import queue
import threading
import cv2


class BufferlessVideoCapture:

    def __init__(self, name, width=None, height=None):
        self.cap = cv2.VideoCapture(name)
        if width is not None and height is not None:
            self.cap.set(cv2.CAP_PROP_FRAME_WIDTH, width)
            self.cap.set(cv2.CAP_PROP_FRAME_HEIGHT, height)
        self.q = queue.Queue()
        t = threading.Thread(target=self._reader)
        t.daemon = True
        t.start()

    # read frames as soon as they are available, keeping only most recent one
    def _reader(self):
        while True:
            ret, frame = self.cap.read()
            if not ret:
                break
            if not self.q.empty():
                try:
                    self.q.get_nowait()   # discard previous (unprocessed) frame
                except queue.Empty:
                    pass
            self.q.put((ret, frame))

    def read(self):
        return self.q.get()