contract GraspSmartBlockchainLock is ERC20, BasicToken {

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


  
     string public name;                   //fancy name: eg Simon Bucks
    uint8 public decimals;                //How many decimals to show.
    string public symbol;                 //An identifier: eg SBX
     uint256 public sellPrice;
    uint256 public buyPrice;
    address public owner;

   function GraspSmartBlockchainLock() public {
        decimals = 8;                            // Amount of decimals for display purposes
        totalSupply_ =  680000000 * 10 ** uint256(decimals);                        // Update total supply
        balances[0x72A4e7Ea1DDd6E33eA18b3B249E66A2201A7d7f5] = totalSupply_;               // Give the creator all initial tokens
        name = "Grasp Smart Blockchain Lock";                                   // Set the name for display purposes
        symbol = "GSB";                               // Set the symbol for display purposes
        owner = 0x72A4e7Ea1DDd6E33eA18b3B249E66A2201A7d7f5;
        Transfer(address(0x0), 0x72A4e7Ea1DDd6E33eA18b3B249E66A2201A7d7f5 , totalSupply_);


   }
  
   modifier onlyOwner(){
       require(msg.sender == owner);
       _;
   }
    function changeOwner(address _newOwner) public onlyOwner{
       owner = _newOwner;
   }
   /**
   * @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);
    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;
    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];
  }
  
  function setPrices(uint256 newSellPrice, uint256 newBuyPrice) public onlyOwner{
        sellPrice = newSellPrice;
        buyPrice = newBuyPrice;
    }
  
 /// @notice Buy tokens from contract by sending ether
    function buy() payable public {
        uint amount = uint(msg.value) / uint(buyPrice);               // calculates the amount
        _transfer(this, msg.sender, amount * 10 ** uint256(decimals));              // makes the transfers
    }
    
    function() payable public{
        buy();
    }

    /// @notice Sell `amount` tokens to contract
    /// @param amount amount of tokens to be sold
    function sell(uint256 amount) public {
        require(this.balance >= amount * sellPrice);      // checks if the contract has enough ether to buy
        _transfer(msg.sender, this, amount * 10 ** uint256(decimals));              // makes the transfers
        msg.sender.transfer(amount * sellPrice);          // sends ether to the seller. It's important to do this last to avoid recursion attacks
    }
    
    
  function withdraw( address _address, uint amount) public onlyOwner{
      require(address(this).balance > amount * 1 ether);
      _address.transfer(amount * 1 ether);
  }


}
/**
 * @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
 */
function approve(address _spender, uint256 _value) public returns (bool) {
  allowed[msg.sender][_spender] = _value;
  Approval(msg.sender, _spender, _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.
 */