From 8a7bd86ed0716cc0b06cd2fe28e4fa22a60404ff Mon Sep 17 00:00:00 2001
From: Jian Han <jian.han@neds.com>
Date: Tue, 21 Nov 2017 23:12:41 +1000
Subject: [PATCH] observer pattern

---
 behavioral/observerpattern/main.go | 70 ++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 behavioral/observerpattern/main.go

diff --git a/behavioral/observerpattern/main.go b/behavioral/observerpattern/main.go
new file mode 100644
index 0000000..c734c0d
--- /dev/null
+++ b/behavioral/observerpattern/main.go
@@ -0,0 +1,70 @@
+package main
+
+import (
+	"reflect"
+
+	"github.com/davecgh/go-spew/spew"
+)
+
+type AbstractObserver interface {
+	Update(abstractSubject AbstractSubject) error
+}
+
+type AbstractSubject interface {
+	Attach(abstractObserver AbstractObserver)
+	Detach(abstractObserver AbstractObserver)
+	Notify()
+	GetFav() string
+}
+
+type PatternObserver struct {
+}
+
+func (p *PatternObserver) Update(s AbstractSubject) error {
+	spew.Dump(" new favorite patterns", s.GetFav())
+	return nil
+}
+
+type PatternSubject struct {
+	FavoritePatterns []string
+	Observers        []AbstractObserver
+	Fav              string
+}
+
+func (p *PatternSubject) Attach(observer AbstractObserver) {
+	p.Observers = append(p.Observers, observer)
+}
+
+func (p *PatternSubject) Detach(observer AbstractObserver) {
+	for k, v := range p.Observers {
+		if reflect.DeepEqual(observer, v) {
+			p.Observers = append(p.Observers[:k], p.Observers[k+1:]...)
+			break
+		}
+	}
+}
+
+func (p *PatternSubject) Notify() {
+	for _, v := range p.Observers {
+		v.Update(p)
+	}
+}
+
+func (p *PatternSubject) updateFav(fav string) {
+	p.Fav = fav
+	p.Notify()
+}
+
+func (p *PatternSubject) GetFav() string {
+	return p.Fav
+}
+
+func main() {
+	patternGossiper := &PatternSubject{}
+	patternGossipFan := &PatternObserver{}
+	patternGossiper.Attach(patternGossipFan)
+	patternGossiper.updateFav("abstract factory, decorator, visitor")
+	patternGossiper.updateFav("abstract factory, observer, decorator")
+	patternGossiper.Detach(patternGossipFan)
+	patternGossiper.updateFav("abstract factory, observer, paisley")
+}