Improve payment hash generation and validation in BillingService

payment-service/src/main/java/com/techtorque/payment_service/service/impl/BillingServiceImpl.java

@@ -380,10 +380,28 @@ public void verifyAndProcessNotification(MultiValueMap<String, String> formData)
     String md5sig = formData.getFirst("md5sig");
     String paymentId = formData.getFirst("payment_id");
 
-    // Generate hash for verification
-    String hashString = merchantId + orderId + payhereAmount + payhereCurrency + 
-                       statusCode + payHereConfig.getMerchantSecret();
-    String generatedHash = PayHereHashUtil.getMd5(hashString);
+    // Format the received amount to 2 decimal places to match how hash was generated
+    String formattedAmount = payhereAmount;
+    try {
+      java.text.DecimalFormat df = new java.text.DecimalFormat("0.00");
+      java.math.BigDecimal bd = new java.math.BigDecimal(payhereAmount);
+      formattedAmount = df.format(bd);
+    } catch (Exception e) {
+      log.warn("Failed to format payhere_amount '{}', using raw value", payhereAmount);
+    }
+
+    // Validate presence of orderId before proceeding
+    if (orderId == null || orderId.isBlank()) {
+      log.warn("Missing order_id in PayHere notification, skipping processing");
+      return;
+    }
+
+    // Generate verification hash according to PayHere docs
+  // md5sig = MD5(merchant_id + order_id + payhere_amount + payhere_currency + status_code + MD5(merchant_secret)).toUpperCase()
+  String hashedSecret = PayHereHashUtil.getMd5(payHereConfig.getMerchantSecret());
+  String hashString = merchantId + orderId + formattedAmount + payhereCurrency + 
+             statusCode + hashedSecret;
+  String generatedHash = PayHereHashUtil.getMd5(hashString);
 
     // Verify signature
     if (!generatedHash.equalsIgnoreCase(md5sig)) {

payment-service/src/test/java/com/techtorque/payment_service/util/PayHereHashUtilTest.java

@@ -0,0 +1,48 @@
+package com.techtorque.payment_service.util;
+
+import org.junit.jupiter.api.Test;
+
+import java.math.BigDecimal;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class PayHereHashUtilTest {
+
+    @Test
+    public void testGeneratePaymentHash_WithPlainSecret() {
+        String merchantId = "1231971";
+        String orderId = "ORDER-ABC-123";
+        BigDecimal amount = new BigDecimal("1000.00");
+        String currency = "LKR";
+        String merchantSecret = "plain-secret-123";
+
+        // Generate expected: hashedSecret = MD5(merchantSecret)
+        String hashedSecret = PayHereHashUtil.getMd5(merchantSecret);
+        String input = merchantId + orderId + "1000.00" + currency + hashedSecret;
+        String expected = PayHereHashUtil.getMd5(input);
+
+        String actual = PayHereHashUtil.generatePaymentHash(merchantId, orderId, amount, currency, merchantSecret);
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void testGeneratePaymentHash_WithBase64Secret() {
+        String merchantId = "1231971";
+        String orderId = "ORD-BASE64";
+        BigDecimal amount = new BigDecimal("250.00");
+        String currency = "LKR";
+
+        // merchant secret base64 - for test use simple known string
+        String plainSecret = "super-secret";
+        String base64Secret = java.util.Base64.getEncoder().encodeToString(plainSecret.getBytes());
+
+        // The util should decode base64 then MD5
+        String hashedSecret = PayHereHashUtil.getMd5(plainSecret); // decode happens internally in generatePaymentHash
+        String input = merchantId + orderId + "250.00" + currency + hashedSecret;
+        String expected = PayHereHashUtil.getMd5(input);
+
+        String actual = PayHereHashUtil.generatePaymentHash(merchantId, orderId, amount, currency, base64Secret);
+        assertEquals(expected, actual);
+    }
+}