Export errors for time series processing (#1134)

* Export errors for time series processing

* Add more

* Update data/time_series_errors.go

* Fix lint

* Keep errors in same format

* Update

* Fix lint

data/time_series.go

@@ -308,7 +308,7 @@ func (p *longRowProcessor) process(longRowIdx int) error {
 	}
 
 	if currentTime.Before(p.lastTime) {
-		return fmt.Errorf("long series must be sorted ascending by time to be converted")
+		return ErrorSeriesUnsorted
 	}
 
 	sliceKey := make(tupleLabels, len(p.tsSchema.FactorIndices)) // factor columns idx:value tuples (used for lookup)
@@ -386,7 +386,7 @@ func (p *longRowProcessor) process(longRowIdx int) error {
 func timeAt(idx int, longFrame *Frame, tsSchema TimeSeriesSchema) (time.Time, error) { // get time.Time regardless if pointer
 	val, ok := longFrame.ConcreteAt(tsSchema.TimeIndex, idx)
 	if !ok {
-		return time.Time{}, fmt.Errorf("can not convert to wide series, input has null time values")
+		return time.Time{}, ErrorNullTimeValues
 	}
 	return val.(time.Time), nil
 }
@@ -420,7 +420,7 @@ func WideToLong(wideFrame *Frame) (*Frame, error) {
 	if err != nil {
 		return nil, err
 	} else if wideLen == 0 {
-		return nil, fmt.Errorf("can not convert to long series, input fields have no rows")
+		return nil, ErrorInputFieldsWithoutRows
 	}
 
 	var uniqueValueNames []string                        // unique names of Fields that are value types

data/time_series_errors.go

@@ -0,0 +1,9 @@
+package data
+
+import "errors"
+
+var (
+	ErrorNullTimeValues         = errors.New("unable to process the data to wide series because input has null time values, make sure all time values are not null")
+	ErrorSeriesUnsorted         = errors.New("unable to process the data because it is not sorted in ascending order by time, please updated your query to sort the data by time if possible")
+	ErrorInputFieldsWithoutRows = errors.New("can not convert to long series, input fields have no rows")
+)