Refactor to eliminate duplicate DateFormat creation

Co-authored-by: LucasXu0 <11863087+LucasXu0@users.noreply.github.com>

frontend/appflowy_flutter/lib/workspace/presentation/widgets/date_picker/widgets/date_time_text_field.dart

@@ -217,9 +217,52 @@ class _DateTimeTextFieldState extends State<DateTimeTextField> {
   }
 
   DateTime? parseDateTimeStr(String string) {
+    final trimmedString = string.trim();
+    
+    // First try to parse using the configured date format
+    try {
+      final result = dateFormat.parseStrict(trimmedString);
+      if (!result.isBefore(kFirstDay) && !result.isAfter(kLastDay)) {
+        return result;
+      }
+    } catch (_) {
+      // If strict parsing fails, try lenient parsing
+      try {
+        final result = dateFormat.parse(trimmedString);
+        if (!result.isBefore(kFirstDay) && !result.isAfter(kLastDay)) {
+          return result;
+        }
+      } catch (_) {
+        // Continue to fallback parser
+      }
+    }
+
+    // If the string includes time, try to parse with the combined format
+    if (widget.includeTime && widget.timeFormat != null) {
+      final combinedFormat = DateFormat(
+        "${widget.dateFormat.pattern} ${widget.timeFormat!.pattern}",
+      );
+      try {
+        final result = combinedFormat.parseStrict(trimmedString);
+        if (!result.isBefore(kFirstDay) && !result.isAfter(kLastDay)) {
+          return result;
+        }
+      } catch (_) {
+        try {
+          final result = combinedFormat.parse(trimmedString);
+          if (!result.isBefore(kFirstDay) && !result.isAfter(kLastDay)) {
+            return result;
+          }
+        } catch (_) {
+          // Continue to fallback parser
+        }
+      }
+    }
+
+    // Fallback to locale-based parsing for natural language dates
     final locale = context.locale.toLanguageTag();
     final parser = AnyDate.fromLocale(locale);
-    final result = parser.tryParse(string);
+    final result = parser.tryParse(trimmedString);
     if (result == null ||
         result.isBefore(kFirstDay) ||
         result.isAfter(kLastDay)) {

frontend/appflowy_flutter/test/widget_test/date_picker_test.dart

@@ -836,6 +836,56 @@ void main() {
       expect(mockState.data.endDateTime, end);
     });
 
+    testWidgets('date format is respected when parsing typed dates',
+        (tester) async {
+      // Test DayMonthYear format (dd/MM/y)
+      await tester.pumpWidget(
+        WidgetTestApp(
+          child: _MockDatePicker(
+            dateFormat: DateFormatPB.DayMonthYear,
+            data: _DatePickerDataStub.empty(),
+          ),
+        ),
+      );
+      await tester.pumpAndSettle();
+
+      final dateTextField = find.byKey(const ValueKey('date_time_text_field_date'));
+      expect(dateTextField, findsOneWidget);
+
+      // Enter 2/9/2025 which should be September 2nd in D/M/Y format
+      await tester.enterText(dateTextField, "2/9/2025");
+      await tester.testTextInput.receiveAction(TextInputAction.done);
+      await tester.pumpAndSettle();
+
+      final expectedDate = DateTime(2025, 9, 2);
+      final mockState = getMockState(tester);
+      expect(mockState.data.dateTime, expectedDate);
+
+      // Test US format (y/MM/dd)
+      mockState.updateDateFormat(DateFormatPB.US);
+      await tester.pumpAndSettle();
+
+      // Enter 2025/2/9 which should be February 9th in Y/M/D format
+      await tester.enterText(dateTextField, "2025/2/9");
+      await tester.testTextInput.receiveAction(TextInputAction.done);
+      await tester.pumpAndSettle();
+
+      final expectedDate2 = DateTime(2025, 2, 9);
+      expect(mockState.data.dateTime, expectedDate2);
+
+      // Test Local format (MM/dd/y)
+      mockState.updateDateFormat(DateFormatPB.Local);
+      await tester.pumpAndSettle();
+
+      // Enter 2/9/2025 which should be February 9th in M/D/Y format
+      await tester.enterText(dateTextField, "2/9/2025");
+      await tester.testTextInput.receiveAction(TextInputAction.done);
+      await tester.pumpAndSettle();
+
+      final expectedDate3 = DateTime(2025, 2, 9);
+      expect(mockState.data.dateTime, expectedDate3);
+    });
+
     testWidgets('same as above but enter time', (tester) async {
       final fourteenth = DateTime(2024, 10, 14, 1);