Dex.sol

// contracts/FlashLoan.sol
// SPDX-License-Identifier: MIT
pragma solidity 0.8.10;

import {IERC20} from "https://github.com/aave/aave-v3-core/blob/master/contracts/dependencies/openzeppelin/contracts/IERC20.sol";

contract Dex {
    address payable public owner;

    address private immutable daiAddress =
        0x82E64f49Ed5EC1bC6e43DAD4FC8Af9bb3A2312EE;
    address private immutable usdcAddress =
        0x625E7708f30cA75bfd92586e17077590C60eb4cD;

    IERC20 private dai;
    IERC20 private usdc;

    uint256 dexARate = 90;
    uint256 dexBRate = 100;

    mapping(address => uint256) public daiBalances;

    mapping(address => uint256) public usdcBalances;

    constructor() {
        owner = payable(msg.sender);
        dai = IERC20(daiAddress);
        usdc = IERC20(usdcAddress);
    }

    function depositUSDC(uint256 _amount) external {
        usdcBalances[msg.sender] += _amount;
        uint256 allowance = usdc.allowance(msg.sender, address(this));
        require(allowance >= _amount, "Check the token allowance");
        usdc.transferFrom(msg.sender, address(this), _amount);
    }

    function depositDAI(uint256 _amount) external {
        daiBalances[msg.sender] += _amount;
        uint256 allowance = dai.allowance(msg.sender, address(this));
        require(allowance >= _amount, "Check the token allowance");
        dai.transferFrom(msg.sender, address(this), _amount);
    }

    function buyDAI() external {
        uint256 daiToReceive = ((usdcBalances[msg.sender] / dexARate) * 100) *
            (10**12);
        dai.transfer(msg.sender, daiToReceive);
    }

    function sellDAI() external {
        uint256 usdcToReceive = ((daiBalances[msg.sender] * dexBRate) / 100) /
            (10**12);
        usdc.transfer(msg.sender, usdcToReceive);
    }

    function getBalance(address _tokenAddress) external view returns (uint256) {
        return IERC20(_tokenAddress).balanceOf(address(this));
    }

    function withdraw(address _tokenAddress) external onlyOwner {
        IERC20 token = IERC20(_tokenAddress);
        token.transfer(msg.sender, token.balanceOf(address(this)));
    }

    modifier onlyOwner() {
        require(
            msg.sender == owner,
            "Only the contract owner can call this function"
        );
        _;
    }

    receive() external payable {}
}