fix(webhooks): ignore episode-level Plex TMDB GUIDs when parsing scrobble events (#53)

Plex attaches TMDB GUIDs that identify the individual episode, not the parent series, so using them as `tmdbId` caused incorrect series lookups. Now only movie scrobbles populate `tmdbId` from the TMDB GUID; episode scrobbles rely on IMDB/TVDB IDs (and the title) to resolve the show via `resolveShowTmdbId`.

- Extract IMDB/TMDB/TVDB prefix constants to avoid magic strings
- Add `parsePlexPayload` test asserting `tmdbId` is `undefined` for episode events
- Add `processWebhook` integration test verifying `resolveShowTmdbId` is called without a TMDB ID for Plex episodes
- Hoist `makePlexForm` helper to module scope so it's available across all describe blocks

packages/core/src/webhooks.ts

@@ -13,6 +13,10 @@ import { logEpisodeWatch, logMovieWatch } from "./tracking";
 
 const log = createLogger("webhooks");
 
+const IMDB_GUID_PREFIX = "imdb://";
+const TMDB_GUID_PREFIX = "tmdb://";
+const TVDB_GUID_PREFIX = "tvdb://";
+
 // ─── Types ──────────────────────────────────────────────────────────
 
 export interface WebhookEvent {
@@ -71,9 +75,14 @@ export function parsePlexPayload(formData: FormData): WebhookEvent | null {
   if (Array.isArray(guids)) {
     for (const g of guids) {
       const id = g.id ?? "";
-      if (id.startsWith("tmdb://")) tmdbId = toOptionalInt(id.slice(7));
-      else if (id.startsWith("imdb://")) imdbId = id.slice(7);
-      else if (id.startsWith("tvdb://")) tvdbId = id.slice(7);
+      if (id.startsWith(TMDB_GUID_PREFIX)) {
+        // Plex episode TMDB GUIDs identify episodes, not series.
+        if (isMovie) tmdbId = toOptionalInt(id.slice(TMDB_GUID_PREFIX.length));
+      } else if (id.startsWith(IMDB_GUID_PREFIX)) {
+        imdbId = id.slice(IMDB_GUID_PREFIX.length);
+      } else if (id.startsWith(TVDB_GUID_PREFIX)) {
+        tvdbId = id.slice(TVDB_GUID_PREFIX.length);
+      }
     }
   }
 

packages/core/test/webhooks.test.ts

@@ -54,6 +54,12 @@ beforeEach(() => {
   mockGetTvDetails.mockReset().mockResolvedValue({ number_of_seasons: 1 });
 });
 
+function makePlexForm(payload: Record<string, unknown>): FormData {
+  const form = new FormData();
+  form.set("payload", JSON.stringify(payload));
+  return form;
+}
+
 // ─── toOptionalInt ──────────────────────────────────────────────────
 
 describe("toOptionalInt", () => {
@@ -86,12 +92,6 @@ describe("toOptionalInt", () => {
 // ─── parsePlexPayload ───────────────────────────────────────────────
 
 describe("parsePlexPayload", () => {
-  function makePlexForm(payload: Record<string, unknown>): FormData {
-    const form = new FormData();
-    form.set("payload", JSON.stringify(payload));
-    return form;
-  }
-
   test("parses a movie scrobble event", () => {
     const result = parsePlexPayload(
       makePlexForm({
@@ -143,6 +143,33 @@ describe("parsePlexPayload", () => {
     });
   });
 
+  test("ignores episode-level Plex TMDB GUIDs", () => {
+    const result = parsePlexPayload(
+      makePlexForm({
+        event: "media.scrobble",
+        Metadata: {
+          type: "episode",
+          title: "Episode Title",
+          grandparentTitle: "The Pitt",
+          parentIndex: 1,
+          index: 14,
+          Guid: [{ id: "imdb://tt35740476" }, { id: "tmdb://6951292" }, { id: "tvdb://11560129" }],
+        },
+      }),
+    );
+    expect(result).toEqual({
+      provider: "plex",
+      mediaType: "episode",
+      title: "Episode Title",
+      tmdbId: undefined,
+      imdbId: "tt35740476",
+      tvdbId: "11560129",
+      seasonNumber: 1,
+      episodeNumber: 14,
+      showTitle: "The Pitt",
+    });
+  });
+
   test("returns null for non-scrobble events", () => {
     expect(parsePlexPayload(makePlexForm({ event: "media.play" }))).toBeNull();
   });
@@ -451,6 +478,38 @@ describe("processWebhook", () => {
     expect(result.status).toBe("success");
   });
 
+  test("resolves parsed Plex episodes without passing the episode TMDB ID", async () => {
+    mockResolveShowTmdbId.mockResolvedValue(1396);
+    const { titleId } = insertTvShow("tv-1", 1396, 1, 14, { title: "The Pitt" });
+    mockGetOrFetchTitleByTmdbId.mockResolvedValue({ id: titleId });
+
+    const event = parsePlexPayload(
+      makePlexForm({
+        event: "media.scrobble",
+        Metadata: {
+          type: "episode",
+          title: "Episode Title",
+          grandparentTitle: "The Pitt",
+          parentIndex: 1,
+          index: 14,
+          Guid: [{ id: "imdb://tt35740476" }, { id: "tmdb://6951292" }, { id: "tvdb://11560129" }],
+        },
+      }),
+    );
+    expect(event).not.toBeNull();
+    if (!event) throw new Error("Expected Plex episode event");
+
+    const result = await processWebhook(connectionId, userId, "plex", event);
+
+    expect(result.status).toBe("success");
+    expect(mockResolveShowTmdbId).toHaveBeenCalledWith({
+      tmdbId: undefined,
+      imdbId: "tt35740476",
+      tvdbId: "11560129",
+      title: "The Pitt",
+    });
+  });
+
   test("returns error when episode cannot be resolved", async () => {
     mockResolveShowTmdbId.mockResolvedValue(null);