prom: add support for default step param (#9866)

Alerting for prometheus have been depending on the step parameter from each query.
In https://github.com/grafana/grafana/pull/9226 we changed the behavior for step in the
frontend which caused problems for alerting. This commit fixes that by introducing a default
min interval value so alerting always have something to depend on. 

closes #9777

pkg/tsdb/prometheus/prometheus_test.go

@@ -2,13 +2,21 @@ package prometheus
 
 import (
 	"testing"
+	"time"
 
+	"github.com/grafana/grafana/pkg/models"
+	"github.com/grafana/grafana/pkg/tsdb"
+
+	"github.com/grafana/grafana/pkg/components/simplejson"
 	p "github.com/prometheus/common/model"
 	. "github.com/smartystreets/goconvey/convey"
 )
 
 func TestPrometheus(t *testing.T) {
 	Convey("Prometheus", t, func() {
+		dsInfo := &models.DataSource{
+			JsonData: simplejson.New(),
+		}
 
 		Convey("converting metric name", func() {
 			metric := map[p.LabelName]p.LabelValue{
@@ -36,5 +44,108 @@ func TestPrometheus(t *testing.T) {
 
 			So(formatLegend(metric, query), ShouldEqual, `http_request_total{app="backend", device="mobile"}`)
 		})
+
+		Convey("parsing query model with step", func() {
+			json := `{
+				"expr": "go_goroutines",
+				"format": "time_series",
+				"refId": "A"
+			}`
+			jsonModel, _ := simplejson.NewJson([]byte(json))
+			queryContext := &tsdb.TsdbQuery{}
+			queryModels := []*tsdb.Query{
+				{Model: jsonModel},
+			}
+
+			Convey("with 48h time range", func() {
+				queryContext.TimeRange = tsdb.NewTimeRange("12h", "now")
+
+				model, err := parseQuery(dsInfo, queryModels, queryContext)
+
+				So(err, ShouldBeNil)
+				So(model.Step, ShouldEqual, time.Second*30)
+			})
+		})
+
+		Convey("parsing query model without step parameter", func() {
+			json := `{
+				"expr": "go_goroutines",
+				"format": "time_series",
+				"intervalFactor": 1,
+				"refId": "A"
+			}`
+			jsonModel, _ := simplejson.NewJson([]byte(json))
+			queryContext := &tsdb.TsdbQuery{}
+			queryModels := []*tsdb.Query{
+				{Model: jsonModel},
+			}
+
+			Convey("with 48h time range", func() {
+				queryContext.TimeRange = tsdb.NewTimeRange("48h", "now")
+
+				model, err := parseQuery(dsInfo, queryModels, queryContext)
+
+				So(err, ShouldBeNil)
+				So(model.Step, ShouldEqual, time.Minute*2)
+			})
+
+			Convey("with 1h time range", func() {
+				queryContext.TimeRange = tsdb.NewTimeRange("1h", "now")
+
+				model, err := parseQuery(dsInfo, queryModels, queryContext)
+
+				So(err, ShouldBeNil)
+				So(model.Step, ShouldEqual, time.Second*15)
+			})
+		})
+
+		Convey("parsing query model with intervalFactor", func() {
+			Convey("high intervalFactor", func() {
+				json := `{
+					"expr": "go_goroutines",
+					"format": "time_series",
+					"intervalFactor": 10,
+					"refId": "A"
+				}`
+				jsonModel, _ := simplejson.NewJson([]byte(json))
+				queryContext := &tsdb.TsdbQuery{}
+				queryModels := []*tsdb.Query{
+					{Model: jsonModel},
+				}
+
+				Convey("with 48h time range", func() {
+					queryContext.TimeRange = tsdb.NewTimeRange("48h", "now")
+
+					model, err := parseQuery(dsInfo, queryModels, queryContext)
+
+					So(err, ShouldBeNil)
+					So(model.Step, ShouldEqual, time.Minute*20)
+				})
+			})
+
+			Convey("low intervalFactor", func() {
+				json := `{
+					"expr": "go_goroutines",
+					"format": "time_series",
+					"intervalFactor": 1,
+					"refId": "A"
+				}`
+				jsonModel, _ := simplejson.NewJson([]byte(json))
+				queryContext := &tsdb.TsdbQuery{}
+				queryModels := []*tsdb.Query{
+					{Model: jsonModel},
+				}
+
+				Convey("with 48h time range", func() {
+					queryContext.TimeRange = tsdb.NewTimeRange("48h", "now")
+
+					model, err := parseQuery(dsInfo, queryModels, queryContext)
+
+					So(err, ShouldBeNil)
+					So(model.Step, ShouldEqual, time.Minute*2)
+				})
+			})
+		})
+
 	})
 }