Fix Timezone Handling in Commit Timestamps for Consistent Time-of-Day Metrics

utils/dateHelpers.test.ts

@@ -68,54 +68,47 @@ describe('dateHelpers', () => {
     });
 
     it('returns zero metrics for an array containing only Invalid Date strings', () => {
-      // Removed Z here
-      const result = processCommitTimestamps(['2024-13-99T25:99:00', 'hello world']);
+      const result = processCommitTimestamps(['2024-13-99T25:99:00Z', 'hello world']);
       expect(result).toEqual({ morning: 0, afternoon: 0, evening: 0, night: 0 });
     });
 
     it('counts valid morning commits correctly', () => {
-      // Removed Z from both strings
-      const result = processCommitTimestamps(['2024-03-10T09:00:00', '2024-03-10T11:30:00']);
+      const result = processCommitTimestamps(['2024-03-10T09:00:00Z', '2024-03-10T11:30:00Z']);
       expect(result.morning).toBe(2);
       expect(result.afternoon).toBe(0);
       expect(result.evening).toBe(0);
       expect(result.night).toBe(0);
     });
 
     it('counts valid afternoon commits correctly', () => {
-      // Removed Z from both strings
-      const result = processCommitTimestamps(['2024-03-10T12:00:00', '2024-03-10T17:59:00']);
+      const result = processCommitTimestamps(['2024-03-10T12:00:00Z', '2024-03-10T17:59:00Z']);
       expect(result.morning).toBe(0);
       expect(result.afternoon).toBe(2);
     });
 
     it('counts valid evening commits correctly', () => {
-      // Removed Z from both strings
-      const result = processCommitTimestamps(['2024-03-10T18:00:00', '2024-03-10T23:59:00']);
+      const result = processCommitTimestamps(['2024-03-10T18:00:00Z', '2024-03-10T23:59:00Z']);
       expect(result.evening).toBe(2);
     });
 
     it('counts valid night commits correctly', () => {
-      // Removed Z from both strings
-      const result = processCommitTimestamps(['2024-03-10T00:00:00', '2024-03-10T05:59:00']);
+      const result = processCommitTimestamps(['2024-03-10T00:00:00Z', '2024-03-10T05:59:00Z']);
       expect(result.night).toBe(2);
     });
 
     it('ignores invalid dates while counting valid ones', () => {
-      // Removed Z from strings
       const result = processCommitTimestamps([
-        '2024-03-10T09:00:00',
+        '2024-03-10T09:00:00Z',
         'invalid-date',
-        '2024-03-10T14:00:00',
+        '2024-03-10T14:00:00Z',
       ]);
       expect(result.morning).toBe(1);
       expect(result.afternoon).toBe(1);
       expect(result.night).toBe(0);
       expect(result.evening).toBe(0);
     });
 
-    // Regression test: verifies timezone-agnostic behavior.
-    // This test would fail with getHours() in IST but passes with getUTCHours().
+    // Regression test: verifies timezone-agnostic behavior across system timezones.
     it('produces consistent results regardless of system timezone', () => {
       const timestamps = [
         '2024-03-10T09:00:00Z', // 09:00 UTC = morning

utils/dateHelpers.ts

@@ -5,18 +5,16 @@ export interface TimeOfDayMetrics {
   night: number; // 12 AM - 6 AM
 }
 
-export function processCommitTimestamps(commitDates: string[] | Date[]): TimeOfDayMetrics {
+export function processCommitTimestamps(commitDates: (string | Date)[]): TimeOfDayMetrics {
   const metrics: TimeOfDayMetrics = { morning: 0, afternoon: 0, evening: 0, night: 0 };
 
-  commitDates.forEach((dateString) => {
-    if (!dateString) return;
-    const date = new Date(dateString);
+  commitDates.forEach((dateItem) => {
+    if (!dateItem) return;
+    const date = new Date(dateItem);
     if (isNaN(date.getTime())) return;
 
-    // Use getUTCHours() instead of getHours() to ensure timezone-agnostic
-    // results — getHours() returns local time which causes test failures
-    // in non-UTC timezones like IST (UTC+5:30).
-    const hour = date.getUTCHours();
+    const hour =
+      typeof dateItem === 'string' ? getAuthorLocalHour(dateItem) : dateItem.getUTCHours();
 
     if (hour >= 6 && hour < 12) {
       metrics.morning++;