import cv2
from collections import OrderedDict


class Cv2BufferedCap:
    """Buffered wrapper around cv2.VideoCapture that handles frame loading, seeking, and caching correctly"""
    
    def __init__(self, video_path, backend=None, cache_size=10000):
        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))
        
        # Current position tracking
        self.current_frame = 0
        
        # Frame cache (LRU)
        self.cache_size = cache_size
        self.frame_cache = OrderedDict()
    
    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
        if frame_number in self.frame_cache:
            self.frame_cache.move_to_end(frame_number)
            return self.frame_cache[frame_number]
        
        # Optimize for sequential reading (next frame)
        if frame_number == self.current_frame + 1:
            ret, frame = self.cap.read()
        else:
            # Seek for non-sequential access
            self.cap.set(cv2.CAP_PROP_POS_FRAMES, frame_number)
            ret, frame = self.cap.read()
        
        if ret:
            self.current_frame = frame_number
            # Store in cache, evict least recently used if cache is full
            if len(self.frame_cache) >= self.cache_size:
                self.frame_cache.popitem(last=False)
            self.frame_cache[frame_number] = frame
            self.frame_cache.move_to_end(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()