Show the last event as a relative time with a UTC tooltip (closes #567)

The "Last event" figure in the webhook page's Statistics block now shows how long ago the newest event arrived, as its two largest units of d, h, m and s with no spaces ("59s", "1m1s", "3d4h"; a zero second unit is left off). It is worked out when the page is served, and a time ahead of the server clock shows "0s". Its tooltip is the full time in UTC. With no event it still shows "none", without a tooltip. A unit test pins each unit boundary, and the headless-browser test checks the figure and its tooltip.

Model: opus-5-5

internal/server/alpine_browser_test.go

@@ -61,7 +61,8 @@ const (
 // event log in a headless browser, served by the real router and so
 // under the real Content-Security-Policy, and checks that the pages'
 // Alpine.js directives, the copy control and the delete prompts work,
-// and that a target's row shows its delivery counts.
+// that a target's row shows its delivery counts, and that the
+// Statistics block shows how long ago the last event arrived.
 func TestAlpineRunsUnderTheSecurityPolicy(t *testing.T) {
 	t.Parallel()
 
@@ -97,6 +98,7 @@ func TestAlpineRunsUnderTheSecurityPolicy(t *testing.T) {
 	checkCopy(ctx, t, page)
 	checkEntrypointEdit(ctx, t, page, page+"/events")
 	checkRecentEvents(ctx, t, page)
+	checkStatsLastEvent(ctx, t, env, webhook.ID, page)
 	checkArchiveChoice(ctx, t, srv.URL+"/hooks/new", page)
 	checkNewWebhookTargets(ctx, t, env, srv.URL+"/hooks/new")
 	checkRefusedNewWebhook(ctx, t, srv.URL+"/hooks/new")
@@ -831,6 +833,41 @@ func checkRecentEvents(ctx context.Context, t *testing.T, url string) {
 		"the event's own page does not show its body")
 }
 
+// checkStatsLastEvent records that the last event of the webhook
+// webhookID arrived 3 days, 4 hours and 30 minutes ago, loads its page,
+// and checks that the Statistics block shows the last event as "3d4h"
+// with the full time in UTC as its tooltip.
+func checkStatsLastEvent(
+	ctx context.Context, t *testing.T, env *testEnv, webhookID, url string,
+) {
+	t.Helper()
+
+	webhookDB, err := env.dbMgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	ago := 3*24*time.Hour + 4*time.Hour + 30*time.Minute
+	arrived := time.Now().Add(-ago)
+	require.NoError(t, database.AddEventTotals(webhookDB,
+		database.EventTotals{LastEventAt: &arrived}))
+
+	figure := `//span[text()="Last event"]` +
+		`/following-sibling::span[text()="3d4h"]`
+
+	var (
+		title string
+		found bool
+	)
+
+	require.NoError(t, chromedp.Run(ctx, loadPage(url)))
+	require.True(t, shown(ctx, figure),
+		`the Statistics block does not show the last event as "3d4h"`)
+	require.NoError(t, chromedp.Run(ctx, chromedp.AttributeValue(
+		figure, "title", &title, &found, chromedp.BySearch,
+	)))
+	assert.Equal(t, arrived.UTC().Format(time.DateTime)+" UTC", title,
+		"the last event's tooltip is not the full time in UTC")
+}
+
 // checkEventLog loads the event log and checks that of its events only
 // the newest, eventID, starts expanded: its row says so and its caret is
 // turned up, and the log's last event, lastEventID, starts collapsed. In