Contract  0x13b8b170796ba1c5a8c05009cebead2b17a76ea5  

pragma solidity ^0.4.24;

// File: 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 public _owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor () internal {
    _owner = msg.sender;
    emit OwnershipTransferred(address(0), _owner);
  }

  /**
   * @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 OwnershipTransferred(_owner, address(0));
    _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/ownership/Pausable.sol

/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is Ownable {
  event Pause();
  event Unpause();

  bool public paused = false;


  /**
   * @dev modifier to allow actions only when the contract IS paused
   */
  modifier whenNotPaused() {
    require(!paused);
    _;
  }

  /**
   * @dev modifier to allow actions only when the contract IS NOT paused
   */
  modifier whenPaused {
    require(paused);
    _;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() onlyOwner whenNotPaused public returns (bool) {
    paused = true;
    emit Pause();
    return true;
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() onlyOwner whenPaused public returns (bool) {
    paused = false;
    emit Unpause();
    return true;
  }
}

// File: 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: 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: 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: 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: 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: 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) private _supportedInterfaces;

  /**
   * @dev A contract implementing SupportsInterfaceWithLookup
   * implement ERC165 itself
   */
  constructor()
    internal
  {
    _registerInterface(_InterfaceId_ERC165);
  }

  /**
   * @dev implement supportsInterface(bytes4) using a lookup table
   */
  function supportsInterface(bytes4 interfaceId)
    external
    view
    returns (bool)
  {
    return _supportedInterfaces[interfaceId];
  }

  /**
   * @dev internal method for registering an interface
   */
  function _registerInterface(bytes4 interfaceId)
    internal
  {
    require(interfaceId != 0xffffffff);
    _supportedInterfaces[interfaceId] = true;
  }
}

// File: 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(_checkOnERC721Received(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 add a token ID to the list of a given address
   * Note that this function is left internal to make ERC721Enumerable possible, but is not
   * intended to be called by custom derived contracts: in particular, it emits no Transfer event.
   * @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
   * Note that this function is left internal to make ERC721Enumerable possible, but is not
   * intended to be called by custom derived contracts: in particular, it emits no Transfer event,
   * and doesn't clear approvals.
   * @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 _checkOnERC721Received(
    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);
  }

  /**
   * @dev Private 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) private {
    require(ownerOf(tokenId) == owner);
    if (_tokenApprovals[tokenId] != address(0)) {
      _tokenApprovals[tokenId] = address(0);
    }
  }
}

// File: 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: 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
   * This function is internal due to language limitations, see the note in ERC721.sol.
   * It is not intended to be called by custom derived contracts: in particular, it emits no Transfer event.
   * @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
   * This function is internal due to language limitations, see the note in ERC721.sol.
   * It is not intended to be called by custom derived contracts: in particular, it emits no Transfer event,
   * and doesn't clear approvals.
   * @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: 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) external view returns (string);
}

// File: openzeppelin-solidity/contracts/token/ERC721/ERC721Metadata.sol

contract ERC721Metadata is ERC165, ERC721, IERC721Metadata {
  // Token name
  string private _name;

  // Token symbol
  string private _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) external 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: 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/token/ERC721Token.sol

/// @title Interface for contracts conforming to ERC-721: Non-Fungible Tokens
/// @author Dieter Shirley <[email protected]> (https://github.com/dete)

contract ERC721Token is ERC721Full("SKULLY", "SKL"), Ownable {
    bytes4 constant InterfaceSignature_ERC721 = 0xd37c58cd;
    bytes4 constant InterfaceSignature_ERC721Enumerable = 0xd37e9d63;
    bytes4 constant InterfaceSignature_ERC721Metadata = 0xd37e139f;
    bytes4 constant InterfaceSignature_ERC165 = 0xd37fc9a7;

    function supportsInterface(bytes4 _interfaceID) external view returns (bool)
    {
        return ((_interfaceID == InterfaceSignature_ERC165)
        || (_interfaceID == InterfaceSignature_ERC721)
        || (_interfaceID == InterfaceSignature_ERC721Enumerable)
        || (_interfaceID == InterfaceSignature_ERC721Metadata));
    }

    function implementsERC721() public pure returns (bool) {
        return true;
    }
}

// File: contracts/auction/ClockAuctionBase.sol

/// @title Auction Core
/// @dev Contains models, variables, and internal methods for the auction.
/// @notice We omit a fallback function to prevent accidental sends to this contract.
contract ClockAuctionBase {

    // Represents an auction on an NFT
    struct Auction {
        // Current owner of NFT
        address seller;
        // Price (in wei) at beginning of auction
        uint128 startingPrice;
        // Price (in wei) at end of auction
        uint128 endingPrice;
        // Duration (in seconds) of auction
        uint64 duration;
        // Time when auction started
        // NOTE: 0 if this auction has been concluded
        uint64 startedAt;
    }

