Issue #109 Address code review feedback

- Exit non-zero on IOException when writing output files
- Use hex format for fallback fingerprint (%07x)
- Use report timestamp instead of Instant.now() in summary
- Extract getDifferentApiCount() helper to reduce duplication
- Use helper in generateFingerprint(), generateSummary(), hasDifferences()

Author: simbo1905

json-java21-api-tracker/src/main/java/io/github/simbo1905/tracker/ApiTracker.java

@@ -956,10 +956,7 @@ static String fetchUpstreamSource(String className) {
     /// @param report the full comparison report
     /// @return 7-character fingerprint or "0000000" if no differences
     static String generateFingerprint(JsonObject report) {
-        final var summary = (JsonObject) report.members().get("summary");
-        final var differentApi = ((JsonNumber) summary.members().get("differentApi")).toNumber().longValue();
-        
-        if (differentApi == 0) {
+        if (getDifferentApiCount(report) == 0) {
             return "0000000";
         }
 
@@ -1002,10 +999,25 @@ static String generateFingerprint(JsonObject report) {
             return hexString.substring(0, 7);
         } catch (NoSuchAlgorithmException e) {
             LOGGER.warning("SHA-256 not available, using fallback fingerprint");
-            return String.format("%07d", stableString.hashCode() & 0xFFFFFFF);
+            return String.format("%07x", stableString.hashCode() & 0xFFFFFFF);
         }
     }
 
+    /// Extracts the differentApi count from a report summary
+    /// @param report the comparison report
+    /// @return the count of classes with different APIs
+    private static long getDifferentApiCount(JsonObject report) {
+        final var summary = (JsonObject) report.members().get("summary");
+        if (summary == null) {
+            return 0;
+        }
+        final var differentApiValue = summary.members().get("differentApi");
+        if (differentApiValue instanceof JsonNumber num) {
+            return num.toNumber().longValue();
+        }
+        return 0;
+    }
+
     /// Generates a terse human-readable summary of the API differences
     /// Suitable for GitHub issue body
     /// @param report the full comparison report
@@ -1017,7 +1029,7 @@ static String generateSummary(JsonObject report) {
 
         final var totalClasses = ((JsonNumber) summary.members().get("totalClasses")).toNumber().longValue();
         final var matchingClasses = ((JsonNumber) summary.members().get("matchingClasses")).toNumber().longValue();
-        final var differentApi = ((JsonNumber) summary.members().get("differentApi")).toNumber().longValue();
+        final var differentApi = getDifferentApiCount(report);
         final var missingUpstream = ((JsonNumber) summary.members().get("missingUpstream")).toNumber().longValue();
 
         sb.append("## API Comparison Summary\n\n");
@@ -1066,7 +1078,8 @@ static String generateSummary(JsonObject report) {
         }
 
         sb.append("---\n");
-        sb.append("*Generated by API Tracker on ").append(Instant.now().toString().split("T")[0]).append("*\n");
+        final var timestamp = ((JsonString) report.members().get("timestamp")).value();
+        sb.append("*Generated by API Tracker on ").append(timestamp.split("T")[0]).append("*\n");
 
         return sb.toString();
     }
@@ -1075,8 +1088,6 @@ static String generateSummary(JsonObject report) {
     /// @param report the comparison report
     /// @return true if differentApi > 0
     static boolean hasDifferences(JsonObject report) {
-        final var summary = (JsonObject) report.members().get("summary");
-        final var differentApi = ((JsonNumber) summary.members().get("differentApi")).toNumber().longValue();
-        return differentApi > 0;
+        return getDifferentApiCount(report) > 0;
     }
 }

json-java21-api-tracker/src/main/java/io/github/simbo1905/tracker/ApiTrackerRunner.java

@@ -96,7 +96,10 @@ private static void writeOutputFiles(String jsonOutput, String fingerprint, Stri
       System.out.println();
       System.out.println("Output files written to: " + outputDir.toAbsolutePath());
     } catch (IOException e) {
-      System.err.println("Warning: Could not write output files: " + e.getMessage());
+      System.err.println("Error: Could not write output files: " + e.getMessage());
+      //noinspection CallToPrintStackTrace
+      e.printStackTrace();
+      System.exit(1);
     }
   }