feat: add RRULE parsing to shared package and improve ProposedEventCard UI

- Add rrule library to shared package for RRULE string parsing
- Add rruleHelpers.ts with parseRRule() returning freq, until, count, interval, byDay
- Add formatters.ts with German date/time formatters for client and server
- Extend CreateEventDTO with exceptionDates field for proposals
- Extend ChatModel schema with exceptionDates, deleteMode, occurrenceDate
- Update proposeUpdateEvent tool to support isRecurring and recurrenceRule params
- ProposedEventCard now shows green "Neue Ausnahme" and "Neues Ende" text
- Add Sport test scenario with dynamic exception and UNTIL responses
- Update CLAUDE.md documentation

CLAUDE.md

@@ -309,7 +309,9 @@ src/
 │                         # DAY_TO_GERMAN, DAY_TO_GERMAN_SHORT, MONTH_TO_GERMAN
 └── utils/
     ├── index.ts
-    └── dateHelpers.ts    # getDay() - get date for specific weekday relative to today
+    ├── dateHelpers.ts    # getDay() - get date for specific weekday relative to today
+    ├── formatters.ts     # formatDate(), formatTime(), formatDateTime(), formatDateWithWeekday() - German locale
+    └── rruleHelpers.ts   # parseRRule() - parse RRULE strings to extract freq, until, count, interval, byDay
 ```
 
 **Key Types:**
@@ -326,7 +328,7 @@ src/
 - `Conversation`: id, userId, createdAt?, updatedAt? (messages loaded separately via lazy loading)
 - `CreateUserDTO`: email, userName, password (for registration)
 - `LoginDTO`: identifier (email OR userName), password
-- `CreateEventDTO`: Used for creating events AND for AI-proposed events
+- `CreateEventDTO`: Used for creating events AND for AI-proposed events, includes optional `exceptionDates` for proposals
 - `GetMessagesOptions`: Cursor-based pagination with `before?: string` and `limit?: number`
 - `ConversationSummary`: id, lastMessage?, createdAt? (for conversation list)
 - `UpdateMessageDTO`: proposalId?, respondedAction? (for marking individual proposals as confirmed/rejected)
@@ -467,7 +469,8 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - `ChatRepository` interface: updateMessage() and updateProposalResponse() for per-proposal respondedAction tracking
   - `GPTAdapter`: Full implementation with OpenAI GPT (gpt-4o-mini model), function calling for calendar operations, collects multiple proposals per response
   - `ai/utils/`: Provider-agnostic shared utilities (systemPrompt, toolDefinitions, toolExecutor, eventFormatter)
-  - `ai/utils/systemPrompt`: Includes RRULE documentation - AI knows to create separate events when times differ by day
+  - `ai/utils/systemPrompt`: Includes RRULE documentation - AI knows to create separate events when times differ by day, warns AI not to put RRULE in description field
+  - `ai/utils/toolDefinitions`: proposeUpdateEvent supports `isRecurring` and `recurrenceRule` parameters for adding UNTIL or modifying recurrence
   - `utils/recurrenceExpander`: Handles RRULE parsing, strips `RRULE:` prefix if present (AI may include it), filters out exceptionDates
   - `logging/`: Structured logging with pino, pino-http middleware, @Logged decorator
   - All repositories and GPTAdapter decorated with @Logged for automatic method logging
@@ -477,7 +480,11 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - `AuthService`: refreshToken()
   - JWT authentication (currently using simple X-User-Id header)
 
-**Shared:** Types, DTOs, constants (Day, Month with German translations), ExpandedEvent type, and date utilities defined and exported.
