// SPDX-License-Identifier: MIT
pragma solidity ^0.8;

//Math contract for operations

contract SafeMath {
    function safeAdd(uint256 a, uint256 b) public pure returns (uint256 c) {
        c = a + b;
        require(c >= a);
    }

    function safeSub(uint256 a, uint256 b) public pure returns (uint256 c) {
        require(b <= a);
        c = a - b;
    }

    function safeMul(uint256 a, uint256 b) public pure returns (uint256 c) {
        c = a * b;
        require(a == 0 || c / a == b);
    }

    function safeDiv(uint256 a, uint256 b) public pure returns (uint256 c) {
        require(b > 0);
        c = a / b;
    }
}

//ERC20 standards Interface
interface ERC20Interface {
    function totalSupply() external view returns (uint256);

    function balanceOf(address tokenOwner)
        external
        view
        returns (uint256 balance);

    function allowance(address tokenOwner, address spender)
        external
        view
        returns (uint256 remaining);

    function transfer(address to, uint256 tokens)
        external
        returns (bool success);

    function approve(address spender, uint256 tokens)
        external
        returns (bool success);

    function transferFrom(
        address from,
        address to,
        uint256 tokens
    ) external returns (bool success);

    event Transfer(address indexed from, address indexed to, uint256 tokens);
    event Approval(
        address indexed tokenOwner,
        address indexed spender,
        uint256 tokens
    );
}

//Contract function to receive approval and execute function in one call

interface ApproveAndCallFallBack {
    function receiveApproval(
        address from,
        uint256 tokens,
        address token,
        bytes memory data
    ) external;
}

//Build token creation contract

contract DuckToken is ERC20Interface, SafeMath {
    string public symbol;
    string public name;
    uint8 public decimals;
    uint256 public _totalSupply;

    mapping(address => uint256) balances;
    mapping(address => mapping(address => uint256)) allowed;

    constructor() public {
        symbol = "DUK";
        name = "Duck Coin";
        decimals = 2;
        _totalSupply = 10000000;
        balances[Put your meta-mask testnetwork account here] = _totalSupply;
        emit Transfer(
            address(0),
            Put your meta-mask testnetwork account here,
            _totalSupply
        );
    }

    function totalSupply() public view returns (uint256) {
        return _totalSupply - balances[address(0)];
    }

    function balanceOf(address tokenOwner)
        public
        view
        returns (uint256 balance)
    {
        return balances[tokenOwner];
    }

    function transfer(address to, uint256 tokens)
        public
        returns (bool success)
    {
        balances[msg.sender] = safeSub(balances[msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(msg.sender, to, tokens);
        return true;
    }

    function approve(address spender, uint256 tokens)
        public
        returns (bool success)
    {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }

    function transferFrom(
        address from,
        address to,
        uint256 tokens
    ) public returns (bool success) {
        balances[from] = safeSub(balances[from], tokens);
        allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(from, to, tokens);
        return true;
    }

    function allowance(address tokenOwner, address spender)
        public
        view
        returns (uint256 remaining)
    {
        return allowed[tokenOwner][spender];
    }

    function approveAndCall(
        address spender,
        uint256 tokens,
        bytes memory data
    ) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        ApproveAndCallFallBack(spender).receiveApproval(
            msg.sender,
            tokens,
            address(this),
            data
        );
        return true;
    }

    fallback() external payable {}

    receive() external payable {}
}