refactor: separate voice controls and configurable Realtime connections

src/voice/realtimeBackend.js

@@ -0,0 +1,90 @@
+import { DEFAULT_VOICE_TIER, resolveVoiceModel } from './voiceCost.js';
+
+/** Realtime-compatible token and SDP requests, independent of microphone/UI ownership. */
+export function createRealtimeBackend({
+  tokenEndpoint = '/api/realtime/token',
+  callsEndpoint = 'https://api.openai.com/v1/realtime/calls',
+  tokenTransport = (...args) => fetch(...args),
+  connectionTransport = (...args) => fetch(...args),
+  timeoutMs = 30_000,
+} = {}) {
+  const scoped = (signal) =>
+    AbortSignal.any([signal, AbortSignal.timeout(timeoutMs)].filter(Boolean));
+  return Object.freeze({
+    protocol: 'openai-realtime',
+    async requestToken({ tier = DEFAULT_VOICE_TIER, signal } = {}) {
+      signal = scoped(signal);
+      signal.throwIfAborted();
+      const separator = tokenEndpoint.includes('?') ? '&' : '?';
+      const url = `${tokenEndpoint}${separator}tier=${encodeURIComponent(resolveVoiceModel(tier).tier)}`;
+      const response = await tokenTransport(url, {
+        signal,
+        cache: 'no-store',
+        redirect: 'error',
+      });
+      signal.throwIfAborted();
+      const data = await response.json().catch(() => null);
+      signal.throwIfAborted();
+      if (!response.ok) {
+        const reason =
+          typeof data?.error === 'string' ? data.error : data?.error?.message;
+        throw new Error(
+          reason || `Realtime token failed: HTTP ${response.status}`,
+        );
+      }
+      const token =
+        data?.value || data?.client_secret?.value || data?.client_secret;
+      if (typeof token !== 'string' || !token)
+        throw new Error(
+          'Realtime token response did not include a client secret',
+        );
+      const expiresAt = data?.expires_at ?? data?.client_secret?.expires_at;
+      if (
+        expiresAt != null &&
+        (!Number.isFinite(expiresAt) || expiresAt * 1000 <= Date.now())
+      )
+        throw new Error(
+          'Realtime client secret has expired; reconnect to request a new one',
+        );
+      return {
+        token,
+        model:
+          response.headers?.get?.('X-GEV-Voice-Model') ||
+          data?.session?.model ||
+          null,
+        tier: response.headers?.get?.('X-GEV-Voice-Tier') || null,
+        expiresAt,
+      };
+    },
+    async negotiate({ offerSdp, credential, signal }) {
+      signal = scoped(signal);
+      signal.throwIfAborted();
+      if (
+        credential.expiresAt != null &&
+        credential.expiresAt * 1000 <= Date.now()
+      )
+        throw new Error(
+          'Realtime client secret has expired; reconnect to request a new one',
+        );
+      const response = await connectionTransport(callsEndpoint, {
+        method: 'POST',
+        body: offerSdp,
+        signal,
+        redirect: 'error',
+        cache: 'no-store',
+        headers: {
+          Authorization: `Bearer ${credential.token}`,
+          'Content-Type': 'application/sdp',
+        },
+      });
+      signal.throwIfAborted();
+      if (!response.ok) {
+        await response.body?.cancel?.().catch(() => {});
+        throw new Error(`Realtime SDP failed: HTTP ${response.status}`);
+      }
+      const answer = await response.text();
+      signal.throwIfAborted();
+      return answer;
+    },
+  });
+}