Add a statistics pane to the webhook page (closes #368)

Each webhook's event database keeps running totals: one row for its
events, with when the newest arrived, and one row per target for its
deliveries, delivered and failed, each with what retention removed.
Every write to them shares the transaction of the rows it counts, and
a delivery already delivered or failed is not settled again.
Deliveries get a finished_at column; it and target_id end the status
index, so each target's deliveries finished in a window come from one
index-range query grouped by target. Retention deletes 1000 expired
events per transaction, pausing 200 ms between them so other writers
get in, and stops between them on shutdown. The pane is its own
template, its figures in tables.

The schema changes in place with nothing back-filled, so an existing
database must be recreated.

Model: opus-5-5

internal/handlers/delivery_replay.go

@@ -299,8 +299,9 @@ func countInFlightDeliveries(
 	return count, err
 }
 
-// createReplayDelivery writes the new pending delivery row and returns
-// the task that carries it to the delivery engine.
+// createReplayDelivery writes the new pending delivery row, adds it to
+// its target's totals in the same transaction, and returns the task
+// that carries it to the delivery engine.
 //
 // The row is written with associations omitted, and neither Event nor
 // Target is populated on it: GORM's SaveBeforeAssociations would
@@ -319,7 +320,16 @@ func createReplayDelivery(
 		Status:   database.DeliveryStatusPending,
 	}
 
-	err := webhookDB.Omit(clause.Associations).Create(dlv).Error
+	err := webhookDB.Transaction(func(tx *gorm.DB) error {
+		err := tx.Omit(clause.Associations).Create(dlv).Error
+		if err != nil {
+			return err
+		}
+
+		return database.AddTargetTotals(tx, database.TargetTotals{
+			TargetID: dlv.TargetID, Deliveries: 1,
+		})
+	})
 	if err != nil {
 		return delivery.Task{}, err
 	}

internal/handlers/export_test.go

@@ -4,7 +4,9 @@ import (
 	"html/template"
 	"log/slog"
 	"net/http"
+	"time"
 
+	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/database"
 )
 
@@ -69,6 +71,29 @@ func (s *Handlers) LoadEventLogViewsForTest(
 	return views
 }
 
+// WebhookStatsForTest returns the figures the statistics pane on a
+// webhook's page shows, from the webhook's entrypoints and targets
+// loaded as that page loads them.
+func (s *Handlers) WebhookStatsForTest(webhookID string) *WebhookStats {
+	var entrypoints []database.Entrypoint
+
+	s.db.DB().Where("webhook_id = ?", webhookID).Find(&entrypoints)
+
+	var targets []database.Target
+
+	s.db.DB().Where("webhook_id = ?", webhookID).Find(&targets)
+
+	return s.loadWebhookStats(webhookID, entrypoints, targets)
+}
+
+// FinishedByTargetForTest exposes finishedByTarget for use in the
+// handlers_test package.
+func FinishedByTargetForTest(
+	webhookDB *gorm.DB, since time.Time,
+) ([]TargetFinished, error) {
+	return finishedByTarget(webhookDB, since)
+}
+
 // AddTemplateForTest registers a template under a page name so that
 // the handlers_test package can drive the render path with a
 // template of its own.

internal/handlers/handlers.go

@@ -91,18 +91,22 @@ type Handlers struct {
 
 // parsePageTemplate parses a page-specific template set from the
 // embedded FS. Each page template is combined with the shared
-// base, htmlheader, and navbar templates. The page file must be
-// listed first so that its root action ({{template "base" .}})
-// becomes the template set's entry point.
-func parsePageTemplate(pageFile string) *template.Template {
+// base, htmlheader, and navbar templates, and with any further files
+// the page includes. The page file must be listed first so that its
+// root action ({{template "base" .}}) becomes the template set's entry
+// point.
+func parsePageTemplate(
+	pageFile string, included ...string,
+) *template.Template {
+	files := append([]string{
+		pageFile,
+		"base.html",
+		"htmlheader.html",
+		"navbar.html",
+	}, included...)
+
 	return template.Must(
-		template.ParseFS(
-			templates.Templates,
-			pageFile,
-			"base.html",
-			"htmlheader.html",
-			"navbar.html",
-		),
+		template.ParseFS(templates.Templates, files...),
 	)
 }
 