+**Shared:**
+- Types, DTOs, constants (Day, Month with German translations), ExpandedEvent type defined and exported
+- `rruleHelpers.ts`: `parseRRule()` parses RRULE strings using rrule library, returns `ParsedRRule` with freq, until, count, interval, byDay
+- `formatters.ts`: German date/time formatters (`formatDate`, `formatTime`, `formatDateTime`, `formatDateWithWeekday`) used by both client and server
+- rrule library added as dependency for RRULE parsing
 
 **Frontend:**
 - **Authentication fully implemented:**
@@ -525,7 +532,7 @@ NODE_ENV=development        # development = pretty logs, production = JSON
 - `ModalBase`: Reusable modal wrapper with backdrop (absolute-positioned behind card), uses CardBase internally - provides click-outside-to-close, Android back button support, and proper scrolling on Android
 - `EventCardBase`: Event card with date/time/recurring icons - uses CardBase for structure
 - `EventCard`: Uses EventCardBase + edit/delete buttons (TouchableOpacity with delayPressIn for scroll-friendly touch handling)
-- `ProposedEventCard`: Uses EventCardBase + confirm/reject buttons for chat proposals (supports create/update/delete actions with deleteMode display)
+- `ProposedEventCard`: Uses EventCardBase + confirm/reject buttons for chat proposals, displays green highlighted text for new changes ("Neue Ausnahme: [date]" for single delete, "Neues Ende: [date]" for UNTIL updates)
 - `DeleteEventModal`: Delete confirmation modal using ModalBase - shows three options for recurring events (single/future/all), simple confirm for non-recurring
 - `EventOverlay` (in calendar.tsx): Day events overlay using ModalBase - shows EventCards for selected day
 - `Themes.tsx`: Theme definitions with THEMES object (defaultLight, defaultDark) including all color tokens (textPrimary, borderPrimary, eventIndicator, secondaryBg, shadowColor, etc.)

apps/client/src/components/ProposedEventCard.tsx

@@ -1,34 +1,15 @@
 import { View, Text, Pressable } from "react-native";
-import { ProposedEventChange, RecurringDeleteMode } from "@calchat/shared";
+import { Feather } from "@expo/vector-icons";
+import { ProposedEventChange, parseRRule, formatDate } from "@calchat/shared";
 import { useThemeStore } from "../stores/ThemeStore";
 import { EventCardBase } from "./EventCardBase";
 
-const DELETE_MODE_LABELS: Record<RecurringDeleteMode, string> = {
-  single: "Nur dieses Vorkommen",
-  future: "Dieses & zukuenftige",
-  all: "Alle Vorkommen",
-};
-
 type ProposedEventCardProps = {
   proposedChange: ProposedEventChange;
   onConfirm: () => void;
   onReject: () => void;
 };
 
-const DeleteModeBadge = ({ mode }: { mode: RecurringDeleteMode }) => {
-  const { theme } = useThemeStore();
-  return (
-    <View
-      className="self-start px-2 py-1 rounded-md mb-2"
-      style={{ backgroundColor: theme.rejectButton }}
-    >
-      <Text style={{ color: theme.buttonText }} className="text-xs font-medium">
-        {DELETE_MODE_LABELS[mode]}
-      </Text>
-    </View>
-  );
-};
-
 const ConfirmRejectButtons = ({
   isDisabled,
   respondedAction,
@@ -84,15 +65,21 @@ export const ProposedEventCard = ({
   onConfirm,
   onReject,
 }: ProposedEventCardProps) => {
+  const { theme } = useThemeStore();
   const event = proposedChange.event;
-  // respondedAction is now part of the proposedChange
   const isDisabled = !!proposedChange.respondedAction;
 
-  // Show delete mode badge for delete actions on recurring events
-  const showDeleteModeBadge =
+  // For delete/single action, the occurrenceDate becomes a new exception
+  const newExceptionDate =
     proposedChange.action === "delete" &&
-    event?.isRecurring &&
-    proposedChange.deleteMode;
+    proposedChange.deleteMode === "single" &&
+    proposedChange.occurrenceDate;
+
