feat(web): shared Postgres read-through cache for MusicBrainz (ApiCache)

Reopening an artist (discography), an album (tracklist), or repeating a lookup
re-hit MusicBrainz every time with no cache and no throttle. Adds a generic
Postgres-backed read-through cache keyed on the LOGICAL operation (not the
request URL) so the worker and web app share entries.

- New ApiCache(key, json, fetchedAt) model + migration (generic name so the
  Last.fm browse cache can ride the same table).
- lib/apicache.ts cached(): read-through, TTL from fetchedAt (tunable, no
  migration), serve-stale-on-outage, never caches null.
- Wrap the high-level MB fns with logical keys + TTLs: discography &
  tracklists & artist-name 30d, searchReleaseGroup 7d, searchArtists 1d.
  Search keys normalized (trim+lowercase) to match the worker byte-for-byte.
- album-modal: a session-scoped Map<rgMbid,Track[]> so reopening is instant
  with zero network (complements the DB cache).
- Test setup clears ApiCache between tests. web 147 tests, tsc + build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/prisma/migrations/20260714090112_add_api_cache/migration.sql

@@ -0,0 +1,11 @@
+-- CreateTable
+CREATE TABLE "ApiCache" (
+    "key" TEXT NOT NULL,
+    "json" JSONB NOT NULL,
+    "fetchedAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "ApiCache_pkey" PRIMARY KEY ("key")
+);
+
+-- CreateIndex
+CREATE INDEX "ApiCache_fetchedAt_idx" ON "ApiCache"("fetchedAt");

web/prisma/schema.prisma

@@ -182,3 +182,15 @@ model ScanWorkItem {
   @@unique([scanId, path])
   @@index([scanId, done, artist, album])
 }
+
+// Generic read-through cache for external API responses shared by web + worker (keyed on
+// the LOGICAL operation, not the request URL, so both processes share entries). TTL is
+// applied at read time from fetchedAt in code (no expiresAt column → tunable, no migration).
+// Named generically so the Last.fm browse cache can ride the same table.
+model ApiCache {
+  key       String   @id
+  json      Json
+  fetchedAt DateTime @default(now())
+
+  @@index([fetchedAt])
+}

web/src/app/_ui/album-modal.tsx

@@ -6,6 +6,10 @@ import { CoverArt } from "./cover-art";
 
 type Track = { position: number; title: string; lengthMs: number | null };
 
+// Session-scoped, per-release-group tracklist cache: reopening the same album modal is
+// instant with zero network. Complements the server-side ApiCache (which spans sessions).
+const trackCache = new Map<string, Track[]>();
+
 function fmt(ms: number | null): string {
   if (ms == null) return "";
   const s = Math.round(ms / 1000);
@@ -39,15 +43,25 @@ export function AlbumModal({
 
   useEffect(() => {
     if (!open) return;
-    if (!album.rgMbid) {
+    const rgMbid = album.rgMbid;
+    if (!rgMbid) {
       setTracks("error");
       return;
     }
+    const hit = trackCache.get(rgMbid);
+    if (hit) {
+      setTracks(hit);
+      return;
+    }
     setTracks("loading");
     let cancelled = false;
-    fetch(`/api/mb/release-groups/${album.rgMbid}/tracks`)
+    fetch(`/api/mb/release-groups/${rgMbid}/tracks`)
       .then((r) => (r.ok ? r.json() : Promise.reject()))
-      .then((d) => !cancelled && setTracks(d.tracks))
+      .then((d) => {
+        if (cancelled) return;
+        trackCache.set(rgMbid, d.tracks);
+        setTracks(d.tracks);
+      })
       .catch(() => !cancelled && setTracks("error"));
     return () => {
       cancelled = true;

