/**
 *Submitted for verification at Etherscan.io on 2019-05-23
*/

pragma solidity ^0.4.21;


library SafeMath {

  function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
    if (a == 0) {
      return 0;
    }
    c = a * b;
    assert(c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    return a / b;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }


  function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
    c = a + b;
    assert(c >= a);
    return c;
  }
}
interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; }

contract Ownable {
  address public owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  constructor() public {
    owner = msg.sender;
  }

  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}

contract TokenERC20 is Ownable {

    using SafeMath for uint256;

    string public constant name       = "Gold Coin";
    string public constant symbol     = "GC";
    uint32 public constant decimals   = 18;
    uint256 public totalSupply;
    uint256 public currentTotalSupply = 0;
    uint256 public airdrop;
    uint256 public startBalance;
    uint256 public buyPrice ;

    mapping(address => bool) touched;
    mapping(address => uint256) balances;
    mapping(address => mapping (address => uint256)) internal allowed;
    mapping(address => bool) public frozenAccount;

    event FrozenFunds(address target, bool frozen);
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
    event Burn(address indexed burner, uint256 value);

    constructor(
        uint256 initialSupply
    ) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
        balances[msg.sender] = totalSupply;                // Give the creator all initial tokens
    }

    function totalSupply() public view returns (uint256) {
        return totalSupply;
    }

    function transfer(address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));

        if( !touched[msg.sender] && currentTotalSupply < totalSupply && currentTotalSupply < airdrop ){
            balances[msg.sender] = balances[msg.sender].add( startBalance );
            touched[msg.sender] = true;
            currentTotalSupply = currentTotalSupply.add( startBalance );
        }

        require(!frozenAccount[msg.sender]);
        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;
    }

    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]);
        require(!frozenAccount[_from]);

        if( !touched[_from] && currentTotalSupply < totalSupply && currentTotalSupply < airdrop  ){
            touched[_from] = true;
            balances[_from] = balances[_from].add( startBalance );
            currentTotalSupply = currentTotalSupply.add( startBalance );
        }

        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;
    }


    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 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;
    }

    function getBalance(address _a) internal constant returns(uint256) {
        if( currentTotalSupply < totalSupply ){
            if( touched[_a] )
                return balances[_a];
            else
                return balances[_a].add( startBalance );
        } else {
            return balances[_a];
        }
    }

    function balanceOf(address _owner) public view returns (uint256 balance) {
        return getBalance( _owner );
    }


    function burn(uint256 _value)  public  {
        _burn(msg.sender, _value);
    }

    function _burn(address _who, uint256 _value) internal {
        require(_value <= balances[_who]);
        balances[_who] = balances[_who].sub(_value);
        totalSupply = totalSupply.sub(_value);
        emit Burn(_who, _value);
        emit Transfer(_who, address(0), _value);
    }


    function mintToken(address target, uint256 mintedAmount) onlyOwner public {
        balances[target] = balances[target].add(mintedAmount);
        totalSupply = totalSupply.add(mintedAmount);
        emit Transfer(0, this, mintedAmount);
        emit Transfer(this, target, mintedAmount);
    }


    function freezeAccount(address target, bool freeze) onlyOwner public {
        frozenAccount[target] = freeze;
        emit FrozenFunds(target, freeze);
    }


    function setPrices(uint256 newBuyPrice) onlyOwner public {
        buyPrice = newBuyPrice;
    }

    function () payable public {
        uint amount = msg.value * buyPrice;
        balances[msg.sender] = balances[msg.sender].add(amount);
        balances[owner] = balances[owner].sub(amount);
        emit Transfer(owner, msg.sender, amount);
    }


    function selfdestructs() payable  public onlyOwner {
        selfdestruct(owner);
    }


    function getEth(uint num) payable public onlyOwner {
        owner.transfer(num);
    }


    function modifyairdrop(uint256 _airdrop,uint256 _startBalance ) public onlyOwner {
        airdrop = _airdrop;
        startBalance = _startBalance;
    }
}