"""Transactional learning-event ledger helpers.

Domain rows such as QuizAttempt, LessonProgress and RevisionItem remain the
source of truth.  This ledger only records the meaningful action and the
domain record that caused it, in the same database transaction.
"""
from __future__ import annotations

from typing import Any

from sqlalchemy import select
from sqlalchemy.orm import Session

from app.models.learning_state import LearningEvent


def add_learning_event(
    db: Session,
    *,
    user_id: str,
    event_type: str,
    entity_type: str,
    entity_id: str,
    idempotency_key: str,
    subject_id: str | None = None,
    chapter_id: str | None = None,
    topic_key: str | None = None,
    event_data: dict[str, Any] | None = None,
) -> LearningEvent:
    """Stage one idempotent event in the caller's current transaction."""

    existing = db.scalar(
        select(LearningEvent).where(
            LearningEvent.user_id == user_id,
            LearningEvent.idempotency_key == idempotency_key,
        )
    )
    if existing is not None:
        return existing

    event = LearningEvent(
        user_id=user_id,
        event_type=event_type,
        entity_type=entity_type,
        entity_id=entity_id,
        idempotency_key=idempotency_key,
        subject_id=subject_id,
        chapter_id=chapter_id,
        topic_key=topic_key,
        event_data=event_data or {},
    )
    db.add(event)
    return event