Feat: Migrate voice transcription from OpenAI Whisper to Google Gemini 1.5 Flash API

telegram.js

@@ -77,34 +77,48 @@ async function downloadTelegramFile(filePath) {
   return await res.arrayBuffer();
 }
 
-// Transcribe OGG/Opus voice data using OpenAI Whisper API
+// Transcribe OGG/Opus voice data using Google Gemini 1.5 Flash API (100% Free)
 async function transcribeVoice(audioBuffer) {
-  if (!process.env.OPENAI_API_KEY) {
-    throw new Error("OPENAI_API_KEY is not configured in .env.");
+  const geminiKey = process.env.GEMINI_API_KEY;
+  if (!geminiKey) {
+    throw new Error("GEMINI_API_KEY is not configured in .env.");
   }
 
-  const formData = new FormData();
-  // Whisper requires the ogg/opus file to have a proper filename extension
-  const blob = new Blob([audioBuffer], { type: "audio/ogg" });
-  formData.append("file", blob, "voice.ogg");
-  formData.append("model", "whisper-1");
-  formData.append("language", "de");
+  const base64Audio = Buffer.from(audioBuffer).toString("base64");
+  const url = `https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash:generateContent?key=${geminiKey}`;
 
-  const res = await fetch("https://api.openai.com/v1/audio/transcriptions", {
+  const res = await fetch(url, {
     method: "POST",
     headers: {
-      Authorization: `Bearer ${process.env.OPENAI_API_KEY}`,
+      "Content-Type": "application/json",
     },
-    body: formData,
+    body: JSON.stringify({
+      contents: [
+        {
+          parts: [
+            {
+              inlineData: {
+                mimeType: "audio/ogg",
+                data: base64Audio,
+              },
+            },
+            {
+              text: "Transkribiere diese Sprachnachricht wortgetreu in deutschen Text. Gib NUR die Transkription zurück, ohne Einleitung, Kommentare oder sonstige Zusätze. Falls nichts verständlich gesprochen wurde, antworte mit einem leeren Text.",
+            },
+          ],
+        },
+      ],
+    }),
   });
 
   if (!res.ok) {
     const errorText = await res.text();
-    throw new Error(`OpenAI Whisper API failed (${res.status}): ${errorText}`);
+    throw new Error(`Gemini API failed (${res.status}): ${errorText}`);
   }
 
   const data = await res.json();
-  return data.text || "";
+  const text = data.candidates?.[0]?.content?.parts?.[0]?.text || "";
+  return text.trim();
 }
 
 // Fetch available contacts from Monica to perform NLP name matching
@@ -180,10 +194,10 @@ async function handleUpdate(update) {
   // 2. Extract text (either message text or transcribe voice note)
   if (voice) {
     isVoice = true;
-    if (!process.env.OPENAI_API_KEY) {
+    if (!process.env.GEMINI_API_KEY) {
       await sendTelegramMessage(
         chatId,
-        "⚠️ <b>Sprachnachrichten deaktiviert:</b>\nEs ist kein <code>OPENAI_API_KEY</code> in der <code>.env</code>-Konfiguration hinterlegt. Bitte sende stattdessen Textnachrichten oder füge den API-Key hinzu.",
+        "⚠️ <b>Sprachnachrichten deaktiviert:</b>\nEs ist kein <code>GEMINI_API_KEY</code> in der <code>.env</code>-Konfiguration hinterlegt. Bitte erstelle einen kostenlosen Key im Google AI Studio und füge ihn hinzu.",
         message.message_id
       );
       return;
@@ -204,7 +218,7 @@ async function handleUpdate(update) {
       // Download file binary
       const audioBuffer = await downloadTelegramFile(fileInfo.result.file_path);
 
-      // Transcribe via Whisper
+      // Transcribe via Gemini
       processedText = await transcribeVoice(audioBuffer);
       if (!processedText.trim()) {
         await sendTelegramMessage(
@@ -262,7 +276,7 @@ async function handleUpdate(update) {
   let responseText = `<b>Eintrag erfasst!</b> ✅\n\n`;
 
   if (isVoice) {
-    responseText += `🎤 <b>Transkription:</b>\n<i>"${escapeHtml(processedText)}"</i>\n\n`;
+    responseText += `🎤 <b>Transkription (Gemini):</b>\n<i>"${escapeHtml(processedText)}"</i>\n\n`;
   }
 
   if (analysis.contact) {