import { useCallback, useState } from 'react';
import type { Particle } from '@/api/types';

export type StreamViewMode = 'player' | 'list';

function decideMode(
  streamParticle: Particle & { type: 'stream' },
  userId: string | undefined,
): StreamViewMode {
  const marker = userId ? streamParticle.playback_markers?.[userId] : undefined;
  const lastChildAt = streamParticle.last_child_created_at;
  const caughtUp =
    !!marker && !!lastChildAt && lastChildAt.getTime() <= marker.getTime();
  return caughtUp ? 'list' : 'player';
}

/**
 * Which mode a stream opens in: the player (autoplay catch-up) when there's
 * unseen content, the browsable list when the user is fully caught up.
 * Decided once on entry from the playback marker vs. the stream's last
 * activity — browsing afterwards advances the marker, but the mode only
 * changes via the user's toggle.
 */
export function useStreamViewMode(
  streamParticle: Particle & { type: 'stream' },
  userId: string | undefined,
): { mode: StreamViewMode; toggle: () => void } {
  const [mode, setMode] = useState<StreamViewMode>(() =>
    decideMode(streamParticle, userId),
  );

  // Re-decide when navigating between streams without an unmount.
  const [prevStreamId, setPrevStreamId] = useState(streamParticle.id);
  if (prevStreamId !== streamParticle.id) {
    setPrevStreamId(streamParticle.id);
    setMode(decideMode(streamParticle, userId));
  }

  const toggle = useCallback(() => {
    setMode((prev) => (prev === 'player' ? 'list' : 'player'));
  }, []);

  return { mode, toggle };
}