"""Utility functions for trendspy."""

import os
import time
import threading
from datetime import datetime
from typing import Callable, Any, TypeVar, cast, Dict, Optional, Tuple, Generic
from functools import wraps

# Type variable for generic function
F = TypeVar('F', bound=Callable[..., Any])
T = TypeVar('T')


class TTLCache(Generic[T]):
    """
    Thread-safe TTL (Time-To-Live) cache for storing temporary data.

    Features:
    - Automatic expiration based on TTL
    - Thread-safe operations
    - Maximum size limit with LRU-style eviction
    - Cache statistics (hits, misses)

    Example:
        >>> cache = TTLCache(ttl=300, max_size=100)  # 5 min TTL, max 100 items
        >>> cache.set('US', trends_data)
        >>> data = cache.get('US')  # Returns data if not expired
        >>> cache.clear()  # Clear all cached data
    """

    def __init__(self, ttl: float = 300.0, max_size: int = 256):
        """
        Initialize TTL cache.

        Args:
            ttl: Time-to-live in seconds (default: 300 = 5 minutes)
            max_size: Maximum number of items to cache (default: 256)
        """
        self._cache: Dict[str, Tuple[T, float]] = {}  # key -> (value, expiry_time)
        self._ttl = ttl
        self._max_size = max_size
        self._lock = threading.RLock()
        self._hits = 0
        self._misses = 0

    def get(self, key: str) -> Optional[T]:
        """
        Get value from cache if exists and not expired.

        Args:
            key: Cache key

        Returns:
            Cached value or None if not found/expired
        """
        with self._lock:
            if key in self._cache:
                value, expiry = self._cache[key]
                if time.time() < expiry:
                    self._hits += 1
                    return value
                else:
                    # Expired, remove it
                    del self._cache[key]
            self._misses += 1
            return None

    def set(self, key: str, value: T) -> None:
        """
        Set value in cache with TTL.

        Args:
            key: Cache key
            value: Value to cache
        """
        with self._lock:
            # Evict oldest entries if at max size
            if len(self._cache) >= self._max_size and key not in self._cache:
                self._evict_expired()
                # If still at max, remove oldest entry
                if len(self._cache) >= self._max_size:
                    oldest_key = next(iter(self._cache))
                    del self._cache[oldest_key]

            expiry = time.time() + self._ttl
            self._cache[key] = (value, expiry)

    def _evict_expired(self) -> int:
        """Remove all expired entries. Returns count of evicted items."""
        now = time.time()
        expired_keys = [k for k, (_, exp) in self._cache.items() if now >= exp]
        for key in expired_keys:
            del self._cache[key]
        return len(expired_keys)

    def clear(self) -> None:
        """Clear all cached data."""
        with self._lock:
            self._cache.clear()
            self._hits = 0
            self._misses = 0

    def stats(self) -> Dict[str, Any]:
        """
        Get cache statistics.

        Returns:
            Dict with hits, misses, size, hit_rate
        """
        with self._lock:
            total = self._hits + self._misses
            hit_rate = (self._hits / total * 100) if total > 0 else 0.0
            return {
                'hits': self._hits,
                'misses': self._misses,
                'size': len(self._cache),
                'max_size': self._max_size,
                'ttl': self._ttl,
                'hit_rate': f"{hit_rate:.1f}%"
            }

    @property
    def ttl(self) -> float:
        """Get current TTL value."""
        return self._ttl

    @ttl.setter
    def ttl(self, value: float) -> None:
        """Set new TTL value (doesn't affect existing entries)."""
        self._ttl = value


# Global RSS cache instance (5 minute TTL, max 256 entries)
_rss_cache: TTLCache = TTLCache(ttl=300.0, max_size=256)


def get_rss_cache() -> TTLCache:
    """Get the global RSS cache instance."""
    return _rss_cache


def clear_rss_cache() -> None:
    """Clear the global RSS cache."""
    _rss_cache.clear()


def get_rss_cache_stats() -> Dict[str, Any]:
    """Get statistics for the global RSS cache."""
    return _rss_cache.stats()


def set_rss_cache_ttl(ttl: float) -> None:
    """
    Set the TTL for the global RSS cache.

    Args:
        ttl: New TTL in seconds (0 to disable caching)
    """
    _rss_cache.ttl = ttl


def get_timestamp() -> str:
    """Get current timestamp in YYYYMMDD-HHMMSS format."""
    return datetime.now().strftime("%Y%m%d-%H%M%S")


def ensure_dir(directory: str) -> str:
    """Ensure directory exists, create if it doesn't."""
    os.makedirs(directory, exist_ok=True)
    return directory


def rate_limit(delay: float = 1.0) -> Callable[[F], F]:
    """Simple rate limiting decorator."""
    def decorator(func: F) -> F:
        last_called = [0.0]

        @wraps(func)
        def wrapper(*args: Any, **kwargs: Any) -> Any:
            elapsed = time.time() - last_called[0]
            if elapsed < delay:
                time.sleep(delay - elapsed)
            result = func(*args, **kwargs)
            last_called[0] = time.time()
            return result
        return cast(F, wrapper)
    return decorator
