# Internal Calendar with CalDAV Sync — Design Spec

## Goal

Add an internal event store to Fable's database, a full calendar UI (month/week grid), and a best-effort push sync to the user's existing external CalDAV server. Fable becomes the source of truth for events; CalDAV is an optional downstream target.

## Background

The existing `services/caldav.py` lets the AI assistant create, update, and delete events directly on an external CalDAV server (Nextcloud, etc.) via tool calls. There is no calendar UI and no internal event storage — all reads go to CalDAV at query time. The `events` DB table and `models/event.py` exist as dead code from an abandoned Radicale integration (created in migration `0019_add_events`); the table exists in the database but all columns are empty.

This design revives the internal event store, adds a REST API and calendar view, and re-wires the AI tools to write through the internal DB so all events are accessible regardless of CalDAV availability.

---

## Architecture

### Source of Truth

Fable's `events` DB table is the single source of truth. CalDAV sync is a best-effort push: after every create, update, or delete, a background task attempts to mirror the change to the user's configured CalDAV server. If CalDAV is unconfigured or unreachable, the operation still succeeds and the event remains in Fable.

### Timezone Handling

- **Storage:** `start_dt` / `end_dt` stored as UTC (`TIMESTAMPTZ`).
- **Display:** FullCalendar configured with `timeZone: 'local'` — renders in the browser's IANA timezone automatically.
- **Input:** Frontend datetime inputs are in local time; converted to a timezone-aware ISO string (with UTC offset) before the API call. Backend parses to UTC.
- **CalDAV push:** Uses the user's `caldav_timezone` setting for iCal `DTSTART`/`DTEND`, consistent with existing behaviour.
- **AI tools:** The LLM receives the user's timezone in the system prompt and sends timezone-aware strings, as today.

---

## Data Model

### `events` table (existing since migration 0019, extend via migration 0029)

| Column | Type | Notes |
|--------|------|-------|
| `id` | `SERIAL PK` | |
| `user_id` | `INT FK users CASCADE` | |
| `project_id` | `INT FK projects SET NULL` nullable | Optional link to a Fable project |
| `uid` | `TEXT` | iCal UID — UUID generated on `create_event`, embedded in CalDAV push |
| `caldav_uid` | `TEXT DEFAULT ''` | **New.** Same value as `uid` after a successful CalDAV push (confirms sync); empty if never synced |
| `title` | `TEXT` | |
| `start_dt` | `TIMESTAMPTZ` | UTC |
| `end_dt` | `TIMESTAMPTZ` nullable | UTC; null for open-ended events |
| `all_day` | `BOOLEAN DEFAULT false` | When true, time component is ignored in display |
| `description` | `TEXT DEFAULT ''` | |
| `location` | `TEXT DEFAULT ''` | |
| `color` | `TEXT DEFAULT ''` | **New.** Hex colour for calendar display (e.g. `#6366f1`) |
| `recurrence` | `TEXT` nullable | iCal RRULE string — stored and forwarded to CalDAV; not exposed in the UI slide-over |
| `created_at` | `TIMESTAMPTZ` | |
| `updated_at` | `TIMESTAMPTZ` | |

**Migration `0029_add_calendar_columns`:** `ALTER TABLE events ADD COLUMN IF NOT EXISTS caldav_uid TEXT DEFAULT ''` and `ADD COLUMN IF NOT EXISTS color TEXT DEFAULT ''`. Raw SQL with `IF NOT EXISTS` guards (table already exists from migration 0019).

**`models/event.py`:** Add two `mapped_column` declarations to the `Event` class:
```python
caldav_uid: Mapped[str] = mapped_column(Text, default="")
color: Mapped[str] = mapped_column(Text, default="")
```
Update `to_dict()` to include `"caldav_uid": self.caldav_uid` and `"color": self.color`.

---

## Service Layer

**`src/fabledassistant/services/events.py`** — owns all event CRUD and CalDAV push coordination.

### Public functions

```
create_event(user_id, title, start_dt, end_dt, all_day, description, location,
             color, recurrence, project_id,
             duration, reminder_minutes, attendees, calendar_name) → Event
get_event(user_id, event_id) → Event
list_events(user_id, date_from, date_to) → list[Event]
search_events(user_id, query, days_ahead=90) → list[Event]
update_event(user_id, event_id, **fields) → Event
delete_event(user_id, event_id) → None
find_events_by_query(user_id, query) → list[Event]
```

`duration`, `reminder_minutes`, `attendees`, and `calendar_name` are accepted by `create_event` for forwarding to CalDAV (they are not stored in the DB). `find_events_by_query` does a case-insensitive `ILIKE` search on `title` and is used by the AI `update_event` / `delete_event` tools.

### CalDAV push — UID strategy

`create_event` generates a UUID and stores it as the event's `uid`. This same UUID must be embedded as the iCal `UID` field when pushing to CalDAV. To enable this, `services/caldav.py`'s `create_event` function is **minimally modified** to accept an optional `uid: str | None = None` parameter; when provided, `event.add("uid", uid)` is called before `cal.add_component(event)`. All other CalDAV functions are unchanged.

On a successful push, `caldav_uid` is set to the same UUID value in the DB (confirming sync). This means `caldav_uid` is Fable's own UID confirmed-as-pushed, not a server-assigned value — which is fine since we generated it.

