loki: backend mode: support all query types (#45619)

* loki: backend mode: support all query types

* loki: backend: adjust vector-parsing field-names

* loki: backend: no interval for streams-dataframes

* loki: backend: enable more query types

* better variable name

* removed unnecessary code

* improve frame-processing

* more unit tests

* improved code

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

* remove unused code

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

* simplify code

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

* lint fix

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

pkg/tsdb/loki/frame_test.go

@@ -0,0 +1,87 @@
+package loki
+
+import (
+	"testing"
+	"time"
+
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFormatName(t *testing.T) {
+	t.Run("converting metric name", func(t *testing.T) {
+		metric := map[string]string{
+			"app":    "backend",
+			"device": "mobile",
+		}
+
+		query := &lokiQuery{
+			LegendFormat: "legend {{app}} {{ device }} {{broken}}",
+		}
+
+		require.Equal(t, "legend backend mobile ", formatName(metric, query))
+	})
+
+	t.Run("build full series name", func(t *testing.T) {
+		metric := map[string]string{
+			"app":    "backend",
+			"device": "mobile",
+		}
+
+		query := &lokiQuery{
+			LegendFormat: "",
+		}
+
+		require.Equal(t, `{app="backend", device="mobile"}`, formatName(metric, query))
+	})
+}
+
+func TestAdjustFrame(t *testing.T) {
+	t.Run("response should be parsed normally", func(t *testing.T) {
+		field1 := data.NewField("", nil, make([]time.Time, 0))
+		field2 := data.NewField("", nil, make([]float64, 0))
+		field2.Labels = data.Labels{"app": "Application", "tag2": "tag2"}
+
+		frame := data.NewFrame("test", field1, field2)
+		frame.SetMeta(&data.FrameMeta{Type: data.FrameTypeTimeSeriesMany})
+
+		query := &lokiQuery{
+			Expr:         "up(ALERTS)",
+			QueryType:    QueryTypeRange,
+			LegendFormat: "legend {{app}}",
+			Step:         time.Second * 42,
+		}
+
+		adjustFrame(frame, query)
+
+		require.Equal(t, frame.Name, "legend Application")
+		require.Equal(t, frame.Meta.ExecutedQueryString, "Expr: up(ALERTS)\nStep: 42s")
+		require.Equal(t, frame.Fields[0].Config.Interval, float64(42000))
+		require.Equal(t, frame.Fields[1].Config.DisplayNameFromDS, "legend Application")
+	})
+
+	t.Run("should set interval-attribute in response", func(t *testing.T) {
+		query := &lokiQuery{
+			Step:      time.Second * 42,
+			QueryType: QueryTypeRange,
+		}
+
+		field1 := data.NewField("", nil, make([]time.Time, 0))
+		field2 := data.NewField("", nil, make([]float64, 0))
+
+		frame := data.NewFrame("test", field1, field2)
+		frame.SetMeta(&data.FrameMeta{Type: data.FrameTypeTimeSeriesMany})
+
+		adjustFrame(frame, query)
+
+		// to keep the test simple, we assume the
+		// first field is the time-field
+		timeField := frame.Fields[0]
+		require.NotNil(t, timeField)
+		require.Equal(t, data.FieldTypeTime, timeField.Type())
+
+		timeFieldConfig := timeField.Config
+		require.NotNil(t, timeFieldConfig)
+		require.Equal(t, float64(42000), timeFieldConfig.Interval)
+	})
+}