Add comprehensive timezone support to CalDAV client parsing

Enhanced CalDAV datetime parsing to match the full timezone capabilities
of external calendar parsing, now supporting:

- Standard IANA timezone identifiers (America/Denver, Europe/London, etc.)
- Mozilla/Thunderbird timezone format (/mozilla.org/20070129_1/Europe/London)
- Windows timezone names (60+ global mappings from "Mountain Standard Time" to IANA)
- Timezone abbreviations (EST, PST, MST, CST)
- Timezone offset parsing (20231225T120000-0500, 2023-12-25T12:00:00-05:00)
- ISO datetime formats with UTC and offset notation
- Comprehensive global timezone coverage (North America, Europe, Asia, Australia, Africa, South America)

This ensures consistent timezone handling across both CalDAV client events
and external calendar imports, providing robust support for international users.

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

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

backend/src/calendar.rs

@@ -330,13 +330,26 @@ impl CalDAVClient {
         event: ical::parser::ical::component::IcalEvent,
     ) -> Result<CalendarEvent, CalDAVError> {
         let mut properties: HashMap<String, String> = HashMap::new();
+        let mut full_properties: HashMap<String, String> = HashMap::new();
 
         // Extract all properties from the event
         for property in &event.properties {
-            properties.insert(
-                property.name.to_uppercase(),
-                property.value.clone().unwrap_or_default(),
-            );
+            let prop_name = property.name.to_uppercase();
+            let prop_value = property.value.clone().unwrap_or_default();
+            
+            properties.insert(prop_name.clone(), prop_value.clone());
+            
+            // Build full property string with parameters for timezone parsing
+            let mut full_prop = format!("{}", prop_name);
+            if let Some(params) = &property.params {
+                for (param_name, param_values) in params {
+                    if !param_values.is_empty() {
+                        full_prop.push_str(&format!(";{}={}", param_name, param_values.join(",")));
+                    }
+                }
+            }
+            full_prop.push_str(&format!(":{}", prop_value));
+            full_properties.insert(prop_name, full_prop);
         }
 
         // Required UID field
@@ -349,11 +362,11 @@ impl CalDAVClient {
         let start = properties
             .get("DTSTART")
             .ok_or_else(|| CalDAVError::ParseError("Missing DTSTART field".to_string()))?;
-        let start = self.parse_datetime(start, properties.get("DTSTART"))?;
+        let start = self.parse_datetime(start, full_properties.get("DTSTART"))?;
 
         // Parse end time (optional - use start time if not present)
         let end = if let Some(dtend) = properties.get("DTEND") {
-            Some(self.parse_datetime(dtend, properties.get("DTEND"))?)
+            Some(self.parse_datetime(dtend, full_properties.get("DTEND"))?)
         } else if let Some(_duration) = properties.get("DURATION") {
             // TODO: Parse duration and add to start time
             Some(start)
@@ -671,16 +684,39 @@ impl CalDAVClient {
         Ok(calendar_paths)
     }
 
-    /// Parse iCal datetime format
+    /// Parse iCal datetime format with timezone support
     fn parse_datetime(
         &self,
         datetime_str: &str,
-        _original_property: Option<&String>,
+        original_property: Option<&String>,
     ) -> Result<DateTime<Utc>, CalDAVError> {
         use chrono::TimeZone;
+        use chrono_tz::Tz;
 
-        // Handle different iCal datetime formats
+        // Extract timezone information from the original property if available
+        let mut timezone_id: Option<&str> = None;
+        if let Some(prop) = original_property {
+            // Look for TZID parameter in the property
+            // Format: DTSTART;TZID=America/Denver:20231225T090000
+            if let Some(tzid_start) = prop.find("TZID=") {
+                let tzid_part = &prop[tzid_start + 5..];
+                if let Some(tzid_end) = tzid_part.find(':') {
+                    timezone_id = Some(&tzid_part[..tzid_end]);
+                } else if let Some(tzid_end) = tzid_part.find(';') {
+                    timezone_id = Some(&tzid_part[..tzid_end]);
+                }
+            }
+        }
+
+        // Clean the datetime string - remove any TZID prefix if present
         let cleaned = datetime_str.replace("TZID=", "").trim().to_string();
+        
+        // Split on colon to separate TZID from datetime if format is "TZID=America/Denver:20231225T090000"
+        let datetime_part = if let Some(colon_pos) = cleaned.find(':') {
+            &cleaned[colon_pos + 1..]
+        } else {
+            &cleaned
+        };
 
