import io
import threading
import wave

from django.conf import settings

# Lazy per-process singleton: each gunicorn worker loads its own copy on first
# use rather than all workers loading the ONNX model at startup (the host runs
# several other containers with limited spare RAM).
_voice = None
_lock = threading.Lock()


def _get_voice():
    global _voice
    if _voice is None:
        with _lock:
            if _voice is None:
                from piper import PiperVoice
                _voice = PiperVoice.load(str(settings.TTS_MODEL_PATH))
    return _voice


def synthesize_wav(text):
    """Synthesize `text` to WAV bytes.

    Never persists or logs `text` — callers must not log it either. The lock
    also serializes inference, since one onnxruntime session isn't meant to
    run concurrent calls within a process.
    """
    voice = _get_voice()
    buf = io.BytesIO()
    with _lock:
        with wave.open(buf, 'wb') as wav_file:
            voice.synthesize_wav(text, wav_file)
    return buf.getvalue()