pragma solidity ^0.4.23;


/**
 * @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.
   */
  function Ownable() public {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @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 {
    require(newOwner != address(0));
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}

// File: contracts\utils\SafeMath.sol

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */
  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;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  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;
  }

  /**
  * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
    c = a + b;
    assert(c >= a);
    return c;
  }
}


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

/**
 * @title Basic token
 * @dev Basic version of StandardToken, with no allowances.
 */
contract BasicToken is ERC20Basic {
  using SafeMath for uint256;

  mapping(address => uint256) balances;

  uint256 totalSupply_;

  /**
  * @dev total number of tokens in existence
  */
  function totalSupply() public view returns (uint256) {
    return totalSupply_;
  }

  /**
  * @dev transfer token for a specified address
  * @param _to The address to transfer to.
  * @param _value The amount to be transferred.
  */
  function transfer(address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[msg.sender]);

    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    emit Transfer(msg.sender, _to, _value);
    return true;
  }

  /**
  * @dev Gets the balance of the specified address.
  * @param _owner The address to query the the balance of.
  * @return An uint256 representing the amount owned by the passed address.
  */
  function balanceOf(address _owner) public view returns (uint256) {
    return balances[_owner];
  }

}


/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
  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
  );
}


/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * @dev https://github.com/ethereum/EIPs/issues/20
 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
contract StandardToken is ERC20, BasicToken {

  mapping (address => mapping (address => uint256)) internal allowed;


  /**
   * @dev Transfer tokens from one address to another
   * @param _from address The address which you want to send tokens from
   * @param _to address The address which you want to transfer to
   * @param _value uint256 the amount of tokens to be transferred
   */
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);

    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    emit Transfer(_from, _to, _value);
    return true;
  }

  /**
   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   *
   * Beware that changing an allowance with this method brings the risk that someone may use both the old
   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   * @param _spender The address which will spend the funds.
   * @param _value The amount of tokens to be spent.
   */
  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
  }

  /**
   * @dev Function to check the amount of tokens that an owner allowed to a spender.
   * @param _owner address The address which owns the funds.
   * @param _spender address The address which will spend the funds.
   * @return A uint256 specifying the amount of tokens still available for the spender.
   */
  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];
  }

  /**
   * @dev Increase the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To increment
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _addedValue The amount of tokens to increase the allowance by.
   */
  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;
  }

  /**
   * @dev Decrease the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To decrement
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _subtractedValue The amount of tokens to decrease the allowance by.
   */
  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;
  }

}


contract AtomicSwappableToken is StandardToken {
  struct HashLockContract {
    address sender;
    address receiver;
    uint amount;
    bytes32 hashlock;
    uint timelock;
    bytes32 secret;
    States state;
  }

  enum States {
    INVALID,
    OPEN,
    CLOSED,
    REFUNDED
  }

  mapping (bytes32 => HashLockContract) private contracts;

  modifier futureTimelock(uint _time) {
    // only requirement is the timelock time is after the last blocktime (now).
    // probably want something a bit further in the future then this.
    // but this is still a useful sanity check:
    require(_time > now);
    _;
}

  modifier contractExists(bytes32 _contractId) {
    require(_contractExists(_contractId));
    _;
  }

  modifier hashlockMatches(bytes32 _contractId, bytes32 _secret) {
    require(contracts[_contractId].hashlock == keccak256(_secret));
    _;
  }

  modifier closable(bytes32 _contractId) {
    require(contracts[_contractId].state == States.OPEN);
    require(contracts[_contractId].timelock > now);
    _;
  }

  modifier refundable(bytes32 _contractId) {
    require(contracts[_contractId].state == States.OPEN);
    require(contracts[_contractId].timelock <= now);
    _;
  }

  event NewHashLockContract (
    bytes32 indexed contractId,
    address indexed sender,
    address indexed receiver,
    uint amount,
    bytes32 hashlock,
    uint timelock
  );

  event SwapClosed(bytes32 indexed contractId);
  event SwapRefunded(bytes32 indexed contractId);


  function open (
    address _receiver,
    bytes32 _hashlock,
    uint _timelock,
    uint _amount
  ) public
    futureTimelock(_timelock)
    returns (bytes32 contractId)
  {
    contractId = keccak256 (
      msg.sender,
      _receiver,
      _amount,
      _hashlock,
      _timelock
    );

    // the new contract must not exist
    require(!_contractExists(contractId));

    // transfer token to this contract
    require(transfer(address(this), _amount));

    contracts[contractId] = HashLockContract(
      msg.sender,
      _receiver,
      _amount,
      _hashlock,
      _timelock,
      0x0,
      States.OPEN
    );

    emit NewHashLockContract(contractId, msg.sender, _receiver, _amount, _hashlock, _timelock);
  }

  function close(bytes32 _contractId, bytes32 _secret)
    public
    contractExists(_contractId)
    hashlockMatches(_contractId, _secret)
    closable(_contractId)
    returns (bool)
  {
    HashLockContract storage c = contracts[_contractId];
    c.secret = _secret;
    c.state = States.CLOSED;
    require(this.transfer(c.receiver, c.amount));
    emit SwapClosed(_contractId);
    return true;
  }

  function refund(bytes32 _contractId)
    public
    contractExists(_contractId)
    refundable(_contractId)
    returns (bool)
  {
    HashLockContract storage c = contracts[_contractId];
    c.state = States.REFUNDED;
    require(this.transfer(c.sender, c.amount));
    emit SwapRefunded(_contractId);
    return true;
  }

  function _contractExists(bytes32 _contractId) internal view returns (bool exists) {
    exists = (contracts[_contractId].sender != address(0));
  }

  function checkContract(bytes32 _contractId)
    public
    view
    contractExists(_contractId)
    returns (
      address sender,
      address receiver,
      uint amount,
      bytes32 hashlock,
      uint timelock,
      bytes32 secret
    )
  {
    HashLockContract memory c = contracts[_contractId];
    return (
      c.sender,
      c.receiver,
      c.amount,
      c.hashlock,
      c.timelock,
      c.secret
    );
  }

}


contract TokenReceiver {
  function receiveApproval(address from, uint amount, address tokenAddress, bytes data) public;
}



contract MagicKeys is AtomicSwappableToken, Ownable {

  string public name;                //The shoes name: e.g. MB
  string public symbol;              //The shoes symbol: e.g. MB
  uint8 public decimals;             //Number of decimals of the smallest unit

  constructor (
    string _name,
    string _symbol
  ) public {
    name = _name;
    symbol = _symbol;
    decimals = 18;  // set as default
  }


  function _mint(address _to, uint _amount) internal returns (bool) {
    totalSupply_ = totalSupply_.add(_amount);
    balances[_to] = balances[_to].add(_amount);
    emit Transfer(address(0), _to, _amount);
  }

  function mint(address _to, uint256 _amount) onlyOwner public returns (bool) {
    _mint(_to, _amount);
    return true;
  }

  function approveAndCall(address _spender, uint _amount, bytes _data) public {
    if(approve(_spender, _amount)) {
      TokenReceiver(_spender).receiveApproval(msg.sender, _amount, address(this), _data);
    }
  }

}