'use client';

import { useCallback, useEffect, useRef, useState } from 'react';
import type { PlazaPost } from '@/types/plaza';
import { PostGrid } from '@/components/feed/PostGrid';

async function loadFeedPage(url: string) {
  const response = await fetch(url);
  const payload = await response.json();
  if (!response.ok) throw new Error(payload?.error?.message ?? '加载失败');
  return payload.data as {
    posts: PlazaPost[];
    next_cursor: string | null;
    has_more: boolean;
  };
}

export function FeedLoadMore({
  initialPosts,
  initialCursor,
  initialHasMore,
  sort,
  categorySlug,
}: {
  initialPosts: PlazaPost[];
  initialCursor: string | null;
  initialHasMore: boolean;
  sort: 'hot' | 'new';
  categorySlug?: string;
}) {
  const [posts, setPosts] = useState(initialPosts);
  const [cursor, setCursor] = useState(initialCursor);
  const [hasMore, setHasMore] = useState(initialHasMore);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);
  const sentinelRef = useRef<HTMLDivElement | null>(null);
  const loadingRef = useRef(false);

  const loadMore = useCallback(async () => {
    if (!hasMore || loadingRef.current || !cursor) return;
    loadingRef.current = true;
    setLoading(true);
    setError(null);
    try {
      const query = new URLSearchParams({ sort, limit: '20', cursor });
      if (categorySlug) query.set('category', categorySlug);
      const data = await loadFeedPage(`/api/plaza/v1/feed?${query.toString()}`);
      setPosts((prev) => [...prev, ...data.posts]);
      setCursor(data.next_cursor);
      setHasMore(data.has_more);
    } catch (err) {
      setError(err instanceof Error ? err.message : '加载失败');
    } finally {
      loadingRef.current = false;
      setLoading(false);
    }
  }, [categorySlug, cursor, hasMore, sort]);

  useEffect(() => {
    if (!hasMore || !cursor) return;
    const node = sentinelRef.current;
    if (!node) return;
    const observer = new IntersectionObserver(
      (entries) => {
        if (entries.some((entry) => entry.isIntersecting)) {
          void loadMore();
        }
      },
      { rootMargin: '240px' },
    );
    observer.observe(node);
    return () => observer.disconnect();
  }, [cursor, hasMore, loadMore]);

  return (
    <div className="space-y-6">
      <PostGrid posts={posts} />
      {error ? <p className="text-center text-sm text-red-700">{error}</p> : null}
      {hasMore ? (
        <div ref={sentinelRef} className="flex justify-center pb-8">
          <button
            type="button"
            onClick={() => void loadMore()}
            disabled={loading || !cursor}
            className="rounded-full border border-[#2f6f57] px-6 py-2.5 text-sm font-semibold text-[#2f6f57] transition hover:bg-[#2f6f57] hover:text-white disabled:opacity-60"
          >
            {loading ? '加载中…' : '加载更多'}
          </button>
        </div>
      ) : null}
    </div>
  );
}