import React from 'react';
import { fetchGallery } from '../services/photosApi';

export type GalleryDelta = {
  photos: Record<string, unknown>[];
  latestPhotoAt: string | null;
  nextCursor: string | null;
};

const emptyDelta: GalleryDelta = {
  photos: [],
  latestPhotoAt: null,
  nextCursor: null,
};

export function usePollGalleryDelta(
  eventToken: string | null,
  options: { intervalMs?: number; locale?: string } = {}
) {
  const intervalMs = options.intervalMs ?? 30000;
  const [data, setData] = React.useState<GalleryDelta>(emptyDelta);
  const [loading, setLoading] = React.useState(Boolean(eventToken));
  const [error, setError] = React.useState<string | null>(null);
  const latestRef = React.useRef<string | null>(null);

  React.useEffect(() => {
    if (!eventToken) {
      setData(emptyDelta);
      setLoading(false);
      setError(null);
      latestRef.current = null;
      return;
    }

    let active = true;
    let timer: number | null = null;

    const poll = async () => {
      if (document.visibilityState === 'hidden') {
        timer = window.setTimeout(poll, intervalMs);
        return;
      }

      try {
        setLoading(true);
        const response = await fetchGallery(eventToken, {
          since: latestRef.current ?? undefined,
          locale: options.locale,
        });
        if (!active) return;
        const photos = Array.isArray(response.data) ? response.data : [];
        const latestPhotoAt = response.latest_photo_at ?? latestRef.current ?? null;
        latestRef.current = latestPhotoAt;
        setData({
          photos,
          latestPhotoAt,
          nextCursor: response.next_cursor ?? null,
        });
        setError(null);
      } catch (err) {
        if (!active) return;
        setError(err instanceof Error ? err.message : 'Failed to load gallery updates');
      } finally {
        if (active) {
          setLoading(false);
          timer = window.setTimeout(poll, intervalMs);
        }
      }
    };

    poll();

    return () => {
      active = false;
      if (timer) {
        window.clearTimeout(timer);
      }
    };
  }, [eventToken, intervalMs, options.locale]);

  return { data, loading, error } as const;
}