Implement comprehensive external calendar event deduplication and fixes

- Add UID-based deduplication to prefer recurring events over single events with same UID
- Implement RRULE-generated instance detection to filter duplicate occurrences
- Add title normalization for case-insensitive matching and consolidation
- Fix external calendar refresh button with proper error handling and loading states
- Update context menu for external events to show only "View Event Details" option
- Add comprehensive multi-pass deduplication: UID → title consolidation → RRULE filtering

This resolves issues where Outlook calendars showed duplicate events with same UID
but different RRULE states (e.g., "Dragster Stand Up" appearing both as recurring
and single events).

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

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

backend/src/handlers/ics_fetcher.rs

@@ -2,7 +2,7 @@ use axum::{
     extract::{Path, State},
     response::Json,
 };
-use chrono::{DateTime, Utc};
+use chrono::{DateTime, Utc, Datelike};
 use ical::parser::ical::component::IcalEvent;
 use reqwest::Client;
 use serde::Serialize;
@@ -138,6 +138,9 @@ fn parse_ics_content(ics_content: &str) -> Result<Vec<VEvent>, Box<dyn std::erro
         }
     }
 
+    // Deduplicate events based on UID, start time, and summary
+    // Outlook sometimes includes duplicate events (recurring exceptions may appear multiple times)
+    events = deduplicate_events(events);
 
     Ok(events)
 }
@@ -407,4 +410,439 @@ fn parse_datetime_with_tz(datetime_str: &str, tzid: Option<&str>) -> Option<Date
     }
 
