"""
Enterprise model lifecycle manager.
Verifies local models, triggers automatic download if missing,
and ensures thread/async-safe initialization across the library.

Author: IntelliDeep Labs Team
License: BSL 1.1
"""

from __future__ import annotations

import asyncio
import hashlib
import logging
import os
import sys
import threading
import zipfile
from dataclasses import dataclass, field
from pathlib import Path
from typing import Dict, List, Optional

logger = logging.getLogger(__name__)


@dataclass(frozen=True)
class ModelConfig:
    """Immutable configuration for a required model."""
    name: str
    expected_dir: str
    zip_filename: str = "nlproxy_models.zip"
    min_files: int = 2  # Minimum files expected after extraction
    type: str = "unknown"  # embedding, nli, perplexity, spacy, etc.


class ModelManager:
    """
    Singleton manager for local model verification and on-demand download.
    Thread-safe and async-compatible. Designed for enterprise library initialization.
    """
    _instance: Optional[ModelManager] = None
    _lock = threading.Lock()
    _async_lock: Optional[asyncio.Lock] = None
    _initialized: bool = False
    _models_dir: Optional[Path] = None

    # Registry of required models
    REQUIRED_MODELS: Dict[str, ModelConfig] = {
        "all-MiniLM-L6-v2": ModelConfig(name="all-MiniLM-L6-v2", expected_dir="all-MiniLM-L6-v2", type="embedding"),
        "nli-distilroberta-base": ModelConfig(name="nli-distilroberta-base", expected_dir="nli-distilroberta-base", type="nli"),
        "distilgpt2": ModelConfig(name="distilgpt2", expected_dir="distilgpt2", type="perplexity"),
    }

    def __new__(cls) -> ModelManager:
        if cls._instance is None:
            with cls._lock:
                if cls._instance is None:
                    cls._instance = super().__new__(cls)
                    cls._async_lock = asyncio.Lock()
        return cls._instance

    @classmethod
    def get_instance(cls, models_dir: Optional[str] = None) -> ModelManager:
        """Get singleton instance and optionally set models directory."""
        instance = cls()
        if models_dir:
            instance._models_dir = Path(models_dir).resolve()
        elif instance._models_dir is None:
            instance._models_dir = Path(os.getenv("NLPROXY_MODELS_DIR", "nlproxy/models")).resolve()
        return instance

    def _is_model_extracted(self, config: ModelConfig) -> bool:
        """Check if model directory exists and contains expected files."""
        model_path = self._models_dir / config.expected_dir
        if not model_path.is_dir():
            return False
        return len(list(model_path.iterdir())) >= config.min_files

    def _has_zip_archive(self, config: ModelConfig) -> bool:
        """Fallback: check if the source zip exists in models_dir."""
        zip_path = self._models_dir / config.zip_filename
        return zip_path.exists() and zip_path.stat().st_size > 0

    def _compute_sha256(self, path: Path) -> str:
        """Compute SHA256 checksum for a file in a streaming manner."""
        hash_obj = hashlib.sha256()
        with path.open("rb") as file_obj:
            for chunk in iter(lambda: file_obj.read(8192), b""):
                hash_obj.update(chunk)
        return hash_obj.hexdigest()

    def verify_zip_checksum(self, zip_path: Path, expected_hash: Optional[str] = None) -> bool:
        """Verify the ZIP archive checksum against an expected SHA256 hash."""
        expected_hash = expected_hash or os.getenv("NLPROXY_MODELS_SHA256")
        if not expected_hash:
            logger.debug("No expected SHA256 checksum provided for ZIP validation.")
            return True

        actual_hash = self._compute_sha256(zip_path)
        if actual_hash.lower() != expected_hash.lower():
            raise ValueError(
                f"ZIP checksum mismatch: expected {expected_hash.lower()}, got {actual_hash.lower()}"
            )

        logger.info("ZIP checksum verification passed.")
        return True

    def verify_all(self) -> bool:
        """Synchronous verification of all required models."""
        return all(self._is_model_extracted(cfg) for cfg in self.REQUIRED_MODELS.values())

    async def ensure_ready(self) -> None:
        """
        Async-safe verification & download trigger.
        Idempotent: safe to call multiple times from different coroutines.
        """
        if self._initialized:
            return

        async with self._async_lock:
            if self._initialized:
                return

            missing = [cfg.name for cfg in self.REQUIRED_MODELS.values() if not self._is_model_extracted(cfg)]
            if missing:
                logger.info(f"Missing models: {', '.join(missing)}. Triggering automatic download...")
                await self._trigger_download()

            # Final verification
            if not self.verify_all():
                raise RuntimeError("Model verification failed after download. Check NLPROXY_MODELS_URL or permissions.")

            self._initialized = True
            logger.info("✅ All required models verified and ready for use.")

    async def _trigger_download(self) -> None:
        """Execute download_models.py in a thread pool to avoid blocking the event loop."""
        # Dynamic import to prevent circular dependencies
        from nlproxy.cli.download_models import main as download_main

        loop = asyncio.get_running_loop()
        # Pass --models-dir explicitly to avoid env var race conditions
        args = ["--models-dir", str(self._models_dir), "--verbose"]
        exit_code = await loop.run_in_executor(None, download_main, args)

        if exit_code != 0:
            raise RuntimeError(f"Model download failed with exit code {exit_code}")

    def sync_ensure_ready(self) -> None:
        """Synchronous wrapper for legacy or CLI initialization contexts."""
        if self._initialized:
            return
        asyncio.run(self.ensure_ready())