pragma solidity ^0.4.18;

/*******************************************************************************
 *
 * Copyright (c) 2018 CryptoKitty Go MDAO.
 * Released under the MIT License.
 * 
 * CKGO - CryptoKitty Go Catnip Contract
 * Version 18.1.5
 *
 * https://cryptokittygo.com
 * support@cryptokittygo.com
 */


/*******************************************************************************
 *
 * SafeMath
 */
library SafeMath {
    function add(uint a, uint b) internal pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function sub(uint a, uint b) internal pure returns (uint c) {
        require(b <= a);
        c = a - b;
    }
    function mul(uint a, uint b) internal pure returns (uint c) {
        c = a * b;
        require(a == 0 || c / a == b);
    }
    function div(uint a, uint b) internal pure returns (uint c) {
        require(b > 0);
        c = a / b;
    }
}


/*******************************************************************************
 *
 * ERC Token Standard #20 Interface
 * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
 */
contract ERC20Interface {
    function totalSupply() public constant returns (uint);
    function balanceOf(address tokenOwner) public constant returns (uint balance);
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}


/*******************************************************************************
 *
 * ApproveAndCallFallBack
 *
 * Contract function to receive approval and execute function in one call
 * (borrowed from MiniMeToken)
 */
contract ApproveAndCallFallBack {
    function receiveApproval(address from, uint256 tokens, address token, bytes data) public;
}


/*******************************************************************************
 *
 * Owned contract
 */
contract Owned {
    address public owner;
    address public newOwner;

    event OwnershipTransferred(address indexed _from, address indexed _to);

    function Owned() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address _newOwner) public onlyOwner {
        newOwner = _newOwner;
    }
    function acceptOwnership() public {
        require(msg.sender == newOwner);

        OwnershipTransferred(owner, newOwner);
        
        owner = newOwner;
        
        newOwner = address(0);
    }
}


/*******************************************************************************
 *
 * @notice Catnip is the official token of the CryptoKitty Go mobile game.
 *         Players can earn catnip within the app, which can be used for
 *         a variety of in-game features (including breeding new kitties).
 *
 *         Symbol       : CKGO
 *         Name         : CryptoKitty Go Catnip
 *         Total supply : 1,000,000,000
 *         Decimals     : 0
 *
 * @dev This is a standard ERC20 token contract, utilizing SafeMath along
 *      with a few additional public descriptors:
 *          - name
 *          - symbol
 *          - title
 */
contract Catnip is ERC20Interface, Owned {
    using SafeMath for uint;

    string public symbol;
    string public name;
    uint8  public decimals;
    uint   public _totalSupply;

    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowed;

    /***************************************************************************
     *
     * Constructor
     */
    function Catnip() public {
        symbol          = 'CKGO';
        name            = 'CryptoKitty Go Catnip';
        decimals        = 0;
        _totalSupply    = 1000000000 * 10 ** uint(decimals);
        balances[owner] = _totalSupply;
        
        Transfer(address(0), owner, _totalSupply);
    }

    /***************************************************************************
     *
     * Total supply
     */
    function totalSupply() public constant returns (uint) {
        return _totalSupply  - balances[address(0)];
    }

    /***************************************************************************
     *
     * Get the token balance for account `tokenOwner`
     */
    function balanceOf(address tokenOwner) public constant returns (uint balance) {
        return balances[tokenOwner];
    }

    /***************************************************************************
     *
     * Transfer the balance from token owner's account to `to` account
     * - Owner's account must have sufficient balance to transfer
     * - 0 value transfers are allowed
     */
    function transfer(address to, uint tokens) public returns (bool success) {
        balances[msg.sender] = balances[msg.sender].sub(tokens);
        balances[to]         = balances[to].add(tokens);
        
        Transfer(msg.sender, to, tokens);
        
        return true;
    }

    /***************************************************************************
     *
     * Token owner can approve for `spender` to transferFrom(...) `tokens`
     * from the token owner's account
     *
     * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
     * recommends that there are no checks for the approval double-spend attack
     * as this should be implemented in user interfaces 
     */
    function approve(address spender, uint tokens) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;

        Approval(msg.sender, spender, tokens);
        
        return true;
    }

    /***************************************************************************
     *
     * Transfer `tokens` from the `from` account to the `to` account.
     *
     * The calling account must already have sufficient tokens approve(...)-d
     * for spending from the `from` account and:
     *     - From account must have sufficient balance to transfer
     *     - Spender must have sufficient allowance to transfer
     *     - 0 value transfers are allowed
     */
    function transferFrom(
    	address from, address to, uint tokens) public returns (
    	bool success) {
        balances[from]            = balances[from].sub(tokens);
        allowed[from][msg.sender] = allowed[from][msg.sender].sub(tokens);
        balances[to]              = balances[to].add(tokens);

        Transfer(from, to, tokens);
        
        return true;
    }

    /***************************************************************************
     *
     * Returns the amount of tokens approved by the owner that can be
     * transferred to the spender's account
     */
    function allowance(
    	address tokenOwner, address spender) public constant returns (
    	uint remaining) {
        return allowed[tokenOwner][spender];
    }

    /***************************************************************************
     *
     * Token owner can approve for `spender` to transferFrom(...) `tokens`
     * from the token owner's account. The `spender` contract function
     * `receiveApproval(...)` is then executed
     */
    function approveAndCall(
    	address spender, uint tokens, bytes data) public returns (
    	bool success) {
        allowed[msg.sender][spender] = tokens;

        Approval(msg.sender, spender, tokens);
        ApproveAndCallFallBack(spender).receiveApproval(msg.sender, tokens, this, data);
        
        return true;
    }

    /***************************************************************************
     *
     * Don't accept ETH
     */
    function () public payable {
        revert();
    }

    /***************************************************************************
     *
     * Owner can transfer out any accidentally sent ERC20 tokens
     */
    function transferAnyERC20Token(
    	address tokenAddress, uint tokens) public onlyOwner returns (
    	bool success) {
        return ERC20Interface(tokenAddress).transfer(owner, tokens);
    }
}