Align multiple series to the same interval with interpolation, fix #1211

pkg/timeseries/align.go

@@ -80,3 +80,64 @@ func (ts TimeSeries) DetectInterval() time.Duration {
 	midIndex := int(math.Floor(float64(len(deltas)) * 0.5))
 	return time.Duration(deltas[midIndex]) * time.Millisecond
 }
+
+// AlignSeriesIntervals aligns series to the same time interval
+func AlignSeriesIntervals(series []*TimeSeriesData) []*TimeSeriesData {
+	if len(series) == 0 {
+		return series
+	}
+
+	minInterval := *series[0].Meta.Interval
+	for _, s := range series {
+		if *s.Meta.Interval < minInterval {
+			minInterval = *s.Meta.Interval
+		}
+	}
+
+	// 0 interval means series is not aligned, so it's tricky to align multiple series
+	if minInterval == 0 {
+		return series
+	}
+
+	for _, s := range series {
+		if s.Len() < 2 || *s.Meta.Interval == minInterval {
+			continue
+		}
+
+		s.TS = s.TS.Interpolate(minInterval)
+	}
+
+	return series
+}
+
+func (ts TimeSeries) Interpolate(interval time.Duration) TimeSeries {
+	if interval <= 0 || ts.Len() < 2 {
+		return ts
+	}
+
+	alignedTs := NewTimeSeries()
+	var frameTs = ts[0].Time
+	var pointFrameTs time.Time
+	var point TimePoint
+	var nextPoint TimePoint
+
+	for i := 0; i < ts.Len()-1; i++ {
+		point = ts[i]
+		nextPoint = ts[i+1]
+		pointFrameTs = point.Time
+
+		if point.Value != nil && nextPoint.Value != nil {
+			frameTs = pointFrameTs.Add(interval)
+			for frameTs.Before(nextPoint.Time) {
+				pointValue := linearInterpolation(frameTs, point, nextPoint)
+				alignedTs = append(alignedTs, TimePoint{Time: frameTs, Value: &pointValue})
+				frameTs = frameTs.Add(interval)
+			}
+		}
+
+		alignedTs = append(alignedTs, TimePoint{Time: pointFrameTs, Value: point.Value})
+		frameTs = frameTs.Add(interval)
+	}
+
+	return alignedTs
+}