from datetime import datetime

from sqlalchemy import CheckConstraint, DateTime, Integer, Text, func
from sqlalchemy.orm import Mapped, mapped_column

from grimoire.models import Base


class InstanceIdentity(Base):
    """The one row naming this database's id lineage.

    Two stores with the same instance id number their rows the same way: one
    is the other, or a restore of it made with the original ids kept. That is
    what lets a backup roll a live instance back by id, and what refuses a
    backup whose ids would land on unrelated rows. Made by the migration, so
    an instance has it before anyone registers.
    """

    __tablename__ = "instance_identity"
    __table_args__ = (CheckConstraint("id = 1", name="ck_instance_identity_single_row"),)

    id: Mapped[int] = mapped_column(Integer, primary_key=True, default=1)
    instance_id: Mapped[str] = mapped_column(Text, nullable=False)
    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), nullable=False, server_default=func.now()
    )