@@ -131,7 +135,7 @@ func New(
 		"profile.html":       parsePageTemplate("profile.html"),
 		"sources_list.html":  parsePageTemplate("sources_list.html"),
 		"sources_new.html":   parsePageTemplate("sources_new.html"),
-		"source_detail.html": parsePageTemplate("source_detail.html"),
+		"source_detail.html": parsePageTemplate("source_detail.html", "webhook_stats.html"),
 		"source_edit.html":   parsePageTemplate("source_edit.html"),
 		"source_logs.html":   parsePageTemplate("source_logs.html"),
 		"target_edit.html":   parsePageTemplate("target_edit.html"),

internal/handlers/source_management.go

@@ -457,6 +457,7 @@ func (h *Handlers) renderSourceDetail(
 		"Targets":     delivery.NewTargetViews(targets),
 		"Events":      events,
 		"BaseURL":     baseURL,
+		"Stats":       h.loadWebhookStats(webhook.ID, entrypoints, targets),
 	}
 
 	h.renderTemplate(w, r, "source_detail.html", data)

internal/handlers/webhook.go

@@ -253,11 +253,12 @@ func requestEventSource(
 	}
 }
 
-// createAndFanOut writes the event and one pending delivery per target
-// in a single transaction, then hands the tasks to the delivery
-// engine. It is the only path by which an event and its deliveries are
-// created, so a resubmitted event is retried, SSRF-guarded and
-// circuit-broken exactly as a received one is.
+// createAndFanOut writes the event and one pending delivery per target,
+// and adds them to the webhook's running totals, in a single
+// transaction, then hands the tasks to the delivery engine. It is the
+// only path by which an event and its deliveries are created, so a
+// resubmitted event is retried, SSRF-guarded and circuit-broken
+// exactly as a received one is.
 //
 // The tasks are returned as well as queued, so a caller can report how
 // many targets the event went to.
@@ -297,6 +298,15 @@ func (h *Handlers) createAndFanOut(
 		return nil, nil, err
 	}
 
+	err = database.AddEventTotals(tx, database.EventTotals{
+		Events: 1, LastEventAt: &event.CreatedAt,
+	})
+	if err != nil {
+		tx.Rollback()
+
+		return nil, nil, err
+	}
+
 	err = tx.Commit().Error
 	if err != nil {
 		return nil, nil, fmt.Errorf(
@@ -355,8 +365,9 @@ func (h *Handlers) finishWebhookResponse(
 }
 
 // buildDeliveryTasks creates one pending delivery per target in the
-// transaction and returns the tasks for the delivery engine. The
-// caller owns the transaction and rolls it back on error.
+// transaction, adds each to its target's totals, and returns the tasks
+// for the delivery engine. The caller owns the transaction and rolls
+// it back on error.
 func buildDeliveryTasks(
 	tx *gorm.DB,
 	event *database.Event,
@@ -380,6 +391,13 @@ func buildDeliveryTasks(
 			)
 		}
 
+		err = database.AddTargetTotals(tx, database.TargetTotals{
+			TargetID: targets[i].ID, Deliveries: 1,
+		})
+		if err != nil {
+			return nil, err
+		}
+
 		tasks = append(tasks, delivery.Task{
 			DeliveryID:   dlv.ID,
 			EventID:      event.ID,

