"""Voice Processor Skeleton.

Phase: B3

Provides a minimal singleton VoiceProcessor with a lazy load() and a
process_pcm_int16 method. For now it only measures timing and returns
pass-through audio.

Future expansion hooks:
- VAD / segmentation
- Feature extraction (MFCCs, log-mel)
- Model inference (ASR, voice conversion, TTS, etc.)
- Streaming state management

The design keeps the API intentionally small so upstream code can remain
stable while internals evolve.
"""
from __future__ import annotations

import threading
import time
from dataclasses import dataclass
from typing import Optional


@dataclass
class VoiceResult:
    """Container for voice processing output.

    For now, just echoes the PCM input.
    """
    pcm: memoryview  # zero-copy view of processed PCM int16 data
    sample_rate: int
    # Future: add tokens, text, features, etc.


class VoiceProcessor:
    _instance: Optional["VoiceProcessor"] = None
    _instance_lock = threading.Lock()

    def __init__(self) -> None:
        self._loaded = False
        self._load_lock = threading.Lock()
        # Placeholder for model / pipeline objects
        self._models_ready = False

    # ------------- Singleton Access -------------
    @classmethod
    def get(cls) -> "VoiceProcessor":
        if cls._instance is None:
            with cls._instance_lock:
                if cls._instance is None:  # double-checked
                    cls._instance = cls()
        return cls._instance

    # ------------- Lifecycle -------------
    def load(self) -> None:
        """Lazy load models / resources.

        Keep it extremely fast right now. Simulate a trivial setup only
        on first call.
        """
        if self._loaded:
            return
        with self._load_lock:
            if self._loaded:
                return
            # Simulate minimal setup work (no sleep to keep fast)
            self._models_ready = True
            self._loaded = True

    # ------------- Processing -------------
    def process_pcm_int16(self, pcm: bytes | bytearray | memoryview, sample_rate: int) -> tuple[memoryview, float]:
        """Process an int16 PCM chunk.

        Returns a tuple of (processed_pcm_memoryview, elapsed_ms).
        Currently pass-through.
        """
        if not self._loaded:
            self.load()
        start = time.time() * 1000.0
        # Pass-through: we could copy but we prefer zero-copy memoryview
        mv = memoryview(pcm)
        # Placeholder for future signal chain
        end = time.time() * 1000.0
        return mv, end - start


# Export singleton accessor
voice_processor = VoiceProcessor.get()