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app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/chainofresposibility/AuthenticationHeader.kt

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+package com.example.algorithmstudy.pattern.behavoiral.chainofresposibility
+
+class AuthenticationHeader(val token: String?, var next: HandlerChain? = null) : HandlerChain {
+    override fun addHeader(inputHeader: String): String =
+        "$inputHeader\nAuthorization : $token".let {
+            next?.addHeader(it) ?: it
+        }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/chainofresposibility/BodyPayloadHeader.kt

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+package com.example.algorithmstudy.pattern.behavoiral.chainofresposibility
+
+class BodyPayloadHeader(val body: String?, var next: HandlerChain? = null) : HandlerChain {
+    override fun addHeader(inputHeader: String): String =
+        "$inputHeader\nContentType : $body".let {
+            next?.addHeader(it) ?: it
+        }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/chainofresposibility/ContentTypeHeader.kt

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+package com.example.algorithmstudy.pattern.behavoiral.chainofresposibility
+
+class ContentTypeHeader(val contentType: String?, var next: HandlerChain? = null) : HandlerChain {
+    override fun addHeader(inputHeader: String): String =
+        "$inputHeader\nContentType : $contentType".let {
+            next?.addHeader(it) ?: it
+        }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/chainofresposibility/HandlerChain.kt

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+package com.example.algorithmstudy.pattern.behavoiral.chainofresposibility
+
+interface HandlerChain {
+    fun addHeader(inputHeader: String): String
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/mediator/ComponentA.kt

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+package com.example.algorithmstudy.pattern.behavoiral.mediator
+
+class ComponentA(private val mediator: Mediator) {
+    fun operationA() {
+        mediator.method(this, "arg A")
+    }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/mediator/ComponentB.kt

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+package com.example.algorithmstudy.pattern.behavoiral.mediator
+
+class ComponentB(private val mediator: Mediator) {
+    fun operationB() {
+        mediator.method(this, "arg B")
+    }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/mediator/ComponentC.kt

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+package com.example.algorithmstudy.pattern.behavoiral.mediator
+
+class ComponentC(private val mediator: Mediator) {
+    fun operationC() {
+        mediator.method(this, "arg C")
+    }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/mediator/ConcreteMediator.kt

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+package com.example.algorithmstudy.pattern.behavoiral.mediator
+
+class ConcreteMediator : Mediator {
+    override fun method(sender: Any, args: Any?) {
+        when (sender) {
+            is ComponentA -> println("arg from A : $args")
+            is ComponentB -> println("arg from B : $args")
+            is ComponentC -> println("arg from C : $args")
+        }
+    }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/mediator/Mediator.kt

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+package com.example.algorithmstudy.pattern.behavoiral.mediator
+
+/**
+ *  ref : https://asvid.github.io/kotlin_mediator_pattern
+ */
+interface Mediator {
+    fun method(sender: Any, args: Any? = null)
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/observer/IObservable.kt

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+package com.example.algorithmstudy.pattern.behavoiral.observer
+
+interface IObservable {
+    val observers: ArrayList<IObserver>
+
+    fun add(observer: IObserver) {
+        observers.add(observer)
+    }
+
+    fun remove(observer: IObserver) {
+        observers.remove(observer)
+    }
+
+    fun sendUpdateEvent() {
+        observers.forEach { it.update() }
+    }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/observer/IObserver.kt

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+package com.example.algorithmstudy.pattern.behavoiral.observer
+
+/**
+ *  ref : https://www.baeldung.com/kotlin/observer-pattern
+ */
+interface IObserver {
+    fun update()
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/observer/NewsLetter.kt

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+package com.example.algorithmstudy.pattern.behavoiral.observer
+
+class NewsLetter : IObservable {
+    override val observers: ArrayList<IObserver> = ArrayList()
+
+    var newestArticleUrl = ""
+        set(value) {
+            field = value
+            sendUpdateEvent()
+        }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/observer/NewsReader.kt

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+package com.example.algorithmstudy.pattern.behavoiral.observer
+
+class NewsReader(private var newsLetter: NewsLetter) : IObserver {
+    override fun update() {
+        println("New article : ${newsLetter.newestArticleUrl}")
+    }
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/templatemethod/Americano.kt

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+package com.example.algorithmstudy.pattern.behavoiral.templatemethod
+
+class Americano : Drink() {
+    override fun addIngredient() = println("Adding 2 shots of espresso")
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/templatemethod/Drink.kt

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+package com.example.algorithmstudy.pattern.behavoiral.templatemethod
+
+/**
+ *  reference :
+ *  - http://www.devll.org/blog/2020/kotlin/template-method-pattern.html
+ *  - https://kimchanjung.github.io/design-pattern/2020/05/28/template-method-pattern/
+ */
+abstract class Drink {
+    fun prepareDrink() {
+        println("prepare ${this.javaClass.simpleName}")
+
+        boilWater()
+        addIngredient()
+        fillWaterInCup()
+
+        println("Finished preparing drink\n")
+    }
+
+    // 템플릿 메소드 : 각 구현 요소에 따라 달라지는 부분
+    protected abstract fun addIngredient()
+
+    // 각 구현 요소들이 공통으로 사용하는 부분
+    private fun boilWater() = println("Boil water")
+    private fun fillWaterInCup() = println("Fill cup with hot water")
+}

app/src/main/java/com/example/algorithmstudy/pattern/behavoiral/templatemethod/OrangeAde.kt