     None
+}
+
+/// Deduplicate events based on UID, start time, and summary
+/// Some calendar systems (like Outlook) may include duplicate events in ICS feeds
+/// This includes both exact duplicates and recurring event instances that would be
+/// generated by existing RRULE patterns, and events with same title but different
+/// RRULE patterns that should be consolidated
+fn deduplicate_events(mut events: Vec<VEvent>) -> Vec<VEvent> {
+    use std::collections::HashMap;
+    
+    let original_count = events.len();
+    
+    // First pass: Group by UID and prefer recurring events over single events with same UID
+    let mut uid_groups: HashMap<String, Vec<VEvent>> = HashMap::new();
+    
+    for event in events.drain(..) {
+        // Debug logging to understand what's happening
+        println!("🔍 Event: '{}' at {} (RRULE: {}) - UID: {}", 
+            event.summary.as_ref().unwrap_or(&"No Title".to_string()),
+            event.dtstart.format("%Y-%m-%d %H:%M"),
+            if event.rrule.is_some() { "Yes" } else { "No" },
+            event.uid
+        );
+        
+        uid_groups.entry(event.uid.clone()).or_insert_with(Vec::new).push(event);
+    }
+    
+    let mut uid_deduplicated_events = Vec::new();
+    
+    for (uid, mut events_with_uid) in uid_groups.drain() {
+        if events_with_uid.len() == 1 {
+            // Only one event with this UID, keep it
+            uid_deduplicated_events.push(events_with_uid.into_iter().next().unwrap());
+        } else {
+            // Multiple events with same UID - prefer recurring over non-recurring
+            println!("🔍 Found {} events with UID '{}'", events_with_uid.len(), uid);
+            
+            // Sort by preference: recurring events first, then by completeness
+            events_with_uid.sort_by(|a, b| {
+                let a_has_rrule = a.rrule.is_some();
+                let b_has_rrule = b.rrule.is_some();
+                
+                match (a_has_rrule, b_has_rrule) {
+                    (true, false) => std::cmp::Ordering::Less,   // a (recurring) comes first
+                    (false, true) => std::cmp::Ordering::Greater, // b (recurring) comes first
+                    _ => {
+                        // Both same type (both recurring or both single) - compare by completeness
+                        event_completeness_score(b).cmp(&event_completeness_score(a))
+                    }
+                }
+            });
+            
+            // Keep the first (preferred) event
+            let preferred_event = events_with_uid.into_iter().next().unwrap();
+            println!("🔄 UID dedup: Keeping '{}' (RRULE: {})",
+                preferred_event.summary.as_ref().unwrap_or(&"No Title".to_string()),
+                if preferred_event.rrule.is_some() { "Yes" } else { "No" }
+            );
+            uid_deduplicated_events.push(preferred_event);
+        }
+    }
+    
+    // Second pass: separate recurring and single events from UID-deduplicated set
+    let mut recurring_events = Vec::new();
+    let mut single_events = Vec::new();
+    
+    for event in uid_deduplicated_events.drain(..) {
+        if event.rrule.is_some() {
+            recurring_events.push(event);
+        } else {
+            single_events.push(event);
+        }
+    }
+    
+    // Third pass: Group recurring events by normalized title and consolidate different RRULE patterns
+    let mut title_groups: HashMap<String, Vec<VEvent>> = HashMap::new();
+    
+    for event in recurring_events.drain(..) {
+        let title = normalize_title(event.summary.as_ref().unwrap_or(&String::new()));
+        title_groups.entry(title).or_insert_with(Vec::new).push(event);
+    }
+    
+    let mut deduplicated_recurring = Vec::new();
+    
+    for (title, events_with_title) in title_groups.drain() {
+        if events_with_title.len() == 1 {
+            // Single event with this title, keep as-is
+            deduplicated_recurring.push(events_with_title.into_iter().next().unwrap());
+        } else {
+            // Multiple events with same title - consolidate or deduplicate
+            println!("🔍 Found {} events with title '{}'", events_with_title.len(), title);
+            
+            // Check if these are actually different recurring patterns for the same logical event
+            let consolidated = consolidate_same_title_events(events_with_title);
+            deduplicated_recurring.extend(consolidated);
+        }
+    }
+    
+    // Fourth pass: filter single events, removing those that would be generated by recurring events
+    let mut deduplicated_single = Vec::new();
+    let mut seen_single: HashMap<String, usize> = HashMap::new();
+    
+    for event in single_events.drain(..) {
+        let normalized_title = normalize_title(event.summary.as_ref().unwrap_or(&String::new()));
+        let dedup_key = format!(
+            "{}|{}", 
+            event.dtstart.format("%Y%m%dT%H%M%S"),
+            normalized_title
+        );
+        
+        // First check for exact duplicates among single events
+        if let Some(&existing_index) = seen_single.get(&dedup_key) {
+            let existing_event: &VEvent = &deduplicated_single[existing_index];
+            let current_completeness = event_completeness_score(&event);
+            let existing_completeness = event_completeness_score(existing_event);
+            
+            if current_completeness > existing_completeness {
+                println!("🔄 Replacing single event: Keeping '{}' over '{}'",
+                    event.summary.as_ref().unwrap_or(&"No Title".to_string()),
+                    existing_event.summary.as_ref().unwrap_or(&"No Title".to_string())
+                );
+                deduplicated_single[existing_index] = event;
+            } else {
+                println!("🚫 Discarding duplicate single event: Keeping existing '{}'",
+                    existing_event.summary.as_ref().unwrap_or(&"No Title".to_string())
+                );
+            }
+            continue;
+        }
+        
+        // Check if this single event would be generated by any recurring event
