From a2d7a40147dba6304415cee3b7595d3256c03b92 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E3=81=AA=E3=82=8B=E3=81=BF?= <narumi@maicoin.com>
Date: Mon, 10 May 2021 17:17:50 +0800
Subject: [PATCH] Add obv indicator

---
 pkg/indicator/obv.go           | 78 ++++++++++++++++++++++++++++++++++
 pkg/indicator/obv_callbacks.go | 15 +++++++
 2 files changed, 93 insertions(+)
 create mode 100644 pkg/indicator/obv.go
 create mode 100644 pkg/indicator/obv_callbacks.go

diff --git a/pkg/indicator/obv.go b/pkg/indicator/obv.go
new file mode 100644
index 000000000..507eeea9a
--- /dev/null
+++ b/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)
+}
diff --git a/pkg/indicator/obv_callbacks.go b/pkg/indicator/obv_callbacks.go
new file mode 100644
index 000000000..b0897152c
--- /dev/null
+++ b/pkg/indicator/obv_callbacks.go
@@ -0,0 +1,15 @@
+// Code generated by "callbackgen -type OBV"; DO NOT EDIT.
+
+package indicator
+
+import ()
+
+func (inc *OBV) OnUpdate(cb func(value float64)) {
+	inc.UpdateCallbacks = append(inc.UpdateCallbacks, cb)
+}
+
+func (inc *OBV) EmitUpdate(value float64) {
+	for _, cb := range inc.UpdateCallbacks {
+		cb(value)
+	}
+}