deckhearth/lib/use-scanner-flash.js

import { useCallback, useEffect, useRef, useState } from 'react';

/**
 * Camera torch / flash control.
 *
 * @param {React.MutableRefObject<MediaStream|null>} streamRef
 *   A ref holding the active MediaStream from the camera hook.
 */
export function useScannerFlash(streamRef) {
  const [flashOn, setFlashOn] = useState(false);
  const [flashSupported, setFlashSupported] = useState(false);

  const streamIdentityRef = useRef(null);

  const getVideoTrack = useCallback(() => {
    const stream = streamRef?.current;
    if (!stream) return null;
    const tracks = stream.getVideoTracks();
    return tracks.length > 0 ? tracks[0] : null;
  }, [streamRef]);

  const probeFlashSupport = useCallback(() => {
    const track = getVideoTrack();
    if (!track) {
      setFlashSupported(false);
      return;
    }

    const capabilities = track.getCapabilities?.();
    setFlashSupported(Boolean(capabilities?.torch));

    const handleEnded = () => {
      setFlashOn(false);
      setFlashSupported(false);
    };
    track.addEventListener('ended', handleEnded);

    return () => {
      track.removeEventListener('ended', handleEnded);
    };
  }, [getVideoTrack]);

  useEffect(() => {
    const check = () => {
      const currentStream = streamRef?.current ?? null;
      if (currentStream !== streamIdentityRef.current) {
        streamIdentityRef.current = currentStream;
        probeFlashSupport();
      }
    };

    const initialTimer = setTimeout(check, 0);
    const interval = setInterval(check, 500);
    return () => {
      clearTimeout(initialTimer);
      clearInterval(interval);
    };
  }, [probeFlashSupport, streamRef]);

  const toggleFlash = useCallback(async () => {
    if (!flashSupported) return;
    const track = getVideoTrack();
    if (!track) return;

    const next = !flashOn;
    try {
      await track.applyConstraints({ advanced: [{ torch: next }] });
      setFlashOn(next);
    } catch (err) {
      console.warn('Torch toggle failed:', err);
    }
  }, [flashSupported, flashOn, getVideoTrack]);

  return { flashSupported, flashOn, toggleFlash };
}