Suppress superseded alerts in the /alerts/active endpoint

internal/app/service.go

@@ -10,6 +10,8 @@ import (
 	"gitea.maximumdirect.net/ejr/weatherfeeder/model"
 )
 
+const nwsAlertURLPrefix = "https://api.weather.gov/alerts/"
+
 // Repository defines outbound data access used by weatherapi use cases.
 type Repository interface {
 	LatestObservation(ctx context.Context) (*model.WeatherObservation, error)
@@ -77,9 +79,10 @@ func (s *Service) LatestActiveAlertRun(ctx context.Context, activeAt time.Time)
 	}
 
 	out := cloneAlertRun(run)
+	supersededIDs := collectSupersededAlertIDs(out.Alerts)
 	alerts := out.Alerts[:0]
 	for _, alert := range out.Alerts {
-		if isActiveAlert(alert, activeAt) {
+		if isActiveAlert(alert, activeAt) && !isSupersededAlert(alert, supersededIDs) {
 			alerts = append(alerts, alert)
 		}
 	}
@@ -181,6 +184,41 @@ func isActiveAlert(alert model.WeatherAlert, activeAt time.Time) bool {
 	return true
 }
 
+func collectSupersededAlertIDs(alerts []model.WeatherAlert) map[string]struct{} {
+	supersededIDs := make(map[string]struct{})
+	for _, alert := range alerts {
+		for _, ref := range alert.References {
+			id := normalizeAlertID(referenceAlertID(ref))
+			if id != "" {
+				supersededIDs[id] = struct{}{}
+			}
+		}
+	}
+	return supersededIDs
+}
+
+func isSupersededAlert(alert model.WeatherAlert, supersededIDs map[string]struct{}) bool {
+	id := normalizeAlertID(alert.ID)
+	if id == "" {
+		return false
+	}
+	_, ok := supersededIDs[id]
+	return ok
+}
+
+func referenceAlertID(ref model.AlertReference) string {
+	if strings.TrimSpace(ref.Identifier) != "" {
+		return ref.Identifier
+	}
+	return ref.ID
+}
+
+func normalizeAlertID(value string) string {
+	value = strings.TrimSpace(value)
+	value = strings.TrimPrefix(value, nwsAlertURLPrefix)
+	return value
+}
+
 func cloneOutlookRun(run *model.WeatherOutlookRun) *model.WeatherOutlookRun {
 	out := *run
 	out.Latitude = copyFloat64(run.Latitude)