internal/handlers/webhook_stats.go

@@ -0,0 +1,259 @@
+package handlers
+
+import (
+	"fmt"
+	"time"
+
+	"gorm.io/gorm"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// The spans of the two recent windows the statistics pane reports on:
+// the last 10 minutes and the last 24 hours.
+const (
+	shortWindow = 10 * time.Minute
+	longWindow  = 24 * time.Hour
+)
+
+// percent turns a fraction into a percentage.
+const percent = 100
+
+// WebhookStats holds the figures in the statistics pane at the top of
+// the webhook page.
+type WebhookStats struct {
+	Entrypoints       int
+	ActiveEntrypoints int
+	Targets           int
+	ActiveTargets     int
+
+	// Lifetime counts every event, delivery and failure the webhook
+	// has had, and WithinRetention those still stored.
+	Lifetime        Counts
+	WithinRetention Counts
+
+	// InProgress counts the deliveries still pending or retrying.
+	InProgress int64
+
+	// LastEventAt is when the newest event arrived, or nil when none
+	// has. Retention does not change it.
+	LastEventAt *time.Time
+
+	Last10Minutes RecentWindow
+	Last24Hours   RecentWindow
+}
+
+// Counts holds a number of events, of deliveries and of failed
+// deliveries.
+type Counts struct {
+	Events     int64
+	Deliveries int64
+	Failures   int64
+}
+
+// RecentWindow holds what happened in one recent window: the events
+// received in it, and the deliveries that became delivered or failed in
+// it.
+type RecentWindow struct {
+	Events    int64
+	Delivered int64
+	Failed    int64
+}
+
+// TargetFinished is how many of one target's deliveries became
+// delivered, and how many failed, in a recent window.
+type TargetFinished struct {
+	TargetID  string
+	Delivered int64
+	Failed    int64
+}
+
+// FailurePercent is the share of the deliveries finished in the window
+// that failed, or a dash when none finished. Deliveries still pending
+// or retrying are not counted either way.
+func (w RecentWindow) FailurePercent() string {
+	finished := w.Delivered + w.Failed
+	if finished == 0 {
+		return "—"
+	}
+
+	return fmt.Sprintf(
+		"%.1f%%", percent*float64(w.Failed)/float64(finished),
+	)
+}
+
+// loadWebhookStats gathers the figures for the statistics pane from the
+// webhook's entrypoints and targets, as the page has already loaded
+// them, and from its event database. It returns nil, and logs why, when
+// the event database cannot be read.
+func (h *Handlers) loadWebhookStats(
+	webhookID string,
+	entrypoints []database.Entrypoint,
+	targets []database.Target,
+) *WebhookStats {
+	stats := &WebhookStats{
+		Entrypoints: len(entrypoints),
+		Targets:     len(targets),
+	}
+
+	for i := range entrypoints {
+		if entrypoints[i].Active {
+			stats.ActiveEntrypoints++
+		}
+	}
+
+	for i := range targets {
+		if targets[i].Active {
+			stats.ActiveTargets++
+		}
+	}
+
+	// Opening an event database that does not exist would create it,
+	// and it would hold nothing to count.
+	if !h.dbMgr.DBExists(webhookID) {
+		return stats
+	}
+
+	webhookDB, err := h.dbMgr.GetDB(webhookID)
+	if err == nil {
+		err = readEventStats(webhookDB, time.Now(), stats)
+	}
+
+	if err != nil {
+		h.log.Error(
+			"failed to read webhook statistics",
+			"webhook_id", webhookID,
+			"error", err,
+		)
+
+		return nil
+	}
+
+	return stats
+}
+
+// readEventStats fills in the figures that come from the webhook's
+// event database. None of them reads every stored row: the totals are
