FEAT: Add SMMA indicator

pkg/indicator/v2/smma.go

@@ -0,0 +1,47 @@
+package indicatorv2
+
+import (
+	"github.com/c9s/bbgo/pkg/types"
+)
+
+type SMMAStream struct {
+	*types.Float64Series
+	window    int
+	rawValues *types.Queue
+	source    types.Float64Source
+}
+
+func SMMA2(source types.Float64Source, window int) *SMMAStream {
+	s := &SMMAStream{
+		Float64Series: types.NewFloat64Series(),
+		window:        window,
+		rawValues:     types.NewQueue(window),
+		source:        source,
+	}
+	s.Bind(source, s)
+	return s
+}
+
+func (s *SMMAStream) Calculate(v float64) float64 {
+	var out float64
+	sourceLen := s.source.Length()
+
+	if sourceLen < s.window {
+		// Until we reach the end of the period, sum the prices.
+
+		// First, calculate the sum, and it will be automatically saved too.
+		s.rawValues.Sum(s.window)
+		// Then save the input value to use it later on.
+		s.rawValues.Update(v)
+	} else if sourceLen == s.window {
+		// We need the SMA for the first time.
+		s.rawValues.Update(v)
+		out = s.rawValues.Mean(s.window)
+	} else {
+		// For all the rest values, just use the formula.
+		last := s.Slice.Last(0)
+		out = (last*float64((s.window-1.0)) + v) / float64(s.window)
+	}
+
+	return out
+}

pkg/indicator/v2/smma_test.go

@@ -0,0 +1,27 @@
+package indicatorv2
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/c9s/bbgo/pkg/types"
+)
+
+func TestSMMA(t *testing.T) {
+	source := types.NewFloat64Series()
+	smma := SMMA2(source, 3)
+
+	data := []float64{10, 20, 30, 40, 50, 60, 70, 80, 90}
+	for _, d := range data {
+		source.PushAndEmit(d)
+	}
+
+	// Assert the first 3 and last 3 value outputs.
+	assert.InDelta(t, 0, smma.Last(len(data)-1), 0.001)
+	assert.InDelta(t, 0, smma.Last(len(data)-2), 0.001)
+	assert.InDelta(t, 20, smma.Last(len(data)-3), 0.001)
+	assert.InDelta(t, 51.97530864197531, smma.Last(2), 0.001)
+	assert.InDelta(t, 61.31687242798355, smma.Last(1), 0.001)
+	assert.InDelta(t, 70.87791495198904, smma.Last(0), 0.001)
+}