From 1328860453bb36492bc71689d6567227190a9b99 Mon Sep 17 00:00:00 2001
From: ismayilmalik <ismayilturksoy@gmail.com>
Date: Mon, 1 Jan 2018 21:29:51 +0300
Subject: [PATCH] implemented chain of responsibility

---
 README.md                                     |  5 ++
 .../chain_of_responsibility.go                | 81 +++++++++++++++++++
 .../chain_of_responsibility_test.go           | 36 +++++++++
 3 files changed, 122 insertions(+)
 create mode 100644 behavioral/chain_of_responsibility/chain_of_responsibility.go
 create mode 100644 behavioral/chain_of_responsibility/chain_of_responsibility_test.go

diff --git a/README.md b/README.md
index 33d8b75..841756a 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,7 @@
 - [Structural patterns](#structural-patterns)
     - [Composition](#composition)
 - [Behavioral patterns](#behavioral-patterns)
+    - [Chain of responsibility](#chain-of-responsibility)
 - [Concurrency patterns](#concurrency-patterns)
 
 ---
@@ -39,6 +40,10 @@ between objects. Behavio ral patterns describe not just patterns of objects or c
 but also the patterns of communication between them. These patterns characterize
 complex control flow that's difficult to follow at run-time. They shift your focus away
 from flow of control to let you concent ratejust on the way objects are interconnected.
+### Chain of responsibility
+Avoid coupling the sender of a request to its receiver by giving more than one
+object a chance to handle the request. Chain the receiving objects and pass the
+request along the chain until an object handles it.
 
 ## Concurrency patterns
 Pattenrs for concurrent work and parallel execution in Go.
\ No newline at end of file
diff --git a/behavioral/chain_of_responsibility/chain_of_responsibility.go b/behavioral/chain_of_responsibility/chain_of_responsibility.go
new file mode 100644
index 0000000..cc62a5b
--- /dev/null
+++ b/behavioral/chain_of_responsibility/chain_of_responsibility.go
@@ -0,0 +1,81 @@
+package chain_of_responsibility
+
+import (
+	"errors"
+	"fmt"
+	"encoding/json"
+)
+
+type Handler interface {
+	Handle(interface{}) error
+}
+
+type Book struct {
+	Title string
+	Author string
+}
+
+func (b Book) String() string {
+	return fmt.Sprintf("%b", b)
+}
+
+type Deserializer struct {
+	next Handler
+}
+
+func (h *Deserializer) Handle(data interface{}) error {
+	var book Book
+	bytes, ok := data.([]byte)
+	if !ok {
+		return errors.New("Unsupported type!")
+	}
+
+	if err := json.Unmarshal(bytes, &book); err != nil {
+		return err
+	}
+	
+	if h.next != nil {
+		return h.next.Handle(book)
+	}
+
+	return nil
+}
+
+type Logger struct {
+	next Handler
+}
+
+func (h *Logger) Handle(data interface{}) error {
+	book, ok := data.(Book)
+	if !ok {
+		return errors.New("Argument is not a Book instance")
+	}
+
+	fmt.Println("Book received! Titlle: '%s' Author: '%s", book.Title, book.Author)
+	if h.next != nil {
+		return h.next.Handle(book)
+	}
+
+	return nil
+}
+
+type BookDb struct {
+	store map[string]Book
+	next Handler
+}
+
+func (h *BookDb) Handle(data interface{}) error {
+	book, ok := data.(Book)
+	if !ok {
+		return errors.New("Argument is not a Book instance")
+	}
+
+	h.store[book.Title]=book
+
+	if h.next != nil {
+		return h.next.Handle(book)
+	}
+
+	return nil
+}
+
diff --git a/behavioral/chain_of_responsibility/chain_of_responsibility_test.go b/behavioral/chain_of_responsibility/chain_of_responsibility_test.go
new file mode 100644
index 0000000..1b0336c
--- /dev/null
+++ b/behavioral/chain_of_responsibility/chain_of_responsibility_test.go
@@ -0,0 +1,36 @@
+package chain_of_responsibility
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestCORPattern(t *testing.T) {
+	book := Book{"Go design patterns", "Ismayil Malik"}
+	bytes, _ := json.Marshal(book)
+	bookDb := &BookDb{
+		make(map[string]Book),
+		nil,
+	}
+	logger := &Logger{
+		next: bookDb,
+	}
+	chain := &Deserializer{
+		next: logger,
+	}
+
+	t.Run(`It will be unmurshalled on deserializer handler then will be logged
+		  on logger handler and at the end will be presisted by third handler`, func(t *testing.T) {
+
+		err := chain.Handle(bytes)
+		if err != nil {
+			t.Fatalf("Something went wrong: %s", err.Error())
+		}
+
+		storedBook := bookDb.store[book.Title]
+		if storedBook != book {
+			t.Errorf("Expected %b but got %b", book, storedBook)
+		}
+	})
+
+}