from pydantic import BaseModel, Field
from typing import List, Optional
from datetime import datetime

class Message(BaseModel):
    sender: str  # "user" or "ai"
    text: Optional[str] = None
    image_url: Optional[str] = None
    voice_url: Optional[str] = None
    created_at: datetime = Field(default_factory=datetime.utcnow)

class Session(BaseModel):
    id: str = Field(default_factory=str, alias="_id")
    user_id: str
    title: str
    messages: List[Message] = []
    created_at: datetime = Field(default_factory=datetime.utcnow)
    updated_at: datetime = Field(default_factory=datetime.utcnow)