import cv2


class Cv2BufferedCap:
    """Buffered wrapper around cv2.VideoCapture that handles frame loading, seeking, and caching correctly"""
    
    def __init__(self, video_path, backend=None):
        self.video_path = video_path
        self.cap = cv2.VideoCapture(str(video_path), backend)
        if not self.cap.isOpened():
            raise ValueError(f"Could not open video: {video_path}")
        
        # Video properties
        self.total_frames = int(self.cap.get(cv2.CAP_PROP_FRAME_COUNT))
        self.fps = self.cap.get(cv2.CAP_PROP_FPS)
        self.frame_width = int(self.cap.get(cv2.CAP_PROP_FRAME_WIDTH))
        self.frame_height = int(self.cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
        
        # Frame cache
        self.frame_cache = {}
        self.cache_access_order = []
        self.MAX_CACHE_FRAMES = 3000
        
        # Current position tracking
        self.current_frame = 0
        
    def _manage_cache(self):
        """Manage cache size using LRU eviction"""
        while len(self.frame_cache) > self.MAX_CACHE_FRAMES:
            oldest_frame = self.cache_access_order.pop(0)
            if oldest_frame in self.frame_cache:
                del self.frame_cache[oldest_frame]
    
    def _add_to_cache(self, frame_number, frame):
        """Add frame to cache"""
        self.frame_cache[frame_number] = frame.copy()
        if frame_number in self.cache_access_order:
            self.cache_access_order.remove(frame_number)
        self.cache_access_order.append(frame_number)
        self._manage_cache()
    
    def _get_from_cache(self, frame_number):
        """Get frame from cache and update LRU"""
        if frame_number in self.frame_cache:
            if frame_number in self.cache_access_order:
                self.cache_access_order.remove(frame_number)
            self.cache_access_order.append(frame_number)
            return self.frame_cache[frame_number].copy()
        return None
    
    def get_frame(self, frame_number):
        """Get frame at specific index - always accurate"""
        # Clamp frame number to valid range
        frame_number = max(0, min(frame_number, self.total_frames - 1))
        
        # Check cache first
        cached_frame = self._get_from_cache(frame_number)
        if cached_frame is not None:
            self.current_frame = frame_number
            return cached_frame
        
        # Not in cache, seek to frame and read
        self.cap.set(cv2.CAP_PROP_POS_FRAMES, frame_number)
        ret, frame = self.cap.read()
        
        if ret:
            self._add_to_cache(frame_number, frame)
            self.current_frame = frame_number
            return frame
        else:
            raise ValueError(f"Failed to read frame {frame_number}")
    
    def advance_frame(self, frames=1):
        """Advance by specified number of frames"""
        new_frame = self.current_frame + frames
        return self.get_frame(new_frame)
    
    def release(self):
        """Release the video capture"""
        if self.cap:
            self.cap.release()
    
    def isOpened(self):
        """Check if capture is opened"""
        return self.cap and self.cap.isOpened()