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+package com.example.algorithmstudy.pattern.behavoiral.templatemethod
+
+class OrangeAde : Drink() {
+    override fun addIngredient() = println("Adding orange")
+}

app/src/test/java/com/example/algorithmstudy/design_pattern/ChainOfResponsibilityTest.kt

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+package com.example.algorithmstudy.design_pattern
+
+import com.example.algorithmstudy.pattern.behavoiral.chainofresposibility.AuthenticationHeader
+import com.example.algorithmstudy.pattern.behavoiral.chainofresposibility.BodyPayloadHeader
+import com.example.algorithmstudy.pattern.behavoiral.chainofresposibility.ContentTypeHeader
+import org.junit.Test
+
+/**
+ *  ChainOfResponsibility 패턴
+ *
+ *  - https://medium.com/@catalinstefan/chain-of-responsibility-design-pattern-in-kotlin-b62f86be274f
+ *  - 체인 형태로 이어 호출을 해야 하는 요구사항에서, 각 호출 단계별로 호출의 유효성과 오류를 확인 가능하며, 이상이 없는 경우 다음 체인까지 진행하도록 하는 패턴
+ */
+class ChainOfResponsibilityTest {
+
+    @Test
+    fun testChainOfResponsibility() {
+        val authenticationHeader = AuthenticationHeader("111")
+        val contentTypeHeader = ContentTypeHeader("json")
+        val bodyPayloadHdader = BodyPayloadHeader("Body: body")
+
+        authenticationHeader.next = contentTypeHeader
+        contentTypeHeader.next = bodyPayloadHdader
+
+        val messageWithAuth = authenticationHeader.addHeader("HEADERS WITH AUTHENTICATION")
+        println(messageWithAuth)
+
+        val messageWithoutAuth = contentTypeHeader.addHeader("HEADERS WITH AUTHENTICATION")
+        println(messageWithoutAuth)
+    }
+}

app/src/test/java/com/example/algorithmstudy/design_pattern/MediatorTest.kt

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+package com.example.algorithmstudy.design_pattern
+
+import com.example.algorithmstudy.pattern.behavoiral.mediator.ComponentA
+import com.example.algorithmstudy.pattern.behavoiral.mediator.ComponentB
+import com.example.algorithmstudy.pattern.behavoiral.mediator.ComponentC
+import com.example.algorithmstudy.pattern.behavoiral.mediator.ConcreteMediator
+import org.junit.Test
+
+/**
+ *  Mediator Pattern
+ *
+ *  - 컴포넌트들은 Mediator를 reference로 가지며, 서로가 소통할 일은 없음
+ *  - Mediator는 각 컴포넌트들을 판단해 각각 필요한 동작을 수행하도록 조정함(말대로 중재자)
+ */
+class MediatorTest {
+
+    @Test
+    fun mediatorTest() {
+        ConcreteMediator().apply {
+            val componentA = ComponentA(this)
+            val componentB = ComponentB(this)
+            val componentC = ComponentC(this)
+
+            method(componentA)
+            method(componentB)
+            method(componentC)
+        }
+    }
+}

app/src/test/java/com/example/algorithmstudy/design_pattern/ObserverTest.kt

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+package com.example.algorithmstudy.design_pattern
+
+import com.example.algorithmstudy.pattern.behavoiral.observer.NewsLetter
+import com.example.algorithmstudy.pattern.behavoiral.observer.NewsReader
+import org.junit.Test
+
+/**
+ *  Observer Pattern test
+ */
+class ObserverTest {
+
+    @Test
+    fun TestObserverPattern() {
+        val newsLetter = NewsLetter()
+        val reader = NewsReader(newsLetter)
+
+        newsLetter.add(reader)
+        newsLetter.newestArticleUrl = "news 1"
+        newsLetter.newestArticleUrl = "news 2"
+        newsLetter.newestArticleUrl = "news 3"
+    }
+}

app/src/test/java/com/example/algorithmstudy/design_pattern/TemplateMethodTest.kt

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+package com.example.algorithmstudy.design_pattern
+
+import com.example.algorithmstudy.pattern.behavoiral.templatemethod.Americano
+import com.example.algorithmstudy.pattern.behavoiral.templatemethod.OrangeAde
+import org.junit.Test
+
+/**
+ *  TemplateMethod 패턴
+ *
+ *  - 공통된 function들은 함께 사용하되, 각 구현 요소별로 다르게 수행할 function을 각각 정의해 사용 가능한 패턴
+ */
+class TemplateMethodTest {
+
+    @Test
+    fun testTemplateMethod() {
+        val americano = Americano()
+        val orangeAde = OrangeAde()
+
+        americano.prepareDrink()
+        orangeAde.prepareDrink()
+    }
+}