Alerting: Add totalsFiltered to RuleResponse for hidden by filters count (#66883)

Alerting: Add totalsFiltered to RuleResponse to facilitate hidden by filters count

Currently, when both a limit_alerts and a matcher/state filter is applied, there is not enough information to determine how many alert instances were hidden by the filters. Only enough to determine the total hidden by the limit and filter combined.

This change adds a separate totalsFiltered field alongside the AlertRule totals that will contain the count of instances after filters but before limits.

pkg/services/ngalert/api/api_prometheus.go

@@ -329,13 +329,15 @@ func (srv PrometheusSrv) toRuleGroup(groupKey ngmodels.AlertRuleGroupKey, folder
 
 		states := srv.manager.GetStatesForRuleUID(rule.OrgID, rule.UID)
 		totals := make(map[string]int64)
+		totalsFiltered := make(map[string]int64)
 		for _, alertState := range states {
 			activeAt := alertState.StartsAt
 			valString := ""
 			if alertState.State == eval.Alerting || alertState.State == eval.Pending {
 				valString = formatValues(alertState)
 			}
-			totals[strings.ToLower(alertState.State.String())] += 1
+			stateKey := strings.ToLower(alertState.State.String())
+			totals[stateKey] += 1
 			// Do not add error twice when execution error state is Error
 			if alertState.Error != nil && rule.ExecErrState != ngmodels.ErrorErrState {
 				totals["error"] += 1
@@ -389,6 +391,12 @@ func (srv PrometheusSrv) toRuleGroup(groupKey ngmodels.AlertRuleGroupKey, folder
 				continue
 			}
 
+			totalsFiltered[stateKey] += 1
+			// Do not add error twice when execution error state is Error
+			if alertState.Error != nil && rule.ExecErrState != ngmodels.ErrorErrState {
+				totalsFiltered["error"] += 1
+			}
+
 			alertingRule.Alerts = append(alertingRule.Alerts, alert)
 		}
 
@@ -408,6 +416,7 @@ func (srv PrometheusSrv) toRuleGroup(groupKey ngmodels.AlertRuleGroupKey, folder
 
 		alertingRule.Rule = newRule
 		alertingRule.Totals = totals
+		alertingRule.TotalsFiltered = totalsFiltered
 		newGroup.Rules = append(newGroup.Rules, alertingRule)
 		newGroup.Interval = float64(rule.IntervalSeconds)
 		// TODO yuri. Change that when scheduler will process alerts in groups