+        let is_rrule_generated = deduplicated_recurring.iter().any(|recurring_event| {
+            // Check if this single event matches the recurring event's pattern (use normalized titles)
+            let single_title = normalize_title(event.summary.as_ref().unwrap_or(&String::new()));
+            let recurring_title = normalize_title(recurring_event.summary.as_ref().unwrap_or(&String::new()));
+            
+            if single_title != recurring_title {
+                return false; // Different events
+            }
+            
+            // Check if this single event would be generated by the recurring event
+            would_event_be_generated_by_rrule(recurring_event, &event)
+        });
+        
+        if is_rrule_generated {
+            println!("🚫 Discarding RRULE-generated instance: '{}' at {} would be generated by recurring event",
+                event.summary.as_ref().unwrap_or(&"No Title".to_string()),
+                event.dtstart.format("%Y-%m-%d %H:%M")
+            );
+        } else {
+            // This is a unique single event
+            seen_single.insert(dedup_key, deduplicated_single.len());
+            deduplicated_single.push(event);
+        }
+    }
+    
+    // Combine recurring and single events
+    let mut result = deduplicated_recurring;
+    result.extend(deduplicated_single);
+    
+    println!("📊 Deduplication complete: {} -> {} events ({} recurring, {} single)", 
+        original_count, result.len(), 
+        result.iter().filter(|e| e.rrule.is_some()).count(),
+        result.iter().filter(|e| e.rrule.is_none()).count()
+    );
+    
+    result
+}
+
+/// Normalize title for grouping similar events
+fn normalize_title(title: &str) -> String {
+    title.trim()
+        .to_lowercase()
+        .chars()
+        .filter(|c| c.is_alphanumeric() || c.is_whitespace())
+        .collect::<String>()
+        .split_whitespace()
+        .collect::<Vec<&str>>()
+        .join(" ")
+}
+
+/// Consolidate events with the same title but potentially different RRULE patterns
+/// This handles cases where calendar systems provide multiple recurring definitions
+/// for the same logical meeting (e.g., one RRULE for Tuesdays, another for Thursdays)
+fn consolidate_same_title_events(events: Vec<VEvent>) -> Vec<VEvent> {
+    if events.is_empty() {
+        return events;
+    }
+    
+    // Log the RRULEs we're working with
+    for event in &events {
+        if let Some(rrule) = &event.rrule {
+            println!("🔍 RRULE for '{}': {}", 
+                event.summary.as_ref().unwrap_or(&"No Title".to_string()),
+                rrule
+            );
+        }
+    }
+    
+    // Check if all events have similar time patterns and could be consolidated
+    let first_event = &events[0];
+    let base_time = first_event.dtstart.time();
+    let base_duration = if let Some(end) = first_event.dtend {
+        Some(end.signed_duration_since(first_event.dtstart))
+    } else {
+        None
+    };
+    
+    // Check if all events have the same time and duration
+    let can_consolidate = events.iter().all(|event| {
+        let same_time = event.dtstart.time() == base_time;
+        let same_duration = match (event.dtend, base_duration) {
+            (Some(end), Some(base_dur)) => end.signed_duration_since(event.dtstart) == base_dur,
+            (None, None) => true,
+            _ => false,
+        };
+        same_time && same_duration
+    });
+    
+    if !can_consolidate {
+        println!("🚫 Cannot consolidate events - different times or durations");
+        // Just deduplicate exact duplicates
+        return deduplicate_exact_recurring_events(events);
+    }
+    
+    // Try to detect if these are complementary weekly patterns
+    let weekly_events: Vec<_> = events.iter()
+        .filter(|e| e.rrule.as_ref().map_or(false, |r| r.contains("FREQ=WEEKLY")))
+        .collect();
+    
+    if weekly_events.len() >= 2 && weekly_events.len() == events.len() {
+        // All events are weekly - try to consolidate into a single multi-day weekly pattern
+        if let Some(consolidated) = consolidate_weekly_patterns(&events) {
+            println!("✅ Successfully consolidated {} weekly patterns into one", events.len());
+            return vec![consolidated];
+        }
+    }
+    
+    // If we can't consolidate, just deduplicate exact matches and keep the most complete one
+    println!("🚫 Cannot consolidate - keeping most complete event");
+    let deduplicated = deduplicate_exact_recurring_events(events);
+    
+    // If we still have multiple events, keep only the most complete one
+    if deduplicated.len() > 1 {
+        let best_event = deduplicated.into_iter()
+            .max_by_key(|e| event_completeness_score(e))
+            .unwrap();
+        
+        println!("🎯 Kept most complete event: '{}'", 
+            best_event.summary.as_ref().unwrap_or(&"No Title".to_string())
+        );
+        vec![best_event]
+    } else {
+        deduplicated
+    }
+}
+
+/// Deduplicate exact recurring event matches
+fn deduplicate_exact_recurring_events(events: Vec<VEvent>) -> Vec<VEvent> {
+    use std::collections::HashMap;
+    
+    let mut seen: HashMap<String, usize> = HashMap::new();
+    let mut deduplicated = Vec::new();
+    
+    for event in events {
+        let dedup_key = format!(
+            "{}|{}|{}", 
+            event.dtstart.format("%Y%m%dT%H%M%S"),
+            event.summary.as_ref().unwrap_or(&String::new()),
+            event.rrule.as_ref().unwrap_or(&String::new())
+        );
+        
+        if let Some(&existing_index) = seen.get(&dedup_key) {
+            let existing_event: &VEvent = &deduplicated[existing_index];
+            let current_completeness = event_completeness_score(&event);
+            let existing_completeness = event_completeness_score(existing_event);
+            
+            if current_completeness > existing_completeness {
+                println!("🔄 Replacing exact duplicate: Keeping more complete event");
+                deduplicated[existing_index] = event;
+            }
+        } else {