+  // For update actions, check if a new UNTIL date is being set
+  const newUntilDate =
+    proposedChange.action === "update" &&
+    event?.recurrenceRule &&
+    parseRRule(event.recurrenceRule)?.until;
 
   if (!event) {
     return null;
@@ -108,8 +95,33 @@ export const ProposedEventCard = ({
         description={event.description}
         isRecurring={event.isRecurring}
       >
-        {showDeleteModeBadge && (
-          <DeleteModeBadge mode={proposedChange.deleteMode!} />
+        {/* Show new exception date for delete/single actions */}
+        {newExceptionDate && (
+          <View className="flex-row items-center mb-2">
+            <Feather
+              name="plus-circle"
+              size={16}
+              color={theme.confirmButton}
+              style={{ marginRight: 8 }}
+            />
+            <Text style={{ color: theme.confirmButton }} className="font-medium">
+              Neue Ausnahme: {formatDate(new Date(proposedChange.occurrenceDate!))}
+            </Text>
+          </View>
+        )}
+        {/* Show new UNTIL date for update actions */}
+        {newUntilDate && (
+          <View className="flex-row items-center mb-2">
+            <Feather
+              name="plus-circle"
+              size={16}
+              color={theme.confirmButton}
+              style={{ marginRight: 8 }}
+            />
+            <Text style={{ color: theme.confirmButton }} className="font-medium">
+              Neues Ende: {formatDate(newUntilDate)}
+            </Text>
+          </View>
         )}
         <ConfirmRejectButtons
           isDisabled={isDisabled}

apps/server/src/ai/utils/eventFormatter.ts

@@ -1,11 +1,12 @@
-import { CalendarEvent } from "@calchat/shared";
+import {
+  CalendarEvent,
+  formatDate,
+  formatTime,
+  formatDateTime,
+} from "@calchat/shared";
 
-// German date/time formatting helpers
-export const formatDate = (d: Date) => d.toLocaleDateString("de-DE");
-export const formatTime = (d: Date) =>
-  d.toLocaleTimeString("de-DE", { hour: "2-digit", minute: "2-digit" });
-export const formatDateTime = (d: Date) =>
-  `${formatDate(d)} ${d.toLocaleTimeString("de-DE")}`;
+// Re-export for backwards compatibility
+export { formatDate, formatTime, formatDateTime };
 
 /**
  * Format a list of events for display in the system prompt.

apps/server/src/ai/utils/systemPrompt.ts

@@ -46,13 +46,20 @@ WICHTIG - Wiederkehrende Termine (RRULE):
   2. "Arbeit" Fr 9:00-13:00 (RRULE mit BYDAY=FR)
 - Nutze NIEMALS BYHOUR/BYMINUTE in RRULE - diese überschreiben die Startzeit nicht wie erwartet!
 - Gültige RRULE-Optionen: FREQ (DAILY/WEEKLY/MONTHLY/YEARLY), BYDAY (MO,TU,WE,TH,FR,SA,SU), INTERVAL, COUNT, UNTIL
+- UNTIL Format: YYYYMMDDTHHMMSSZ (UTC) z.B. UNTIL=20260310T000000Z
+- WICHTIG: Schreibe die RRULE NIEMALS in das description-Feld! Nutze IMMER das recurrenceRule-Feld!
 
 WICHTIG - Antwortformat:
 - Halte deine Textantworten SEHR KURZ (1-2 Sätze maximal)
 - Die Event-Details (Titel, Datum, Uhrzeit, Beschreibung) werden dem Benutzer automatisch in separaten Karten angezeigt
 - Wiederhole NIEMALS die Event-Details im Text! Der Benutzer sieht sie bereits in den Karten
-- Gute Beispiele: "Alles klar!" oder "Hier sind deine Termine:"
-- Schlechte Beispiele: Lange Listen mit allen Terminen und ihren Details im Text
+- Verwende kontextbezogene Antworten in der GEGENWARTSFORM je nach Aktion:
+  - Bei Termin-Erstellung: "Ich schlage folgenden Termin vor:" oder "Neuer Termin:"
+  - Bei Termin-Änderung: "Ich schlage folgende Änderung vor:" oder "Änderung:"
+  - Bei Termin-Löschung: "Ich schlage vor, diesen Termin zu löschen:" oder "Löschung:"
+  - Bei Übersichten: "Hier sind deine Termine:"
+- WICHTIG: Verwende NIEMALS Vergangenheitsform wie "Ich habe ... vorgeschlagen" - immer Gegenwartsform!
