refactor(playback): extract playback helpers to shrink playbackService (1/10)

File-size decomposition (no behavior change). Move the self-contained
SimpleEventEmitter and extractWebSeedsFromMagnet (+ its WEBSEED_PARAM_KEYS and
the now-sole safeDecodeURIComponent consumer) out of playbackService.js into a
new js/services/playbackHelpers.js and import them back.

playbackService.js: 1350 -> 1274 lines (now under its original 1289 baseline).
Re-recorded the smaller baseline in check-file-size.mjs to lock the reduction.

Build + full unit suite green.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

js/services/playbackHelpers.js

@@ -0,0 +1,98 @@
+// js/services/playbackHelpers.js
+//
+// Small, self-contained helpers extracted from playbackService.js to keep that
+// orchestrator under the file-size budget. Pure logic with no dependency on the
+// playback session state.
+
+import { safeDecodeURIComponent } from "../utils/safeDecode.js";
+
+/**
+ * Minimal synchronous event emitter used by the playback session to surface
+ * status/fallback/sourcechange events to the coordinator. Errors thrown by a
+ * listener are swallowed (and optionally logged) so one bad listener can't
+ * abort the rest of the playback pipeline.
+ */
+export class SimpleEventEmitter {
+  constructor(logger = null) {
+    this.logger = typeof logger === "function" ? logger : null;
+    this.listeners = new Map();
+  }
+
+  on(eventName, handler) {
+    if (typeof handler !== "function") {
+      return () => {};
+    }
+    if (!this.listeners.has(eventName)) {
+      this.listeners.set(eventName, new Set());
+    }
+    const handlers = this.listeners.get(eventName);
+    handlers.add(handler);
+    return () => {
+      handlers.delete(handler);
+      if (!handlers.size) {
+        this.listeners.delete(eventName);
+      }
+    };
+  }
+
+  emit(eventName, detail) {
+    const handlers = this.listeners.get(eventName);
+    if (!handlers || !handlers.size) {
+      return;
+    }
+    for (const handler of Array.from(handlers)) {
+      try {
+        handler(detail);
+      } catch (err) {
+        if (this.logger) {
+          this.logger("[PlaybackService] Listener error", err);
+        }
+      }
+    }
+  }
+}
+
+const WEBSEED_PARAM_KEYS = new Set(["ws", "webseed"]);
+
+/**
+ * Extract every web seed URL (`ws=`/`webseed=`) from a magnet's query string,
+ * in order, decoded. Used to seed WebTorrent's urlList from the magnet.
+ *
+ * @param {string} magnetUri
+ * @returns {string[]}
+ */
+export const extractWebSeedsFromMagnet = (magnetUri) => {
+  if (typeof magnetUri !== "string") {
+    return [];
+  }
+  const trimmed = magnetUri.trim();
+  if (!trimmed) {
+    return [];
+  }
+  const [withoutFragment] = trimmed.split("#", 1);
+  const [, query = ""] = withoutFragment.split("?", 2);
+  if (!query) {
+    return [];
+  }
+
+  const webSeeds = [];
+  for (const segment of query.split("&")) {
+    if (!segment) {
+      continue;
+    }
+    const [rawKey, rawValue = ""] = segment.split("=", 2);
+    if (!rawKey) {
+      continue;
+    }
+    const key = rawKey.trim().toLowerCase();
+    if (!WEBSEED_PARAM_KEYS.has(key)) {
+      continue;
+    }
+    const decodedValue = safeDecodeURIComponent(rawValue.replace(/\+/g, "%20"));
+    const candidate = decodedValue.trim();
+    if (candidate) {
+      webSeeds.push(candidate);
+    }
+  }
+  return webSeeds;
+};

js/services/playbackService.js

@@ -1,7 +1,10 @@
 import { userLogger } from "../utils/logger.js";
-import { safeDecodeURIComponent } from "../utils/safeDecode.js";
 import { PLAYBACK_START_TIMEOUT } from "../constants.js";
 import { getCurrentVideo, setCurrentVideo } from "../state/appState.js";
+import {
+  SimpleEventEmitter,
+  extractWebSeedsFromMagnet,
+} from "./playbackHelpers.js";
 // js/services/playbackService.js
 