+// one row for the events and one per target for the deliveries, and
+// every other figure is read from an index, over only the rows it
+// counts.
+func readEventStats(
+	db *gorm.DB, now time.Time, stats *WebhookStats,
+) error {
+	err := readTotals(db, stats)
+	if err != nil {
+		return err
+	}
+
+	err = db.Model(&database.Delivery{}).
+		Where("status IN ?", []database.DeliveryStatus{
+			database.DeliveryStatusPending,
+			database.DeliveryStatusRetrying,
+		}).
+		Count(&stats.InProgress).Error
+	if err != nil {
+		return fmt.Errorf("counting deliveries in progress: %w", err)
+	}
+
+	stats.Last10Minutes, err = readRecentWindow(
+		db, now.Add(-shortWindow),
+	)
+	if err != nil {
+		return err
+	}
+
+	stats.Last24Hours, err = readRecentWindow(
+		db, now.Add(-longWindow),
+	)
+
+	return err
+}
+
+// readTotals fills in the lifetime and within-retention figures, and
+// when the last event arrived, from the running totals: the events'
+// row, and the targets' rows summed.
+func readTotals(db *gorm.DB, stats *WebhookStats) error {
+	var events database.EventTotals
+
+	err := db.Take(&events).Error
+	if err != nil {
+		return fmt.Errorf("reading event totals: %w", err)
+	}
+
+	var targets []database.TargetTotals
+
+	err = db.Find(&targets).Error
+	if err != nil {
+		return fmt.Errorf("reading target totals: %w", err)
+	}
+
+	stats.Lifetime.Events = events.Events
+	stats.WithinRetention.Events = events.Events - events.EventsRemoved
+	stats.LastEventAt = events.LastEventAt
+
+	for _, t := range targets {
+		stats.Lifetime.Deliveries += t.Deliveries
+		stats.Lifetime.Failures += t.Failed
+		stats.WithinRetention.Deliveries += t.Deliveries - t.DeliveriesRemoved
+		stats.WithinRetention.Failures += t.Failed - t.FailedRemoved
+	}
+
+	return nil
+}
+
+// readRecentWindow counts the events received, and the deliveries that
+// became delivered or failed, since the given time.
+func readRecentWindow(
+	db *gorm.DB, since time.Time,
+) (RecentWindow, error) {
+	var w RecentWindow
+
+	err := db.Model(&database.Event{}).
+		Where("created_at >= ?", since).
+		Count(&w.Events).Error
+	if err != nil {
+		return w, fmt.Errorf("counting recent events: %w", err)
+	}
+
+	byTarget, err := finishedByTarget(db, since)
+	if err != nil {
+		return w, err
+	}
+
+	for _, f := range byTarget {
+		w.Delivered += f.Delivered
+		w.Failed += f.Failed
+	}
+
+	return w, nil
+}
+
+// finishedByTarget counts, for each target, the deliveries that became
+// delivered and those that failed since the given time, in one query
+// over just that window of the deliveries' status index. A target with
+// neither is left out.
+func finishedByTarget(
+	db *gorm.DB, since time.Time,
+) ([]TargetFinished, error) {
+	var byTarget []TargetFinished
+
+	err := db.Model(&database.Delivery{}).
+		Select("target_id, "+
+			"count(CASE WHEN status = ? THEN 1 END) AS delivered, "+
+			"count(CASE WHEN status = ? THEN 1 END) AS failed",
+			database.DeliveryStatusDelivered,
+			database.DeliveryStatusFailed).
+		Where("status IN ? AND finished_at >= ?",
+			[]database.DeliveryStatus{
+				database.DeliveryStatusDelivered,
+				database.DeliveryStatusFailed,
+			}, since).
+		Group("target_id").
+		Find(&byTarget).Error
+	if err != nil {
+		return nil, fmt.Errorf(
+			"counting deliveries finished by target: %w", err,
+		)
+	}
+
+	return byTarget, nil
+}

