ساخت صرافی غیرمتمرکز با سالیدیتی

// SPDX-License-Identifier: MIT
pragma solidity ^.8.;

// ERC20 Interface
interface IERC20 {
    function transfer(address to, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
    function balanceOf(address account) external view returns (uint256);
}

contract SimpleDEX {
    // Struct to hold token exchange data
    struct Order {
        address token;
        uint256 amount;
        uint256 price; // Price in wei
    }

    // Mapping of user orders
    mapping(uint256 => Order) public orders;
    uint256 public orderCount;

    // Event declaration for logging
    event OrderPlaced(uint256 orderId, address token, uint256 amount, uint256 price);

    // Place an order to sell tokens
    function placeOrder(address _token, uint256 _amount, uint256 _price) external returns (uint256) {
        IERC20(_token).transferFrom(msg.sender, address(this), _amount); // Transfer tokens to DEX
        orderCount++;
        orders[orderCount] = Order(_token, _amount, _price);
        emit OrderPlaced(orderCount, _token, _amount, _price);
        return orderCount;
    }

    // Buy tokens from DEX
    function buyToken(uint256 _orderId) external payable {
        Order storage order = orders[_orderId];

        require(msg.value >= order.price, "Not enough ETH sent");
        require(order.amount > , "Order does not exist");

        // Transfer tokens to buyer
        IERC20(order.token).transfer(msg.sender, order.amount);
        
        // Send ETH to seller
        payable(address(this)).transfer(msg.value);

        // Update order
        order.amount = ; // Order completed
    }

    // Retrieve balance of a specific token for a user
    function getTokenBalance(address _token) external view returns (uint256) {
        return IERC20(_token).balanceOf(msg.sender);
    }
}