Fix all-day event date display bug: events created 9/4-9/6 now show correctly instead of 9/3-9/5

- Backend: Store all-day events at noon UTC instead of midnight to avoid timezone boundary issues
- Backend: Remove local timezone conversion for all-day events in series handler
- Frontend: Skip timezone conversion when extracting dates from all-day events for display
- Frontend: Extract dates directly from UTC for all-day events in event_spans_date function

The issue was that timezone conversion of UTC midnight could shift dates backward in western timezones.
Now all-day events use noon UTC storage and pure date extraction without timezone conversion.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/src/handlers/events.rs

@@ -852,10 +852,11 @@ fn parse_event_datetime(
         .map_err(|_| format!("Invalid date format: {}. Expected YYYY-MM-DD", date_str))?;
 
     if all_day {
-        // For all-day events, use midnight UTC
+        // For all-day events, use noon UTC to avoid timezone boundary issues
+        // This ensures the date remains correct when converted to any local timezone
         let datetime = date
-            .and_hms_opt(0, 0, 0)
-            .ok_or_else(|| "Failed to create midnight datetime".to_string())?;
+            .and_hms_opt(12, 0, 0)
+            .ok_or_else(|| "Failed to create noon datetime".to_string())?;
         Ok(Utc.from_utc_datetime(&datetime))
     } else {
         // Parse the time

backend/src/handlers/series.rs

@@ -262,8 +262,8 @@ pub async fn update_event_series(
     Json(request): Json<UpdateEventSeriesRequest>,
 ) -> Result<Json<UpdateEventSeriesResponse>, ApiError> {
     println!(
-        "🔄 Update event series request received: series_uid='{}', update_scope='{}'",
-        request.series_uid, request.update_scope
+        "🔄 Update event series request received: series_uid='{}', update_scope='{}', recurrence_count={:?}, recurrence_end_date={:?}",
+        request.series_uid, request.update_scope, request.recurrence_count, request.recurrence_end_date
     );
 
     // Extract and verify token
@@ -397,8 +397,9 @@ pub async fn update_event_series(
     };
 
     let (start_datetime, end_datetime) = if request.all_day {
+        // For all-day events, use noon UTC to avoid timezone boundary issues
         let start_dt = start_date
-            .and_hms_opt(0, 0, 0)
+            .and_hms_opt(12, 0, 0)
             .ok_or_else(|| ApiError::BadRequest("Invalid start date".to_string()))?;
 
         // For all-day events, also preserve the original date pattern
@@ -414,20 +415,13 @@ pub async fn update_event_series(
         };
 
         let end_dt = end_date
-            .and_hms_opt(23, 59, 59)
+            .and_hms_opt(12, 0, 0)
             .ok_or_else(|| ApiError::BadRequest("Invalid end date".to_string()))?;
 
-        // Convert from local time to UTC
-        let start_local = chrono::Local.from_local_datetime(&start_dt)
-            .single()
-            .ok_or_else(|| ApiError::BadRequest("Ambiguous start datetime".to_string()))?;
-        let end_local = chrono::Local.from_local_datetime(&end_dt)
-            .single()
-            .ok_or_else(|| ApiError::BadRequest("Ambiguous end datetime".to_string()))?;
-        
+        // For all-day events, use UTC directly (no local conversion needed)
         (
-            start_local.with_timezone(&chrono::Utc),
-            end_local.with_timezone(&chrono::Utc),
+            chrono::Utc.from_utc_datetime(&start_dt),
+            chrono::Utc.from_utc_datetime(&end_dt),
         )
     } else {
         let start_time = if !request.start_time.is_empty() {
@@ -765,9 +759,36 @@ fn update_entire_series(
     updated_event.last_modified = Some(now);
     // Keep original created timestamp to preserve event history
 
-    // For simple updates (like drag operations), preserve the existing RRULE
-    // For more complex updates, we might need to regenerate it, but for now keep it simple
-    // updated_event.rrule remains unchanged from the clone
+    // Update RRULE if recurrence parameters are provided
+    if let Some(ref existing_rrule) = updated_event.rrule {
+        let mut new_rrule = existing_rrule.clone();
+        println!("🔄 Original RRULE: {}", existing_rrule);
+        
+        // Update COUNT if provided
+        if let Some(count) = request.recurrence_count {
+            println!("🔄 Updating RRULE with new COUNT: {}", count);
+            // Remove old COUNT or UNTIL parameters
+            new_rrule = new_rrule.split(';')
+                .filter(|part| !part.starts_with("COUNT=") && !part.starts_with("UNTIL="))
+                .collect::<Vec<_>>()
+                .join(";");
+            // Add new COUNT
+            new_rrule = format!("{};COUNT={}", new_rrule, count);
+        } else if let Some(ref end_date) = request.recurrence_end_date {
+            println!("🔄 Updating RRULE with new UNTIL: {}", end_date);
+            // Remove old COUNT or UNTIL parameters
+            new_rrule = new_rrule.split(';')
+                .filter(|part| !part.starts_with("COUNT=") && !part.starts_with("UNTIL="))
+                .collect::<Vec<_>>()
+                .join(";");
+            // Add new UNTIL (convert YYYY-MM-DD to YYYYMMDD format)
+            let until_date = end_date.replace("-", "");
+            new_rrule = format!("{};UNTIL={}", new_rrule, until_date);
+        }
+        
+        println!("🔄 Updated RRULE: {}", new_rrule);
+        updated_event.rrule = Some(new_rrule);
+    }
 