After every write to the DB:

- `create_event` → `asyncio.create_task(_push_create(event, user_id, extra_fields))`
- `update_event` → `asyncio.create_task(_push_update(event, user_id))`
- `delete_event` → `asyncio.create_task(_push_delete(caldav_uid, user_id))` if `caldav_uid` is set

Each push function calls the relevant function in `services/caldav.py`, marks `caldav_uid` on success, and logs a warning on failure. CalDAV being unconfigured is treated as a no-op (not an error).

### Match policy for AI update/delete tools

`find_events_by_query` returns all events where `title ILIKE '%query%'`. The calling tool applies the same match-count policy as the existing CalDAV tools: zero matches → raise `ValueError("No event found matching '…'.")`; more than 3 matches → raise `ValueError("Too many matches (N) for '…'. Be more specific. Found: …")`. One or two matches use the first result.

---

## REST API

**`src/fabledassistant/routes/events.py`** — new blueprint, registered in `app.py`.

| Method | Path | Description |
|--------|------|-------------|
| `GET` | `/api/events?from=&to=` | List events in ISO datetime range |
| `POST` | `/api/events` | Create event |
| `GET` | `/api/events/:id` | Get single event |
| `PATCH` | `/api/events/:id` | Partial update |
| `DELETE` | `/api/events/:id` | Delete event |

All routes require `@login_required`. Ownership enforced in the service layer (404 if event not owned by requesting user).

---

## AI Tool Rewiring

Calendar tools in `services/tools.py` are updated to call `services/events.py` instead of `services/caldav.py` directly. The `is_caldav_configured` gate that currently hides these tools is **removed** — calendar tools are always available since the internal DB is always present. The tool definitions currently grouped under `_CALDAV_TOOLS` (appended to the tools list only when `is_caldav_configured` is true) must be moved into the unconditional `_CORE_TOOLS` list (or equivalent always-included list). The tool parameter names and LLM-facing descriptions do not change.

| Tool | Change |
|------|--------|
| `create_event` | Calls `events.create_event(...)` — all existing params forwarded |
| `list_events` | Calls `events.list_events(...)` |
| `search_events` | Calls `events.search_events(...)` |
| `update_event` | Calls `events.find_events_by_query(...)`, then `events.update_event(...)` |
| `delete_event` | Calls `events.find_events_by_query(...)`, then `events.delete_event(...)` |

---

## Frontend

### Dependencies

```
@fullcalendar/vue3
@fullcalendar/daygrid      # month view
@fullcalendar/timegrid     # week / day view
@fullcalendar/interaction  # drag-to-move, resize, click-to-create
```

All MIT licensed.

### Components

**`frontend/src/views/CalendarView.vue`** — main view at `/calendar`:
- FullCalendar instance with `timeZone: 'local'`, `initialView: 'dayGridMonth'`, header toolbar toggling between month and week
- Loads events for the visible date range via `GET /api/events?from=&to=`
- Re-fetches when the visible range changes
- Click on empty date cell → opens `EventSlideOver` in create mode, pre-filled with the clicked date
- Click on existing event → opens `EventSlideOver` in edit mode
- Drag event to new date/time → `PATCH /api/events/:id` with updated times (optimistic update, revert on error)
- Resize event → same

**`frontend/src/components/EventSlideOver.vue`** — reusable slide-over panel (same pattern as the workspace task slide-over):
- Fields: title (required), start date/time, end date/time, all-day toggle, location, description, colour picker, optional project selector
- `recurrence` is **not** a form field — it is stored and pushed to CalDAV via AI tools only
- Create mode: `POST /api/events`
- Edit mode: `PATCH /api/events/:id` + delete button (`DELETE /api/events/:id`)
- Closes on save, cancel, or Escape

**`frontend/src/api/client.ts`** — add typed helpers and `EventEntry` / `CreateEventBody` interfaces:

```typescript
interface EventEntry {
  id: number; uid: string; title: string;
  start_dt: string; end_dt: string | null;
  all_day: boolean; description: string; location: string;
  color: string; recurrence: string | null;
  project_id: number | null; caldav_uid: string;
  created_at: string; updated_at: string;
}

listEvents(from: string, to: string): Promise<EventEntry[]>
createEvent(body: CreateEventBody): Promise<EventEntry>
getEvent(id: number): Promise<EventEntry>
updateEvent(id: number, body: Partial<CreateEventBody>): Promise<EventEntry>
deleteEvent(id: number): Promise<void>
```

### Navigation

- `/calendar` added to Vue Router
- Sidebar nav item added
- Keyboard shortcut: `g` + `l` (ca**l**endar) — `c` is already taken by chat

---

## Error Handling

- CalDAV push failures are logged at `WARNING` level and do not surface to the user
- If CalDAV is unconfigured, push is skipped silently
- Drag-to-move/resize failures (PATCH error) revert the event to its previous position in FullCalendar's UI via the `revert` callback
- 404 returned for event access by non-owner

---

## Testing

- `tests/test_events_service.py` — unit tests for `create_event`, `list_events`, `search_events`, `update_event`, `delete_event`, `find_events_by_query` with mocked DB session; separate test verifying CalDAV push background task is fired
- `tests/test_events_routes.py` — route tests for all five endpoints verifying ownership enforcement and correct status codes
- TypeScript check (`make typecheck`) after all frontend changes

---

## Out of Scope

- Pull sync (importing events from CalDAV into Fable) — possible future upgrade
- Recurring event expansion in the UI (RRULE stored and forwarded to CalDAV via AI tools only)
- Shared calendars / multi-user event invites
- Event notifications / reminders in the Fable push system