From 6e85c16614ca18e3d5d2babf08b12ffb522ee552 Mon Sep 17 00:00:00 2001
From: Quentin Fuxa <quentin.fuxa@gmail.com>
Date: Sun, 18 Jan 2026 15:27:00 +0100
Subject: [PATCH] Refactor TranscriptionEngine singleton

---
 whisperlivekit/core.py | 57 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 47 insertions(+), 10 deletions(-)

diff --git a/whisperlivekit/core.py b/whisperlivekit/core.py
index c306f52..30a8da7 100644
--- a/whisperlivekit/core.py
+++ b/whisperlivekit/core.py
@@ -1,5 +1,4 @@
 import logging
-import sys
 import threading
 from argparse import Namespace
 from dataclasses import asdict
@@ -15,7 +14,7 @@ class TranscriptionEngine:
     _instance = None
     _initialized = False
     _lock = threading.Lock()  # Thread-safe singleton lock
-    
+
     def __new__(cls, *args, **kwargs):
         # Double-checked locking pattern for thread-safe singleton
         if cls._instance is None:
@@ -24,7 +23,18 @@ class TranscriptionEngine:
                 if cls._instance is None:
                     cls._instance = super().__new__(cls)
         return cls._instance
-    
+
+    @classmethod
+    def reset(cls):
+        """Reset the singleton so a new instance can be created.
+
+        For testing only — allows switching backends between test runs.
+        In production, the singleton should never be reset.
+        """
+        with cls._lock:
+            cls._instance = None
+            cls._initialized = False
+
     def __init__(self, config=None, **kwargs):
         # Thread-safe initialization check
         with TranscriptionEngine._lock:
@@ -102,6 +112,17 @@ class TranscriptionEngine:
                 self.tokenizer = None
                 self.asr = VoxtralHFStreamingASR(**transcription_common_params)
                 logger.info("Using Voxtral HF Transformers streaming backend")
+            elif config.backend == "qwen3":
+                from whisperlivekit.qwen3_asr import Qwen3ASR
+                self.asr = Qwen3ASR(**transcription_common_params)
+                self.asr.confidence_validation = config.confidence_validation
+                self.asr.tokenizer = None
+                self.asr.buffer_trimming = config.buffer_trimming
+                self.asr.buffer_trimming_sec = config.buffer_trimming_sec
+                self.asr.backend_choice = "qwen3"
+                from whisperlivekit.warmup import warmup_asr
+                warmup_asr(self.asr, config.warmup_file)
+                logger.info("Using Qwen3-ASR backend with LocalAgreement policy")
             elif config.backend_policy == "simulstreaming":
                 simulstreaming_params = {
                     "disable_fast_encoder": config.disable_fast_encoder,
@@ -173,26 +194,42 @@ class TranscriptionEngine:
                 )
 
 
-def online_factory(args, asr):
-    if getattr(args, 'backend', None) == "voxtral-mlx":
+def online_factory(args, asr, language=None):
+    """Create an online ASR processor for a session.
+
+    Args:
+        args: Configuration namespace.
+        asr: Shared ASR backend instance.
+        language: Optional per-session language override (e.g. "en", "fr", "auto").
+            If provided and the backend supports it, transcription will use
+            this language instead of the server-wide default.
+    """
+    # Wrap the shared ASR with a per-session language if requested
+    if language is not None:
+        from whisperlivekit.session_asr_proxy import SessionASRProxy
+        asr = SessionASRProxy(asr, language)
+
+    backend = getattr(args, 'backend', None)
+    if backend == "voxtral-mlx":
         from whisperlivekit.voxtral_mlx_asr import VoxtralMLXOnlineProcessor
         return VoxtralMLXOnlineProcessor(asr)
-    if getattr(args, 'backend', None) == "voxtral":
+    if backend == "voxtral":
         from whisperlivekit.voxtral_hf_streaming import VoxtralHFStreamingOnlineProcessor
         return VoxtralHFStreamingOnlineProcessor(asr)
+    if backend == "qwen3":
+        return OnlineASRProcessor(asr)
     if args.backend_policy == "simulstreaming":
         from whisperlivekit.simul_whisper import SimulStreamingOnlineProcessor
         return SimulStreamingOnlineProcessor(asr)
     return OnlineASRProcessor(asr)
-  
-  
+
+
 def online_diarization_factory(args, diarization_backend):
     if args.diarization_backend == "diart":
         online = diarization_backend
         # Not the best here, since several user/instances will share the same backend, but diart is not SOTA anymore and sortformer is recommended
     elif args.diarization_backend == "sortformer":
-        from whisperlivekit.diarization.sortformer_backend import \
-            SortformerDiarizationOnline
+        from whisperlivekit.diarization.sortformer_backend import SortformerDiarizationOnline
         online = SortformerDiarizationOnline(shared_model=diarization_backend)
     else:
         raise ValueError(f"Unknown diarization backend: {args.diarization_backend}")