     // Copy the updated event back to existing_event for the main handler
     *existing_event = updated_event.clone();

frontend/src/app.rs

@@ -478,7 +478,10 @@ pub fn App() -> Html {
                                     params.13, // categories
                                     params.14, // reminder
                                     params.15, // recurrence
-                                    params.17, // calendar_path (skipping recurrence_days)
+                                    params.16, // recurrence_days
+                                    params.18, // recurrence_count
+                                    params.19, // recurrence_until
+                                    params.17, // calendar_path
                                     scope,
                                     event_data_for_update.occurrence_date.map(|d| d.format("%Y-%m-%d").to_string()), // occurrence_date
                                 )
@@ -759,6 +762,9 @@ pub fn App() -> Html {
                                             original_event.categories.join(","),
                                             reminder_str.clone(),
                                             recurrence_str.clone(),
+                                            vec![false; 7],
+                                            None,
+                                            None,
                                             original_event.calendar_path.clone(),
                                             scope.clone(),
                                             occurrence_date,

frontend/src/components/create_event_modal.rs

@@ -290,16 +290,32 @@ fn vevent_to_creation_data(event: &crate::models::ical::VEvent, available_calend
         // Reminders - TODO: Parse alarm from VEvent if needed
         reminder: ReminderType::None,
         
-        // Recurrence - TODO: Parse RRULE if needed for advanced editing
-        recurrence: if event.rrule.is_some() {
-            RecurrenceType::Daily // Default, could be enhanced to parse actual RRULE
+        // Recurrence - Parse RRULE if present
+        recurrence: if let Some(ref rrule_str) = event.rrule {
+            parse_rrule_frequency(rrule_str)
         } else {
             RecurrenceType::None
         },
-        recurrence_interval: 1,
-        recurrence_until: None,
-        recurrence_count: None,
-        recurrence_days: vec![false; 7],
+        recurrence_interval: if let Some(ref rrule_str) = event.rrule {
+            parse_rrule_interval(rrule_str)
+        } else {
+            1
+        },
+        recurrence_until: if let Some(ref rrule_str) = event.rrule {
+            parse_rrule_until(rrule_str)
+        } else {
+            None
+        },
+        recurrence_count: if let Some(ref rrule_str) = event.rrule {
+            parse_rrule_count(rrule_str)
+        } else {
+            None
+        },
+        recurrence_days: if let Some(ref rrule_str) = event.rrule {
+            parse_rrule_days(rrule_str)
+        } else {
+            vec![false; 7]
+        },
         
