feat: exchange contract with yield tracking

Author: dannweeeee

src/Exchange.sol

@@ -24,6 +24,9 @@ contract Exchange is ReentrancyGuard, Ownable {
     uint256 public fee = 100; // 100 basis points fee (1%)
     address public feeCollector;
 
+    uint256 public lastUpdateTime;
+    uint256 public lastPricePerShare;
+
     event Transfer(address indexed from, address indexed to, uint256 amount, string uen);
     event FeeUpdated(uint256 newFee);
     event FeeCollectorUpdated(address newFeeCollector);
@@ -39,6 +42,8 @@ contract Exchange is ReentrancyGuard, Ownable {
         usdcToken = IERC20(_usdcAddress);
         feeCollector = address(this);
         vault = IERC4626(_vaultAddress);
+        lastUpdateTime = block.timestamp;
+        lastPricePerShare = vault.convertToAssets(1e6);
     }
 
     /////////////////////////
@@ -161,4 +166,89 @@ contract Exchange is ReentrancyGuard, Ownable {
         usdcToken.safeTransfer(_to, _amount);
         emit FeesWithdrawn(_to, _amount);
     }
+
+    /**
+     * @notice Get current price per share
+     * @return Current price of 1 share in terms of assets (USDC)
+     */
+    function getCurrentPricePerShare() public view returns (uint256) {
+        return vault.convertToAssets(1e6);
+    }
+
+    /**
+     * @notice Get vault metrics
+     * @return totalAssets Total assets in vault
+     * @return totalShares Total shares issued
+     * @return pricePerShare Current price per share
+     */
+    function getVaultMetrics() public view returns (uint256 totalAssets, uint256 totalShares, uint256 pricePerShare) {
+        totalAssets = vault.totalAssets();
+        totalShares = vault.totalSupply();
+        pricePerShare = getCurrentPricePerShare();
+    }
+
+    /**
+     * @notice Calculate APY between two price points
+     * @param startPrice Starting price per share
+     * @param endPrice Ending price per share
+     * @param timeElapsedInSeconds Time elapsed between prices in seconds
+     * @return apy Annual Percentage Yield in basis points (1% = 100)
+     */
+    function calculateAPY(uint256 startPrice, uint256 endPrice, uint256 timeElapsedInSeconds)
+        public
+        pure
+        returns (uint256 apy)
+    {
+        require(timeElapsedInSeconds > 0, "Time elapsed must be > 0");
+        require(startPrice > 0, "Start price must be > 0");
+
+        // Calculate yield for the period
+        uint256 yield = ((endPrice - startPrice) * 1e6) / startPrice;
+
+        // Annualize it (multiply by seconds in year and divide by elapsed time)
+        uint256 secondsInYear = 365 days;
+        apy = (yield * secondsInYear) / timeElapsedInSeconds;
+
+        return apy;
+    }
+
+    /**
+     * @notice Get current APY based on last update
+     * @return Current APY in basis points (1% = 100)
+     */
+    function getCurrentAPY() external view returns (uint256) {
+        uint256 currentPrice = getCurrentPricePerShare();
+        uint256 timeElapsed = block.timestamp - lastUpdateTime;
+
+        return calculateAPY(lastPricePerShare, currentPrice, timeElapsed);
+    }
+
+    /**
+     * @notice Update the stored price per share
+     * @dev This can be called periodically to update the reference point for APY calculations
+     */
+    function updatePricePerShare() external {
+        lastPricePerShare = getCurrentPricePerShare();
+        lastUpdateTime = block.timestamp;
+    }
+
+    /**
+     * @notice Get detailed yield information
+     * @return currentPrice Current price per share
+     * @return lastPrice Last recorded price per share
+     * @return timeSinceLastUpdate Seconds since last update
+     * @return currentAPY Current APY in basis points
+     */
+    function getYieldInfo()
+        external
+        view
+        returns (uint256 currentPrice, uint256 lastPrice, uint256 timeSinceLastUpdate, uint256 currentAPY)
+    {
+        currentPrice = getCurrentPricePerShare();
+        lastPrice = lastPricePerShare;
+        timeSinceLastUpdate = block.timestamp - lastUpdateTime;
+        currentAPY = calculateAPY(lastPrice, currentPrice, timeSinceLastUpdate);
+
+        return (currentPrice, lastPrice, timeSinceLastUpdate, currentAPY);
+    }
 }