = tokenIdBytes[i];
            index++;
        }
        
        return string(tokenURIBytes);
    }

}

// File: contracts/lib/openzeppelin-solidity/contracts/ownership/Ownable.sol

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
  address private _owner;


  event OwnershipRenounced(address indexed previousOwner);
  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor() public {
    _owner = msg.sender;
  }

  /**
   * @return the address of the owner.
   */
  function owner() public view returns(address) {
    return _owner;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(isOwner());
    _;
  }

  /**
   * @return true if `msg.sender` is the owner of the contract.
   */
  function isOwner() public view returns(bool) {
    return msg.sender == _owner;
  }

  /**
   * @dev Allows the current owner to relinquish control of the contract.
   * @notice Renouncing to ownership will leave the contract without an owner.
   * It will not be possible to call the functions with the `onlyOwner`
   * modifier anymore.
   */
  function renounceOwnership() public onlyOwner {
    emit OwnershipRenounced(_owner);
    _owner = address(0);
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) public onlyOwner {
    _transferOwnership(newOwner);
  }

  /**
   * @dev Transfers control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function _transferOwnership(address newOwner) internal {
    require(newOwner != address(0));
    emit OwnershipTransferred(_owner, newOwner);
    _owner = newOwner;
  }
}

// File: contracts/access/roles/ReferrerRole.sol

contract ReferrerRole is Ownable {
    using Roles for Roles.Role;

    event ReferrerAdded(address indexed account);
    event ReferrerRemoved(address indexed account);

    Roles.Role private referrers;

    constructor() public {
        referrers.add(msg.sender);
    }

    modifier onlyReferrer() {
        require(isReferrer(msg.sender));
        _;
    }
    
    function isReferrer(address account) public view returns (bool) {
        return referrers.has(account);
    }

    function addReferrer(address account) public onlyOwner() {
        referrers.add(account);
        emit ReferrerAdded(account);
    }

    function removeReferrer(address account) public onlyOwner() {
        referrers.remove(account);
        emit ReferrerRemoved(account);
    }

}

// File: contracts/lib/openzeppelin-solidity/contracts/utils/ReentrancyGuard.sol

/**
 * @title Helps contracts guard against reentrancy attacks.
 * @author Remco Bloemen <remco@2π.com>, Eenae <alexey@mixbytes.io>
 * @dev If you mark a function `nonReentrant`, you should also
 * mark it `external`.
 */
contract ReentrancyGuard {

  /// @dev counter to allow mutex lock with only one SSTORE operation
  uint256 private _guardCounter = 1;

  /**
   * @dev Prevents a contract from calling itself, directly or indirectly.
   * If you mark a function `nonReentrant`, you should also
   * mark it `external`. Calling one `nonReentrant` function from
   * another is not supported. Instead, you can implement a
   * `private` function doing the actual work, and an `external`
   * wrapper marked as `nonReentrant`.
   */
  modifier nonReentrant() {
    _guardCounter += 1;
    uint256 localCounter = _guardCounter;
    _;
    require(localCounter == _guardCounter);
  }

}

// File: contracts/HeroCrowdsale.sol

contract HeroCrowdsale is ReferrerRole, Pausable, ReentrancyGuard {
    using SafeMath for uint256;

    struct HeroSale {
        uint128 highestPrice;
        uint128 previousPrice;
        uint128 priceIncreaseTo;
        uint64  since;
        uint64  until;
        uint64  previousSaleAt;
        uint16  lowestPriceRate;
        uint16  decreaseRate;
        uint16  supplyLimit;
        uint16  suppliedCounts;
        uint8   currency;
        bool    exists;
    }
    
    mapping(uint16 => HeroSale) public heroTypeToHeroSales;
    mapping(uint16 => uint256[]) public heroTypeIds;
    mapping(uint16 => mapping(address => bool)) public hasAirDropHero;

