Expressions: Use enumerations rather than strings (#83741)

pkg/expr/mathexp/resample.go

@@ -7,8 +7,23 @@ import (
 	"github.com/grafana/grafana-plugin-sdk-go/data"
 )
 
+// The upsample function
+// +enum
+type Upsampler string
+
+const (
+	// Use the last seen value
+	UpsamplerPad Upsampler = "pad"
+
+	// backfill
+	UpsamplerBackfill Upsampler = "backfilling"
+
+	// Do not fill values (nill)
+	UpsamplerFillNA Upsampler = "fillna"
+)
+
 // Resample turns the Series into a Number based on the given reduction function
-func (s Series) Resample(refID string, interval time.Duration, downsampler string, upsampler string, from, to time.Time) (Series, error) {
+func (s Series) Resample(refID string, interval time.Duration, downsampler ReducerID, upsampler Upsampler, from, to time.Time) (Series, error) {
 	newSeriesLength := int(float64(to.Sub(from).Nanoseconds()) / float64(interval.Nanoseconds()))
 	if newSeriesLength <= 0 {
 		return s, fmt.Errorf("the series cannot be sampled further; the time range is shorter than the interval")
@@ -37,19 +52,19 @@ func (s Series) Resample(refID string, interval time.Duration, downsampler strin
 		var value *float64
 		if len(vals) == 0 { // upsampling
 			switch upsampler {
-			case "pad":
+			case UpsamplerPad:
 				if lastSeen != nil {
 					value = lastSeen
 				} else {
 					value = nil
 				}
-			case "backfilling":
+			case UpsamplerBackfill:
 				if sIdx == s.Len() { // no vals left
 					value = nil
 				} else {
 					_, value = s.GetPoint(sIdx)
 				}
-			case "fillna":
+			case UpsamplerFillNA:
 				value = nil
 			default:
 				return s, fmt.Errorf("upsampling %v not implemented", upsampler)
@@ -61,15 +76,15 @@ func (s Series) Resample(refID string, interval time.Duration, downsampler strin
 			ff := Float64Field(*fVec)
 			var tmp *float64
 			switch downsampler {
-			case "sum":
+			case ReducerSum:
 				tmp = Sum(&ff)
-			case "mean":
+			case ReducerMean:
 				tmp = Avg(&ff)
-			case "min":
+			case ReducerMin:
 				tmp = Min(&ff)
-			case "max":
+			case ReducerMax:
 				tmp = Max(&ff)
-			case "last":
+			case ReducerLast:
 				tmp = Last(&ff)
 			default:
 				return s, fmt.Errorf("downsampling %v not implemented", downsampler)

pkg/expr/mathexp/resample_test.go

@@ -13,8 +13,8 @@ func TestResampleSeries(t *testing.T) {
 	var tests = []struct {
 		name             string
 		interval         time.Duration
-		downsampler      string
-		upsampler        string
+		downsampler      ReducerID
+		upsampler        Upsampler
 		timeRange        backend.TimeRange
 		seriesToResample Series
 		series           Series