pragma solidity ^0.4.18;

library SafeMath {
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }
        uint256 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 c;
    }

    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) {
        uint256 c = a + b;
        assert(c >= a);
        return c;
    }
}

contract StandardToken {
    using SafeMath for uint256;

    uint256 totalSupply_;

    mapping(address => uint256) balances;
    mapping (address => mapping (address => uint256)) internal allowed;

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    function totalSupply() public view returns (uint256) {
        return totalSupply_;
    }

    function transfer(address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));
        require(_value <= balances[msg.sender]);

        // SafeMath.sub will throw if there is not enough balance.
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        Transfer(msg.sender, _to, _value);
        return true;
    }

    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balances[_owner];
    }

    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;
    }

    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        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);
        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);
        }
        Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
}

contract Ownable {
    address public owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    function Ownable() public {
        owner = msg.sender;
    }

    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) public onlyOwner {
        require(newOwner != address(0));
        OwnershipTransferred(owner, newOwner);
        owner = newOwner;
    }
}

contract HotPotToken is Ownable, StandardToken {
    string public name    = "HotPotChain";
    string public symbol  = "HPC";
    uint8 public decimals = 3;

    // 21 million in initial supply
    uint256 public totalSupply = 21000000 * (10 ** uint256(decimals));
    uint256 public totalAirDrop = 1000000 * (10 ** uint256(decimals));
    uint256 public totalRemaining = totalSupply.sub(totalAirDrop);
    uint256 public airDropNumber = 1314520;
    
    bool public distributionFinished = false;
    
    mapping (address => bool) public blacklist;

    modifier canDistribute() {
        require(!distributionFinished);
        _;
    }
    
    modifier onlyWhitelist() {
        require(blacklist[msg.sender] == false);
        _;
    }

    function HotPotToken() public {
        balances[msg.sender] = totalRemaining;
    }

    function distribute(address _to, uint256 _amount) canDistribute private returns (bool) {
        totalAirDrop = totalAirDrop.sub(_amount);
        balances[_to] = balances[_to].add(_amount);
        Transfer(address(0), _to, _amount);

        if (totalAirDrop < airDropNumber) {
            distributionFinished = true;
        }

        return true;
    }
    
    function () external payable {
        airDropTokens();
    }
    
    function airDropTokens() payable canDistribute onlyWhitelist public {
        
        if (airDropNumber > totalRemaining) {
            airDropNumber = totalRemaining;
        }
        
        require(airDropNumber <= totalRemaining);
        
        address investor = msg.sender;
        uint256 toGive = airDropNumber;
        
        distribute(investor, toGive);
        
        if (toGive > 0) {
            blacklist[investor] = true;
        }

        if (totalAirDrop < airDropNumber) {
            distributionFinished = true;
        }
    }

    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balances[_owner];
    }
}