         // Try different parsing formats
         let formats = [
@@ -690,17 +726,145 @@ impl CalDAVClient {
         ];
 
         for format in &formats {
-            if let Ok(dt) = chrono::NaiveDateTime::parse_from_str(&cleaned, format) {
-                return Ok(Utc.from_utc_datetime(&dt));
+            // Try parsing as UTC first (if it has Z suffix)
+            if datetime_part.ends_with('Z') {
+                if let Ok(dt) = chrono::NaiveDateTime::parse_from_str(&datetime_part[..datetime_part.len()-1], "%Y%m%dT%H%M%S") {
+                    return Ok(dt.and_utc());
+                }
             }
-            if let Ok(date) = chrono::NaiveDate::parse_from_str(&cleaned, format) {
+            
+            // Try parsing with timezone offset (e.g., 20231225T120000-0500)
+            if let Ok(dt) = DateTime::parse_from_str(datetime_part, "%Y%m%dT%H%M%S%z") {
+                return Ok(dt.with_timezone(&Utc));
+            }
+            
+            // Try ISO format with timezone offset (e.g., 2023-12-25T12:00:00-05:00)
+            if let Ok(dt) = DateTime::parse_from_str(datetime_part, "%Y-%m-%dT%H:%M:%S%z") {
+                return Ok(dt.with_timezone(&Utc));
+            }
+            
+            // Try ISO format with Z suffix (e.g., 2023-12-25T12:00:00Z)
+            if let Ok(dt) = DateTime::parse_from_str(datetime_part, "%Y-%m-%dT%H:%M:%SZ") {
+                return Ok(dt.with_timezone(&Utc));
+            }
+            
+            // Try parsing as naive datetime
+            if let Ok(naive_dt) = chrono::NaiveDateTime::parse_from_str(datetime_part, format) {
+                // If we have timezone information, convert accordingly
+                if let Some(tz_id) = timezone_id {
+                    let tz_result = if tz_id.starts_with("/mozilla.org/") {
+                        // Mozilla/Thunderbird format: /mozilla.org/20070129_1/Europe/London
+                        tz_id.split('/').last().and_then(|tz_name| tz_name.parse::<Tz>().ok())
+                    } else if tz_id.contains('/') {
+                        // Standard timezone format: America/New_York, Europe/London
+                        tz_id.parse::<Tz>().ok()
+                    } else {
+                        // Try common abbreviations and Windows timezone names
+                        match tz_id {
+                            // Standard abbreviations
+                            "EST" => Some(Tz::America__New_York),
+                            "PST" => Some(Tz::America__Los_Angeles),
+                            "MST" => Some(Tz::America__Denver), 
+                            "CST" => Some(Tz::America__Chicago),
+                            
+                            // North America - Windows timezone names to IANA mapping
+                            "Mountain Standard Time" => Some(Tz::America__Denver),
+                            "Eastern Standard Time" => Some(Tz::America__New_York),
+                            "Central Standard Time" => Some(Tz::America__Chicago),
+                            "Pacific Standard Time" => Some(Tz::America__Los_Angeles),
+                            "Mountain Daylight Time" => Some(Tz::America__Denver),
+                            "Eastern Daylight Time" => Some(Tz::America__New_York),
+                            "Central Daylight Time" => Some(Tz::America__Chicago),
+                            "Pacific Daylight Time" => Some(Tz::America__Los_Angeles),
+                            "Hawaiian Standard Time" => Some(Tz::Pacific__Honolulu),
+                            "Alaskan Standard Time" => Some(Tz::America__Anchorage),
+                            "Alaskan Daylight Time" => Some(Tz::America__Anchorage),
+                            "Atlantic Standard Time" => Some(Tz::America__Halifax),
+                            "Newfoundland Standard Time" => Some(Tz::America__St_Johns),
+                            
+                            // Europe
+                            "GMT Standard Time" => Some(Tz::Europe__London),
+                            "Greenwich Standard Time" => Some(Tz::UTC),
+                            "W. Europe Standard Time" => Some(Tz::Europe__Berlin),
+                            "Central Europe Standard Time" => Some(Tz::Europe__Warsaw),
+                            "Romance Standard Time" => Some(Tz::Europe__Paris),
+                            "Central European Standard Time" => Some(Tz::Europe__Belgrade),
+                            "E. Europe Standard Time" => Some(Tz::Europe__Bucharest),
+                            "FLE Standard Time" => Some(Tz::Europe__Helsinki),
+                            "GTB Standard Time" => Some(Tz::Europe__Athens),
