pragma solidity ^0.4.25;

/******************************************/
/*     Netkiller Standard safe token      */
/******************************************/
/* Author netkiller <netkiller@msn.com>   */
/* Home http://www.netkiller.cn           */
/* Version 2018-09-30                     */
/******************************************/

/**
 * @title SafeMath
 * @dev Math operations with safety checks that revert on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, reverts on overflow.
  */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;
    require(c / a == b);

    return c;
  }

  /**
  * @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
  */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b > 0); // Solidity only automatically asserts 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;
  }

  /**
  * @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a);
    uint256 c = a - b;

    return c;
  }

  /**
  * @dev Adds two numbers, reverts on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a);

    return c;
  }

  /**
  * @dev Divides two numbers and returns the remainder (unsigned integer modulo),
  * reverts when dividing by zero.
  */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0);
    return a % b;
  }
}

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 NetkillerToken is Ownable{
    
    using SafeMath for uint256;
    
    string public name;
    string public symbol;
    uint public decimals;
    uint256 public totalSupply;
    
    // This creates an array with all balances
    mapping (address => uint256) internal balances;
    mapping (address => mapping (address => uint256)) internal allowed;

    // This generates a public event on the blockchain that will notify clients
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    constructor(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol,
        uint decimalUnits
    ) public {
        owner = msg.sender;
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol; 
        decimals = decimalUnits;
        totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
        balances[msg.sender] = totalSupply;                // Give the creator all initial token
    }

    function balanceOf(address _address) view public returns (uint256 balance) {
        return balances[_address];
    }
    
    /* Internal transfer, only can be called by this contract */
    function _transfer(address _from, address _to, uint256 _value) internal {
        require (_to != address(0));                        // Prevent transfer to 0x0 address. Use burn() instead
        require (balances[_from] >= _value);                // Check if the sender has enough
        require (balances[_to] + _value > balances[_to]);   // Check for overflows
        balances[_from] = balances[_from].sub(_value);      // Subtract from the sender
        balances[_to] = balances[_to].add(_value);          // Add the same to the recipient
        emit Transfer(_from, _to, _value);
    }

    function transfer(address _to, uint256 _value) public returns (bool success) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= balances[_from]);
        require(_value <= allowed[_from][msg.sender]);     // Check allowance
        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 success) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    function allowance(address _owner, address _spender) view public returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }

    function airdrop(address[] _to, uint256 _value) onlyOwner public returns (bool success) {
        
        require(_value > 0 && balanceOf(msg.sender) >= _value.mul(_to.length));
        
        for (uint i=0; i<_to.length; i++) {
            _transfer(msg.sender, _to[i], _value);
        }
        return true;
    }
    
    function batchTransfer(address[] _to, uint256[] _value) onlyOwner public returns (bool success) {
        require(_to.length == _value.length);

        uint256 amount = 0;
        for(uint n=0;n<_value.length;n++){
            amount = amount.add(_value[n]);
        }
        
        require(amount > 0 && balanceOf(msg.sender) >= amount);
        
        for (uint i=0; i<_to.length; i++) {
            transfer(_to[i], _value[i]);
        }
        return true;
    }
}