+            seen.insert(dedup_key, deduplicated.len());
+            deduplicated.push(event);
+        }
+    }
+    
+    deduplicated
+}
+
+/// Attempt to consolidate multiple weekly RRULE patterns into a single pattern
+fn consolidate_weekly_patterns(events: &[VEvent]) -> Option<VEvent> {
+    use std::collections::HashSet;
+    
+    let mut all_days = HashSet::new();
+    let mut base_event = None;
+    
+    for event in events {
+        let Some(rrule) = &event.rrule else { continue; };
+        
+        if !rrule.contains("FREQ=WEEKLY") {
+            continue;
+        }
+        
+        // Extract BYDAY if present
+        if let Some(byday_part) = rrule.split(';').find(|part| part.starts_with("BYDAY=")) {
+            let days_str = byday_part.strip_prefix("BYDAY=").unwrap_or("");
+            for day in days_str.split(',') {
+                all_days.insert(day.trim().to_string());
+            }
+        } else {
+            // If no BYDAY specified, use the weekday from the start date
+            let weekday = match event.dtstart.weekday() {
+                chrono::Weekday::Mon => "MO",
+                chrono::Weekday::Tue => "TU", 
+                chrono::Weekday::Wed => "WE",
+                chrono::Weekday::Thu => "TH",
+                chrono::Weekday::Fri => "FR",
+                chrono::Weekday::Sat => "SA",
+                chrono::Weekday::Sun => "SU",
+            };
+            all_days.insert(weekday.to_string());
+        }
+        
+        // Use the first event as the base (we already know they have same time/duration)
+        if base_event.is_none() {
+            base_event = Some(event.clone());
+        }
+    }
+    
+    if all_days.is_empty() || base_event.is_none() {
+        return None;
+    }
+    
+    // Create consolidated RRULE
+    let mut base = base_event.unwrap();
+    let days_list: Vec<_> = all_days.into_iter().collect();
+    let byday_str = days_list.join(",");
+    
+    // Build new RRULE with consolidated BYDAY
+    let new_rrule = if let Some(existing_rrule) = &base.rrule {
+        // Remove existing BYDAY and add our consolidated one
+        let parts: Vec<_> = existing_rrule.split(';')
+            .filter(|part| !part.starts_with("BYDAY="))
+            .collect();
+        format!("{};BYDAY={}", parts.join(";"), byday_str)
+    } else {
+        format!("FREQ=WEEKLY;BYDAY={}", byday_str)
+    };
+    
+    base.rrule = Some(new_rrule);
+    
+    println!("🔗 Consolidated weekly pattern: BYDAY={}", byday_str);
+    Some(base)
+}
+
+/// Check if a single event would be generated by a recurring event's RRULE
+fn would_event_be_generated_by_rrule(recurring_event: &VEvent, single_event: &VEvent) -> bool {
+    let Some(rrule) = &recurring_event.rrule else {
+        return false; // No RRULE to check against
+    };
+    
+    // Parse basic RRULE patterns
+    if rrule.contains("FREQ=DAILY") {
+        // Daily recurrence
+        let interval = extract_interval_from_rrule(rrule).unwrap_or(1);
+        let days_diff = (single_event.dtstart.date_naive() - recurring_event.dtstart.date_naive()).num_days();
+        
+        if days_diff >= 0 && days_diff % interval as i64 == 0 {
+            // Check if times match (allowing for timezone differences within same day)
+            let recurring_time = recurring_event.dtstart.time();
+            let single_time = single_event.dtstart.time();
+            return recurring_time == single_time;
+        }
+    } else if rrule.contains("FREQ=WEEKLY") {
+        // Weekly recurrence
+        let interval = extract_interval_from_rrule(rrule).unwrap_or(1);
+        let days_diff = (single_event.dtstart.date_naive() - recurring_event.dtstart.date_naive()).num_days();
+        
+        // First check if it's the same day of week and time
+        let recurring_weekday = recurring_event.dtstart.weekday();
+        let single_weekday = single_event.dtstart.weekday();
+        let recurring_time = recurring_event.dtstart.time();
+        let single_time = single_event.dtstart.time();
+        
+        if recurring_weekday == single_weekday && recurring_time == single_time && days_diff >= 0 {
+            // Calculate how many weeks apart they are
+            let weeks_diff = days_diff / 7;
+            // Check if this falls on an interval boundary
+            return weeks_diff % interval as i64 == 0;
+        }
+    } else if rrule.contains("FREQ=MONTHLY") {
+        // Monthly recurrence - simplified check
+        let months_diff = (single_event.dtstart.year() - recurring_event.dtstart.year()) * 12 
+            + (single_event.dtstart.month() as i32 - recurring_event.dtstart.month() as i32);
+        
+        if months_diff >= 0 {
+            let interval = extract_interval_from_rrule(rrule).unwrap_or(1) as i32;
+            if months_diff % interval == 0 {
+                // Same day of month and time
+                return recurring_event.dtstart.day() == single_event.dtstart.day()
+                    && recurring_event.dtstart.time() == single_event.dtstart.time();
+            }
+        }
+    }
+    
+    false
+}
+
+/// Extract INTERVAL value from RRULE string, defaulting to 1 if not found
+fn extract_interval_from_rrule(rrule: &str) -> Option<u32> {
+    for part in rrule.split(';') {
+        if part.starts_with("INTERVAL=") {
+            return part.strip_prefix("INTERVAL=")
+                .and_then(|s| s.parse().ok());
+        }
+    }
+    Some(1) // Default interval is 1 if not specified
+}
+
+/// Calculate a completeness score for an event based on how many optional fields are filled
+fn event_completeness_score(event: &VEvent) -> u32 {
+    let mut score = 0;
+    
+    if event.summary.is_some() { score += 1; }
+    if event.description.is_some() { score += 1; }
+    if event.location.is_some() { score += 1; }
+    if event.dtend.is_some() { score += 1; }
+    if event.rrule.is_some() { score += 1; }
+    if !event.categories.is_empty() { score += 1; }
+    if !event.alarms.is_empty() { score += 1; }
+    if event.organizer.is_some() { score += 1; }
+    if !event.attendees.is_empty() { score += 1; }
+    
+    score
 }