from sqlmodel import SQLModel, Field, Relationship
from typing import Optional, List
from datetime import datetime


class Message(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    chat_id: int = Field(foreign_key="chat.id")
    role: str = Field(index=True)  # "user" | "assistant"
    content: str
    created_at: datetime = Field(default_factory=datetime.utcnow)

    chat: Optional["Chat"] = Relationship(back_populates="messages")


class Chat(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    title: str = Field(default="New Chat")
    created_at: datetime = Field(default_factory=datetime.utcnow)

    messages: List[Message] = Relationship(back_populates="chat")