+- Schlechte Beispiele: "Alles klar!" (zu unspezifisch), lange Listen mit Termin-Details im Text
 - Bei Rückfragen oder wenn keine Termine erstellt werden, kannst du ausführlicher antworten
 
 Existierende Termine des Benutzers:

apps/server/src/ai/utils/toolDefinitions.ts

@@ -131,7 +131,16 @@ export const TOOL_DEFINITIONS: ToolDefinition[] = [
         },
         description: {
           type: "string",
-          description: "New description (optional)",
+          description: "New description (optional). NEVER put RRULE here!",
+        },
+        isRecurring: {
+          type: "boolean",
+          description: "Whether this is a recurring event (optional)",
+        },
+        recurrenceRule: {
+          type: "string",
+          description:
+            "RRULE format string (optional). Use to add UNTIL or modify recurrence. Format: FREQ=DAILY;UNTIL=20260310T000000Z",
         },
       },
       required: ["eventId"],

apps/server/src/ai/utils/toolExecutor.ts

@@ -88,6 +88,9 @@ export function executeToolCall(
         updates.startTime = new Date(args.startTime as string);
       if (args.endTime) updates.endTime = new Date(args.endTime as string);
       if (args.description) updates.description = args.description;
+      if (args.isRecurring !== undefined)
+        updates.isRecurring = args.isRecurring;
+      if (args.recurrenceRule) updates.recurrenceRule = args.recurrenceRule;
 
       // Build event object for display (merge existing with updates)
       const displayEvent = {
@@ -96,7 +99,11 @@ export function executeToolCall(
         endTime: (updates.endTime as Date) || existingEvent.endTime,
         description:
           (updates.description as string) || existingEvent.description,
-        isRecurring: existingEvent.isRecurring,
+        isRecurring:
+          (updates.isRecurring as boolean) ?? existingEvent.isRecurring,
+        recurrenceRule:
+          (updates.recurrenceRule as string) || existingEvent.recurrenceRule,
+        exceptionDates: existingEvent.exceptionDates,
       };
 
       return {
@@ -149,6 +156,8 @@ export function executeToolCall(
             endTime: existingEvent.endTime,
             description: existingEvent.description,
             isRecurring: existingEvent.isRecurring,
+            recurrenceRule: existingEvent.recurrenceRule,
+            exceptionDates: existingEvent.exceptionDates,
           },
           deleteMode: existingEvent.isRecurring ? deleteMode : undefined,
           occurrenceDate: existingEvent.isRecurring

apps/server/src/controllers/ChatController.ts

@@ -35,6 +35,10 @@ export class ChatController {
     try {
       const userId = req.user!.userId;
       const { conversationId, messageId } = req.params;
+
+      // DEBUG: Log incoming request body to trace deleteMode issue
+      log.debug({ body: req.body }, "confirmEvent request body");
+
       const {
         proposalId,
         action,

apps/server/src/repositories/mongo/models/ChatModel.ts

@@ -25,6 +25,7 @@ const EventSchema = new Schema<CreateEventDTO>(
     note: { type: String },
     isRecurring: { type: Boolean },
     recurrenceRule: { type: String },
+    exceptionDates: { type: [String] },
   },
   { _id: false },
 );
@@ -57,6 +58,11 @@ const ProposedChangeSchema = new Schema<ProposedEventChange>(
       type: String,
       enum: ["confirm", "reject"],
     },
+    deleteMode: {
+      type: String,
+      enum: ["single", "future", "all"],
+    },
+    occurrenceDate: { type: String },
   },
   { _id: false },
 );

apps/server/src/services/ChatService.ts

@@ -27,8 +27,34 @@ let responseIndex = 0;
 // Static test responses (event proposals)
 const staticResponses: TestResponse[] = [
   // {{{
+  // === SPORT TEST SCENARIO (3 steps) ===
+  // Response 0: Wiederkehrendes Event - jeden Mittwoch Sport
+  {
+    content:
