import type { Bus } from './bus';

const DAY_MS = 24 * 60 * 60 * 1000;

export interface SweepResult {
  eventsDeleted: number;
  abandonedDeletedDeliveries: number;
}

/**
 * Retention sweep:
 *
 * - Delete events older than `eventsRetentionDays` whose deliveries are
 *   ALL terminal (succeeded/abandoned). Foreign-key cascade removes
 *   their deliveries.
 * - Delete `abandoned` deliveries older than `failedRetentionDays`. Their
 *   parent event may stick around if it still has non-terminal deliveries
 *   for other subscribers; but if that was its last delivery, the event
 *   itself becomes a candidate for the next sweep cycle.
 *
 * Idempotent and cheap. Called from the dispatcher's idle loop, no
 * separate cron needed.
 */
export function retentionSweep(bus: Bus): SweepResult {
  const now = Date.now();
  const eventsCutoff = now - bus.retention.eventsRetentionDays * DAY_MS;
  const failedCutoff = now - bus.retention.failedRetentionDays * DAY_MS;

  // Drop ancient abandoned deliveries first so the events they belong
  // to can become eligible for full deletion in the same pass.
  // Use RETURNING + .all() so the count reflects rows we actually
  // touched, not cascade artifacts.
  const droppedAbandoned = bus.db
    .query<{ event_id: number }, [number]>(
      `DELETE FROM deliveries
         WHERE status = 'abandoned'
           AND finished_at IS NOT NULL
           AND finished_at < ?
       RETURNING event_id`,
    )
    .all(failedCutoff);

  // Delete events whose every delivery is terminal AND the event is old
  // enough. A subquery counts non-terminal deliveries per event; events
  // with zero are eligible. RETURNING gives us the exact count without
  // counting CASCADE child rows.
  const droppedEvents = bus.db
    .query<{ id: number }, [number]>(
      `DELETE FROM events
         WHERE emitted_at < ?
           AND id NOT IN (
             SELECT DISTINCT event_id FROM deliveries
              WHERE status NOT IN ('succeeded', 'abandoned')
           )
       RETURNING id`,
    )
    .all(eventsCutoff);

  return {
    eventsDeleted: droppedEvents.length,
    abandonedDeletedDeliveries: droppedAbandoned.length,
  };
}