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


class ChatMessage(BaseModel):
    """MongoDB ChatMessage model.

    Field alignment with the LLM layer (ai_service/db/database.py):
    - ``role``    (was ``sender``)  — user | assistant | scan_event
    - ``content`` (was ``message``) — message body
    - ``plant_id``                  — links message to a plant thread
    - ``scan_id``                   — optional link to a scan_history document
    """
    id: Optional[str] = Field(default=None, alias="_id")
    plant_id: str  # Reference to plant (AI layer is per-plant)
    user_id: Optional[str] = None  # Reference to user (None for scan_event)
    role: str  # user | assistant | scan_event
    content: str  # message body
    scan_id: Optional[Any] = None  # reference to scan_history document
    created_at: datetime = Field(default_factory=datetime.utcnow)

    class Config:
        populate_by_name = True