// ============================================================
// useSessionList — 会话历史列表管理
// 职责：会话 CRUD、消息持久化、切换会话
// ============================================================

import { useCallback, useEffect, useRef, useState } from "react";
import { v4 as uuidv4 } from "uuid";
import {
  loadSessionSummaries,
  saveSessionSummaries,
  loadSessionMessages,
  saveSessionMessages,
  deleteSessionMessages,
} from "../lib/storage";
import type { ChatMessage, SessionSummary } from "../types";

/** 截取预览文本 */
function getPreview(text: string, maxLen = 50): string {
  const clean = text.replace(/[\n\r]/g, " ").trim();
  return clean.length > maxLen ? clean.slice(0, maxLen) + "…" : clean;
}

export function useSessionList() {
  const [sessions, setSessions] = useState<SessionSummary[]>(() => loadSessionSummaries());
  const [activeSessionId, setActiveSessionId] = useState<string | null>(null);
  const sessionsRef = useRef(sessions);
  useEffect(() => { sessionsRef.current = sessions; }, [sessions]);

  /** 创建新会话 */
  const createSession = useCallback((): string => {
    const id = uuidv4();
    const now = Date.now();
    const summary: SessionSummary = {
      id,
      title: "新对话",
      createdAt: now,
      lastActiveAt: now,
      messageCount: 0,
      preview: "",
    };
    setSessions((prev) => [summary, ...prev]);
    setActiveSessionId(id);
    // 持久化
    const all = [summary, ...sessionsRef.current];
    saveSessionSummaries(all);
    return id;
  }, []);

  /** 删除会话 */
  const deleteSession = useCallback((id: string) => {
    setSessions((prev) => prev.filter((s) => s.id !== id));
    deleteSessionMessages(id);
    const remaining = sessionsRef.current.filter((s) => s.id !== id);
    saveSessionSummaries(remaining);
    // 如果删除的是当前会话，清空 active
    setActiveSessionId((prev) => (prev === id ? null : prev));
  }, []);

  /** 重命名会话 */
  const renameSession = useCallback((id: string, title: string) => {
    setSessions((prev) => prev.map((s) => (s.id === id ? { ...s, title } : s)));
    const updated = sessionsRef.current.map((s) => (s.id === id ? { ...s, title } : s));
    saveSessionSummaries(updated);
  }, []);

  /** 保存当前会话的消息历史 */
  const saveCurrentSession = useCallback((messages: ChatMessage[]) => {
    const id = sessionsRef.current.length > 0 ? sessionsRef.current[0].id : null;
    // 找到 activeSessionId 对应的会话
    // 这里不依赖 activeSessionId state，而是通过参数传入
    return messages;
  }, []);

  /** 保存指定会话的消息并更新摘要 */
  const persistSession = useCallback((sessionId: string, messages: ChatMessage[]) => {
    if (!sessionId) return;
    saveSessionMessages(sessionId, messages);
    // 更新摘要
    const firstUserMsg = messages.find((m) => m.role === "user");
    const title = firstUserMsg ? getPreview(firstUserMsg.content, 20) : "新对话";
    const lastMsg = messages[messages.length - 1];
    const summary: Partial<SessionSummary> = {
      title,
      messageCount: messages.length,
      lastActiveAt: lastMsg?.timestamp || Date.now(),
      preview: lastMsg ? getPreview(lastMsg.content) : "",
    };
    setSessions((prev) => {
      const updated = prev.map((s) => (s.id === sessionId ? { ...s, ...summary } : s));
      saveSessionSummaries(updated);
      return updated;
    });
  }, []);

  /** 加载指定会话的消息历史 */
  const loadMessages = useCallback((sessionId: string): ChatMessage[] => {
    return loadSessionMessages(sessionId);
  }, []);

  /** 选择会话（返回需要加载的消息） */
  const selectSession = useCallback((id: string): ChatMessage[] => {
    setActiveSessionId(id);
    return loadSessionMessages(id);
  }, []);

  return {
    sessions,
    activeSessionId,
    setActiveSessionId,
    createSession,
    deleteSession,
    renameSession,
    persistSession,
    loadMessages,
    selectSession,
  };
}