more iterating on macd, need to get a better handle on how to test.

sma_series.go

@@ -0,0 +1,90 @@
+package chart
+
+const (
+	// DefaultSimpleMovingAveragePeriod is the default number of values to average.
+	DefaultSimpleMovingAveragePeriod = 16
+)
+
+// SMASeries is a computed series.
+type SMASeries struct {
+	Name  string
+	Style Style
+	YAxis YAxisType
+
+	Period      int
+	InnerSeries ValueProvider
+}
+
+// GetName returns the name of the time series.
+func (sma SMASeries) GetName() string {
+	return sma.Name
+}
+
+// GetStyle returns the line style.
+func (sma SMASeries) GetStyle() Style {
+	return sma.Style
+}
+
+// GetYAxis returns which YAxis the series draws on.
+func (sma SMASeries) GetYAxis() YAxisType {
+	return sma.YAxis
+}
+
+// Len returns the number of elements in the series.
+func (sma SMASeries) Len() int {
+	return sma.InnerSeries.Len()
+}
+
+// GetValue gets a value at a given index.
+func (sma SMASeries) GetValue(index int) (x float64, y float64) {
+	if sma.InnerSeries == nil {
+		return
+	}
+	px, _ := sma.InnerSeries.GetValue(index)
+	x = px
+	y = sma.getAverage(index)
+	return
+}
+
+// GetLastValue computes the last moving average value but walking back window size samples,
+// and recomputing the last moving average chunk.
+func (sma SMASeries) GetLastValue() (x float64, y float64) {
+	if sma.InnerSeries == nil {
+		return
+	}
+	seriesLen := sma.InnerSeries.Len()
+	px, _ := sma.InnerSeries.GetValue(seriesLen - 1)
+	x = px
+	y = sma.getAverage(seriesLen - 1)
+	return
+}
+
+// GetPeriod returns the window size.
+func (sma SMASeries) GetPeriod(defaults ...int) int {
+	if sma.Period == 0 {
+		if len(defaults) > 0 {
+			return defaults[0]
+		}
+		return DefaultSimpleMovingAveragePeriod
+	}
+	return sma.Period
+}
+
+func (sma SMASeries) getAverage(index int) float64 {
+	period := sma.GetPeriod()
+	floor := MaxInt(0, index-period)
+	var accum float64
+	var count float64
+	for x := index; x >= floor; x-- {
+		_, vy := sma.InnerSeries.GetValue(x)
+		accum += vy
+		count += 1.0
+	}
+	return accum / count
+}
+
+// Render renders the series.
+func (sma *SMASeries) Render(r Renderer, canvasBox Box, xrange, yrange Range, defaults Style) {
+	style := sma.Style.WithDefaultsFrom(defaults)
+	DrawLineSeries(r, canvasBox, xrange, yrange, style, sma)
+}