    HeroAsset public heroAsset;
    uint16 constant internal SUPPLY_LIMIT_MAX = 10000;
    uint256 internal ethBackRate;

    event AddSalesEvent(
        uint16 indexed heroType,
        uint128 startPrice,
        uint256 lowestPrice,
        uint256 becomeLowestAt
    );

    event SoldHeroEvent(
        uint16 indexed heroType,
        uint256 soldPrice,
        uint64  soldAt,
        uint256 priceIncreaseTo,
        uint256 lowestPrice,
        uint256 becomeLowestAt,
        address purchasedBy,
        address indexed referrer,
        uint8   currency
    );

    constructor() public {
        ethBackRate = 20;
    }

    function setHeroAssetAddress(address _heroAssetAddress) external onlyOwner() {
        heroAsset = HeroAsset(_heroAssetAddress);
    }

    function changeEthBackRate(uint256 _newEthBackRate) external onlyOwner() {
        ethBackRate = _newEthBackRate;
    }

    function withdrawEther() external onlyOwner() {
        owner().transfer(address(this).balance);
    }

    function addSales(
        uint16 _heroType,
        uint128 _startPrice,
        uint16 _lowestPriceRate,
        uint16 _decreaseRate,
        uint64 _since,
        uint64 _until,
        uint16 _supplyLimit,
        uint8  _currency
    ) external onlyOwner() {
        require(!heroTypeToHeroSales[_heroType].exists, "this heroType is already added sales");
        require(0 <= _lowestPriceRate && _lowestPriceRate <= 100, "lowestPriceRate should be between 0 and 100");
        require(1 <= _decreaseRate && _decreaseRate <= 100, "decreaseRate should be should be between 1 and 100");
        require(_until > _since, "until should be later than since");

        HeroSale memory _herosale = HeroSale({
            highestPrice: _startPrice,
            previousPrice: _startPrice,
            priceIncreaseTo: _startPrice,
            since:_since,
            until:_until,
            previousSaleAt: _since,
            lowestPriceRate: _lowestPriceRate,
            decreaseRate: _decreaseRate,
            supplyLimit:_supplyLimit,
            suppliedCounts: 0,
            currency: _currency,
            exists: true
        });

        heroTypeToHeroSales[_heroType] = _herosale;
        heroAsset.setSupplyLimit(_heroType, _supplyLimit);

        uint256 _lowestPrice = uint256(_startPrice).mul(_lowestPriceRate).div(100);
        uint256 _becomeLowestAt = uint256(86400).mul(uint256(100).sub(_lowestPriceRate)).div(_decreaseRate).add(_since);

        emit AddSalesEvent(
            _heroType,
            _startPrice,
            _lowestPrice,
            _becomeLowestAt
        );
    }

    function purchase(uint16 _heroType, address _referrer) external whenNotPaused() nonReentrant() payable {
    // solium-disable-next-line security/no-block-members
        return purchaseImpl(_heroType, uint64(block.timestamp), _referrer);
    }

    function airDrop(uint16 _heroType, address _referrer) external whenNotPaused() {
        HeroSale storage heroSales = heroTypeToHeroSales[_heroType];
        require(airDropHero(_heroType), "currency is not 2 (airdrop)");
        require(!hasAirDropHero[_heroType][msg.sender]);
        uint64 _at = uint64(block.timestamp);
        require(isOnSale(_heroType, _at), "out of sales period");

        createHero(_heroType, msg.sender);
        hasAirDropHero[_heroType][msg.sender] = true;
        heroSales.suppliedCounts++;
        heroSales.previousSaleAt = _at;
        address referrer;
        if (_referrer == msg.sender){
            referrer = address(0x0);
        } else {
            referrer = _referrer;
        }

        emit SoldHeroEvent(
            _heroType,
            1,
            _at,
            1,
            1,
            1,
            msg.sender,
            referrer,
            2
        );
    }

    function computeCurrentPrice(uint16 _heroType) external view returns (uint8, uint256){
        // solium-disable-next-line security/no-block-members
        return computeCurrentPriceImpl(_heroType, uint64(block.timestamp));
    }

    function canBePurchasedByETH(uint16 _heroType) internal view returns (bool){
        return (heroTypeToHeroSales[_heroType].currency == 0);
    }

    function airDropHero(uint16 _heroType) internal view returns (bool){
        return (heroTypeToHeroSales[_heroType].currency == 2);
    }

    function isOnSale(uint16 _heroType, uint64 _now) internal view returns (bool){
        HeroSale storage heroSales = heroTypeToHeroSales[_heroType];
        require(heroSales.exists, "not exist sales of this heroType");