 /**
@@ -21,46 +24,6 @@ import { getCurrentVideo, setCurrentVideo } from "../state/appState.js";
  *   old session is cancelled and doesn't overwrite the new one.
  */
 
-class SimpleEventEmitter {
-  constructor(logger = null) {
-    this.logger = typeof logger === "function" ? logger : null;
-    this.listeners = new Map();
-  }
-
-  on(eventName, handler) {
-    if (typeof handler !== "function") {
-      return () => {};
-    }
-    if (!this.listeners.has(eventName)) {
-      this.listeners.set(eventName, new Set());
-    }
-    const handlers = this.listeners.get(eventName);
-    handlers.add(handler);
-    return () => {
-      handlers.delete(handler);
-      if (!handlers.size) {
-        this.listeners.delete(eventName);
-      }
-    };
-  }
-
-  emit(eventName, detail) {
-    const handlers = this.listeners.get(eventName);
-    if (!handlers || !handlers.size) {
-      return;
-    }
-    for (const handler of Array.from(handlers)) {
-      try {
-        handler(detail);
-      } catch (err) {
-        if (this.logger) {
-          this.logger("[PlaybackService] Listener error", err);
-        }
-      }
-    }
-  }
-}
-
 const HOSTED_URL_SUCCESS_MESSAGE = "✅ Streaming from hosted URL";
 const DEFAULT_UNSUPPORTED_BTITH_MESSAGE =
   "This magnet link is missing a compatible BitTorrent v1 info hash.";
@@ -68,44 +31,6 @@ const AUTH_STATUS_CODES = new Set([401, 403]);
 const SSL_ERROR_PATTERN = /(ssl|cert|certificate)/i;
 const CORS_ERROR_PATTERN = /cors/i;
 const PROBE_CACHE_TTL_MS = 45000;
-const WEBSEED_PARAM_KEYS = new Set(["ws", "webseed"]);
-
-const extractWebSeedsFromMagnet = (magnetUri) => {
-  if (typeof magnetUri !== "string") {
-    return [];
-  }
-  const trimmed = magnetUri.trim();
-  if (!trimmed) {
-    return [];
-  }
-  const [withoutFragment] = trimmed.split("#", 1);
-  const [, query = ""] = withoutFragment.split("?", 2);
-  if (!query) {
-    return [];
-  }
-
-  const webSeeds = [];
-  for (const segment of query.split("&")) {
-    if (!segment) {
-      continue;
-    }
-    const [rawKey, rawValue = ""] = segment.split("=", 2);
-    if (!rawKey) {
-      continue;
-    }
-    const key = rawKey.trim().toLowerCase();
-    if (!WEBSEED_PARAM_KEYS.has(key)) {
-      continue;
-    }
-    const decodedValue = safeDecodeURIComponent(rawValue.replace(/\+/g, "%20"));
-    const candidate = decodedValue.trim();
-    if (candidate) {
-      webSeeds.push(candidate);
-    }
-  }
-  return webSeeds;
-};
-
 const getHostedUrlFailureDetails = (probeResult = {}) => {
   const outcome = probeResult?.outcome || "error";
   const status = Number.isFinite(probeResult?.status)

scripts/check-file-size.mjs

@@ -58,7 +58,7 @@ const GRANDFATHERED = {
   "js/ui/views/VideoListView.js": 1359,
   "js/ui/components/UploadModal.js": 1319,
   "js/ui/components/SimilarContentCard.js": 1303,
-  "js/services/playbackService.js": 1289,
+  "js/services/playbackService.js": 1274,
   "js/services/authService.js": 1335,
   "js/ui/zapController.js": 1206,
   "js/services/r2Service.js": 1194,