Adding upstream version 2.1.2.

Signed-off-by: Daniel Baumann <daniel@debian.org>

concat_series.go

@@ -0,0 +1,44 @@
+package chart
+
+// ConcatSeries is a special type of series that concatenates its `InnerSeries`.
+type ConcatSeries []Series
+
+// Len returns the length of the concatenated set of series.
+func (cs ConcatSeries) Len() int {
+	total := 0
+	for _, s := range cs {
+		if typed, isValuesProvider := s.(ValuesProvider); isValuesProvider {
+			total += typed.Len()
+		}
+	}
+
+	return total
+}
+
+// GetValue returns the value at the (meta) index (i.e 0 => totalLen-1)
+func (cs ConcatSeries) GetValue(index int) (x, y float64) {
+	cursor := 0
+	for _, s := range cs {
+		if typed, isValuesProvider := s.(ValuesProvider); isValuesProvider {
+			len := typed.Len()
+			if index < cursor+len {
+				x, y = typed.GetValues(index - cursor) //FENCEPOSTS.
+				return
+			}
+			cursor += typed.Len()
+		}
+	}
+	return
+}
+
+// Validate validates the series.
+func (cs ConcatSeries) Validate() error {
+	var err error
+	for _, s := range cs {
+		err = s.Validate()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}