# File: backend/app/services/session_service.py (新建)
# Description: 管理会话数据的服务 (内存实现)

from typing import Dict, List, Optional
from app.models.pydantic_models import SessionRead, SessionCreateRequest, SessionCreateResponse, AssistantRead
from app.services.assistant_service import assistant_service_instance # 需要获取助手信息
from datetime import datetime, timezone
import uuid
# 导入 ChatService 以调用 LLM 生成标题 (避免循环导入，考虑重构)
# from app.services.chat_service import chat_service_instance

# 内存数据库存储会话
# key: session_id (str), value: SessionRead object
sessions_db: Dict[str, SessionRead] = {}

class SessionService:
    """会话数据的 CRUD 及标题生成服务"""

    async def create_session(self, session_data: SessionCreateRequest) -> SessionCreateResponse:
        """创建新会话并生成标题"""
        assistant = assistant_service_instance.get_assistant(session_data.assistant_id)
        if not assistant:
            raise ValueError("指定的助手不存在")

        new_id = f"session-{uuid.uuid4()}"
        created_time = datetime.now(timezone.utc)

        # --- TODO: 调用 LLM 生成标题 ---
        # title_prompt = f"根据以下用户第一条消息，为此对话生成一个简洁的标题（不超过10个字）:\n\n{session_data.first_message}"
        # generated_title = await chat_service_instance.generate_text(title_prompt) # 需要一个简单的文本生成方法

        # 模拟标题生成
        generated_title = f"关于 \"{session_data.first_message[:15]}...\""
        print(f"为新会话 {new_id} 生成标题: {generated_title}")
        # --- 模拟结束 ---

        new_session = SessionRead(
            id=new_id,
            title=generated_title,
            assistant_id=session_data.assistant_id,
            created_at=created_time.isoformat() # 存储 ISO 格式字符串
        )
        sessions_db[new_id] = new_session
        print(f"会话已创建: {new_id}")

        return SessionCreateResponse(
            id=new_session.id,
            title=new_session.title,
            assistant_id=new_session.assistant_id,
            created_at=new_session.created_at
        )

    def get_sessions_by_assistant(self, assistant_id: str) -> List[SessionRead]:
        """获取指定助手的所有会话"""
        return [s for s in sessions_db.values() if s.assistant_id == assistant_id]

    def get_session(self, session_id: str) -> Optional[SessionRead]:
        """获取单个会话"""
        return sessions_db.get(session_id)

    def delete_session(self, session_id: str) -> bool:
        """删除会话"""
        if session_id in sessions_db:
            del sessions_db[session_id]
            print(f"会话已删除: {session_id}")
            # TODO: 删除关联的消息
            return True
        return False

    def delete_sessions_by_assistant(self, assistant_id: str) -> int:
        """删除指定助手的所有会话"""
        ids_to_delete = [s.id for s in sessions_db.values() if s.assistant_id == assistant_id]
        count = 0
        for session_id in ids_to_delete:
            if self.delete_session(session_id):
                count += 1
        print(f"删除了助手 {assistant_id} 的 {count} 个会话")
        return count


# 创建服务实例
session_service_instance = SessionService()