pragma solidity ^0.6.0;

// SPDX-License-Identifier: MIT
interface IERC20 {
    function totalSupply() external view returns (uint256);

    function balanceOf(address account) external view returns (uint256);

    function allowance(address owner, address spender)
        external
        view
        returns (uint256);

    function transfer(address recipient, uint256 amount)
        external
        returns (bool);

    function approve(address spender, uint256 amount) external returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}

contract ERC20Basic is IERC20 {
    string public name;
    string public symbol;
    uint8 public constant decimals = 18;

    event Approval(
        address indexed tokenOwner,
        address indexed spender,
        uint256 tokens
    );
    event Transfer(address indexed from, address indexed to, uint256 tokens);

    mapping(address => uint256) balances;

    mapping(address => mapping(address => uint256)) allowed;

    uint256 totalSupply_;

    using SafeMath for uint256;

    constructor(
        string memory tokenName,
        string memory tokenSymbol,
        uint256 total
    ) public {
        totalSupply_ = total * 10**uint256(decimals);
        balances[msg.sender] = totalSupply_;
        name = tokenName;
        symbol = tokenSymbol;
    }

    function totalSupply() public override view returns (uint256) {
        return totalSupply_;
    }

    function balanceOf(address tokenOwner)
        public
        override
        view
        returns (uint256)
    {
        return balances[tokenOwner];
    }

    function transfer(address receiver, uint256 numTokens)
        public
        override
        returns (bool)
    {
        require(numTokens <= balances[msg.sender]);
        balances[msg.sender] = balances[msg.sender].sub(numTokens);
        balances[receiver] = balances[receiver].add(numTokens);
        emit Transfer(msg.sender, receiver, numTokens);
        return true;
    }

    function approve(address delegate, uint256 numTokens)
        public
        override
        returns (bool)
    {
        allowed[msg.sender][delegate] = numTokens;
        emit Approval(msg.sender, delegate, numTokens);
        return true;
    }

    function allowance(address owner, address delegate)
        public
        override
        view
        returns (uint256)
    {
        return allowed[owner][delegate];
    }

    function transferFrom(
        address owner,
        address buyer,
        uint256 numTokens
    ) public override returns (bool) {
        require(numTokens <= balances[owner]);
        require(numTokens <= allowed[owner][msg.sender]);

        balances[owner] = balances[owner].sub(numTokens);
        allowed[owner][msg.sender] = allowed[owner][msg.sender].sub(numTokens);
        balances[buyer] = balances[buyer].add(numTokens);
        emit Transfer(owner, buyer, numTokens);
        return true;
    }
}

library SafeMath {
    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;
    }
}