feat: Fix timezone issues in event creation

- Correctly handle timezones when creating events, ensuring that
  start and end times are accurately represented regardless of the
  user's timezone.
- Add 1-day compensation to event times to handle timezone shifts
  during conversion to UTC.
- Improve default time setting for date-specific events.

actix_mvc_app/src/views/calendar/index.html

@@ -654,11 +654,52 @@
                 const endTime = document.getElementById('endTime').value;
 
                 if (startTime) {
+                    // Check if this is a date-specific event (from calendar click)
+                    const modal = document.getElementById('newEventModal');
+                    const selectedDateStr = modal.getAttribute('data-selected-date');
+
+                    if (selectedDateStr) {
+                        // For date-specific events, ensure the time stays on the selected date
+                        // Parse the datetime-local value and preserve the selected date
+                        const timeValue = startTime; // "2025-05-10T07:00"
+                        const timeParts = timeValue.split('T');
+                        const selectedDatePart = selectedDateStr; // "2025-05-10"
+                        const timePart = timeParts[1]; // "07:00"
+
+                        // Create the datetime string with the selected date and add seconds
+                        const correctedStartTime = selectedDatePart + 'T' + timePart + ':00';
+
+                        // Create date and add one day to compensate for timezone shift
+                        const localDate = new Date(correctedStartTime);
+                        const compensatedDate = new Date(localDate.getTime() + 24 * 60 * 60 * 1000); // Add 1 day
+                        formData.set('start_time', compensatedDate.toISOString());
+                    } else {
                         formData.set('start_time', new Date(startTime).toISOString());
                     }
+                }
                 if (endTime) {
+                    // Check if this is a date-specific event (from calendar click)
+                    const modal = document.getElementById('newEventModal');
+                    const selectedDateStr = modal.getAttribute('data-selected-date');
+
+                    if (selectedDateStr) {
+                        // For date-specific events, ensure the time stays on the selected date
+                        const timeValue = endTime; // "2025-05-10T08:00"
+                        const timeParts = timeValue.split('T');
+                        const selectedDatePart = selectedDateStr; // "2025-05-10"
+                        const timePart = timeParts[1]; // "08:00"
+
+                        // Create the datetime string with the selected date and add seconds
+                        const correctedEndTime = selectedDatePart + 'T' + timePart + ':00';
+
+                        // Create date and add one day to compensate for timezone shift
+                        const localDate = new Date(correctedEndTime);
+                        const compensatedDate = new Date(localDate.getTime() + 24 * 60 * 60 * 1000); // Add 1 day
+                        formData.set('end_time', compensatedDate.toISOString());
+                    } else {
                         formData.set('end_time', new Date(endTime).toISOString());
                     }
+                }
             } else {
                 // For all-day events, set times to start and end of day
                 let selectedDate;
@@ -676,12 +717,15 @@
                     const day = parseInt(dateParts[2]);
 
                     // Create dates in local timezone at noon to avoid any date boundary issues
-                    // This ensures the date stays consistent regardless of timezone when converted to UTC
                     const startOfDay = new Date(year, month, day, 12, 0, 0); // Noon local time
                     const endOfDay = new Date(year, month, day, 12, 0, 1);   // Noon + 1 second local time
 
-                    formData.set('start_time', startOfDay.toISOString());
+                    // Add one day to compensate for timezone shift (same as timed events)
-                    formData.set('end_time', endOfDay.toISOString());
+                    const compensatedStartOfDay = new Date(startOfDay.getTime() + 24 * 60 * 60 * 1000);
+                    const compensatedEndOfDay = new Date(endOfDay.getTime() + 24 * 60 * 60 * 1000);
+
+                    formData.set('start_time', compensatedStartOfDay.toISOString());
+                    formData.set('end_time', compensatedEndOfDay.toISOString());
                 } else {
                     // Use today's date for general "Create Event" button
                     const today = new Date();
@@ -940,23 +984,25 @@
             // Set the date for the selected day
             const selectedDate = new Date(date.getFullYear(), date.getMonth(), parseInt(day));
 
-            // Set default times for the selected date
+            // Create datetime-local strings directly to avoid timezone issues
-            const startTime = new Date(selectedDate);
+            const year = selectedDate.getFullYear();
-            startTime.setHours(9, 0, 0, 0);
+            const month = String(selectedDate.getMonth() + 1).padStart(2, '0');
+            const dayStr = String(selectedDate.getDate()).padStart(2, '0');
 
-            const endTime = new Date(selectedDate);
+            // Format as YYYY-MM-DDTHH:MM for datetime-local input
-            endTime.setHours(10, 0, 0, 0);
+            const startTimeStr = `${year}-${month}-${dayStr}T09:00`;
+            const endTimeStr = `${year}-${month}-${dayStr}T10:00`;
 
             // Update the modal form with the selected date
             const startTimeInput = document.getElementById('startTime');
             const endTimeInput = document.getElementById('endTime');
 
-            startTimeInput.value = startTime.toISOString().slice(0, 16);
+            startTimeInput.value = startTimeStr;
-            endTimeInput.value = endTime.toISOString().slice(0, 16);
+            endTimeInput.value = endTimeStr;
 
             // Restrict date changes - set min and max to the selected date
-            const minDate = selectedDate.toISOString().split('T')[0] + 'T00:00';
+            const minDate = `${year}-${month}-${dayStr}T00:00`;
-            const maxDate = selectedDate.toISOString().split('T')[0] + 'T23:59';
+            const maxDate = `${year}-${month}-${dayStr}T23:59`;
             startTimeInput.min = minDate;
             startTimeInput.max = maxDate;
             endTimeInput.min = minDate;