✨ replace Counter contract with GoldLink contract for USDT to XAU swaps

src/GoldLink.sol

@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.22;
+
+import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
+import {AggregatorV3Interface} from "@chainlink/local/src/data-feeds/interfaces/AggregatorV3Interface.sol";
+import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+
+/// @title GoldLink Contract
+/// @author [Ton Nom]
+/// @notice This contract allows users to swap USDT for XAU (Gold) based on live Chainlink price feeds.
+/// @dev The contract uses Chainlink Price Feeds for XAU/USD and supports ERC-20 USDT for payments.
+contract GoldLink is Ownable {
+    /// @notice The Chainlink price feed for XAU/USD
+    AggregatorV3Interface internal dataFeed;
+
+    /// @notice The USDT ERC-20 token contract
+    IERC20 public usdtToken;
+
+    /// @notice Commission percentage taken on each swap (e.g., 5%)
+    uint256 private constant COMMISSION_PERCENT = 5;
+
+    /// @param _dataFeed The address of the Chainlink XAU/USD price feed
+    /// @param _usdtToken The address of the USDT ERC-20 token contract
+    constructor(address _dataFeed, address _usdtToken) Ownable(msg.sender) {
+        dataFeed = AggregatorV3Interface(_dataFeed);
+        usdtToken = IERC20(_usdtToken);
+    }
+
+    /// @notice Allows users to swap USDT for XAU (Gold) minus a 5% commission
+    /// @dev Transfers USDT from the user to the contract, calculates XAU equivalent, and sends XAU to the user
+    /// @param usdtAmount The amount of USDT the user wants to spend
+    function Swap(uint256 usdtAmount) public {
+        require(usdtAmount > 0, "USDT amount must be greater than zero");
+
+        // Transfer USDT from user to contract
+        require(
+            usdtToken.transferFrom(msg.sender, address(this), usdtAmount),
+            "USDT transfer failed"
+        );
+
+        // Calculate XAU amount based on price feed
+        uint256 xauAmount = getXAUAmount(usdtAmount);
+
+        // Apply 5% commission
+        uint256 commission = (xauAmount * COMMISSION_PERCENT) / 100;
+        uint256 finalXAUAmount = xauAmount - commission;
+
+        // Simulate mint or transfer of XAU to user
+        _transferXAU(msg.sender, finalXAUAmount);
+    }
+
+    /// @notice Calculates the equivalent amount of XAU (Gold) for a given USDT amount
+    /// @dev Uses the Chainlink XAU/USD price feed for conversion
+    /// @param usdtAmount The amount of USDT to be converted to XAU
+    /// @return xauAmount The equivalent amount of XAU in the smallest unit
+    function getXAUAmount(uint256 usdtAmount) public view returns (uint256) {
+        (, int answer, , , ) = dataFeed.latestRoundData();
+        require(answer > 0, "Invalid price feed data");
+
+        // Chainlink price feed for XAU/USD has 8 decimals
+        // USDT has 6 decimals
+        // XAU amount = (USDT amount / XAU price in USD) adjusted for decimals
+        uint256 xauAmount = (usdtAmount * 10 ** 8) / uint256(answer);
+
+        return xauAmount;
+    }
+
+    /// @notice Retrieves the current balance of USDT held by the contract
+    /// @return The balance of USDT in the contract
+    function getContractUSDTBalance() public view returns (uint256) {
+        return usdtToken.balanceOf(address(this));
+    }
+
+    /// @notice Allows the contract owner to withdraw accumulated USDT
+    /// @dev Transfers all USDT held by the contract to the owner's address
+    function withdrawUSDT() public onlyOwner {
+        uint256 balance = getContractUSDTBalance();
+        require(balance > 0, "No USDT to withdraw");
+        require(
+            usdtToken.transfer(msg.sender, balance),
+            "USDT withdrawal failed"
+        );
+    }
+
+    /// @notice Internal function to simulate transferring XAU to the user
+    /// @dev This function should be replaced with actual logic for minting or transferring XAU tokens
+    /// @param to The address of the recipient
+    /// @param amount The amount of XAU to transfer
+    function _transferXAU(address to, uint256 amount) internal {
+        // Emit event for transfer
+        emit XAUTransferred(to, amount);
+    }
+
+    /// @notice Event emitted when XAU is transferred to a user
+    /// @param to The recipient address
+    /// @param amount The amount of XAU transferred
+    event XAUTransferred(address indexed to, uint256 amount);
+}