spotify

.gitignore

@@ -0,0 +1,3 @@
+.env
+data/
+node_modules/

Dockerfile

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+FROM node:24-alpine
+
+WORKDIR /app
+
+COPY package.json package-lock.json ./
+RUN npm ci --omit=dev
+
+COPY src ./src
+
+ENV PORT=9783
+EXPOSE 9783
+
+CMD ["node", "src/index.js"]

README.md

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+# spotify-last-known
+
+Tiny background service that:
+
+1. Polls Spotify `currently-playing`
+2. Persists the last known track to a local JSON file
+3. Serves it publicly over HTTP (with CORS)
+
+## Setup
+
+Create an `.env` (or export env vars) with:
+
+- `SPOTIFY_CLIENT_ID`
+- `SPOTIFY_CLIENT_SECRET`
+- `SPOTIFY_REFRESH_TOKEN`
+
+Optional:
+
+- `PORT` (default: `9783`)
+- `POLL_MS` (default: `8000`)
+- `STATE_PATH` (default: `./data/last-known.json`)
+
+## Run
+
+```bash
+npm i
+npm start
+```
+
+Endpoints:
+
+- `GET /last-known` -> persisted state JSON
+- `GET /healthz` -> `{ ok: true }`
+
+## Notes
+
+- Intended for a single machine / single instance.
+- JSON is written atomically using a temp file + rename.

data/last-known.json

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+{
+  "title": "Under Pressure - Remastered 2011",
+  "artist": "Queen, David Bowie",
+  "album": "Hot Space (Deluxe Remastered Version)",
+  "albumArtUrl": "https://i.scdn.co/image/ab67616d0000b273a1e05e1048e2cf2737adf742",
+  "trackUrl": "https://open.spotify.com/track/11IzgLRXV7Cgek3tEgGgjw",
+  "durationMs": 248440,
+  "stoppedAtMs": 1776291721795,
+  "stoppedProgressMs": 4603,
+  "lastUpdatedAtMs": null
+}

docker-compose.yml

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+services:
+  spotify-last-known:
+    build: .
+    container_name: spotify-last-known
+    restart: unless-stopped
+    environment:
+      PORT: "9783"
+      POLL_MS: "8000"
+      STATE_PATH: "/data/last-known.json"
+      SPOTIFY_CLIENT_ID: "${SPOTIFY_CLIENT_ID}"
+      SPOTIFY_CLIENT_SECRET: "${SPOTIFY_CLIENT_SECRET}"
+      SPOTIFY_REFRESH_TOKEN: "${SPOTIFY_REFRESH_TOKEN}"
+    volumes:
+      - spotify_last_known_data:/data
+    networks:
+      - caddy
+
+volumes:
+  spotify_last_known_data:
+
+networks:
+  caddy:
+    external: true

package-lock.json

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+}

package.json

@@ -0,0 +1,13 @@
+{
+  "name": "spotify-last-known",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "node --watch src/index.js",
+    "start": "node src/index.js"
+  },
+  "dependencies": {
+    "express": "^4.19.2"
+  }
+}