internal/handlers/webhook_stats_test.go

@@ -0,0 +1,569 @@
+package handlers_test
+
+import (
+	"net/http"
+	"regexp"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/fx/fxtest"
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/handlers"
+	"sneak.berlin/go/webhooker/internal/logger"
+	"sneak.berlin/go/webhooker/internal/session"
+)
+
+// statsEntrypoint adds an entrypoint to a webhook and returns its path.
+func statsEntrypoint(
+	t *testing.T, db *database.Database, webhookID string, active bool,
+) string {
+	t.Helper()
+
+	ep := &database.Entrypoint{
+		WebhookID: webhookID,
+		Path:      uuid.New().String(),
+	}
+
+	require.NoError(t, db.DB().Omit(clause.Associations).Create(ep).Error)
+	require.NoError(t, db.DB().Model(ep).Update("active", active).Error)
+
+	return ep.Path
+}
+
+// statsDelivery returns an event's delivery to a target.
+func statsDelivery(
+	t *testing.T, webhookDB *gorm.DB, eventID, targetID string,
+) database.Delivery {
+	t.Helper()
+
+	var d database.Delivery
+
+	require.NoError(t, webhookDB.Where(
+		"event_id = ? AND target_id = ?", eventID, targetID,
+	).First(&d).Error)
+
+	return d
+}
+
+// statsFinish settles a delivery as the delivery engine does: its
+// final status and the time it finished, and one more on its target's
+// delivered or failed total, in one transaction.
+func statsFinish(
+	t *testing.T,
+	webhookDB *gorm.DB,
+	d database.Delivery,
+	status database.DeliveryStatus,
+	at time.Time,
+) {
+	t.Helper()
+
+	add := database.TargetTotals{TargetID: d.TargetID, Delivered: 1}
+	if status == database.DeliveryStatusFailed {
+		add = database.TargetTotals{TargetID: d.TargetID, Failed: 1}
+	}
+
+	require.NoError(t, webhookDB.Transaction(func(tx *gorm.DB) error {
+		err := tx.Model(&database.Delivery{}).
+			Where("id = ?", d.ID).
+			Updates(map[string]any{"status": status, "finished_at": at}).
+			Error
+		if err != nil {
+			return err
+		}
+
+		return database.AddTargetTotals(tx, add)
+	}))
+}
+
+// statsAge moves an event's arrival back to the given time.
+func statsAge(
+	t *testing.T, webhookDB *gorm.DB, eventID string, at time.Time,
+) {
+	t.Helper()
+
+	require.NoError(t, webhookDB.Model(&database.Event{}).
+		Where("id = ?", eventID).
+		Update("created_at", at).Error)
+}
+
+// statsTargetTotals reads a webhook database's target totals, keyed by
+// target.
+func statsTargetTotals(
+	t *testing.T, webhookDB *gorm.DB,
+) map[string]database.TargetTotals {
+	t.Helper()
+
+	var rows []database.TargetTotals
+
+	require.NoError(t, webhookDB.Find(&rows).Error)
+
+	byTarget := make(map[string]database.TargetTotals, len(rows))
+	for _, row := range rows {
+		byTarget[row.TargetID] = row
+	}
+
+	return byTarget
+}
+
+// statsHistory is the webhook seedStatsHistory builds: its event
+// database, its newest event, and its two active targets.
+type statsHistory struct {
+	webhook       *database.Webhook
+	webhookDB     *gorm.DB
+	newest        database.Event
+	first, second string
+}
+
+// seedStatsHistory builds the webhook the statistics test checks: 14
+// days of retention, twelve entrypoints (one inactive) and six targets
+// (four inactive). Ten events arrive through the receiver, and so each
+// has a delivery to the two active targets. The oldest event is past
+// retention, the next 30 hours old, the next six hours old, the other
+// seven just in. Six deliveries are settled as the delivery engine
+// would, two of them inside a recent window though their event arrived
+// before it. The newest event's delivery to the second target is
+// retrying, the rest are left pending, and a replay adds a pending
+// delivery to the oldest event. Once retention has removed the oldest
+// event, every figure in the pane differs from every other.
+func seedStatsHistory(
+	t *testing.T,
+	h *handlers.Handlers,
+	sess *session.Session,
+	db *database.Database,
+	dbMgr *database.WebhookDBManager,
+) statsHistory {
+	t.Helper()
+
+	wh := &database.Webhook{UserID: deleteTestUserID, Name: "stats", RetentionDays: 14}
+	require.NoError(t, db.DB().Omit(clause.Associations).Create(wh).Error)
+
+	path := statsEntrypoint(t, db, wh.ID, true)
+	for range 10 {
