DexTwo.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import '@openzeppelin-08/token/ERC20/IERC20.sol';
import '@openzeppelin-08/token/ERC20/ERC20.sol';
import '@openzeppelin-08/access/Ownable.sol';

contract DexTwo is Ownable {
  address public token1;
  address public token2;

  constructor() Ownable(msg.sender) {}

  function setTokens(address _token1, address _token2) public onlyOwner {
    token1 = _token1;
    token2 = _token2;
  }

  function addLiquidity(
    address token_address,
    uint256 amount
  ) public onlyOwner {
    IERC20(token_address).transferFrom(msg.sender, address(this), amount);
  }

  // The implementation of the `swap` method has changed.
  function swap(address from, address to, uint256 amount) public {
    require(IERC20(from).balanceOf(msg.sender) >= amount, 'Not enough to swap');
    uint256 swapAmount = getSwapPrice(from, to, amount);
    IERC20(from).transferFrom(msg.sender, address(this), amount);
    IERC20(to).approve(address(this), swapAmount);
    IERC20(to).transferFrom(address(this), msg.sender, swapAmount);
  }

  function getSwapPrice(
    address from,
    address to,
    uint256 amount
  ) public view returns (uint256) {
    return ((amount * IERC20(to).balanceOf(address(this))) /
      IERC20(from).balanceOf(address(this)));
  }

  function approve(address spender, uint256 amount) public {
    SwappableTokenTwo(token1).approve(msg.sender, spender, amount);
    SwappableTokenTwo(token2).approve(msg.sender, spender, amount);
  }

  function balanceOf(
    address token,
    address account
  ) public view returns (uint256) {
    return IERC20(token).balanceOf(account);
  }
}

contract SwappableTokenTwo is ERC20 {
  address private _dex;

  constructor(
    address dexInstance,
    string memory name,
    string memory symbol,
    uint256 initialSupply
  ) ERC20(name, symbol) {
    _mint(msg.sender, initialSupply);
    _dex = dexInstance;
  }

  function approve(address owner, address spender, uint256 amount) public {
    require(owner != _dex, 'InvalidApprover');
    super._approve(owner, spender, amount);
  }
}