pragma solidity 0.4.24;

/**
 * https://github.com/OpenZeppelin/openzeppelin-solidity/blob/master/contracts/math/SafeMath.sol
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

    /**
    * @dev Multiplies two numbers, throws on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
        // Gas optimization: this is cheaper than asserting '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;
        }

        c = a * b;
        assert(c / a == b);
        return c;
    }

    /**
    * @dev Integer division of two numbers, truncating the quotient.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b > 0);
        // uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
        return a / b;
    }

    /**
    * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    /**
    * @dev Adds two numbers, throws on overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
        c = a + b;
        assert(c >= a);
        return c;
    }
}

/**
 * ERC Token Standard #20 Interface
 * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
 */
contract ERC20Interface {
    uint256 public totalSupply;
    
    function balanceOf(address tokenOwner) public view returns (uint256 balance);
    function allowance(address tokenOwner, address spender) public view returns (uint256 remaining);
    function transfer(address to, uint256 tokens) public returns (bool success);
    function approve(address spender, uint256 tokens) public returns (bool success);
    function transferFrom(address from, address to, uint256 tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint256 tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint256 tokens);
}

contract UBYToken is ERC20Interface {
    using SafeMath for uint256;

    string public symbol;
    string public name;
    uint8 public decimals;

    mapping(address => uint256) public balances;
    mapping(address => mapping(address => uint256)) public allowed;

    modifier onlyPayloadSize(uint size) {
        assert(msg.data.length == size + 4);
        _;
    }

    constructor() public {
        symbol = "UB";
        name = "Ucoin UBY";
        decimals = 18;
        totalSupply = 300000000 * 10**uint(decimals);
        balances[msg.sender] = totalSupply;
        emit Transfer(address(0), msg.sender, totalSupply);
    }


    /**
     * Get the token balance for account `tokenOwner`
     */
    function balanceOf(address tokenOwner) public view returns (uint256 balanceOfOwner) {
        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, uint256 tokens) onlyPayloadSize(2 * 32) public returns (bool success) {
        require(to != address(0));
        require(tokens <= balances[msg.sender]);

        balances[msg.sender] = balances[msg.sender].sub(tokens);
        balances[to] = balances[to].add(tokens);

        emit 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, uint256 tokens) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit 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, uint256 tokens) onlyPayloadSize(3 * 32) public returns (bool success) {
        require(to != address(0));
        require(tokens <= balances[from]);
        require(tokens <= allowed[from][msg.sender]);

        balances[from] = balances[from].sub(tokens);
        allowed[from][msg.sender] = allowed[from][msg.sender].sub(tokens);
        balances[to] = balances[to].add(tokens);

        emit 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 view returns (uint256 remaining) {
        return allowed[tokenOwner][spender];
    }


    /**
     * Don't accept ETH
     */
    function () public payable {
        revert();
    }
}