+		statsEntrypoint(t, db, wh.ID, true)
+	}
+
+	statsEntrypoint(t, db, wh.ID, false)
+
+	first := seedConfiguredTarget(
+		t, db, wh.ID, database.TargetTypeHTTP,
+		`{"url":"`+replayTargetURL+`"}`,
+	)
+	second := seedTarget(t, db, wh.ID, database.TargetTypeLog)
+
+	for range 4 {
+		inactive := seedTarget(t, db, wh.ID, database.TargetTypeLog)
+		require.NoError(t, db.DB().Model(inactive).
+			Update("active", false).Error)
+	}
+
+	router := receiverRouter(h)
+
+	for range 10 {
+		require.Equal(t, http.StatusOK, postReceiver(t, router, path))
+	}
+
+	webhookDB, err := dbMgr.GetDB(wh.ID)
+	require.NoError(t, err)
+
+	events := listEvents(t, webhookDB)
+	require.Len(t, events, 10)
+
+	oldest, yesterday, middle, newest := events[0], events[1], events[2], events[9]
+	now := time.Now()
+
+	statsAge(t, webhookDB, oldest.ID, now.Add(-15*24*time.Hour))
+	statsAge(t, webhookDB, yesterday.ID, now.Add(-30*time.Hour))
+	statsAge(t, webhookDB, middle.ID, now.Add(-6*time.Hour))
+
+	oldestFailure := statsDelivery(t, webhookDB, oldest.ID, first.ID)
+	statsFinish(t, webhookDB, oldestFailure,
+		database.DeliveryStatusFailed, now.Add(-14*24*time.Hour))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, yesterday.ID, first.ID),
+		database.DeliveryStatusFailed, now.Add(-29*time.Hour))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, yesterday.ID, second.ID),
+		database.DeliveryStatusFailed, now.Add(-23*time.Hour))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, middle.ID, second.ID),
+		database.DeliveryStatusFailed, now.Add(-5*time.Hour))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, middle.ID, first.ID),
+		database.DeliveryStatusFailed, now.Add(-time.Minute))
+	statsFinish(t, webhookDB,
+		statsDelivery(t, webhookDB, newest.ID, first.ID),
+		database.DeliveryStatusDelivered, now.Add(-2*time.Minute))
+
+	retrying := statsDelivery(t, webhookDB, newest.ID, second.ID)
+	require.NoError(t, webhookDB.Model(&retrying).
+		Update("status", database.DeliveryStatusRetrying).Error)
+
+	require.Equal(t, http.StatusSeeOther,
+		postReplay(t, h, sess, wh.ID, oldestFailure.ID).Code)
+
+	return statsHistory{
+		webhook: wh, webhookDB: webhookDB, newest: newest,
+		first: first.ID, second: second.ID,
+	}
+}
+
+// statsPrune runs the real retention reaper until it has removed one
+// event from the webhook's database, then stops it.
+func statsPrune(
+	t *testing.T,
+	db *database.Database,
+	dbMgr *database.WebhookDBManager,
+	log *logger.Logger,
+	webhookDB *gorm.DB,
+) {
+	t.Helper()
+
+	lc := fxtest.NewLifecycle(t)
+	database.NewRetentionReaper(lc, database.RetentionReaperParams{
+		Config: &config.Config{
+			RetentionSweepInterval: 10 * time.Millisecond,
+		},
+		Database:  db,
+		DBManager: dbMgr,
+		Logger:    log,
+	})
+
+	lc.RequireStart()
+
+	require.Eventually(t, func() bool {
+		var totals database.EventTotals
+
+		err := webhookDB.Take(&totals).Error
+
+		return err == nil && totals.EventsRemoved == 1
+	}, 10*time.Second, 10*time.Millisecond)
+
+	lc.RequireStop()
+}
+
+// statsPane returns the text of the statistics pane in a rendered
+// webhook page, everything from its heading to the next heading on the
+// page, with the markup taken out and each run of space made one
+// space. A table then reads header by header and row by row, each
+// row's label followed by its figures in column order.
+func statsPane(t *testing.T, page string) string {
+	t.Helper()
+
+	_, pane, found := strings.Cut(page, ">Statistics</h2>")
+	require.True(t, found, "the page has no statistics pane")
+
+	pane, _, _ = strings.Cut(pane, "<h2")
+	pane = regexp.MustCompile(`<[^>]*>`).ReplaceAllString(pane, " ")
+
+	return strings.Join(strings.Fields(pane), " ")
+}
+
+// assertStatsTargets checks, for the history seedStatsHistory builds,
+// each target's totals and its deliveries finished in the last 24
+// hours. The first target has ten deliveries and the replay, the
+// second ten; the inactive targets have none and so no row.
+func assertStatsTargets(t *testing.T, hist statsHistory) {
+	t.Helper()
+
+	first, second := hist.first, hist.second
+
+	assert.Equal(t, map[string]database.TargetTotals{
