import logging
import gc
import time
from typing import Dict, Any, Optional, Callable
from dataclasses import dataclass, field
from threading import Lock
import torch

logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)


@dataclass
class ModelInfo:
    """Information about a registered model."""
    name: str
    loader: Callable[[], Any]
    is_critical: bool = False  # Critical models are not unloaded under memory pressure
    estimated_memory_gb: float = 0.0
    is_loaded: bool = False
    last_used: float = 0.0
    model_instance: Any = None


class ModelManager:
    """
    Singleton model manager for unified model lifecycle management.
    Handles lazy loading, caching, and intelligent memory management.
    """

    _instance = None
    _lock = Lock()

    def __new__(cls):
        if cls._instance is None:
            with cls._lock:
                if cls._instance is None:
                    cls._instance = super().__new__(cls)
                    cls._instance._initialized = False
        return cls._instance

    def __init__(self):
        if self._initialized:
            return

        self._models: Dict[str, ModelInfo] = {}
        self._memory_threshold = 0.80  # Trigger cleanup at 80% GPU memory usage
        self._device = self._detect_device()

        logger.info(f"🔧 ModelManager initialized on {self._device}")
        self._initialized = True

    def _detect_device(self) -> str:
        """Detect best available device."""
        if torch.cuda.is_available():
            return "cuda"
        elif hasattr(torch.backends, 'mps') and torch.backends.mps.is_available():
            return "mps"
        return "cpu"

    def register_model(
        self,
        name: str,
        loader: Callable[[], Any],
        is_critical: bool = False,
        estimated_memory_gb: float = 0.0
    ):
        """
        Register a model for managed loading.

        Args:
            name: Unique model identifier
            loader: Callable that returns the loaded model
            is_critical: If True, model won't be unloaded under memory pressure
            estimated_memory_gb: Estimated GPU memory usage in GB
        """
        if name in self._models:
            logger.warning(f"⚠️ Model '{name}' already registered, updating")

        self._models[name] = ModelInfo(
            name=name,
            loader=loader,
            is_critical=is_critical,
            estimated_memory_gb=estimated_memory_gb,
            is_loaded=False,
            last_used=0.0,
            model_instance=None
        )
        logger.info(f"📝 Registered model: {name} (critical={is_critical}, ~{estimated_memory_gb:.1f}GB)")

    def load_model(self, name: str) -> Any:
        """
        Load a model by name. Returns cached instance if already loaded.

        Args:
            name: Model identifier

        Returns:
            Loaded model instance

        Raises:
            KeyError: If model not registered
            RuntimeError: If loading fails
        """
        if name not in self._models:
            raise KeyError(f"Model '{name}' not registered")

        model_info = self._models[name]

        # Return cached instance
        if model_info.is_loaded and model_info.model_instance is not None:
            model_info.last_used = time.time()
            logger.debug(f"📦 Using cached model: {name}")
            return model_info.model_instance

        # Check memory pressure before loading
        self.check_memory_pressure()

        # Load the model
        try:
            logger.info(f"📥 Loading model: {name}")
            start_time = time.time()

            model_instance = model_info.loader()

            model_info.model_instance = model_instance
            model_info.is_loaded = True
            model_info.last_used = time.time()

            load_time = time.time() - start_time
            logger.info(f"✅ Model '{name}' loaded in {load_time:.1f}s")

            return model_instance

        except Exception as e:
            logger.error(f"❌ Failed to load model '{name}': {e}")
            raise RuntimeError(f"Model loading failed: {e}")

    def unload_model(self, name: str):
        """
        Unload a specific model to free memory.

        Args:
            name: Model identifier
        """
        if name not in self._models:
            return

        model_info = self._models[name]

        if not model_info.is_loaded:
            return

        try:
            logger.info(f"🗑️ Unloading model: {name}")

            # Delete model instance
            if model_info.model_instance is not None:
                del model_info.model_instance

            model_info.model_instance = None
            model_info.is_loaded = False

            # Cleanup
            gc.collect()
            if torch.cuda.is_available():
                torch.cuda.empty_cache()

            logger.info(f"✅ Model '{name}' unloaded")

        except Exception as e:
            logger.error(f"❌ Error unloading model '{name}': {e}")

    def check_memory_pressure(self) -> bool:
        """
        Check GPU memory usage and unload least-used non-critical models if needed.

        Returns:
            True if cleanup was performed
        """
        if not torch.cuda.is_available():
            return False

        allocated = torch.cuda.memory_allocated() / 1024**3
        total = torch.cuda.get_device_properties(0).total_memory / 1024**3
        usage_ratio = allocated / total

        if usage_ratio < self._memory_threshold:
            return False

        logger.warning(f"⚠️ Memory pressure detected: {usage_ratio:.1%} used")

        # Find non-critical models sorted by last used time
        unloadable = [
            (name, info) for name, info in self._models.items()
            if info.is_loaded and not info.is_critical
        ]
        unloadable.sort(key=lambda x: x[1].last_used)

        # Unload oldest non-critical models
        cleaned = False
        for name, info in unloadable:
            self.unload_model(name)
            cleaned = True

            # Re-check memory
            new_ratio = torch.cuda.memory_allocated() / torch.cuda.get_device_properties(0).total_memory
            if new_ratio < self._memory_threshold * 0.7:  # Target 70% of threshold
                break

        return cleaned

    def force_cleanup(self):
        """Force cleanup all non-critical models and clear caches."""
        logger.info("🧹 Force cleanup initiated")

        # Unload all non-critical models
        for name, info in self._models.items():
            if info.is_loaded and not info.is_critical:
                self.unload_model(name)

        # Aggressive garbage collection
        for _ in range(5):
            gc.collect()

        if torch.cuda.is_available():
            torch.cuda.empty_cache()
            torch.cuda.ipc_collect()
            torch.cuda.synchronize()

        logger.info("✅ Force cleanup completed")

    def get_memory_status(self) -> Dict[str, Any]:
        """
        Get detailed memory status.

        Returns:
            Dictionary with memory statistics
        """
        status = {
            "device": self._device,
            "models": {},
            "total_estimated_gb": 0.0
        }

        # Model status
        for name, info in self._models.items():
            status["models"][name] = {
                "loaded": info.is_loaded,
                "critical": info.is_critical,
                "estimated_gb": info.estimated_memory_gb,
                "last_used": info.last_used
            }
            if info.is_loaded:
                status["total_estimated_gb"] += info.estimated_memory_gb

        # GPU memory
        if torch.cuda.is_available():
            allocated = torch.cuda.memory_allocated() / 1024**3
            total = torch.cuda.get_device_properties(0).total_memory / 1024**3
            cached = torch.cuda.memory_reserved() / 1024**3

            status["gpu"] = {
                "allocated_gb": round(allocated, 2),
                "total_gb": round(total, 2),
                "cached_gb": round(cached, 2),
                "free_gb": round(total - allocated, 2),
                "usage_percent": round((allocated / total) * 100, 1)
            }

        return status

    def get_loaded_models(self) -> list:
        """Get list of currently loaded model names."""
        return [name for name, info in self._models.items() if info.is_loaded]

    def is_model_loaded(self, name: str) -> bool:
        """Check if a specific model is loaded."""
        if name not in self._models:
            return False
        return self._models[name].is_loaded


# Global singleton instance
_model_manager = None


def get_model_manager() -> ModelManager:
    """Get the global ModelManager singleton instance."""
    global _model_manager
    if _model_manager is None:
        _model_manager = ModelManager()
    return _model_manager