"""Audit trail helpers. Audit rows are append-only: the application exposes
no endpoint that updates or deletes them."""
from typing import Any

from sqlalchemy.ext.asyncio import AsyncSession

from app.models import AuditLog, Ncr


def _fmt(value: Any) -> str | None:
    if value is None:
        return None
    if isinstance(value, bool):
        return "true" if value else "false"
    return str(value)


def audit_event(
    db: AsyncSession,
    *,
    user_id: int,
    action: str,
    ncr_id: int | None = None,
    field_name: str | None = None,
    old_value: Any = None,
    new_value: Any = None,
    detail: str | None = None,
) -> None:
    db.add(
        AuditLog(
            ncr_id=ncr_id,
            user_id=user_id,
            action=action,
            field_name=field_name,
            old_value=_fmt(old_value),
            new_value=_fmt(new_value),
            detail=detail,
        )
    )


def apply_field_updates(
    db: AsyncSession,
    ncr: Ncr,
    user_id: int,
    updates: dict[str, Any],
    action: str = "update",
) -> dict[str, tuple[Any, Any]]:
    """Set attributes on the NCR, writing one audit row per actually-changed
    field. Returns {field: (old, new)} for the fields that changed."""
    changes: dict[str, tuple[Any, Any]] = {}
    for field, new_value in updates.items():
        old_value = getattr(ncr, field)
        if old_value == new_value:
            continue
        setattr(ncr, field, new_value)
        changes[field] = (old_value, new_value)
        audit_event(
            db,
            ncr_id=ncr.id,
            user_id=user_id,
            action=action,
            field_name=field,
            old_value=old_value,
            new_value=new_value,
        )
    return changes