+		first:  {TargetID: first, Deliveries: 11, Delivered: 1, Failed: 3},
+		second: {TargetID: second, Deliveries: 10, Failed: 2},
+	}, statsTargetTotals(t, hist.webhookDB))
+
+	lastDay, err := handlers.FinishedByTargetForTest(
+		hist.webhookDB, time.Now().Add(-24*time.Hour),
+	)
+	require.NoError(t, err)
+	assert.ElementsMatch(t, []handlers.TargetFinished{
+		{TargetID: first, Delivered: 1, Failed: 1},
+		{TargetID: second, Failed: 2},
+	}, lastDay)
+}
+
+// assertStatsPaneAfterPrune checks the rendered statistics pane for the
+// history seedStatsHistory builds, once retention has removed the
+// oldest event: each figure after its label, in its column.
+func assertStatsPaneAfterPrune(
+	t *testing.T,
+	h *handlers.Handlers,
+	sess *session.Session,
+	hist statsHistory,
+) {
+	t.Helper()
+
+	pane := statsPane(t, renderSourceDetailPage(t, h, sess, hist.webhook.ID))
+	lastEvent := hist.newest.CreatedAt.UTC().Format("2006-01-02 15:04:05 UTC")
+
+	assert.Contains(t, pane, "Entrypoints 12 (11 active) "+
+		"Targets 6 (2 active) "+
+		"Deliveries in progress 13 "+
+		"Last event "+lastEvent+" "+
+		"Retention 14 days")
+	assert.Contains(t, pane, "Lifetime Within retention "+
+		"Events 10 9 "+
+		"Deliveries 21 18 "+
+		"Failures 5 4")
+	assert.Contains(t, pane, "Last 10 minutes Last 24 hours "+
+		"Events 7 8 "+
+		"Failures 1 3 "+
+		"Failure percentage 50.0% 75.0%")
+}
+
+// TestWebhookStats_EveryFigureAcrossRetentionPrune checks every figure
+// the statistics pane shows for the history seedStatsHistory builds,
+// and each target's totals and recent figures, before and after the
+// real retention reaper removes the oldest event.
+func TestWebhookStats_EveryFigureAcrossRetentionPrune(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+		log   *logger.Logger
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr, &log)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	hist := seedStatsHistory(t, h, sess, db, dbMgr)
+	first, second := hist.first, hist.second
+
+	stats := h.WebhookStatsForTest(hist.webhook.ID)
+	require.NotNil(t, stats)
+
+	assert.Equal(t, 12, stats.Entrypoints)
+	assert.Equal(t, 11, stats.ActiveEntrypoints)
+	assert.Equal(t, 6, stats.Targets)
+	assert.Equal(t, 2, stats.ActiveTargets)
+	assert.Equal(t, handlers.Counts{Events: 10, Deliveries: 21, Failures: 5},
+		stats.Lifetime)
+	assert.Equal(t, stats.Lifetime, stats.WithinRetention)
+	assert.Equal(t, int64(15), stats.InProgress)
+	require.NotNil(t, stats.LastEventAt)
+	assert.True(t, hist.newest.CreatedAt.Equal(*stats.LastEventAt))
+	assert.Equal(t, handlers.RecentWindow{
+		Events: 7, Delivered: 1, Failed: 1,
+	}, stats.Last10Minutes)
+	assert.Equal(t, handlers.RecentWindow{
+		Events: 8, Delivered: 1, Failed: 3,
+	}, stats.Last24Hours)
+	assert.Equal(t, "50.0%", stats.Last10Minutes.FailurePercent())
+	assert.Equal(t, "75.0%", stats.Last24Hours.FailurePercent())
+
+	assertStatsTargets(t, hist)
+
+	// Retention removes the oldest event with its three deliveries:
+	// the first target's failed one and the pending replay, and the
+	// second target's pending one.
+	statsPrune(t, db, dbMgr, log, hist.webhookDB)
+
+	after := h.WebhookStatsForTest(hist.webhook.ID)
+	require.NotNil(t, after)
+
+	assert.Equal(t, stats.Lifetime, after.Lifetime)
+	assert.Equal(t, handlers.Counts{Events: 9, Deliveries: 18, Failures: 4},
+		after.WithinRetention)
+	assert.Equal(t, int64(13), after.InProgress)
+	assert.Equal(t, stats.LastEventAt, after.LastEventAt)
+	assert.Equal(t, stats.Last10Minutes, after.Last10Minutes)
+	assert.Equal(t, stats.Last24Hours, after.Last24Hours)
+
+	assert.Equal(t, map[string]database.TargetTotals{
+		first: {
+			TargetID: first, Deliveries: 11, Delivered: 1, Failed: 3,
+			DeliveriesRemoved: 2, FailedRemoved: 1,
+		},
+		second: {
+			TargetID: second, Deliveries: 10, Failed: 2,
+			DeliveriesRemoved: 1,
+		},
+	}, statsTargetTotals(t, hist.webhookDB))
+
+	assertStatsPaneAfterPrune(t, h, sess, hist)
+}
+
+// TestWebhookStats_LastEventSurvivesPruningEveryEvent checks that once
+// retention has removed every event, the pane still shows when the last
+// one arrived rather than "none".
