Event log: show only the events with a failed or a pending delivery (closes #390)

The event log had no way to list only the events whose delivery failed, and once it showed only the 50 newest, an older failure could not be found at all. It now has All, Failed (N) and Pending (N) links, carried in a `show` query parameter, so they work without the page's script library. Each filtered list keeps the 50-row limit and newest-first order, and lists an event once. It finds matching deliveries through `idx_deliveries_status` and looks their events up by ID, so its cost follows the matches, not the webhook's size. Replay returns to the list it was pressed in. The heading line says what a filter counts.

Model: opus-5-5

internal/handlers/source_management.go

@@ -1110,6 +1110,15 @@ func (h *Handlers) ownedWebhook(
 	return webhook, true
 }
 
+// The event log's show query parameter and its two values: the events
+// with a failed delivery, and those with a delivery still pending or
+// retrying.
+const (
+	showParam   = "show"
+	showFailed  = "failed"
+	showPending = "pending"
+)
+
 // HandleSourceLogs shows the request/response logs for a
 // webhook.
 func (h *Handlers) HandleSourceLogs() http.HandlerFunc {
@@ -1129,17 +1138,36 @@ func (h *Handlers) HandleSourceLogs() http.HandlerFunc {
 			return
 		}
 
+		// Any other value of show lists every event, as no value
+		// does.
+		show := r.URL.Query().Get(showParam)
+
+		statuses := eventLogStatuses(show)
+		if statuses == nil {
+			show = ""
+		}
+
 		evts, total, ok := h.loadEventsWithDeliveries(
-			w, r, webhook, targets,
+			w, r, webhook, targets, statuses,
 		)
 		if !ok {
 			return
 		}
 
+		failed, pending, err := h.countFailedAndPendingEvents(webhook.ID)
+		if err != nil {
+			h.serverError(w, r, "failed to count events", err)
+
+			return
+		}
+
 		data := map[string]any{
-			tmplKeyWebhook: &webhook,
-			"Events":       evts,
-			"TotalEvents":  total,
+			tmplKeyWebhook:  &webhook,
+			"Events":        evts,
+			"TotalEvents":   total,
+			"Show":          show,
+			"FailedEvents":  failed,
+			"PendingEvents": pending,
 		}
 
 		h.renderTemplate(w, r, "source_logs.html", data)
@@ -1201,9 +1229,10 @@ func (h *Handlers) loadTargetMap(
 
 // loadEventsWithDeliveries loads the recentEventLimit newest events
 // and their deliveries from the per-webhook database, and the total
-// number of events stored. Events come back as capped projections
-// rather than database.Event rows: see eventLogColumns for why the
-// cut happens in SQL.
+// number of events stored. Given delivery statuses, both cover only
+// the events with a delivery in one of them. Events come back as
+// capped projections rather than database.Event rows: see
+// eventLogColumns for why the cut happens in SQL.
 //
 // The bool reports whether the load succeeded. It is false
 // once this has answered the request with an error, and the
@@ -1213,6 +1242,7 @@ func (h *Handlers) loadEventsWithDeliveries(
 	r *http.Request,
 	webhook database.Webhook,
 	targetMap map[string]eventLogTarget,
+	statuses []database.DeliveryStatus,
 ) ([]EventLogView, int64, bool) {
 	if !h.dbMgr.DBExists(webhook.ID) {
 		return nil, 0, true
@@ -1227,7 +1257,14 @@ func (h *Handlers) loadEventsWithDeliveries(
 		return nil, 0, false
 	}
 
-	rows, totalEvents := loadEventLogRows(webhookDB, webhook.ID)
+	rows, totalEvents, err := loadEventLogRows(
+		webhookDB, webhook.ID, statuses,
+	)
+	if err != nil {
+		h.serverError(w, r, "failed to load events", err)
+
+		return nil, 0, false
+	}
 
 	result, ok := h.eventLogViews(
 		w, r, webhookDB, webhook.ID, rows, targetMap,
@@ -1321,25 +1358,142 @@ func (h *Handlers) eventLogViews(
 
