pragma solidity ^0.4.21;

library SafeMath {
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }
        uint256 c = a * b;
        require(c / a == b);
        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a / b;
        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        return a - b;
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);
        return c;
    }
}

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));
        emit OwnershipTransferred(owner, newOwner);
        owner = newOwner;
    }
}

contract BabyCoin is Ownable {
    
    using SafeMath for uint256;
    
    string public name;
    string public symbol;
    uint32 public decimals = 18;
    uint256 public totalSupply;
    uint256 public currentTotalSupply = 0;
    uint256 public airdropNum = 2 ether;
    uint256 public airdropSupply = 2000;

    mapping(address => bool) touched;
    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);

    /**
     * Constructor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function BabyCoin(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
        balances[msg.sender] = totalSupply;                // Give the creator all initial tokens
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol;                               // Set the symbol for display purposes
    }

    function _airdrop(address _owner) internal {
        if(!touched[_owner] && currentTotalSupply < airdropSupply) {
            touched[_owner] = true;
            balances[_owner] = balances[_owner].add(airdropNum);
            currentTotalSupply = currentTotalSupply.add(airdropNum);
        }
    }

    function _transfer(address _from, address _to, uint256 _value) internal {
        require(_to != 0x0);
        _airdrop(_from);
        require(_value <= balances[_from]);
        require(balances[_to] + _value >= balances[_to]);
        uint256 previousBalances = balances[_from] + balances[_to];
        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(_from, _to, _value);        
        assert(balances[_from] + balances[_to] == previousBalances);
    }
  
    function transfer(address _to, uint256 _value) public returns (bool) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        require(_value <= allowed[_from][msg.sender]);
        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 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 _who) internal constant returns (uint256)
    {
        if(currentTotalSupply < airdropSupply && _who != owner) {
            if(touched[_who])
                return balances[_who];
            else
                return balances[_who].add(airdropNum);
        } else
            return balances[_who];
    }
    
    function balanceOf(address _owner) public view returns (uint256 balance) {
        return getBalance(_owner);
    }
}