Add obv indicator

pkg/indicator/obv.go

@@ -0,0 +1,78 @@
+package indicator
+
+import (
+	"time"
+
+	"github.com/c9s/bbgo/pkg/types"
+)
+
+/*
+obv implements on-balance volume indicator
+
+On-Balance Volume (OBV) Definition
+- https://www.investopedia.com/terms/o/onbalancevolume.asp
+*/
+//go:generate callbackgen -type OBV
+type OBV struct {
+	types.IntervalWindow
+	Values   Float64Slice
+	PrePrice float64
+
+	EndTime         time.Time
+	UpdateCallbacks []func(value float64)
+}
+
+func (inc *OBV) update(kLine types.KLine, priceF KLinePriceMapper) {
+	price := priceF(kLine)
+	volume := kLine.Volume
+
+	if len(inc.Values) == 0 {
+		inc.PrePrice = price
+		inc.Values.Push(volume)
+		return
+	}
+
+	preOBV := inc.Values[len(inc.Values)-1]
+
+	var sign float64 = 0.0
+	if volume > inc.PrePrice {
+		sign = 1.0
+	} else if volume < inc.PrePrice {
+		sign = -1.0
+	}
+	obv := preOBV + sign*volume
+	inc.Values.Push(obv)
+}
+
+func (inc *OBV) Last() float64 {
+	if len(inc.Values) == 0 {
+		return 0.0
+	}
+	return inc.Values[len(inc.Values)-1]
+}
+
+func (inc *OBV) calculateAndUpdate(kLines []types.KLine) {
+	var priceF = KLineClosePriceMapper
+
+	for i, k := range kLines {
+		if inc.EndTime != zeroTime && k.EndTime.Before(inc.EndTime) {
+			continue
+		}
+
+		inc.update(k, priceF)
+		inc.EmitUpdate(inc.Last())
+		inc.EndTime = kLines[i].EndTime
+	}
+
+}
+func (inc *OBV) handleKLineWindowUpdate(interval types.Interval, window types.KLineWindow) {
+	if inc.Interval != interval {
+		return
+	}
+
+	inc.calculateAndUpdate(window)
+}
+
+func (inc *OBV) Bind(updater KLineWindowUpdater) {
+	updater.OnKLineWindowUpdate(inc.handleKLineWindowUpdate)
+}