// Author: fruit.com.cn
import { useCallback, useEffect, useRef, useState } from 'react';
import { useSearchParams } from 'react-router-dom';
import { useLocale, useUi } from '../../app/providers/AppProviders';
import { CommentsSheet } from '../../shared/components/CommentsSheet';
import { ShortsSkeleton } from '../../shared/components/skeletons';
import { useFollowedChannels } from '../../shared/hooks/useFollowedChannels';
import { useToast } from '../../shared/hooks/useToast';
import { normalizePage } from '../../shared/lib/pagination';
import { dramaApi } from '../../entities/drama/api';
import { normalizeDrama, uniqueDramas } from '../../entities/drama/model';
import { ShortSlide } from './components/ShortSlide';

const PAGE_SIZE = 6;
const PRELOAD_THRESHOLD = 2;

export function ShortsFeedPage() {
  const { locale } = useLocale();
  const { sidebarOpen } = useUi();
  const [params] = useSearchParams();
  const startId = params.get('start');
  const [items, setItems] = useState([]);
  const [activeId, setActiveId] = useState('');
  const [status, setStatus] = useState({ loading: true, error: '', hasMore: true });
  const { channels: followedChannels, toggle: toggleFollow } = useFollowedChannels();
  const [commentsVideo, setCommentsVideo] = useState(null);
  const toast = useToast();
  const feedRef = useRef(null);
  const cursorRef = useRef(null);
  const loadingRef = useRef(false);
  const requestIdRef = useRef(0);

  const loadPage = useCallback(async (reset) => {
    if (loadingRef.current && !reset) return;
    const requestId = requestIdRef.current + 1;
    requestIdRef.current = requestId;
    loadingRef.current = true;
    setStatus((prev) => ({ ...prev, loading: true, error: '' }));
    try {
      const payload = await dramaApi.feed({ cursor: reset ? null : cursorRef.current, size: PAGE_SIZE });
      if (requestId !== requestIdRef.current) return;
      const list = uniqueDramas(normalizePage(payload).list.map((item) => normalizeDrama(item, locale.code)));
      cursorRef.current = payload?.nextCursor ?? null;
      setItems((prev) => (reset ? list : uniqueDramas([...prev, ...list])));
      setStatus({ loading: false, error: '', hasMore: Boolean(payload?.hasMore) });
    } catch (error) {
      if (requestId !== requestIdRef.current) return;
      setStatus((prev) => ({ ...prev, loading: false, error: error.message || 'Request failed' }));
    } finally {
      if (requestId === requestIdRef.current) loadingRef.current = false;
    }
  }, [locale.code]);

  useEffect(() => {
    cursorRef.current = null;
    setItems([]);
    setActiveId('');
    setStatus({ loading: true, error: '', hasMore: true });
    loadPage(true);
  }, [loadPage]);

  useEffect(() => {
    if (!items.length) return;
    if (items.some((item) => item.id === activeId)) return;
    const startIndex = startId ? items.findIndex((item) => item.id === startId) : -1;
    const nextIndex = startIndex >= 0 ? startIndex : 0;
    const node = feedRef.current;
    if (node && nextIndex > 0) node.scrollTop = nextIndex * node.clientHeight;
    setActiveId(items[nextIndex].id);
  }, [activeId, items, startId]);

  useEffect(() => {
    const node = feedRef.current;
    if (!node) return undefined;
    const observer = new IntersectionObserver((entries) => {
      entries.forEach((entry) => {
        if (entry.isIntersecting) setActiveId(entry.target.dataset.id);
      });
    }, { root: node, threshold: 0.7 });
    node.querySelectorAll('[data-id]').forEach((slide) => observer.observe(slide));
    return () => observer.disconnect();
  }, [items.length]);

  useEffect(() => {
    if (!status.hasMore || status.loading || !activeId) return;
    const index = items.findIndex((item) => item.id === activeId);
    if (index >= items.length - PRELOAD_THRESHOLD) loadPage(false);
  }, [activeId, items, loadPage, status.hasMore, status.loading]);

  const activeIndex = Math.max(0, items.findIndex((item) => item.id === activeId));
  const move = (delta) => {
    const node = feedRef.current;
    if (!node) return;
    const next = Math.min(items.length - 1, Math.max(0, activeIndex + delta));
    if (next !== activeIndex) node.scrollTo({ top: next * node.clientHeight, behavior: 'smooth' });
  };

  const shareVideo = async (video) => {
    const url = `${window.location.origin}/watch/${video.id}`;
    if (navigator.share) {
      try {
        await navigator.share({ title: video.title, url });
        return;
      } catch (error) {
        if (error?.name === 'AbortError') return;
      }
    }
    try {
      await navigator.clipboard.writeText(url);
      toast.show(locale.linkCopied);
    } catch {
      toast.show(url);
    }
  };

  useEffect(() => {
    const onKeyDown = (event) => {
      if (event.key === 'ArrowDown' || event.key === 'PageDown') { event.preventDefault(); move(1); }
      if (event.key === 'ArrowUp' || event.key === 'PageUp') { event.preventDefault(); move(-1); }
    };
    window.addEventListener('keydown', onKeyDown);
    return () => window.removeEventListener('keydown', onKeyDown);
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [activeIndex, items.length]);

  return (
    <>
      <section className={`shorts-stage ${sidebarOpen ? '' : 'shorts-stage-wide'}`}>
        {status.loading && !items.length && <ShortsSkeleton label={locale.loading} />}
        {status.error && <div className="shorts-state warning">{status.error}</div>}
        {!status.loading && !status.error && !items.length && <div className="shorts-state">{locale.empty}</div>}
        <div className="shorts-scroll" ref={feedRef} aria-label={locale.shortTitle}>
          {items.map((video) => (
            <ShortSlide
              key={video.id}
              video={video}
              active={video.id === activeId}
              followed={followedChannels.includes(video.channel)}
              onToggleFollow={() => toggleFollow(video.channel)}
              onOpenComments={() => setCommentsVideo(video)}
              onShare={() => shareVideo(video)}
            />
          ))}
        </div>
        {items.length > 1 && (
          <div className="feed-arrows">
            <button onClick={() => move(-1)} disabled={!activeIndex} aria-label="Previous video" type="button">↑</button>
            <button onClick={() => move(1)} disabled={activeIndex >= items.length - 1} aria-label="Next video" type="button">↓</button>
          </div>
        )}
      </section>
      {commentsVideo && <CommentsSheet video={commentsVideo} locale={locale} onClose={() => setCommentsVideo(null)} />}
      {toast.message && <div className="shorts-toast">{toast.message}</div>}
    </>
  );
}