web/src/lib/apicache.test.ts

@@ -0,0 +1,54 @@
+import { describe, it, expect, vi } from "vitest";
+import { cached, normKey } from "./apicache";
+import { prisma } from "@/lib/db";
+
+describe("cached (read-through)", () => {
+  it("fetches once, then serves the cached value without re-fetching", async () => {
+    const fetchFresh = vi.fn(async () => ({ v: 1 }));
+    const first = await cached("k1", 3600, fetchFresh);
+    const second = await cached("k1", 3600, fetchFresh);
+    expect(first).toEqual({ v: 1 });
+    expect(second).toEqual({ v: 1 });
+    expect(fetchFresh).toHaveBeenCalledTimes(1); // second served from cache
+  });
+
+  it("re-fetches once the TTL has elapsed", async () => {
+    const fetchFresh = vi.fn(async () => ({ v: 2 }));
+    await cached("k2", 3600, fetchFresh);
+    // backdate the row beyond the ttl
+    await prisma.apiCache.update({ where: { key: "k2" }, data: { fetchedAt: new Date(Date.now() - 7200_000) } });
+    await cached("k2", 3600, fetchFresh);
+    expect(fetchFresh).toHaveBeenCalledTimes(2);
+  });
+
+  it("serves a stale value when the fresh fetch throws", async () => {
+    await cached("k3", 3600, async () => ({ v: "old" }));
+    await prisma.apiCache.update({ where: { key: "k3" }, data: { fetchedAt: new Date(Date.now() - 7200_000) } });
+    const result = await cached("k3", 3600, async () => {
+      throw new Error("upstream down");
+    });
+    expect(result).toEqual({ v: "old" }); // stale-on-outage
+  });
+
+  it("rethrows when the fetch fails and there is no cached row", async () => {
+    await expect(
+      cached("k4", 3600, async () => {
+        throw new Error("boom");
+      }),
+    ).rejects.toThrow("boom");
+    // nothing was cached
+    expect(await prisma.apiCache.findUnique({ where: { key: "k4" } })).toBeNull();
+  });
+
+  it("does not cache null results", async () => {
+    const fetchFresh = vi.fn(async () => null);
+    await cached("k5", 3600, fetchFresh);
+    await cached("k5", 3600, fetchFresh);
+    expect(fetchFresh).toHaveBeenCalledTimes(2); // null never cached → always re-fetched
+    expect(await prisma.apiCache.findUnique({ where: { key: "k5" } })).toBeNull();
+  });
+
+  it("normKey trims and lowercases", () => {
+    expect(normKey("  Radiohead ")).toBe("radiohead");
+  });
+});

web/src/lib/apicache.ts

@@ -0,0 +1,39 @@
+import { prisma } from "@/lib/db";
+
+// Read-through cache over the shared ApiCache table. Keyed on the LOGICAL operation (not the
+// request URL) so the worker and web app share entries. TTL is applied here from fetchedAt,
+// so TTLs are tunable in code with no migration. On a fetch failure a stale row is served.
+// Null/undefined results are NOT cached (keeps negative caching out + avoids Prisma JsonNull).
+
+export const CACHE_TTL = {
+  DAY: 86_400,
+  WEEK: 7 * 86_400,
+  MONTH: 30 * 86_400,
+};
+
+export async function cached<T>(key: string, ttlSec: number, fetchFresh: () => Promise<T>): Promise<T> {
+  const hit = await prisma.apiCache.findUnique({ where: { key } });
+  if (hit && (Date.now() - hit.fetchedAt.getTime()) / 1000 < ttlSec) {
+    return hit.json as T;
+  }
+  try {
+    const fresh = await fetchFresh();
+    if (fresh !== null && fresh !== undefined) {
+      await prisma.apiCache.upsert({
+        where: { key },
+        create: { key, json: fresh as object },
+        update: { json: fresh as object, fetchedAt: new Date() },
+      });
+    }
+    return fresh;
+  } catch (e) {
+    if (hit) return hit.json as T; // serve stale on an upstream outage
+    throw e;
+  }
+}
+
+/** Normalize a free-text search term so casing/whitespace don't fragment the cache. MUST
+ *  match the worker's normalization byte-for-byte (both: trim + lowercase). */
+export function normKey(s: string): string {
+  return s.trim().toLowerCase();
+}