        if (heroSales.since <= _now && _now <= heroSales.until) {
            return true;
        } else {
            return false;
        }
    }

    function computeCurrentPriceImpl(uint16 _heroType, uint64 _at) internal view returns (uint8, uint256) {
        HeroSale storage heroSales = heroTypeToHeroSales[_heroType];
        require(heroSales.exists, "not exist sales of this heroType");
        require(heroSales.previousSaleAt <= _at, "current timestamp should not be faster than previousSaleAt");

        uint256 _lowestPrice = uint256(heroSales.highestPrice).mul(heroSales.lowestPriceRate).div(100);
        uint256 _secondsPassed = uint256(_at).sub(heroSales.previousSaleAt);
        uint256 _decreasedPrice = uint256(heroSales.priceIncreaseTo).mul(_secondsPassed).mul(heroSales.decreaseRate).div(100).div(86400);
        uint256 currentPrice;

        if (uint256(heroSales.priceIncreaseTo).sub(_lowestPrice) > _decreasedPrice){
            currentPrice = uint256(heroSales.priceIncreaseTo).sub(_decreasedPrice);
        } else {
            currentPrice = _lowestPrice;
        }

        return (1, currentPrice);
    }

    function purchaseImpl(uint16 _heroType, uint64 _at, address _referrer)
        internal
    {
        HeroSale storage heroSales = heroTypeToHeroSales[_heroType];
        require(canBePurchasedByETH(_heroType), "currency is not 0 (eth)");
        require(isOnSale(_heroType, _at), "out of sales period");
        (, uint256 _price) = computeCurrentPriceImpl(_heroType, _at);
        require(msg.value >= _price, "value is less than the price");

        createHero(_heroType, msg.sender);
        if (msg.value > _price){
            msg.sender.transfer(msg.value.sub(_price));
        }
        address referrer;
        if (_referrer == msg.sender){
            referrer = address(0x0);
        } else {
            referrer = _referrer;
        }
        if ((referrer != address(0x0)) && isReferrer(referrer)) {
            referrer.transfer(_price.mul(ethBackRate).div(100));
        }
        heroSales.previousPrice = uint128(_price);
        heroSales.suppliedCounts++;
        heroSales.previousSaleAt = _at;
        if (heroSales.previousPrice > heroSales.highestPrice){
            heroSales.highestPrice = heroSales.previousPrice;
        }
        uint256 _priceIncreaseTo;
        uint256 _lowestPrice;
        uint256 _becomeLowestAt;
        if (heroSales.supplyLimit > heroSales.suppliedCounts){
            _priceIncreaseTo = SafeMath.add(_price, _price.div((uint256(heroSales.supplyLimit).sub(heroSales.suppliedCounts))));
            heroSales.priceIncreaseTo = uint128(_priceIncreaseTo);
            _lowestPrice = uint256(heroSales.lowestPriceRate).mul(heroSales.highestPrice).div(100);
            _becomeLowestAt = uint256(86400).mul(100).mul((_priceIncreaseTo.sub(_lowestPrice))).div(_priceIncreaseTo).div(heroSales.decreaseRate).add(_at);
        } else {
            _priceIncreaseTo = heroSales.previousPrice;
            heroSales.priceIncreaseTo = uint128(_priceIncreaseTo);
            _lowestPrice = heroSales.previousPrice;
            _becomeLowestAt = _at;
        }
        emit SoldHeroEvent(
            _heroType,
            _price,
            _at,
            _priceIncreaseTo,
            _lowestPrice,
            _becomeLowestAt,
            msg.sender,
            referrer,
            0
        );
    }

    function createHero(uint16 _heroType, address _owner) internal {
        require(heroTypeToHeroSales[_heroType].exists, "not exist sales of this heroType");
        require(heroTypeIds[_heroType].length < heroTypeToHeroSales[_heroType].supplyLimit, "Heroes cant be created more than supplyLimit");

        uint256 _heroId = uint256(_heroType).mul(SUPPLY_LIMIT_MAX).add(heroTypeIds[_heroType].length).add(1);
        heroTypeIds[_heroType].push(_heroId);
        heroAsset.mintHeroAsset(_owner, _heroId);
    }
}