memby/server/internal/api/server_alerts.go

package api

import (
	"context"
	"fmt"
	"time"

	"github.com/ponzischeme89/memby/server/internal/library"
)

// News about the service itself, as opposed to news about what is in it.
//
// Both producers here answer the same question a viewer would otherwise have to guess
// at: why the library changed under them, and why playback stopped working. They are
// the alerts most worth showing *during* a film, which is why they are worded to be read
// in one glance and never ask for an action.
const (
	// A refresh is only interesting while it is recent — long enough that a set switched
	// on shortly afterwards still learns why there is something new on the home screen,
	// short enough that it is never yesterday's news.
	librarySyncAlertWindow = 30 * time.Minute

	// Reachability is a live fact, so its window is short: a TV waking up half an hour
	// after Emby went down should find out by asking, not by being told about the past.
	reachabilityAlertWindow = 10 * time.Minute

	// embyFailureThreshold is how many probes in a row must fail before it is announced.
	// One timeout is a hiccup — a restart, a slow scan — and telling a room full of
	// people about it is worse than saying nothing.
	embyFailureThreshold = 3
)

// AnnounceLibrarySync tells every TV that the catalogue moved.
//
// Only a run that actually changed something is announced: the import is scheduled, so
// most passes find nothing, and an hourly "nothing happened" banner would train viewers
// to ignore the one that matters. Removals alone are deliberately silent — a title
// disappearing is not something to celebrate mid-film.
func (s *Server) AnnounceLibrarySync(ctx context.Context, result library.Result) {
	if result.Changed <= 0 {
		return
	}
	now := time.Now().UTC()
	s.publishAlert(ctx, clientAlert{
		// Keyed on the minute the sync finished: two runs are two pieces of news, but a
		// retried publish of the same run is not.
		ID:      fmt.Sprintf("library:%d", now.Truncate(time.Minute).Unix()),
		Kind:    alertKindLibrarySync,
		Label:   "LIBRARY UPDATED",
		Title:   librarySyncTitle(result.Changed),
		Message: "Memby has finished refreshing — it is on the home screen now.",
		AiredAt: now.Format(time.RFC3339),
	}, librarySyncAlertWindow)
}

func librarySyncTitle(changed int) string {
	if changed == 1 {
		return "1 title added or updated"
	}
	return fmt.Sprintf("%d titles added or updated", changed)
}

// WatchEmbyReachability announces Emby going away and coming back.
//
// This is the one alert that matters more during playback than on the home screen: video
// direct-plays from Emby, so when Emby stops answering a film stops with no explanation
// the viewer can act on. The gateway keeps serving /v1/status either way, which is what
// makes it able to say so.
//
// Only *transitions* are announced. A server that is down stays down, and repeating it
// every minute would bury everything else.
func (s *Server) WatchEmbyReachability(ctx context.Context, interval time.Duration) {
	if interval <= 0 {
		return
	}
	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	// Start out assuming reachable: a gateway booting while Emby is down should not
	// open with a banner about a state nobody has seen change.
	reachable := true
	failures := 0
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			probeCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
			err := s.emby.Ping(probeCtx)
			cancel()

			if err != nil {
				failures++
				if reachable && failures >= embyFailureThreshold {
					reachable = false
					s.log.Warn("emby unreachable, announcing", "error", err)
					s.publishAlert(ctx, s.reachabilityAlert(false), reachabilityAlertWindow)
				}
				continue
			}
			if !reachable {
				s.log.Info("emby reachable again, announcing")
				s.publishAlert(ctx, s.reachabilityAlert(true), reachabilityAlertWindow)
			}
			reachable = true
			failures = 0
		}
	}
}

// reachabilityAlert is timestamped per transition, so the "back online" banner never
// collides with the "not responding" one it replaces.
func (s *Server) reachabilityAlert(up bool) clientAlert {
	now := time.Now().UTC()
	if up {
		return clientAlert{
			ID:      fmt.Sprintf("emby:up:%d", now.Unix()),
			Kind:    alertKindServerUp,
			Label:   "SERVER BACK ONLINE",
			Title:   "Emby is responding again",
			Message: "Playback and browsing are working normally.",
			AiredAt: now.Format(time.RFC3339),
		}
	}
	return clientAlert{
		ID:    fmt.Sprintf("emby:down:%d", now.Unix()),
		Kind:  alertKindServerDown,
		Label: "SERVER NOT RESPONDING",
		Title: "Emby has stopped communicating",
		// Says what the viewer will see rather than what failed: a diagnosis they cannot
		// act on from the sofa is worse than none.
		Message: "Playback may stop until it is back. Memby will say when it returns.",
		AiredAt: now.Format(time.RFC3339),
	}
}