# File: backend/app/db/models.py (New - Database models)
# Description: SQLAlchemy ORM 模型定义

from sqlalchemy import Column, String, Float, ForeignKey, Text, DateTime, Integer
from sqlalchemy.orm import relationship
from sqlalchemy.sql import func # For default timestamps
from app.db.database import Base
import uuid
from datetime import datetime, timezone

def generate_uuid():
    return str(uuid.uuid4())

class AssistantModel(Base):
    __tablename__ = "assistants"

    id = Column(String, primary_key=True, default=generate_uuid)
    name = Column(String(50), nullable=False, index=True)
    description = Column(String(200), nullable=True)
    avatar = Column(String(5), nullable=True)
    system_prompt = Column(Text, nullable=False)
    model = Column(String, nullable=False)
    temperature = Column(Float, nullable=False, default=0.7)
    created_at = Column(DateTime(timezone=True), server_default=func.now())
    updated_at = Column(DateTime(timezone=True), onupdate=func.now())

    sessions = relationship("SessionModel", back_populates="assistant", cascade="all, delete-orphan")

class SessionModel(Base):
    __tablename__ = "sessions"

    id = Column(String, primary_key=True, default=generate_uuid)
    title = Column(String(100), nullable=False, default="New Chat")
    assistant_id = Column(String, ForeignKey("assistants.id"), nullable=False, index=True)
    created_at = Column(DateTime(timezone=True), server_default=func.now())
    updated_at = Column(DateTime(timezone=True), onupdate=func.now(), index=True) # Index for sorting

    assistant = relationship("AssistantModel", back_populates="sessions")
    messages = relationship("MessageModel", back_populates="session", cascade="all, delete-orphan", order_by="MessageModel.created_at") # Order messages by time

class MessageModel(Base):
    __tablename__ = "messages"

    id = Column(String, primary_key=True, default=generate_uuid)
    session_id = Column(String, ForeignKey("sessions.id"), nullable=False, index=True)
    sender = Column(String(10), nullable=False) # 'user' or 'ai' or 'system'
    text = Column(Text, nullable=False)
    order = Column(Integer, nullable=False) # Explicit order within session
    created_at = Column(DateTime(timezone=True), server_default=func.now())

    session = relationship("SessionModel", back_populates="messages")