pragma solidity ^0.4.24;


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * See https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender)
    public view returns (uint256);

  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
  );
}

contract Ownable {

    address public owner;

    constructor() public {
        owner = msg.sender;
    }

    modifier onlyOwner() {                                                  // to ensure only owner can manipulate a wallet
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) public onlyOwner {
        require(newOwner != address(0));                                    // to ensure the owner's address isn't an uninitialised address, "0x0"
        owner = newOwner;
    }
}

/**
 * @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); // 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 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;
  }
}

contract Coingrid is ERC20, Ownable {
	string public name;
	string public symbol;
	uint8 public decimals;

	address public crowdsale;

	bool public paused;

	using SafeMath for uint256;

	mapping(address => uint256) balances;
	mapping (address => mapping (address => uint256)) internal allowed;

	event Burn(address indexed burner, uint256 value);

	uint256 totalSupply_;

	modifier canMove() {
		require(paused == false || msg.sender == crowdsale);
		_;
	}

	constructor() public {
		totalSupply_ = 100 * 1000000 * 1 ether; // 18 decimals, 100 Million CGT
		name = "Coingrid";
		symbol = "CGT";
		decimals = 18;
		paused = true;
		balances[msg.sender] = totalSupply_;
		emit Transfer(0x0, msg.sender, totalSupply_);
	}

	function totalSupply() public view returns (uint256) {
		return totalSupply_;
	}

	/**
	* @dev Transfer token for a specified address
	* @param _to The address to transfer to.
	* @param _value The amount to be transferred.
	*/
	function transfer(address _to, uint256 _value) public canMove returns (bool) {
		require(_value <= balances[msg.sender]);
		require(_to != address(0));

		balances[msg.sender] = balances[msg.sender].sub(_value);
		balances[_to] = balances[_to].add(_value);
		emit Transfer(msg.sender, _to, _value);
		return true;
	}

	/**
	* @dev Gets the balance of the specified address.
	* @param _owner The address to query the the balance of.
	* @return An uint256 representing the amount owned by the passed address.
	*/
	function balanceOf(address _owner) public view returns (uint256) {
		return balances[_owner];
	}

	/**
	 * @dev Transfer tokens from one address to another
	 * @param _from address The address which you want to send tokens from
	 * @param _to address The address which you want to transfer to
	 * @param _value uint256 the amount of tokens to be transferred
	 */
	function transferFrom(
		address _from,
		address _to,
		uint256 _value
	)
		public
		canMove
		returns (bool)
	{
		require(_value <= balances[_from]);
		require(_value <= allowed[_from][msg.sender]);
		require(_to != address(0));

		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;
	}

	/**
	 * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
	 * Beware that changing an allowance with this method brings the risk that someone may use both the old
	 * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
	 * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
	 * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
	 * @param _spender The address which will spend the funds.
	 * @param _value The amount of tokens to be spent.
	 */
	function approve(address _spender, uint256 _value) public returns (bool) {
		allowed[msg.sender][_spender] = _value;
		emit Approval(msg.sender, _spender, _value);
		return true;
	}

	/**
	 * @dev Function to check the amount of tokens that an owner allowed to a spender.
	 * @param _owner address The address which owns the funds.
	 * @param _spender address The address which will spend the funds.
	 * @return A uint256 specifying the amount of tokens still available for the spender.
	 */
	function allowance(
		address _owner,
		address _spender
	 )
		public
		view
		returns (uint256)
	{
		return allowed[_owner][_spender];
	}

	/**
	 * @dev Increase the amount of tokens that an owner allowed to a spender.
	 * approve should be called when allowed[_spender] == 0. To increment
	 * allowed value is better to use this function to avoid 2 calls (and wait until
	 * the first transaction is mined)
	 * From MonolithDAO Token.sol
	 * @param _spender The address which will spend the funds.
	 * @param _addedValue The amount of tokens to increase the allowance by.
	 */
	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;
	}

	/**
	 * @dev Decrease the amount of tokens that an owner allowed to a spender.
	 * approve should be called when allowed[_spender] == 0. To decrement
	 * allowed value is better to use this function to avoid 2 calls (and wait until
	 * the first transaction is mined)
	 * From MonolithDAO Token.sol
	 * @param _spender The address which will spend the funds.
	 * @param _subtractedValue The amount of tokens to decrease the allowance by.
	 */
	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;
	}

	/**
	  * @dev Burns a specific amount of tokens.
	  * @param _value The amount of token to be burned.
	*/
	function burn(uint256 _value) onlyOwner public {
		_burn(msg.sender, _value);
	}

	function _burn(address _who, uint256 _value) internal {
		require(_value <= balances[_who]);
		// no need to require value <= totalSupply, since that would imply the
		// sender's balance is greater than the totalSupply, which *should* be an assertion failure

		balances[_who] = balances[_who].sub(_value);
		totalSupply_ = totalSupply_.sub(_value);
		emit Burn(_who, _value);
		emit Transfer(_who, address(0), _value);
	}

	function pause() onlyOwner public {
		paused = true;
	}

	function unpause() onlyOwner public {
		paused = false;
	}

	function setCrowdsale(address _crowdsale) onlyOwner public {
		crowdsale = _crowdsale;
	}

	/// @dev This will be invoked by the owner, when owner wants to rescue tokens
	/// @param token Token which will we rescue to the owner from the contract
	function recoverTokens(ERC20 token) onlyOwner public {
		token.transfer(owner, tokensToBeReturned(token));
	}

	/// @dev Interface function, can be overwritten by the superclass
	/// @param token Token which balance we will check and return
	/// @return The amount of tokens (in smallest denominator) the contract owns
	function tokensToBeReturned(ERC20 token) public view returns (uint) {
		return token.balanceOf(this);
	}

}