Extract the shared realtime audio graph owner

frontend/audio-graph.js

@@ -0,0 +1,69 @@
+/* One lifetime owner for the player's realtime AudioContext and media sources. */
+(function (root) {
+  'use strict';
+
+  function create(options = {}) {
+    const getConstructor = options.getConstructor || (() => root.AudioContext || root.webkitAudioContext);
+    let context = null;
+    const sources = new Map();
+    const routes = new Map();
+    const failed = new Map();
+
+    function getContext(contextOptions) {
+      if (context) return context;
+      const Constructor = getConstructor();
+      if (typeof Constructor !== 'function') throw new Error('Web Audio is unavailable');
+      context = contextOptions === undefined ? new Constructor() : new Constructor(contextOptions);
+      return context;
+    }
+
+    function source(element) {
+      if (!element) throw new TypeError('A media element is required');
+      if (sources.has(element)) return sources.get(element);
+      if (failed.has(element)) throw failed.get(element);
+      try {
+        const created = getContext().createMediaElementSource(element);
+        sources.set(element, created);
+        return created;
+      } catch (error) {
+        // MediaElementSource cannot be undone. Remember failure so a later
+        // route change can never attempt a second source for this element.
+        failed.set(element, error);
+        throw error;
+      }
+    }
+
+    function connect(element, destination) {
+      const mediaSource = source(element);
+      if (!destination) throw new TypeError('An audio destination is required');
+      if (routes.get(element) === destination) return mediaSource;
+      if (routes.has(element)) mediaSource.disconnect();
+      mediaSource.connect(destination);
+      routes.set(element, destination);
+      return mediaSource;
+    }
+
+    function routeAll(elements, destination) {
+      for (const element of elements || []) connect(element, destination);
+    }
+
+    function snapshot() {
+      return {
+        contextCreated: !!context,
+        sampleRate: context?.sampleRate || null,
+        sourceCount: sources.size,
+        failedCount: failed.size,
+        routedCount: routes.size,
+      };
+    }
+
+    return { context: getContext, source, connect, routeAll, snapshot };
+  }
+
+  const singleton = create();
+  const api = { create, context: (...args) => singleton.context(...args), source: (...args) => singleton.source(...args),
+    connect: (...args) => singleton.connect(...args), routeAll: (...args) => singleton.routeAll(...args),
+    snapshot: () => singleton.snapshot() };
+  if (typeof module !== 'undefined' && module.exports) module.exports = api;
+  else root.AudioGraph = api;
+})(typeof window !== 'undefined' ? window : globalThis);