Untitled

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;

import "forge-std/console.sol";

interface Token {
    /// @param _owner The address from which the balance will be retrieved
    /// @return balance the balance
    function balanceOf(address _owner) external view returns (uint256 balance);

    /// @notice send `_value` token to `_to` from `msg.sender`
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return success Whether the transfer was successful or not
    function transfer(
        address _to,
        uint256 _value
    ) external returns (bool success);

    /// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
    /// @param _from The address of the sender
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return success Whether the transfer was successful or not
    function transferFrom(
        address _from,
        address _to,
        uint256 _value
    ) external returns (bool success);

    /// @notice `msg.sender` approves `_addr` to spend `_value` tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @param _value The amount of wei to be approved for transfer
    /// @return success Whether the approval was successful or not
    function approve(
        address _spender,
        uint256 _value
    ) external returns (bool success);

    /// @param _owner The address of the account owning tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @return remaining Amount of remaining tokens allowed to spent
    function allowance(
        address _owner,
        address _spender
    ) external view returns (uint256 remaining);

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(
        address indexed _owner,
        address indexed _spender,
        uint256 _value
    );
}

contract Standard_Token is Token {
    uint256 private constant MAX_UINT256 = 2 ** 256 - 1;
    mapping(address => uint256) public balances;
    mapping(address => mapping(address => uint256)) public allowed;
    uint256 public totalSupply;
    /*
    NOTE:
    The following variables are OPTIONAL vanities. One does not have to include them.
    They allow one to customise the token contract & in no way influences the core functionality.
    Some wallets/interfaces might not even bother to look at this information.
    */
    string public name; //fancy name: eg Simon Bucks
    uint8 public decimals; //How many decimals to show.
    string public symbol; //An identifier: eg SBX

    constructor(
        uint256 _initialAmount,
        string memory _tokenName,
        uint8 _decimalUnits,
        string memory _tokenSymbol
    ) {
        balances[msg.sender] = _initialAmount; // Give the creator all initial tokens
        totalSupply = _initialAmount; // Update total supply
        name = _tokenName; // Set the name for display purposes
        decimals = _decimalUnits; // Amount of decimals for display purposes
        symbol = _tokenSymbol; // Set the symbol for display purposes
    }

    function transfer(
        address _to,
        uint256 _value
    ) public override returns (bool success) {
        require(
            balances[msg.sender] >= _value,
            "token balance is lower than the value requested"
        );
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        emit Transfer(msg.sender, _to, _value); //solhint-disable-line indent, no-unused-vars
        return true;
    }

    function transferFrom(
        address _from,
        address _to,
        uint256 _value
    ) public override returns (bool success) {
        uint256 allowance = allowed[_from][msg.sender];
        require(
            balances[_from] >= _value && allowance >= _value,
            "token balance or allowance is lower than amount requested"
        );
        balances[_to] += _value;
        balances[_from] -= _value;
        if (allowance < MAX_UINT256) {
            allowed[_from][msg.sender] -= _value;
        }
        emit Transfer(_from, _to, _value); //solhint-disable-line indent, no-unused-vars
        return true;
    }

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

    function approve(
        address _spender,
        uint256 _value
    ) public override returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value); //solhint-disable-line indent, no-unused-vars
        return true;
    }

    function allowance(
        address _owner,
        address _spender
    ) public view override returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }

    function mintToken(address _to, uint _amount) public {
        balances[_to] += _amount;
    }
}

contract Payment {
    function transferERC20(
        address _token,
        address _to,
        uint256 _amount
    ) public {
        Token(_token).transferFrom(msg.sender, _to, _amount);
    }
}


//////////////////////////////////////////// Test

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;

import {Test, Vm} from "forge-std/Test.sol";
import "forge-std/console.sol";
import {Standard_Token, Payment} from "../src/HelloWorld.sol";

contract testSample is Test {
    Standard_Token public _Standard_Token;
    Payment public _Payment;

    address private immutable SELLER = address(1);
    address private constant BUYER = address(2);

    function setUp() public {
        _Standard_Token = new Standard_Token(0, "Token", 18, "Token");
        _Payment = new Payment();

        _Standard_Token.mintToken(SELLER, 10e18);
    }

    function testTransfer(address, address, uint) public {
        // console user balance
        console.log(
            "balance of SELLER before",
            _Standard_Token.balanceOf(SELLER)
        );
        // vm setup to seller account
        vm.startPrank(SELLER);
        // TX1, Approve
        _Standard_Token.approve(address(_Payment), 5e18);
        // TX2, Transfer
        _Payment.transferERC20(address(_Standard_Token), address(0), 5e18);
        console.log(
            "balance of SELLER after",
            _Standard_Token.balanceOf(SELLER)
        );
    }
}