feat: implement tier-a4 tts voice output replies

src/models/tts.ts

@@ -0,0 +1,88 @@
+import type { OutboundAttachment } from '../channels/types.js';
+
+export type TtsOutputFormat = 'mp3' | 'wav' | 'opus';
+
+export interface TtsSynthesisConfig {
+  endpoint?: string;
+  apiKey?: string;
+  model?: string;
+  voice?: string;
+  format?: TtsOutputFormat;
+}
+
+function outputFormatToMimeType(format: TtsOutputFormat): string {
+  switch (format) {
+    case 'wav':
+      return 'audio/wav';
+    case 'opus':
+      return 'audio/ogg';
+    case 'mp3':
+    default:
+      return 'audio/mpeg';
+  }
+}
+
+function outputFormatToExtension(format: TtsOutputFormat): string {
+  switch (format) {
+    case 'wav':
+      return 'wav';
+    case 'opus':
+      return 'ogg';
+    case 'mp3':
+    default:
+      return 'mp3';
+  }
+}
+
+/** Synthesize speech via an OpenAI-compatible /v1/audio/speech endpoint. */
+export async function synthesizeSpeechAttachment(
+  text: string,
+  config: TtsSynthesisConfig,
+): Promise<OutboundAttachment | null> {
+  const trimmed = text.trim();
+  if (!trimmed) {
+    return null;
+  }
+  if (!config.endpoint) {
+    return null;
+  }
+
+  const format = config.format ?? 'mp3';
+  const model = config.model ?? 'gpt-4o-mini-tts';
+  const voice = config.voice ?? 'alloy';
+
+  const headers: Record<string, string> = {
+    'Content-Type': 'application/json',
+  };
+  if (config.apiKey) {
+    headers.Authorization = `Bearer ${config.apiKey}`;
+  }
+
+  const response = await fetch(config.endpoint, {
+    method: 'POST',
+    headers,
+    body: JSON.stringify({
+      model,
+      voice,
+      input: trimmed,
+      response_format: format,
+    }),
+  });
+
+  if (!response.ok) {
+    const detail = await response.text().catch(() => '');
+    throw new Error(
+      `TTS request failed: ${response.status} ${response.statusText}${detail ? ` - ${detail.slice(0, 200)}` : ''}`,
+    );
+  }
+
+  const audioBytes = await response.arrayBuffer();
+  const data = Buffer.from(audioBytes).toString('base64');
+  const extension = outputFormatToExtension(format);
+
+  return {
+    mimeType: outputFormatToMimeType(format),
+    data,
+    filename: `flynn-reply-${Date.now()}.${extension}`,
+  };
+}