+                            "Russian Standard Time" => Some(Tz::Europe__Moscow),
+                            "Turkey Standard Time" => Some(Tz::Europe__Istanbul),
+                            
+                            // Asia
+                            "China Standard Time" => Some(Tz::Asia__Shanghai),
+                            "Tokyo Standard Time" => Some(Tz::Asia__Tokyo),
+                            "Korea Standard Time" => Some(Tz::Asia__Seoul),
+                            "Singapore Standard Time" => Some(Tz::Asia__Singapore),
+                            "India Standard Time" => Some(Tz::Asia__Kolkata),
+                            "Pakistan Standard Time" => Some(Tz::Asia__Karachi),
+                            "Bangladesh Standard Time" => Some(Tz::Asia__Dhaka),
+                            "Thailand Standard Time" => Some(Tz::Asia__Bangkok),
+                            "SE Asia Standard Time" => Some(Tz::Asia__Bangkok),
+                            "Myanmar Standard Time" => Some(Tz::Asia__Yangon),
+                            "Sri Lanka Standard Time" => Some(Tz::Asia__Colombo),
+                            "Nepal Standard Time" => Some(Tz::Asia__Kathmandu),
+                            "Central Asia Standard Time" => Some(Tz::Asia__Almaty),
+                            "West Asia Standard Time" => Some(Tz::Asia__Tashkent),
+                            "N. Central Asia Standard Time" => Some(Tz::Asia__Novosibirsk),
+                            "North Asia Standard Time" => Some(Tz::Asia__Krasnoyarsk),
+                            "North Asia East Standard Time" => Some(Tz::Asia__Irkutsk),
+                            "Yakutsk Standard Time" => Some(Tz::Asia__Yakutsk),
+                            "Vladivostok Standard Time" => Some(Tz::Asia__Vladivostok),
+                            "Magadan Standard Time" => Some(Tz::Asia__Magadan),
+                            
+                            // Australia & Pacific
+                            "AUS Eastern Standard Time" => Some(Tz::Australia__Sydney),
+                            "AUS Central Standard Time" => Some(Tz::Australia__Adelaide),
+                            "W. Australia Standard Time" => Some(Tz::Australia__Perth),
+                            "Tasmania Standard Time" => Some(Tz::Australia__Hobart),
+                            "New Zealand Standard Time" => Some(Tz::Pacific__Auckland),
+                            "Fiji Standard Time" => Some(Tz::Pacific__Fiji),
+                            "Tonga Standard Time" => Some(Tz::Pacific__Tongatapu),
+                            
+                            // Africa & Middle East
+                            "South Africa Standard Time" => Some(Tz::Africa__Johannesburg),
+                            "Egypt Standard Time" => Some(Tz::Africa__Cairo),
+                            "Israel Standard Time" => Some(Tz::Asia__Jerusalem),
+                            "Iran Standard Time" => Some(Tz::Asia__Tehran),
+                            "Arabic Standard Time" => Some(Tz::Asia__Baghdad),
+                            "Arab Standard Time" => Some(Tz::Asia__Riyadh),
+                            
+                            // South America
+                            "SA Eastern Standard Time" => Some(Tz::America__Sao_Paulo),
+                            "Argentina Standard Time" => Some(Tz::America__Buenos_Aires),
+                            "SA Western Standard Time" => Some(Tz::America__La_Paz),
+                            "SA Pacific Standard Time" => Some(Tz::America__Bogota),
+                            
+                            _ => None,
+                        }
+                    };
+
+                    if let Some(tz) = tz_result {
+                        // Convert from the specified timezone to UTC
+                        if let Some(local_dt) = tz.from_local_datetime(&naive_dt).single() {
+                            return Ok(local_dt.with_timezone(&Utc));
+                        }
+                    }
+                    // If timezone parsing fails, fall back to UTC
+                }
+                // No timezone info or parsing failed - treat as UTC
+                return Ok(Utc.from_utc_datetime(&naive_dt));
+            }
+            
+            // Try parsing as date only
+            if let Ok(date) = chrono::NaiveDate::parse_from_str(datetime_part, format) {
                 return Ok(Utc.from_utc_datetime(&date.and_hms_opt(0, 0, 0).unwrap()));
             }
         }
 
         Err(CalDAVError::ParseError(format!(
-            "Unable to parse datetime: {}",
-            datetime_str
+            "Unable to parse datetime: {} (cleaned: {}, timezone: {:?})",
+            datetime_str, datetime_part, timezone_id
         )))
     }