Resume paused scrapes from their cursor

media-scrape/src/engine.ts

@@ -182,6 +182,22 @@ export class ScrapeEngine {
         this.stopRequested.add(id);
     }
 
+    /** Continue a paused scrape from its stored cursor instead of walking the top again. */
+    async resume(scrapeId: string, backend: ScrapeBackend): Promise<ScrapeMeta | null> {
+        const meta = this.active.get(scrapeId) ?? readScrapeMeta(join(this.options.rootDir, scrapeId));
+        if (!meta) return null;
+        if (meta.state === "running" || meta.state === "queued") return { ...meta };
+
+        this.stopRequested.delete(scrapeId);
+        meta.state = "queued";
+        this.active.set(scrapeId, meta);
+        writeScrapeMeta(join(this.options.rootDir, scrapeId), meta);
+
+        this.queue.push({ meta, dir: join(this.options.rootDir, scrapeId), backend });
+        void this.processQueue();
+        return { ...meta };
+    }
+
     /** Cache previews for rows a finished or paused scrape never reached. Returns the count. */
     async backfillPreviews(scrapeId: string): Promise<number> {
         const meta = this.active.get(scrapeId) ?? readScrapeMeta(join(this.options.rootDir, scrapeId));

media-scrape/test/run.ts

@@ -877,6 +877,33 @@ void (async () => {
         assert.equal(existsSync(join(dir, `${poster?.hash}.webp`)), true);
     });
 
+    await test("engine resumes a paused scrape from its cursor", async () => {
+        const first = new FakeBackend([
+            { messages: [message("500"), message("499")] },
+            { messages: [message("498")] }
+        ]);
+
+        const engine = engineFor(root, first);
+        const started = await engine.start({ channelId: "140", guildId: null, mode: "links", backend: first });
+        engine.stop(started.id);
+        await engine.processQueue();
+
+        let meta = engine.get(started.id);
+        assert.equal(meta?.state, "paused");
+        assert.equal(meta?.cursor, "499");
+        assert.equal(meta?.messages, 2);
+
+        const second = new FakeBackend([{ messages: [message("498")] }]);
+        await engine.resume(started.id, second);
+        await engine.processQueue();
+
+        meta = engine.get(started.id);
+        assert.equal(meta?.state, "done");
+        assert.equal(meta?.messages, 3);
+        assert.equal(meta?.cursor, "498");
+        assert.equal(second.calls[0].before, "499");
+    });
+
     await test("backfillPreviews fills rows left by a preview-less walk", async () => {
         const backend = new FakeBackend([
             {