pragma solidity ^0.4.22;

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 Ownable {
    address public owner;
    address public newOwner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor() public {
        owner = msg.sender;
        newOwner = address(0);
    }

    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }
    modifier onlyNewOwner() {
        require(msg.sender != address(0));
        require(msg.sender == newOwner);
        _;
    }

    function transferOwnership(address _newOwner) public onlyOwner {
        require(_newOwner != address(0));
        newOwner = _newOwner;
    }

    function acceptOwnership() public onlyNewOwner returns(bool) {
        emit OwnershipTransferred(owner, newOwner);        
        owner = newOwner;
        newOwner = 0x0;
    }
}

contract Pausable is Ownable {
    event Pause();
    event Unpause();

    bool public paused = false;

    modifier whenNotPaused() {
        require(!paused);
        _;
    }

    modifier whenPaused() {
        require(paused);
        _;
    }

    function pause() onlyOwner whenNotPaused public {
        paused = true;
        emit Pause();
    }

    function unpause() onlyOwner whenPaused public {
        paused = false;
        emit Unpause();
    }
}

contract ERC20 {
    function totalSupply() public view returns (uint256);
    function balanceOf(address who) public view returns (uint256);
    function allowance(address owner, address spender) public view returns (uint256);
    function transfer(address to, uint256 value) public returns (bool);
    function transferFrom(address from, address to, uint256 value) public returns (bool);
    function approve(address spender, uint256 value) public returns (bool);

    event Approval(address indexed owner, address indexed spender, uint256 value);
    event Transfer(address indexed from, address indexed to, uint256 value);
}


interface TokenRecipient {
    function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; 
}


contract ROA is ERC20, Ownable, Pausable {

    using SafeMath for uint256;

    string public name;
    string public symbol;
    uint8 constant public decimals =8;
    uint256 internal initialSupply;
    uint256 internal totalSupply_;

    mapping(address => uint256) internal balances;
    mapping(address => mapping(address => uint256)) internal allowed;

    constructor() public {
        name = "ROA COIN";
        symbol = "ROA";
        initialSupply = 8000000000;
        totalSupply_ = initialSupply * 10 ** uint(decimals);
        balances[owner] = totalSupply_;
        emit Transfer(address(0), owner, totalSupply_);
    }

    function () public payable {
        revert();
    }

    function totalSupply() public view returns (uint256) {
        return totalSupply_;
    }

    function transfer(address _to, uint256 _value) public whenNotPaused 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);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    function balanceOf(address _holder) public view returns (uint256 balance) {
        return balances[_holder];
    }

    function transferFrom(address _from, address _to, uint256 _value) public whenNotPaused 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);
        emit Transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public whenNotPaused returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    
    function approveAndCall(address _spender, uint256 _value, bytes _extraData) public returns (bool success) {
        require(isContract(_spender));
        TokenRecipient spender = TokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    function increaseApproval(address _spender, uint256 _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, uint256 _subtractedValue) public returns (bool)
    {
        uint256 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 allowance(address _holder, address _spender) public view returns (uint256) {
        return allowed[_holder][_spender];
    }

    function claimToken(ERC20 token, address _to, uint256 _value) public onlyOwner returns (bool) {
        token.transfer(_to, _value);
        return true;
    }

    function isContract(address addr) internal view returns (bool) {
        uint size;
        assembly{size := extcodesize(addr)}
        return size > 0;
    }

}