web/src/lib/musicbrainz.ts

@@ -1,3 +1,5 @@
+import { cached, normKey, CACHE_TTL } from "@/lib/apicache";
+
 const MB_BASE = "https://musicbrainz.org/ws/2";
 const USER_AGENT = "Lyra/0.1 ( https://git.jger.nl/Jonathan/Lyra )";
 
@@ -30,15 +32,20 @@ function toReleaseGroup(g: any): ReleaseGroupInfo {
 }
 
 export async function searchArtists(query: string): Promise<ArtistHit[]> {
+  const q = normKey(query);
+  if (!q) return [];
+  return cached(`artist-search:${q}`, CACHE_TTL.DAY, async () => {
     const data = await mbGet(`/artist?query=${encodeURIComponent(query)}&fmt=json&limit=8`);
     return (data.artists ?? []).map((a: any) => ({
       mbid: a.id,
       name: a.name ?? "",
       disambiguation: a.disambiguation ?? "",
     }));
+  });
 }
 
 export async function browseReleaseGroups(artistMbid: string): Promise<ReleaseGroupInfo[]> {
+  return cached(`artist-rgs:${artistMbid}`, CACHE_TTL.MONTH, async () => {
     const out: ReleaseGroupInfo[] = [];
     let offset = 0;
     for (;;) {
@@ -52,6 +59,7 @@ export async function browseReleaseGroups(artistMbid: string): Promise<ReleaseGr
       if (groups.length === 0 || offset >= total) break;
     }
     return out;
+  });
 }
 
 function escapeLucenePhrase(s: string): string {
@@ -94,6 +102,12 @@ function albumPreferenceRank(g: any): number {
 }
 
 export async function searchReleaseGroup(artist: string, album: string): Promise<ReleaseGroupMatch | null> {
+  return cached(`rg-search:${normKey(artist)}|${normKey(album)}`, CACHE_TTL.WEEK, () =>
+    _searchReleaseGroup(artist, album),
+  );
+}
+
+async function _searchReleaseGroup(artist: string, album: string): Promise<ReleaseGroupMatch | null> {
   const art = escapeLucenePhrase(artist);
   const stripped = stripEditionQualifiers(album);
   // Decreasing precision: exact phrase on the given title, then on the edition-stripped
@@ -121,11 +135,14 @@ export async function searchReleaseGroup(artist: string, album: string): Promise
 export type Track = { position: number; title: string; lengthMs: number | null };
 
 export async function getArtistName(mbid: string): Promise<string> {
+  return cached(`artist-name:${mbid}`, CACHE_TTL.MONTH, async () => {
     const data = await mbGet(`/artist/${encodeURIComponent(mbid)}?fmt=json`);
     return data.name ?? "";
+  });
 }
 
 export async function browseReleaseGroupTracks(rgMbid: string): Promise<Track[]> {
+  return cached(`rg-tracks:${rgMbid}`, CACHE_TTL.MONTH, async () => {
     const data = await mbGet(
       `/release?release-group=${encodeURIComponent(rgMbid)}&inc=recordings&fmt=json&limit=25`,
     );
@@ -149,4 +166,5 @@ export async function browseReleaseGroupTracks(rgMbid: string): Promise<Track[]>
       }
     }
     return tracks;
+  });
 }

web/src/test/setup.ts

@@ -17,4 +17,5 @@ beforeEach(async () => {
   await prisma.watchedArtist.deleteMany();
   await prisma.discoverySuggestion.deleteMany();
   await prisma.config.deleteMany();
+  await prisma.apiCache.deleteMany(); // read-through cache must not leak across tests
 });