import { memo, useCallback, useEffect, useRef, useState } from "react";
import type { Comment, User } from "../types.ts";
import { CommentList } from "./CommentList";

interface CommentPanelProps {
  /** 侧栏打开且停在「评论」标签页 */
  open: boolean;
  author: User;
  createdAt: string | Date;
  awemeId: string;
}

interface CommentsApiResponse {
  comments?: Comment[];
  total?: number;
  hasMore?: boolean;
  mode?: string;
  seed?: string | number;
  snapshot?: string | number;
}

// 侧栏「评论」标签页的内容（外壳与标签切换在 SidePanel 里）
export const CommentPanel = memo(function CommentPanel({
  open,
  author,
  createdAt,
  awemeId,
}: CommentPanelProps) {
  const [comments, setComments] = useState<Comment[]>([]);
  const [loading, setLoading] = useState(false);
  const [hasMore, setHasMore] = useState(true);
  const [hasOpened, setHasOpened] = useState(open);

  const scrollRef = useRef<HTMLDivElement>(null);
  const sentinelRef = useRef<HTMLDivElement>(null);
  const loadingRef = useRef(false);
  const abortControllerRef = useRef<AbortController | null>(null);
  const commentsCountRef = useRef(0);
  const hasMoreRef = useRef(true);
  const rankParamsRef = useRef<{ seed: string; snapshot: string } | null>(null);

  useEffect(() => {
    if (open) setHasOpened(true);
  }, [open]);

  const loadComments = useCallback(
    async (reset = false): Promise<void> => {
      if (loadingRef.current && !reset) return;
      if (!reset && !hasMoreRef.current) return;

      abortControllerRef.current?.abort();
      const controller = new AbortController();
      abortControllerRef.current = controller;

      loadingRef.current = true;
      setLoading(true);

      try {
        const skip = reset ? 0 : commentsCountRef.current;
        const query = new URLSearchParams({
          skip: String(skip),
          take: String(20),
          mode: "ranked",
        });
        const currentRank = reset ? null : rankParamsRef.current;
        if (currentRank) {
          query.set("seed", currentRank.seed);
          query.set("snapshot", currentRank.snapshot);
        }

        const response = await fetch(
          `/api/comments/${awemeId}?${query.toString()}`,
          { signal: controller.signal },
        );
        const data = (await response.json()) as CommentsApiResponse;
        if (controller.signal.aborted) return;

        const incoming = Array.isArray(data.comments) ? data.comments : [];

        setComments((prev) => {
          const source = reset ? incoming : [...prev, ...incoming];
          const seen = new Set<string>();
          const deduped = source.filter((c) => {
            if (seen.has(c.cid)) return false;
            seen.add(c.cid);
            return true;
          });
          commentsCountRef.current = deduped.length;
          return deduped;
        });

        const nextHasMore = Boolean(data.hasMore);
        hasMoreRef.current = nextHasMore;
        setHasMore(nextHasMore);

        if (data.mode === "ranked" && data.seed && data.snapshot) {
          if (reset || !rankParamsRef.current) {
            rankParamsRef.current = {
              seed: String(data.seed),
              snapshot: String(data.snapshot),
            };
          }
        } else if (reset) {
          rankParamsRef.current = null;
        }
      } catch (error) {
        if (error instanceof DOMException && error.name === "AbortError") {
          return;
        }
        console.error("加载评论失败:", error);
      } finally {
        if (abortControllerRef.current === controller) {
          setLoading(false);
          loadingRef.current = false;
        }
      }
    },
    [awemeId],
  );

  // 切换作品时清理旧评论状态与未完成请求
  useEffect(() => {
    abortControllerRef.current?.abort();
    loadingRef.current = false;
    commentsCountRef.current = 0;
    hasMoreRef.current = true;
    rankParamsRef.current = null;
    setComments([]);
    setHasMore(true);
    setLoading(false);

    if (open) {
      void loadComments(true);
    }

    return () => {
      abortControllerRef.current?.abort();
    };
  }, [awemeId, open, loadComments]);

  // Intersection Observer 监听底部触发分页加载（单容器）
  useEffect(() => {
    if (!open) return;
    const rootEl = scrollRef.current;
    const targetEl = sentinelRef.current;
    if (!rootEl || !targetEl) return;

    const io = new IntersectionObserver(
      (entries) => {
        const entry = entries[0];
        if (
          entry?.isIntersecting &&
          !loadingRef.current &&
          hasMoreRef.current
        ) {
          void loadComments(false);
        }
      },
      {
        root: rootEl,
        rootMargin: "0px 0px 200px 0px",
        threshold: 0,
      },
    );

    io.observe(targetEl);
    return () => io.disconnect();
  }, [open, hasMore, loadComments]);

  return (
    <div ref={scrollRef} className="p-3 overflow-auto comment-scroll flex-1">
      {(open || hasOpened) && (
        <>
          <CommentList
            author={author}
            createdAt={createdAt}
            comments={comments}
          />

          {hasMore && <div ref={sentinelRef} className="h-1 w-full" />}

          {loading && (
            <div className="py-4 text-center text-white/60 text-sm">
              加载中...
            </div>
          )}
          {!hasMore && comments.length > 0 && (
            <div className="py-4 text-center text-white/40 text-sm">
              没有更多评论了
            </div>
          )}
        </>
      )}
    </div>
  );
});