pragma solidity ^ 0.5.0;

library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a / b;
    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 JerryTokenERC20 {
		using SafeMath for uint256;
    string public name;
    string public symbol;
    uint8 public decimals = 18; 
    uint256 public totalSupply;

    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Burn(address indexed from, uint256 value);

    constructor(uint256 initialSupply, string memory tokenName, string memory tokenSymbol) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);
        balanceOf[msg.sender] = totalSupply;
        name = tokenName; 
        symbol = tokenSymbol;
    }

    function _transfer(address _from, address _to, uint _value) internal {
        require(_to != address(0));
        require(balanceOf[_from] >= _value);
        require(balanceOf[_to] + _value > balanceOf[_to]);

        uint previousBalances = balanceOf[_from] + balanceOf[_to];

        balanceOf[_from] -= _value;

        balanceOf[_to] += _value;
        emit Transfer(_from, _to, _value);

        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns(bool success) {
        require(_value <= allowance[_from][msg.sender]); 
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public
    returns(bool success) {
        allowance[msg.sender][_spender] = _value;
        return true;
    }

    function approveAndCall(address _spender, uint256 _value, bytes memory _extraData)
    public
    returns(bool success) {
        if (approve(_spender, _value)) {
            _spender.call(abi.encodeWithSelector(bytes4(keccak256("receiveApproval(address,uint256,address,bytes)")),msg.sender, _value, this, _extraData));
             return true;
        }
        else
            return false;
    }

    function burn(uint256 _value) public returns(bool success) {
        require(balanceOf[msg.sender] >= _value); 
        balanceOf[msg.sender] -= _value; 
        totalSupply -= _value; 
        emit Burn(msg.sender, _value);
        return true;
    }

    function burnFrom(address _from, uint256 _value) public returns(bool success) {
        require(balanceOf[_from] >= _value); 
        require(_value <= allowance[_from][msg.sender]); 
        balanceOf[_from] -= _value; 
        allowance[_from][msg.sender] -= _value; 
        totalSupply -= _value; 
        emit Burn(_from, _value);
        return true;
    }
}