src/index.js

@@ -0,0 +1,220 @@
+import express from "express";
+import { mkdir, readFile, rename, writeFile } from "node:fs/promises";
+import { dirname, resolve } from "node:path";
+
+const NOW_PLAYING_ENDPOINT =
+  "https://api.spotify.com/v1/me/player/currently-playing";
+const TOKEN_ENDPOINT = "https://accounts.spotify.com/api/token";
+
+function requiredEnv(name) {
+  const v = process.env[name];
+  if (!v) throw new Error(`Missing env var: ${name}`);
+  return v;
+}
+
+const PORT = Number(process.env.PORT || 9783);
+const POLL_MS = Number(process.env.POLL_MS || 8000);
+const STATE_PATH = resolve(
+  process.cwd(),
+  process.env.STATE_PATH && process.env.STATE_PATH.trim()
+    ? process.env.STATE_PATH
+    : "data/last-known.json",
+);
+
+const DEFAULT_STATE = {
+  title: null,
+  artist: null,
+  album: null,
+  albumArtUrl: null,
+  trackUrl: null,
+  durationMs: null,
+  stoppedAtMs: null,
+  stoppedProgressMs: null,
+  lastUpdatedAtMs: null,
+};
+
+function coerceState(v) {
+  if (!v || typeof v !== "object") return { ...DEFAULT_STATE };
+  return {
+    title: typeof v.title === "string" ? v.title : null,
+    artist: typeof v.artist === "string" ? v.artist : null,
+    album: typeof v.album === "string" ? v.album : null,
+    albumArtUrl: typeof v.albumArtUrl === "string" ? v.albumArtUrl : null,
+    trackUrl: typeof v.trackUrl === "string" ? v.trackUrl : null,
+    durationMs: typeof v.durationMs === "number" ? v.durationMs : null,
+    stoppedAtMs: typeof v.stoppedAtMs === "number" ? v.stoppedAtMs : null,
+    stoppedProgressMs:
+      typeof v.stoppedProgressMs === "number" ? v.stoppedProgressMs : null,
+    lastUpdatedAtMs:
+      typeof v.lastUpdatedAtMs === "number" ? v.lastUpdatedAtMs : null,
+  };
+}
+
+async function readState() {
+  try {
+    const text = await readFile(STATE_PATH, "utf8");
+    return coerceState(JSON.parse(text));
+  } catch {
+    return { ...DEFAULT_STATE };
+  }
+}
+
+async function writeState(next) {
+  await mkdir(dirname(STATE_PATH), { recursive: true });
+  const tmp = `${STATE_PATH}.tmp`;
+  await writeFile(tmp, JSON.stringify(next, null, 2) + "\n", "utf8");
+  await rename(tmp, STATE_PATH);
+}
+
+let cachedAccessToken = null; // { token, expiresAtMs }
+
+async function getAccessToken() {
+  const now = Date.now();
+  if (cachedAccessToken && cachedAccessToken.expiresAtMs > now) {
+    return cachedAccessToken.token;
+  }
+
+  const client_id = requiredEnv("SPOTIFY_CLIENT_ID");
+  const client_secret = requiredEnv("SPOTIFY_CLIENT_SECRET");
+  const refresh_token = requiredEnv("SPOTIFY_REFRESH_TOKEN");
+
+  const basic = Buffer.from(`${client_id}:${client_secret}`).toString("base64");
+
+  const res = await fetch(TOKEN_ENDPOINT, {
+    method: "POST",
+    headers: {
+      Authorization: `Basic ${basic}`,
+      "Content-Type": "application/x-www-form-urlencoded",
+    },
+    body: new URLSearchParams({
+      grant_type: "refresh_token",
+      refresh_token,
+    }),
+  });
+
+  if (!res.ok) {
+    const text = await res.text().catch(() => "");
+    throw new Error(`Spotify token error: ${res.status} ${text}`);
+  }
+
+  const data = await res.json();
+  cachedAccessToken = {
+    token: data.access_token,
+    expiresAtMs: Date.now() + data.expires_in * 1000 - 30_000,
+  };
+  return cachedAccessToken.token;
+}
+
+async function pollOnce() {
+  const nowMs = Date.now();
+  const prev = await readState();
+
+  let accessToken;
+  try {
+    accessToken = await getAccessToken();
+  } catch {
+    return;
+  }
+
+  const res = await fetch(NOW_PLAYING_ENDPOINT, {
+    headers: { Authorization: `Bearer ${accessToken}` },
+  });
+
+  if (res.status === 204) {
+    if (prev.title && !prev.stoppedAtMs) {
+      await writeState({ ...prev, stoppedAtMs: nowMs });
+    }
+    return;
+  }
+
+  if (res.status === 401) {
+    cachedAccessToken = null;
+    return;
+  }
+
+  if (!res.ok) return;
+
+  const data = await res.json();
+  const item = data?.item;
+
+  const title = item?.name ?? null;
+  const artist =
+    item?.artists?.map((a) => a?.name).filter(Boolean).join(", ") ?? null;
+  const album = item?.album?.name ?? null;
+  const albumArtUrl = item?.album?.images?.[0]?.url ?? null;
+  const trackUrl = item?.external_urls?.spotify ?? null;
+  const durationMs =
+    typeof item?.duration_ms === "number" ? item.duration_ms : null;
+  const progressMs =
+    typeof data?.progress_ms === "number" ? data.progress_ms : null;
+  const isPlaying = Boolean(data?.is_playing);
+
+  if (!title) return;
+
+  const next = {
+    title,
+    artist,
+    album,
+    albumArtUrl,
+    trackUrl,
+    durationMs,
+    stoppedAtMs: isPlaying ? null : prev.stoppedAtMs ?? nowMs,
+    stoppedProgressMs: !isPlaying
+      ? typeof progressMs === "number"
+        ? progressMs
+        : prev.stoppedProgressMs
+      : null,
+    lastUpdatedAtMs: isPlaying ? nowMs : prev.lastUpdatedAtMs,
+  };
+
+  await writeState(next);
+}
+
+let pollTimer = null;
+async function startPolling() {
+  requiredEnv("SPOTIFY_CLIENT_ID");
+  requiredEnv("SPOTIFY_CLIENT_SECRET");
+  requiredEnv("SPOTIFY_REFRESH_TOKEN");
+
+  await writeState(await readState());
+
+  const tick = async () => {
+    try {
+      await pollOnce();
+    } catch {
+      // keep polling
+    }
+  };
+
+  await tick();
+  pollTimer = setInterval(tick, POLL_MS);
+}
+
+const app = express();
+
+app.use((req, res, next) => {
+  res.setHeader("Access-Control-Allow-Origin", "*");
+  res.setHeader("Access-Control-Allow-Methods", "GET,OPTIONS");
+  res.setHeader("Access-Control-Allow-Headers", "Content-Type");
+  if (req.method === "OPTIONS") return res.status(204).end();
+  next();
+});
+
+app.get("/healthz", (req, res) => {
+  res.json({ ok: true });
+});
+
+app.get("/last-known", async (req, res) => {
+  const state = await readState();
+  res.setHeader("Cache-Control", "no-store");
+  res.json(state);
+});
+
+app.listen(PORT, () => {
+  console.log(`[spotify-last-known] listening on :${PORT}`);
+  console.log(`[spotify-last-known] state: ${STATE_PATH}`);
+  startPolling().catch((e) => {
+    console.error("[spotify-last-known] failed to start polling:", e);
+    process.exitCode = 1;
+  });
+});