 // loadEventLogRows reads the event log projection of the
 // recentEventLimit newest events, newest first, and the total number
-// of events stored.
+// of events stored, both narrowed by statuses as eventsWithStatus
+// narrows them.
 func loadEventLogRows(
-	webhookDB *gorm.DB, webhookID string,
-) ([]eventLogRow, int64) {
-	var totalEvents int64
-
-	webhookDB.Model(&database.Event{}).Where(
-		"webhook_id = ?", webhookID,
-	).Count(&totalEvents)
+	webhookDB *gorm.DB,
+	webhookID string,
+	statuses []database.DeliveryStatus,
+) ([]eventLogRow, int64, error) {
+	totalEvents, err := countEventsWithStatus(
+		webhookDB, webhookID, statuses,
+	)
+	if err != nil {
+		return nil, 0, err
+	}
 
 	var rows []eventLogRow
 
-	webhookDB.Model(&database.Event{}).Select(
+	err = eventsWithStatus(webhookDB, webhookID, statuses).Select(
 		eventLogColumns, maxRenderedBodyBytes, maxRenderedBodyBytes,
-	).Where(
-		"webhook_id = ?", webhookID,
-	).Order("created_at DESC").Limit(recentEventLimit).Find(&rows)
+	).Order("created_at DESC").Limit(recentEventLimit).Find(&rows).Error
 
-	return rows, totalEvents
+	return rows, totalEvents, err
+}
+
+// eventLogStatuses returns the delivery statuses the event log's show
+// value lists events by, or nil for one that lists every event.
+func eventLogStatuses(show string) []database.DeliveryStatus {
+	switch show {
+	case showFailed:
+		return []database.DeliveryStatus{database.DeliveryStatusFailed}
+	case showPending:
+		return []database.DeliveryStatus{
+			database.DeliveryStatusPending,
+			database.DeliveryStatusRetrying,
+		}
+	default:
+		return nil
+	}
+}
+
+// eventsWithStatus selects the webhook's events, or, given statuses,
+// the recentEventLimit newest of those with at least one delivery in
+// one of them.
+//
+// Given statuses, its cost follows the matching deliveries. SQLite
+// never reorders a CROSS JOIN, so it reads each join's left side
+// first: the distinct event IDs of the matching deliveries, through
+// idx_deliveries_status; then each of those events by ID, sorted to
+// keep the newest; then the rows of only the events kept, so no other
+// event's body is read. With a plain "id IN (matching deliveries)"
+// condition instead, SQLite, which keeps no statistics on these
+// tables, walks every event newest first.
+func eventsWithStatus(
+	webhookDB *gorm.DB,
+	webhookID string,
+	statuses []database.DeliveryStatus,
+) *gorm.DB {
+	if statuses == nil {
+		return webhookDB.Model(&database.Event{}).Where(
+			"webhook_id = ?", webhookID,
+		)
+	}
+
+	matching := webhookDB.Model(&database.Delivery{}).
+		Distinct("event_id").Where("status IN ?", statuses)
+
+	newest := webhookDB.Table("(?) AS matching", matching).
+		Joins("CROSS JOIN events ON events.id = matching.event_id").
+		Where(
+			"events.webhook_id = ? AND events.deleted_at IS NULL",
+			webhookID,
+		).
+		Order("events.created_at DESC").Limit(recentEventLimit).
+		Select("events.id AS event_id")
+
+	return webhookDB.Table("(?) AS newest", newest).
+		Joins("CROSS JOIN events ON events.id = newest.event_id")
+}
+
+// countEventsWithStatus counts the webhook's events with at least one
+// delivery in one of the statuses, or every event when statuses is
+// nil. Given statuses, it counts the distinct events of the matching
+// deliveries and reads nothing but those deliveries, through
+// idx_deliveries_status, where counting the events would read every
+// event row. That is the same number, because retention deletes an
+// event's deliveries with it.
+func countEventsWithStatus(
+	webhookDB *gorm.DB,
+	webhookID string,
+	statuses []database.DeliveryStatus,
+) (int64, error) {
+	var count int64
+
+	if statuses == nil {
+		err := webhookDB.Model(&database.Event{}).Where(
+			"webhook_id = ?", webhookID,
+		).Count(&count).Error
+
+		return count, err
+	}
+
+	err := webhookDB.Model(&database.Delivery{}).Distinct("event_id").
+		Where("status IN ?", statuses).Count(&count).Error
+
+	return count, err
+}
+
+// countFailedAndPendingEvents returns how many of the webhook's events
+// the event log lists when it shows only those with a failed delivery,
+// and when it shows only those with a delivery pending or retrying.
+func (h *Handlers) countFailedAndPendingEvents(
+	webhookID string,
+) (int64, int64, error) {
+	if !h.dbMgr.DBExists(webhookID) {
+		return 0, 0, nil
+	}
+
+	webhookDB, err := h.dbMgr.GetDB(webhookID)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	failed, err := countEventsWithStatus(
+		webhookDB, webhookID, eventLogStatuses(showFailed),
+	)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	pending, err := countEventsWithStatus(
+		webhookDB, webhookID, eventLogStatuses(showPending),
+	)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	return failed, pending, nil
 }
 
 // resubmitCounts reports, for each of the page's events, how many