    // Reference to contract tracking NFT ownership
    ERC721Token public nonFungibleContract;

    // Cut owner takes on each auction, measured in basis points (1/100 of a percent).
    // Values 0-10,000 map to 0%-100%
    uint256 public ownerCut;

    // Map from token ID to their corresponding auction.
    mapping (uint256 => Auction) tokenIdToAuction;

    event AuctionCreated(uint256 tokenId, uint256 startingPrice, uint256 endingPrice, uint256 duration);
    event AuctionSuccessful(uint256 tokenId, uint256 totalPrice, address winner);
    event AuctionCancelled(uint256 tokenId);
    event Money(address from, string actionType, uint256 sum, uint256 cut, uint256 tokenId, uint256 blockNumber);

    function isOwnerOf(address _claimant, uint256 _tokenId) internal view returns (bool) {
        return (nonFungibleContract.ownerOf(_tokenId) == _claimant);
    }

    function _escrow(address _owner, uint256 _tokenId) internal {
        nonFungibleContract.transferFrom(_owner, this, _tokenId);
    }

    function _transfer(address _receiver, uint256 _tokenId) internal {
        nonFungibleContract.transferFrom(this, _receiver, _tokenId);
    }

    function _addAuction(uint256 _tokenId, Auction _auction) internal {
        require(_auction.duration >= 1 minutes);

        tokenIdToAuction[_tokenId] = _auction;

        emit AuctionCreated(uint256(_tokenId), uint256(_auction.startingPrice), uint256(_auction.endingPrice), uint256(_auction.duration));
    }

    function _cancelAuction(uint256 _tokenId, address _seller) internal {
        _removeAuction(_tokenId);
        _transfer(_seller, _tokenId);
        emit AuctionCancelled(_tokenId);
    }

    function _bid(uint256 _tokenId, uint256 _bidAmount, address _sender) internal returns (uint256, address) {
        Auction storage auction = tokenIdToAuction[_tokenId];

        require(_isOnAuction(auction));

        uint256 price = _currentPrice(auction);
        require(_bidAmount >= price);

        address seller = auction.seller;

        _removeAuction(_tokenId);

        if (price > 0) {
            uint256 auctioneerCut = _computeCut(price);
            uint256 sellerProceeds = price - auctioneerCut;
            seller.transfer(sellerProceeds);

            emit Money(_sender, "AuctionSuccessful", price, auctioneerCut, _tokenId, block.number);
        }

        uint256 bidExcess = _bidAmount - price;

        _sender.transfer(bidExcess);

        emit AuctionSuccessful(_tokenId, price, _sender);

        return (price, seller);
    }

    function _removeAuction(uint256 _tokenId) internal {
        delete tokenIdToAuction[_tokenId];
    }

    function _isOnAuction(Auction storage _auction) internal view returns (bool) {
        return (_auction.startedAt > 0 && _auction.startedAt < now);
    }

    function _currentPrice(Auction storage _auction) internal view returns (uint256) {
        uint256 secondsPassed = 0;

        if (now > _auction.startedAt) {
            secondsPassed = now - _auction.startedAt;
        }

        return _computeCurrentPrice(_auction.startingPrice, _auction.endingPrice, _auction.duration, secondsPassed);
    }

    function _computeCurrentPrice(uint256 _startingPrice, uint256 _endingPrice,
        uint256 _duration, uint256 _secondsPassed) internal pure returns (uint256) {
        if (_secondsPassed >= _duration) {
            return _endingPrice;
        } else {
            int256 totalPriceChange = int256(_endingPrice) - int256(_startingPrice);

            int256 currentPriceChange = totalPriceChange * int256(_secondsPassed) / int256(_duration);

            int256 currentPrice = int256(_startingPrice) + currentPriceChange;

            return uint256(currentPrice);
        }
    }

    function _computeCut(uint256 _price) internal view returns (uint256) {
        return uint256(_price * ownerCut / 10000);
    }

}

// File: contracts/auction/ClockAuction.sol

/// @title Clock auction for non-fungible tokens.
/// @notice We omit a fallback function to prevent accidental sends to this contract.
contract ClockAuction is Pausable, ClockAuctionBase {

    /// @dev The ERC-165 interface signature for ERC-721.
    ///  Ref: https://github.com/ethereum/EIPs/issues/165
    ///  Ref: https://github.com/ethereum/EIPs/issues/721
    bytes4 constant InterfaceSignature_ERC721 = bytes4(0xd37c58cd);

    /// @dev Constructor creates a reference to the NFT ownership contract
    ///  and verifies the owner cut is in the valid range.
    /// @param _nftAddress - address of a deployed contract implementing
    ///  the Nonfungible Interface.
    /// @param _cut - percent cut the owner takes on each auction, must be
    ///  between 0-10,000.

