apollo/services/trackers/SpotifyTracker.js

const axios = require("axios");
const logger = require("../logging");
const fs = require("fs/promises");
const fss = require("fs");
const Song = require("../../models/song");

class SpotifyTracker {
  #config = null;
  #token = null;
  #cache = null;
  #auth = null;

  constructor(config, token = null) {
    this.#config = config;
    this.#token = token;
    this.#cache = null;
    this.#auth = new Buffer.from(config.client_id + ':' + config.client_secret).toString('base64');
  }

  async poll(useCache = false) {
    if (this.#token == null)
      return [];
    if (useCache)
      return this.#cache;

    if (this.#token.expires_at < Date.now() + 300)
      await this.#refreshTokenIfNeeded();

    try {
      const response = await axios.get("https://api.spotify.com/v1/me/player/currently-playing",
        {
          headers: {
            "Authorization": "Bearer " + this.#token.access_token
          }
        }
      );

      if (!response.data) {
        this.#cache = [];
        return this.#cache;
      }

      this.#cache = [this.#transform(response.data)];
      return this.#cache;
    } catch (ex) {
      logger.error(ex, "Failed to get currently playing data from Spotify.");
      return [];
    }
  }

  async loadCredentials() {
    if (!fss.existsSync("credentials.spotify.json")) {
      logger.info("No Spotify credentials found.");
      return;
    }
  
    const content = await fs.readFile("credentials.spotify.json", "utf-8");
    this.#token = JSON.parse(content);
  }

  #transform(data) {
    const item = data.item;
    const artists = item.artists.map(a => a.name);
    const year = null;
    const state = data.is_playing ? "playing" : "paused";
    return new Song(item.id, item.name, item.album.name, artists, year, item.duration_ms, data.progress_ms, "spotify", state, "spotify");
  }

  async #refreshTokenIfNeeded() {
    if (!this.#token || this.#token.expires_at && this.#token.expires_at - Date.now() > 900)
      return false;

    const response = await axios.post("https://accounts.spotify.com/api/token",
      {
        client_id: this.#config.client_id,
        refresh_token: this.#token.refresh_token,
        grant_type: "refresh_token"
      },
      {
        headers: {
          "Authorization": "Basic " + this.#auth,
          "Content-Type": "application/x-www-form-urlencoded"
        }
      }
    );

    const data = response.data;
    data["expires_at"] = Date.now() + data["expires_in"] * 1000;
    if (!data["refresh_token"])
      data["refresh_token"] = this.#token.refresh_token;

    this.#token = data;
    await fs.writeFile("credentials.spotify.json", JSON.stringify(data));
    logger.debug("Updated access token for Spotify.");
    return true;
  }
}

module.exports = SpotifyTracker;