         // Advanced recurrence
         monthly_by_day: None,
@@ -327,4 +343,113 @@ fn vevent_to_creation_data(event: &crate::models::ical::VEvent, available_calend
         original_uid: Some(event.uid.clone()), // Preserve original UID for editing
         occurrence_date: Some(start_local.date()), // The occurrence date being edited
     }
+}
+
+// Parse RRULE frequency component
+fn parse_rrule_frequency(rrule: &str) -> RecurrenceType {
+    if rrule.contains("FREQ=DAILY") {
+        RecurrenceType::Daily
+    } else if rrule.contains("FREQ=WEEKLY") {
+        RecurrenceType::Weekly
+    } else if rrule.contains("FREQ=MONTHLY") {
+        RecurrenceType::Monthly
+    } else if rrule.contains("FREQ=YEARLY") {
+        RecurrenceType::Yearly
+    } else {
+        RecurrenceType::None
+    }
+}
+
+// Parse RRULE interval component
+fn parse_rrule_interval(rrule: &str) -> u32 {
+    if let Some(start) = rrule.find("INTERVAL=") {
+        let interval_part = &rrule[start + 9..];
+        if let Some(end) = interval_part.find(';') {
+            interval_part[..end].parse().unwrap_or(1)
+        } else {
+            interval_part.parse().unwrap_or(1)
+        }
+    } else {
+        1
+    }
+}
+
+// Parse RRULE count component
+fn parse_rrule_count(rrule: &str) -> Option<u32> {
+    if let Some(start) = rrule.find("COUNT=") {
+        let count_part = &rrule[start + 6..];
+        if let Some(end) = count_part.find(';') {
+            count_part[..end].parse().ok()
+        } else {
+            count_part.parse().ok()
+        }
+    } else {
+        None
+    }
+}
+
+// Parse RRULE until component
+fn parse_rrule_until(rrule: &str) -> Option<chrono::NaiveDate> {
+    if let Some(start) = rrule.find("UNTIL=") {
+        let until_part = &rrule[start + 6..];
+        let until_str = if let Some(end) = until_part.find(';') {
+            &until_part[..end]
+        } else {
+            until_part
+        };
+        
+        // UNTIL can be in format YYYYMMDD or YYYYMMDDTHHMMSSZ
+        let date_part = if until_str.len() >= 8 {
+            &until_str[..8]
+        } else {
+            until_str
+        };
+        
+        // Parse YYYYMMDD format
+        if date_part.len() == 8 {
+            if let (Ok(year), Ok(month), Ok(day)) = (
+                date_part[0..4].parse::<i32>(),
+                date_part[4..6].parse::<u32>(),
+                date_part[6..8].parse::<u32>(),
+            ) {
+                chrono::NaiveDate::from_ymd_opt(year, month, day)
+            } else {
+                None
+            }
+        } else {
+            None
+        }
+    } else {
+        None
+    }
+}
+
+// Parse RRULE BYDAY component for weekly recurrence
+fn parse_rrule_days(rrule: &str) -> Vec<bool> {
+    let mut days = vec![false; 7]; // [Sun, Mon, Tue, Wed, Thu, Fri, Sat]
+    
+    if let Some(start) = rrule.find("BYDAY=") {
+        let byday_part = &rrule[start + 6..];
+        let byday_str = if let Some(end) = byday_part.find(';') {
+            &byday_part[..end]
+        } else {
+            byday_part
+        };
+        
+        // Parse comma-separated day codes: SU,MO,TU,WE,TH,FR,SA
+        for day_code in byday_str.split(',') {
+            match day_code.trim() {
+                "SU" => days[0] = true, // Sunday
+                "MO" => days[1] = true, // Monday
+                "TU" => days[2] = true, // Tuesday
+                "WE" => days[3] = true, // Wednesday
+                "TH" => days[4] = true, // Thursday
+                "FR" => days[5] = true, // Friday
+                "SA" => days[6] = true, // Saturday
+                _ => {} // Ignore unknown day codes
+            }
+        }
+    }
+    
+    days
 }

frontend/src/components/week_view.rs

@@ -1320,11 +1320,23 @@ fn calculate_event_layout(events: &[VEvent], date: NaiveDate, time_increment: u3
 
 // Check if an all-day event spans the given date
 fn event_spans_date(event: &VEvent, date: NaiveDate) -> bool {
-    let start_date = event.dtstart.with_timezone(&Local).date_naive();
+    let start_date = if event.all_day {
+        // For all-day events, extract date directly from UTC without timezone conversion
+        // since all-day events are stored at noon UTC to avoid timezone boundary issues
+        event.dtstart.date_naive()
+    } else {
+        event.dtstart.with_timezone(&Local).date_naive()
+    };
+    
     let end_date = if let Some(dtend) = event.dtend {
-        // For all-day events, dtend is often set to the day after the last day
-        // So we need to subtract a day to get the actual last day of the event
-        dtend.with_timezone(&Local).date_naive() - chrono::Duration::days(1)
+        if event.all_day {
+            // For all-day events, dtend is set to the day after the last day (RFC 5545)
+            // Extract date directly from UTC and subtract a day to get actual last day
+            dtend.date_naive() - chrono::Duration::days(1)
+        } else {
+            // For timed events, use timezone conversion
+            dtend.with_timezone(&Local).date_naive()
+        }
     } else {
         // Single day event
         start_date

frontend/src/services/calendar_service.rs

@@ -1678,6 +1678,9 @@ impl CalendarService {
         categories: String,
         reminder: String,
         recurrence: String,
+        recurrence_days: Vec<bool>,
+        recurrence_count: Option<u32>,
+        recurrence_until: Option<String>,
         calendar_path: Option<String>,
         update_scope: String,
         occurrence_date: Option<String>,
@@ -1706,10 +1709,10 @@ impl CalendarService {
             "categories": categories,
             "reminder": reminder,
             "recurrence": recurrence,
-            "recurrence_days": vec![false; 7], // Default - could be enhanced
-            "recurrence_interval": 1_u32, // Default interval
-            "recurrence_end_date": None as Option<String>, // No end date by default
-            "recurrence_count": None as Option<u32>, // No count limit by default
+            "recurrence_days": recurrence_days,
+            "recurrence_interval": 1_u32, // Default interval - could be enhanced to be a parameter
+            "recurrence_end_date": recurrence_until,
+            "recurrence_count": recurrence_count,
             "calendar_path": calendar_path,
             "update_scope": update_scope,
             "occurrence_date": occurrence_date