    constructor(address _nftAddress, uint256 _cut) public {
        require(_cut <= 10000);
        ownerCut = _cut;

        ERC721Token candidateContract = ERC721Token(_nftAddress);
        require(candidateContract.supportsInterface(InterfaceSignature_ERC721));
        nonFungibleContract = candidateContract;
    }

    /// @dev Remove all Ether from the contract, which is the owner's cuts
    ///  as well as any Ether sent directly to the contract address.
    ///  Always transfers to the NFT contract, but can be called either by
    ///  the owner or the NFT contract.
    function withdrawBalance() external {
        address nftAddress = address(nonFungibleContract);

        require(msg.sender == _owner || msg.sender == nftAddress);
        // We are using this boolean method to make sure that even if one fails it will still work
        _owner.transfer(address(this).balance);
    }

    /// @dev Creates and begins a new auction.
    /// @param _tokenId - ID of token to auction, sender must be owner.
    /// @param _startingPrice - Price of item (in wei) at beginning of auction.
    /// @param _endingPrice - Price of item (in wei) at end of auction.
    /// @param _duration - Length of time to move between starting
    ///  price and ending price (in seconds).
    /// @param _seller - Seller, if not the message sender
    function createAuction(
        uint256 _tokenId,
        uint256 _startingPrice,
        uint256 _endingPrice,
        uint256 _duration,
        address _seller
    ) external whenNotPaused {
        // Sanity check that no inputs overflow how many bits we've allocated
        // to store them in the auction struct.
        require(_startingPrice == uint256(uint128(_startingPrice)));
        require(_endingPrice == uint256(uint128(_endingPrice)));
        require(_duration == uint256(uint64(_duration)));
        require(isOwnerOf(msg.sender, _tokenId));
        _escrow(msg.sender, _tokenId);
        Auction memory auction = Auction(
            _seller,
            uint128(_startingPrice),
            uint128(_endingPrice),
            uint64(_duration),
            uint64(now)
        );
        _addAuction(_tokenId, auction);
    }

    /// @dev Bids on an open auction, completing the auction and transferring
    ///  ownership of the NFT if enough Ether is supplied.
    /// @param _tokenId - ID of token to bid on.
    function bid(uint256 _tokenId) external payable whenNotPaused {
        // _bid will throw if the bid or funds transfer fails
        _bid(_tokenId, msg.value, msg.sender);
        _transfer(msg.sender, _tokenId);
    }

    /// @dev Cancels an auction that hasn't been won yet.
    ///  Returns the NFT to original owner.
    /// @notice This is a state-modifying function that can
    ///  be called while the contract is paused.
    /// @param _tokenId - ID of token on auction
    function cancelAuction(uint256 _tokenId) external {
        Auction storage auction = tokenIdToAuction[_tokenId];
        require(_isOnAuction(auction));
        address seller = auction.seller;
        require(msg.sender == seller);
        _cancelAuction(_tokenId, seller);
    }

    function cancelAuctionByAdmin(uint256 _tokenId) onlyOwner external {
        Auction storage auction = tokenIdToAuction[_tokenId];
        require(_isOnAuction(auction));
        _cancelAuction(_tokenId, auction.seller);
    }

    /// @dev Returns auction info for an NFT on auction.
    /// @param _tokenId - ID of NFT on auction.
    function getAuction(uint256 _tokenId) external view returns (
        address seller,
        uint256 startingPrice,
        uint256 endingPrice,
        uint256 duration,
        uint256 startedAt
    ) {
        Auction storage auction = tokenIdToAuction[_tokenId];
        require(_isOnAuction(auction));
        return (
            auction.seller,
            auction.startingPrice,
            auction.endingPrice,
            auction.duration,
            auction.startedAt
        );
    }

    /// @dev Returns the current price of an auction.
    /// @param _tokenId - ID of the token price we are checking.
    function getCurrentPrice(uint256 _tokenId) external view returns (uint256) {
        Auction storage auction = tokenIdToAuction[_tokenId];
        require(_isOnAuction(auction));
        return _currentPrice(auction);
    }

    // TMP
    function getContractBalance() onlyOwner external view returns (uint256) {
        return address(this).balance;
    }

}

// File: contracts/token/PO8BaseToken.sol

library MySafeMath {
    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) {
        // assert(b > 0); // Solidity automatically throws 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 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;
    }
}

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; }

contract ERC20 {
    function totalSupply() public view returns (uint256);
    function balanceOf(address who) public view returns (uint256);
    function transfer(address to, uint256 value) public;
    function allowance(address owner, address spender) public view returns (uint256);
    function transferFrom(address from, address to, uint256 value) public returns (bool);
    function approve(address spender, uint256 value) public returns (bool);

    event Approval(address indexed owner, address indexed spender, uint256 value);
    event Transfer(address indexed from, address indexed to, uint256 value);
}

contract PO8BaseToken is ERC20 {
    using MySafeMath for uint256;

