register-referentie/services/event-subscriber/EventSubscriber.Application/NotificationProjector.cs

namespace EventSubscriber.Application;

/// <summary>
/// Projects inbound NRC notifications into the read projection. Tolerates duplicate and
/// out-of-order deliveries (CLAUDE.md §8.6): the notification log dedups, and the projection
/// upsert is idempotent on the zaak id. Rebuilds the projection by replaying the log.
/// </summary>
public sealed class NotificationProjector(INotificationLog log, IProjectionStore store)
{
    /// <summary>Handle one inbound notification. Reacts to a zaak being created (INGEDIEND) and a
    /// status being set (INGESCHREVEN); ignores everything else.</summary>
    public async Task HandleAsync(Notification notification, CancellationToken ct = default)
    {
        if (!notification.IsZaakCreated && !notification.IsZaakStatusSet)
            return;

        var recorded = new RecordedNotification(
            notification.IdempotencyKey, notification.Actie, notification.ZaakId, notification.Resource);

        // Atomic record-or-skip: a duplicate (or concurrent) delivery is recognised and dropped
        // before it touches the projection, so the projection stays a faithful derived artefact.
        if (!await log.TryRecordAsync(recorded, ct))
            return;

        await store.UpsertAsync(ToEntry(recorded), ct);
    }

    /// <summary>Rebuild the projection from the durable notification log (PRD §8.4).</summary>
    public async Task RebuildAsync(CancellationToken ct = default)
    {
        await store.ClearAsync(ct);
        foreach (var recorded in await log.AllAsync(ct))
            await store.UpsertAsync(ToEntry(recorded), ct);
    }

    /// <summary>The projection row for an accepted notification: a status-set maps to INGESCHREVEN,
    /// a zaak-create to INGEDIEND. bsn/naam are deferred (ADR-0008).</summary>
    private static RegisterEntry ToEntry(RecordedNotification recorded)
        => new(recorded.ZaakId, recorded.Resource == "status"
            ? RegistrationStatus.Ingeschreven
            : RegistrationStatus.Ingediend);
}