Alerting: rule backtesting API (#57318)

* Implement backtesting engine that can process regular rule specification (with queries to datasource) as well as special kind of rules that have data frame instead of query.
* declare a new API endpoint and model
* add feature toggle `alertingBacktesting`

pkg/services/ngalert/api/api_testing.go

@@ -1,10 +1,12 @@
 package api
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
 	"strconv"
+	"time"
 
 	"github.com/grafana/grafana-plugin-sdk-go/data"
 
@@ -13,9 +15,12 @@ import (
 	"github.com/grafana/grafana/pkg/models"
 	"github.com/grafana/grafana/pkg/services/accesscontrol"
 	"github.com/grafana/grafana/pkg/services/datasources"
+	"github.com/grafana/grafana/pkg/services/featuremgmt"
 	apimodels "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
+	"github.com/grafana/grafana/pkg/services/ngalert/backtesting"
 	"github.com/grafana/grafana/pkg/services/ngalert/eval"
 	ngmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
+	"github.com/grafana/grafana/pkg/setting"
 	"github.com/grafana/grafana/pkg/util"
 )
 
@@ -25,6 +30,9 @@ type TestingApiSrv struct {
 	log             log.Logger
 	accessControl   accesscontrol.AccessControl
 	evaluator       eval.EvaluatorFactory
+	cfg             *setting.UnifiedAlertingSettings
+	backtesting     *backtesting.Engine
+	featureManager  featuremgmt.FeatureToggles
 }
 
 func (srv TestingApiSrv) RouteTestGrafanaRuleConfig(c *models.ReqContext, body apimodels.TestRulePayload) response.Response {
@@ -136,3 +144,71 @@ func (srv TestingApiSrv) RouteEvalQueries(c *models.ReqContext, cmd apimodels.Ev
 
 	return response.JSONStreaming(http.StatusOK, evalResults)
 }
+
+func (srv TestingApiSrv) BacktestAlertRule(c *models.ReqContext, cmd apimodels.BacktestConfig) response.Response {
+	if !srv.featureManager.IsEnabled(featuremgmt.FlagAlertingBacktesting) {
+		return ErrResp(http.StatusNotFound, nil, "Backgtesting API is not enabled")
+	}
+
+	if cmd.From.After(cmd.To) {
+		return ErrResp(400, nil, "From cannot be greater than To")
+	}
+
+	noDataState, err := ngmodels.NoDataStateFromString(string(cmd.NoDataState))
+
+	if err != nil {
+		return ErrResp(400, err, "")
+	}
+	forInterval := time.Duration(cmd.For)
+	if forInterval < 0 {
+		return ErrResp(400, nil, "Bad For interval")
+	}
+
+	intervalSeconds, err := validateInterval(srv.cfg, time.Duration(cmd.Interval))
+	if err != nil {
+		return ErrResp(400, err, "")
+	}
+
+	if !authorizeDatasourceAccessForRule(&ngmodels.AlertRule{Data: cmd.Data}, func(evaluator accesscontrol.Evaluator) bool {
+		return accesscontrol.HasAccess(srv.accessControl, c)(accesscontrol.ReqSignedIn, evaluator)
+	}) {
+		return errorToResponse(fmt.Errorf("%w to query one or many data sources used by the rule", ErrAuthorization))
+	}
+
+	rule := &ngmodels.AlertRule{
+		// ID:             0,
+		// Updated:        time.Time{},
+		// Version:        0,
+		// NamespaceUID:   "",
+		// DashboardUID:   nil,
+		// PanelID:        nil,
+		// RuleGroup:      "",
+		// RuleGroupIndex: 0,
+		// ExecErrState:   "",
+		Title: cmd.Title,
+		// prefix backtesting- is to distinguish between executions of regular rule and backtesting in logs (like expression engine, evaluator, state manager etc)
+		UID:             "backtesting-" + util.GenerateShortUID(),
+		OrgID:           c.OrgID,
+		Condition:       cmd.Condition,
+		Data:            cmd.Data,
+		IntervalSeconds: intervalSeconds,
+		NoDataState:     noDataState,
+		For:             forInterval,
+		Annotations:     cmd.Annotations,
+		Labels:          cmd.Labels,
+	}
+
+	result, err := srv.backtesting.Test(c.Req.Context(), c.SignedInUser, rule, cmd.From, cmd.To)
+	if err != nil {
+		if errors.Is(err, backtesting.ErrInvalidInputData) {
+			return ErrResp(400, err, "Failed to evaluate")
+		}
+		return ErrResp(500, err, "Failed to evaluate")
+	}
+
+	body, err := data.FrameToJSON(result, data.IncludeAll)
+	if err != nil {
+		return ErrResp(500, err, "Failed to convert frame to JSON")
+	}
+	return response.JSON(http.StatusOK, body)
+}