Expressions: Use enumerations rather than strings (#83741)

pkg/expr/commands.go

@@ -205,14 +205,14 @@ func (gr *ReduceCommand) Execute(ctx context.Context, _ time.Time, vars mathexp.
 type ResampleCommand struct {
 	Window        time.Duration
 	VarToResample string
-	Downsampler   string
-	Upsampler     string
+	Downsampler   mathexp.ReducerID
+	Upsampler     mathexp.Upsampler
 	TimeRange     TimeRange
 	refID         string
 }
 
 // NewResampleCommand creates a new ResampleCMD.
-func NewResampleCommand(refID, rawWindow, varToResample string, downsampler string, upsampler string, tr TimeRange) (*ResampleCommand, error) {
+func NewResampleCommand(refID, rawWindow, varToResample string, downsampler mathexp.ReducerID, upsampler mathexp.Upsampler, tr TimeRange) (*ResampleCommand, error) {
 	// TODO: validate reducer here, before execution
 	window, err := gtime.ParseDuration(rawWindow)
 	if err != nil {
@@ -271,7 +271,11 @@ func UnmarshalResampleCommand(rn *rawNode) (*ResampleCommand, error) {
 		return nil, fmt.Errorf("expected resample downsampler to be a string, got type %T", upsampler)
 	}
 
-	return NewResampleCommand(rn.RefID, window, varToResample, downsampler, upsampler, rn.TimeRange)
+	return NewResampleCommand(rn.RefID, window,
+		varToResample,
+		mathexp.ReducerID(downsampler),
+		mathexp.Upsampler(upsampler),
+		rn.TimeRange)
 }
 
 // NeedsVars returns the variable names (refIds) that are dependencies