    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 totalSupply_;

    mapping(address => uint256) balances;
    mapping (address => mapping (address => uint256)) internal allowed;

    constructor(string _name, string _symbol, uint8 _decimals, uint256 _totalSupply) public{
        name = _name;
        symbol = _symbol;
        decimals = _decimals;
        totalSupply_ = _totalSupply;
    }

    function totalSupply() public view returns (uint256) {
        return totalSupply_;
    }

    function balanceOf(address _owner) public view returns (uint256) {
        return balances[_owner];
    }

    function _transfer(address _from, address _to, uint256 _value) internal {
        require(_to != address(0));
        require(balances[_from] >= _value);
        require(balances[_to].add(_value) > balances[_to]);


        uint256 previousBalances = balances[_from].add(balances[_to]);
        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(_from, _to, _value);

        assert(balances[_from].add(balances[_to]) == previousBalances);
    }

    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        require(_value <= allowed[_from][msg.sender]);     // Check allowance
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        _transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function allowance(address _owner, address _spender) public view returns (uint256) {
        return allowed[_owner][_spender];
    }

    function approveAndCall(address _spender, uint256 _value, bytes _extraData) public returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
        allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }

    function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
        uint oldValue = allowed[msg.sender][_spender];
        if (_subtractedValue > oldValue) {
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
}

// File: contracts/auction/SaleClockAuction.sol

/// @title Clock auction modified for sale of skull
/// @notice We omit a fallback function to prevent accidental sends to this contract.
contract SaleClockAuction is ClockAuction {

    // @dev Sanity check that allows us to ensure that we are pointing to the
    //  right auction in our setSaleAuctionAddress() call.
    bool public isSaleClockAuction = true;
    mapping (uint256 => uint256) totalBuySkull;
    event ClaimToken(address owner, uint256 tokenId);


    // Delegate constructor
    constructor(address _nftAddr, uint256 _cut) public
        ClockAuction(_nftAddr, _cut) {}

    /// @dev Creates and begins a new auction.
    /// @param _tokenId - ID of token to auction, sender must be owner.
    /// @param _startingPrice - Price of item (in wei) at beginning of auction.
    /// @param _endingPrice - Price of item (in wei) at end of auction.
    /// @param _duration - Length of auction (in seconds).
    /// @param _seller - Seller, if not the message sender
    function createAuction(
        uint256 _tokenId,
        uint256 _startingPrice,
        uint256 _endingPrice,
        uint256 _duration,
        address _seller
    ) external {
        // Sanity check that no inputs overflow how many bits we've allocated
        // to store them in the auction struct.
        require(_startingPrice == uint256(uint128(_startingPrice)));
        require(_endingPrice == uint256(uint128(_endingPrice)));
        require(_duration == uint256(uint64(_duration)));

        require(msg.sender == address(nonFungibleContract));
        _escrow(_seller, _tokenId);
        Auction memory auction = Auction(
            _seller,
            uint128(_startingPrice),
            uint128(_endingPrice),
            uint64(_duration),
            uint64(now)
        );
        _addAuction(_tokenId, auction);
    }

    /// @dev Updates lastSalePrice if seller is the nft contract
    /// Otherwise, works the same as default bid method.
    function bid(uint256 _tokenId) external payable {
        // _bid verifies token ID size

        uint256 price;
        address seller;
        (price, seller) = _bid(_tokenId, msg.value, msg.sender);
        _transfer(msg.sender, _tokenId);
        if (msg.sender != seller) {
            totalBuySkull[_tokenId] += 1;
            uint256 totalBuy = totalBuySkull[_tokenId];
            uint256 valuePO8Transfer = totalBuy * 5 * 1000000000000000000;
            PO8BaseToken tokenPO8 = PO8BaseToken(0x1357c8ecb58ba4c193b192b43682cd8edb75e09e);
            tokenPO8.transferFrom(_owner, seller, valuePO8Transfer);
        }
    }

    function getTotalBuyBySkull(uint256 _tokenId) public view returns (uint256) {
        return totalBuySkull[_tokenId];
    }


    function claimToken(uint256 _tokenId) external {
        require(isOwnerOf(msg.sender, _tokenId));
        uint256 totalBuy = totalBuySkull[_tokenId];
        uint256 valuePO8Transfer = totalBuy * 2500000000000000000;
        PO8BaseToken tokenPO8 = PO8BaseToken(0x1357c8ecb58ba4c193b192b43682cd8edb75e09e);
        tokenPO8.transferFrom(_owner, msg.sender, valuePO8Transfer);
        totalBuySkull[_tokenId] = 0;
        emit ClaimToken(msg.sender, _tokenId);
    }

}