+      "Super! Ich erstelle dir einen wiederkehrenden Termin für Sport jeden Mittwoch:",
+    proposedChanges: [
+      {
+        id: "sport-create",
+        action: "create",
+        event: {
+          title: "Sport",
+          startTime: getDay("Wednesday", 1, 18, 0),
+          endTime: getDay("Wednesday", 1, 19, 30),
+          description: "Wöchentliches Training",
+          isRecurring: true,
+          recurrenceRule: "FREQ=WEEKLY;BYDAY=WE",
+        },
+      },
+    ],
+  },
+  // Response 1: Ausnahme hinzufügen (2 Wochen später) - DYNAMIC placeholder
+  { content: "" },
+  // Response 2: UNTIL hinzufügen (nach 6 Wochen) - DYNAMIC placeholder
+  { content: "" },
+  // Response 3: Weitere Ausnahme in 2 Wochen - DYNAMIC placeholder
+  { content: "" },
   // === MULTI-EVENT TEST RESPONSES ===
-  // Response 0: 3 Meetings an verschiedenen Tagen
+  // Response 3: 3 Meetings an verschiedenen Tagen
   {
     content: "Alles klar! Ich erstelle dir 3 Team-Meetings für diese Woche:",
     proposedChanges: [
@@ -319,12 +345,133 @@ async function getTestResponse(
 ): Promise<TestResponse> {
   const responseIdx = index % staticResponses.length;
 
-  // Dynamic responses: fetch events from DB and format
+  // === SPORT TEST SCENARIO (Dynamic responses) ===
+  // Response 1: Add exception to "Sport" (2 weeks later)
+  if (responseIdx === 1) {
+    const events = await eventRepo.findByUserId(userId);
+    const sportEvent = events.find((e) => e.title === "Sport");
+    if (sportEvent) {
+      // Calculate date 2 weeks from the first occurrence
+      const exceptionDate = new Date(sportEvent.startTime);
+      exceptionDate.setDate(exceptionDate.getDate() + 14);
+      const exceptionDateStr = exceptionDate.toISOString().split("T")[0];
+
+      return {
+        content:
+          "Verstanden! Ich füge eine Ausnahme für den Sport-Termin in 2 Wochen hinzu:",
+        proposedChanges: [
+          {
+            id: "sport-exception",
+            action: "delete",
+            eventId: sportEvent.id,
+            deleteMode: "single",
+            occurrenceDate: exceptionDateStr,
+            event: {
+              title: sportEvent.title,
+              startTime: exceptionDate,
+              endTime: new Date(
+                exceptionDate.getTime() + 90 * 60 * 1000,
+              ), // +90 min
+              description: sportEvent.description,
+              isRecurring: sportEvent.isRecurring,
+              recurrenceRule: sportEvent.recurrenceRule,
+              exceptionDates: sportEvent.exceptionDates,
+            },
+          },
+        ],
+      };
+    }
+    return {
+      content: "Ich konnte keinen Termin 'Sport' finden. Bitte erstelle ihn zuerst.",
+    };
+  }
+
+  // Response 2: Add UNTIL to "Sport" (after 6 weeks total)
+  if (responseIdx === 2) {
+    const events = await eventRepo.findByUserId(userId);
+    const sportEvent = events.find((e) => e.title === "Sport");
+    if (sportEvent) {
+      // Calculate UNTIL date: 6 weeks from start
+      const untilDate = new Date(sportEvent.startTime);
+      untilDate.setDate(untilDate.getDate() + 42); // 6 weeks
+      const untilStr = untilDate.toISOString().replace(/[-:]/g, "").split(".")[0] + "Z";
+
+      const newRule = `FREQ=WEEKLY;BYDAY=WE;UNTIL=${untilStr}`;
+
+      return {
+        content:
+          "Alles klar! Ich beende die Sport-Serie nach 6 Wochen:",
+        proposedChanges: [
+          {
+            id: "sport-until",
+            action: "update",
+            eventId: sportEvent.id,
+            updates: { recurrenceRule: newRule },
+            event: {
+              title: sportEvent.title,
+              startTime: sportEvent.startTime,
+              endTime: sportEvent.endTime,
+              description: sportEvent.description,
+              isRecurring: sportEvent.isRecurring,
