from datetime import datetime

from sqlalchemy import BigInteger, DateTime, ForeignKey, Index, Integer, String, Text
from sqlalchemy.orm import Mapped, mapped_column, relationship

from app.models.base import Base, utcnow
from app.models.user import User


class AuditLog(Base):
    """Immutable audit record. The application exposes no update or delete
    path for these rows; one row per changed field (field_name null for
    record-level events such as create/transition/attachment/reopen)."""

    __tablename__ = "audit_log"
    __table_args__ = (
        Index("ix_audit_log_ncr", "ncr_id", "created_at"),
        Index("ix_audit_log_created_at", "created_at"),
    )

    # BigInteger on MySQL; plain INTEGER on SQLite (required for autoincrement).
    id: Mapped[int] = mapped_column(
        BigInteger().with_variant(Integer, "sqlite"), primary_key=True, autoincrement=True
    )
    # Nullable so admin actions without an NCR (settings, role changes) are auditable too.
    ncr_id: Mapped[int | None] = mapped_column(
        ForeignKey("ncrs.id", ondelete="SET NULL"), nullable=True
    )
    user_id: Mapped[int] = mapped_column(ForeignKey("users.id"))
    created_at: Mapped[datetime] = mapped_column(DateTime, default=utcnow)
    action: Mapped[str] = mapped_column(String(40))
    field_name: Mapped[str | None] = mapped_column(String(100), nullable=True)
    old_value: Mapped[str | None] = mapped_column(Text, nullable=True)
    new_value: Mapped[str | None] = mapped_column(Text, nullable=True)
    detail: Mapped[str | None] = mapped_column(String(500), nullable=True)

    user: Mapped[User] = relationship(lazy="selectin")