import { useEffect, useState } from "react";
import type { PlaylistItem, PlaylistResponse } from "@/lib/playback-context";

// 侧栏列表（作者作品 / 搜索结果 / hashtag）缓存在模块里：切换作品时播放页会重新挂载，
// 但客户端导航不会清掉 JS 内存，所以在列表里上下切换时可以立刻拿到列表，不用每次重新请求。
const STALE_MS = 60_000;

type CacheEntry = PlaylistResponse & { fetchedAt: number };
const cache = new Map<string, CacheEntry>();
const inflight = new Map<string, Promise<PlaylistResponse>>();

function loadPlaylist(query: string): Promise<PlaylistResponse> {
  const pending = inflight.get(query);
  if (pending) return pending;
  const promise = fetch(`/api/playlist${query}`)
    .then(async (res) => {
      if (!res.ok) throw new Error(`加载列表失败 (${res.status})`);
      const data = (await res.json()) as PlaylistResponse;
      cache.set(query, { ...data, fetchedAt: Date.now() });
      return data;
    })
    .finally(() => inflight.delete(query));
  inflight.set(query, promise);
  return promise;
}

export type PlaylistState = {
  items: PlaylistItem[] | null;
  /** 列表总数（可能多于 items：侧栏最多列出 500 个） */
  total: number;
  loading: boolean;
  error: string | null;
};

/**
 * 按播放上下文（/api/playlist 的查询串，含 ?）取作品列表。
 * query 为空或 enabled 为 false 时不请求。
 */
export function usePlaylist(query: string, enabled: boolean): PlaylistState {
  const [state, setState] = useState<PlaylistState>(() => {
    const cached = query ? cache.get(query) : undefined;
    return {
      items: cached?.items ?? null,
      total: cached?.total ?? 0,
      loading: false,
      error: null,
    };
  });

  useEffect(() => {
    if (!query || !enabled) return;
    const cached = cache.get(query);
    setState({
      items: cached?.items ?? null,
      total: cached?.total ?? 0,
      loading: !cached,
      error: null,
    });
    if (cached && Date.now() - cached.fetchedAt < STALE_MS) return;

    let cancelled = false;
    loadPlaylist(query)
      .then((data) => {
        if (!cancelled) {
          setState({
            items: data.items,
            total: data.total,
            loading: false,
            error: null,
          });
        }
      })
      .catch((err: unknown) => {
        if (cancelled) return;
        setState((prev) => ({
          ...prev,
          loading: false,
          error: err instanceof Error ? err.message : "加载失败",
        }));
      });
    return () => {
      cancelled = true;
    };
  }, [query, enabled]);

  return state;
}