+              recurrenceRule: newRule,
+              exceptionDates: sportEvent.exceptionDates,
+            },
+          },
+        ],
+      };
+    }
+    return {
+      content: "Ich konnte keinen Termin 'Sport' finden. Bitte erstelle ihn zuerst.",
+    };
+  }
+
+  // Response 3: Add another exception to "Sport" (2 weeks after the first exception)
   if (responseIdx === 3) {
+    const events = await eventRepo.findByUserId(userId);
+    const sportEvent = events.find((e) => e.title === "Sport");
+    if (sportEvent) {
+      // Calculate date 4 weeks from the first occurrence (2 weeks after the first exception)
+      const exceptionDate = new Date(sportEvent.startTime);
+      exceptionDate.setDate(exceptionDate.getDate() + 28); // 4 weeks
+      const exceptionDateStr = exceptionDate.toISOString().split("T")[0];
+
+      return {
+        content:
+          "Alles klar! Ich füge eine weitere Ausnahme für den Sport-Termin hinzu:",
+        proposedChanges: [
+          {
+            id: "sport-exception-2",
+            action: "delete",
+            eventId: sportEvent.id,
+            deleteMode: "single",
+            occurrenceDate: exceptionDateStr,
+            event: {
+              title: sportEvent.title,
+              startTime: exceptionDate,
+              endTime: new Date(
+                exceptionDate.getTime() + 90 * 60 * 1000,
+              ), // +90 min
+              description: sportEvent.description,
+              isRecurring: sportEvent.isRecurring,
+              recurrenceRule: sportEvent.recurrenceRule,
+              exceptionDates: sportEvent.exceptionDates,
+            },
+          },
+        ],
+      };
+    }
+    return {
+      content: "Ich konnte keinen Termin 'Sport' finden. Bitte erstelle ihn zuerst.",
+    };
+  }
+
+  // Dynamic responses: fetch events from DB and format
+  // (Note: indices shifted by +3 due to new sport responses)
+  if (responseIdx === 6) {
     return { content: await getWeeksOverview(eventRepo, userId, 2) };
   }
 
-  if (responseIdx === 4) {
+  if (responseIdx === 7) {
     // Delete "Meeting mit Jens"
     const events = await eventRepo.findByUserId(userId);
     const jensEvent = events.find((e) => e.title === "Meeting mit Jens");
@@ -350,11 +497,11 @@ async function getTestResponse(
     return { content: "Ich konnte keinen Termin 'Meeting mit Jens' finden." };
   }
 
-  if (responseIdx === 8) {
+  if (responseIdx === 11) {
     return { content: await getWeeksOverview(eventRepo, userId, 1) };
   }
 
-  if (responseIdx === 10) {
+  if (responseIdx === 13) {
     // Update "Telefonat mit Mama" +3 days and change time to 13:00
     const events = await eventRepo.findByUserId(userId);
     const mamaEvent = events.find((e) => e.title === "Telefonat mit Mama");
@@ -387,7 +534,7 @@ async function getTestResponse(
     return { content: "Ich konnte keinen Termin 'Telefonat mit Mama' finden." };
   }
 
-  if (responseIdx === 13) {
+  if (responseIdx === 16) {
     const now = new Date();
     return {
       content: await getMonthOverview(

package-lock.json

@@ -12535,7 +12535,10 @@
     },
     "packages/shared": {
       "name": "@calchat/shared",
-      "version": "1.0.0"
+      "version": "1.0.0",
+      "dependencies": {
+        "rrule": "^2.8.1"
+      }
     }
   }
 }

packages/shared/package.json

@@ -7,5 +7,8 @@
   "exports": {
     ".": "./src/index.ts",
     "./*": "./src/*"
+  },
+  "dependencies": {
+    "rrule": "^2.8.1"
   }
 }

packages/shared/src/models/CalendarEvent.ts

@@ -28,6 +28,7 @@ export interface CreateEventDTO {
   note?: string;
   isRecurring?: boolean;
   recurrenceRule?: string;
+  exceptionDates?: string[]; // For display in proposals
 }
 
 export interface UpdateEventDTO {

packages/shared/src/utils/formatters.ts

@@ -0,0 +1,48 @@
+/**
+ * German date/time formatting helpers.
