"""
对话分支模型 — 支持从任意历史点分叉对话

参考 Claude Code src/commands/branch/branch.ts
"""
from __future__ import annotations

import uuid
from datetime import datetime
from sqlalchemy import Column, String, Text, Integer, DateTime, JSON, Boolean
from sqlalchemy.dialects.mysql import CHAR
from app.core.database import Base


class ConversationBranch(Base):
    """对话分支 — 保存某个时间点的完整对话快照"""

    __tablename__ = "conversation_branches"

    id = Column(CHAR(36), primary_key=True, default=lambda: str(uuid.uuid4()), comment="分支ID")
    user_id = Column(String(36), nullable=False, index=True, comment="用户ID")
    agent_id = Column(String(36), nullable=True, comment="关联Agent ID")
    agent_name = Column(String(200), nullable=True, comment="Agent 名称（冗余便于展示）")

    # 溯源链
    parent_session_id = Column(String(100), nullable=False, comment="分叉来源会话ID")
    branch_session_id = Column(String(100), nullable=False, unique=True, comment="新分支会话ID")

    # 元信息
    title = Column(String(500), nullable=False, comment="分支标题（取自首条用户消息）")
    message_count = Column(Integer, default=0, comment="快照包含的消息数")
    first_user_message = Column(Text, nullable=True, comment="首条用户消息（用于列表展示）")

    # 完整消息快照 (JSON)
    messages = Column(JSON, nullable=True, comment="分支创建时的完整消息列表")

    # 状态
    is_active = Column(Boolean, default=True, comment="是否活跃")

    created_at = Column(DateTime, default=datetime.now, comment="创建时间")

    def __repr__(self):
        return f"<ConversationBranch(id={self.id}, title={self.title}, messages={self.message_count})>"