#!/usr/bin/env python3
import argparse
import sys

import cv2 as cv


parser = argparse.ArgumentParser(description="Capture one frame from an OpenCV camera.")
parser.add_argument("--camera", type=int, default=0, help="camera index, usually 0 for the default camera")
parser.add_argument("--output", default="capture.jpg", help="image file to write")
parser.add_argument("--warmup-frames", type=int, default=5, help="frames to read before saving the output frame")
args = parser.parse_args()

cap = cv.VideoCapture(args.camera)
if not cap.isOpened():
    sys.exit(f"Cannot open camera {args.camera}")

try:
    backend = cap.getBackendName()
    frame = None

    for _ in range(max(args.warmup_frames, 0) + 1):
        ok, frame = cap.read()
        if not ok or frame is None:
            sys.exit("Cannot read a frame from the camera")

    height, width = frame.shape[:2]

    if not cv.imwrite(args.output, frame):
        sys.exit(f"Cannot write {args.output}")

    print(f"Opened camera {args.camera} with backend {backend}")
    print(f"Frame size: {width}x{height}")
    print(f"Saved frame: {args.output}")
finally:
    cap.release()