+func TestWebhookStats_LastEventSurvivesPruningEveryEvent(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+		log   *logger.Logger
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr, &log)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := &database.Webhook{
+		UserID: deleteTestUserID, Name: "pruned", RetentionDays: 1,
+	}
+	require.NoError(t, db.DB().Omit(clause.Associations).Create(wh).Error)
+
+	path := statsEntrypoint(t, db, wh.ID, true)
+	require.Equal(t, http.StatusOK,
+		postReceiver(t, receiverRouter(h), path))
+
+	webhookDB, err := dbMgr.GetDB(wh.ID)
+	require.NoError(t, err)
+
+	events := listEvents(t, webhookDB)
+	require.Len(t, events, 1)
+
+	arrived := events[0].CreatedAt
+
+	statsAge(t, webhookDB, events[0].ID, time.Now().Add(-50*time.Hour))
+	statsPrune(t, db, dbMgr, log, webhookDB)
+	require.Empty(t, listEvents(t, webhookDB))
+
+	stats := h.WebhookStatsForTest(wh.ID)
+	require.NotNil(t, stats)
+	require.NotNil(t, stats.LastEventAt)
+	assert.True(t, arrived.Equal(*stats.LastEventAt))
+
+	pane := statsPane(t, renderSourceDetailPage(t, h, sess, wh.ID))
+	assert.Contains(t, pane,
+		"Last event "+arrived.UTC().Format("2006-01-02 15:04:05 UTC"))
+}
+
+// TestWebhookStats_LastEventInUTC checks that the pane shows when the
+// last event arrived in UTC, as the event list does, when the time was
+// stored in another zone, as it is on a host whose local time is not
+// UTC.
+func TestWebhookStats_LastEventInUTC(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+
+	webhookDB, err := dbMgr.GetDB(wh.ID)
+	require.NoError(t, err)
+
+	arrived := time.Date(2026, time.March, 4, 22, 30, 0, 0,
+		time.FixedZone("EST", -5*60*60))
+	require.NoError(t, database.AddEventTotals(webhookDB,
+		database.EventTotals{Events: 1, LastEventAt: &arrived}))
+
+	pane := statsPane(t, renderSourceDetailPage(t, h, sess, wh.ID))
+	assert.Contains(t, pane, "Last event 2026-03-05 03:30:00 UTC")
+}
+
+// TestWebhookStats_PaneShowsRetentionPeriod checks that the statistics
+// pane itself, not only the line at the foot of the page, shows the
+// webhook's retention period, for a finite one and for forever.
+func TestWebhookStats_PaneShowsRetentionPeriod(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h    *handlers.Handlers
+		sess *session.Session
+		db   *database.Database
+	)
+
+	app := newTestApp(t, &h, &sess, &db)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	tests := []struct {
+		retentionDays int
+		want          string
+	}{
+		{30, "30 days"},
+		{database.RetentionForeverDays, "forever"},
+	}
+
+	for _, tt := range tests {
+		wh := &database.Webhook{
+			UserID:        deleteTestUserID,
+			Name:          "retention",
+			RetentionDays: tt.retentionDays,
+		}
+		require.NoError(t,
+			db.DB().Omit(clause.Associations).Create(wh).Error)
+
+		pane := statsPane(t, renderSourceDetailPage(t, h, sess, wh.ID))
+		assert.Contains(t, pane, "Retention "+tt.want)
+	}
+}
+
+// TestWebhookStats_WebhookWithNoEvents covers a webhook whose event
+// database has never been opened: every count is zero, the
+// percentages are a dash, and showing the page does not create the
+// database.
+func TestWebhookStats_WebhookWithNoEvents(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+
+	assert.Equal(t, &handlers.WebhookStats{}, h.WebhookStatsForTest(wh.ID))
+	assert.Equal(t, "—", handlers.RecentWindow{}.FailurePercent())
+
+	pane := statsPane(t, renderSourceDetailPage(t, h, sess, wh.ID))
+	assert.Contains(t, pane, "Last event none")
+	assert.Contains(t, pane, "Failure percentage — —")
+	assert.False(t, dbMgr.DBExists(wh.ID))
+}
+
+// TestRecentWindow_FailurePercent pins the percentage: failed
+// deliveries out of all that finished in the window.
+func TestRecentWindow_FailurePercent(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		window handlers.RecentWindow
+		want   string
+	}{
+		{handlers.RecentWindow{}, "—"},
+		{handlers.RecentWindow{Events: 4}, "—"},
+		{handlers.RecentWindow{Delivered: 3, Failed: 1}, "25.0%"},
+		{handlers.RecentWindow{Failed: 2}, "100.0%"},
+		{handlers.RecentWindow{Delivered: 2}, "0.0%"},
+	}
+
+	for _, tt := range tests {
+		assert.Equal(t, tt.want, tt.window.FailurePercent(), tt.window)
+	}
+}