+ * Used across client and server.
+ */
+
+/**
+ * Format date as DD.MM.YYYY
+ */
+export function formatDate(date: Date): string {
+  const d = new Date(date);
+  return d.toLocaleDateString("de-DE", {
+    day: "2-digit",
+    month: "2-digit",
+    year: "numeric",
+  });
+}
+
+/**
+ * Format time as HH:MM
+ */
+export function formatTime(date: Date): string {
+  const d = new Date(date);
+  return d.toLocaleTimeString("de-DE", {
+    hour: "2-digit",
+    minute: "2-digit",
+  });
+}
+
+/**
+ * Format date and time as DD.MM.YYYY HH:MM:SS
+ */
+export function formatDateTime(date: Date): string {
+  const d = new Date(date);
+  return `${formatDate(d)} ${d.toLocaleTimeString("de-DE")}`;
+}
+
+/**
+ * Format date with weekday as "Mo., DD.MM.YYYY"
+ */
+export function formatDateWithWeekday(date: Date): string {
+  const d = new Date(date);
+  return d.toLocaleDateString("de-DE", {
+    weekday: "short",
+    day: "2-digit",
+    month: "2-digit",
+    year: "numeric",
+  });
+}

packages/shared/src/utils/index.ts

@@ -1 +1,3 @@
 export * from "./dateHelpers";
+export * from "./rruleHelpers";
+export * from "./formatters";

packages/shared/src/utils/rruleHelpers.ts

@@ -0,0 +1,49 @@
+import { rrulestr, Frequency } from "rrule";
+
+export interface ParsedRRule {
+  freq: string; // "YEARLY", "MONTHLY", "WEEKLY", "DAILY", etc.
+  until?: Date;
+  count?: number;
+  interval?: number;
+  byDay?: string[]; // ["MO", "WE", "FR"]
+}
+
+const FREQ_NAMES: Record<Frequency, string> = {
+  [Frequency.YEARLY]: "YEARLY",
+  [Frequency.MONTHLY]: "MONTHLY",
+  [Frequency.WEEKLY]: "WEEKLY",
+  [Frequency.DAILY]: "DAILY",
+  [Frequency.HOURLY]: "HOURLY",
+  [Frequency.MINUTELY]: "MINUTELY",
+  [Frequency.SECONDLY]: "SECONDLY",
+};
+
+/**
+ * Parses an RRULE string and extracts the relevant fields.
+ * Handles both with and without "RRULE:" prefix.
+ */
+export function parseRRule(ruleString: string): ParsedRRule | null {
+  if (!ruleString) {
+    return null;
+  }
+
+  try {
+    // Ensure RRULE: prefix is present
+    const normalized = ruleString.startsWith("RRULE:")
+      ? ruleString
+      : `RRULE:${ruleString}`;
+
+    const rule = rrulestr(normalized);
+    const options = rule.options;
+
+    return {
+      freq: FREQ_NAMES[options.freq] || "UNKNOWN",
+      until: options.until || undefined,
+      count: options.count || undefined,
+      interval: options.interval > 1 ? options.interval : undefined,
+      byDay: options.byweekday?.map((d) => d.toString()) || undefined,
+    };
+  } catch {
+    return null;
+  }
+}