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app/src/main/java/com/example/algorithmstudy/pattern/structure/proxy/ProtectedProxyInterface.kt

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+package com.example.algorithmstudy.pattern.structure.proxy
+
+interface ProtectedProxyInterface {
+    fun fetch(user: User): ProxyData
+}

app/src/main/java/com/example/algorithmstudy/pattern/structure/proxy/ProtectedProxyLoader.kt

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+package com.example.algorithmstudy.pattern.structure.proxy
+
+class ProtectedProxyLoader : ProtectedProxyInterface {
+    private val proxyData: ProxyData by lazy {
+        ProxyData("PROXY DATA")
+    }
+
+    // fetch 가능한 수준을 MEDIUM 이상으로 설정
+    override fun fetch(user: User): ProxyData {
+        return when (user.authorizeLevel) {
+            User.AuthorizeLevel.TOP -> proxyData
+            User.AuthorizeLevel.MEDIUM -> proxyData
+            User.AuthorizeLevel.LOW -> throw IllegalAccessException("Unauthorized access.")
+        }
+    }
+}

app/src/main/java/com/example/algorithmstudy/pattern/structure/proxy/ProxyData.kt

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+package com.example.algorithmstudy.pattern.structure.proxy
+
+data class ProxyData(val data: String)

app/src/main/java/com/example/algorithmstudy/pattern/structure/proxy/ProxyLoaderInterface.kt

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+package com.example.algorithmstudy.pattern.structure.proxy
+
+interface ProxyLoaderInterface {
+    fun fetch(): ProxyData
+}

app/src/main/java/com/example/algorithmstudy/pattern/structure/proxy/User.kt

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+package com.example.algorithmstudy.pattern.structure.proxy
+
+/**
+ *  권한설정이 추가되어 있는 user를 가정한 data class
+ */
+data class User(
+    val name: String,
+    var authorizeLevel: AuthorizeLevel
+) {
+    enum class AuthorizeLevel {
+        TOP,
+        MEDIUM,
+        LOW
+    }
+}

app/src/main/java/com/example/algorithmstudy/pattern/structure/proxy/VirtualProxyLoader.kt

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+package com.example.algorithmstudy.pattern.structure.proxy
+
+class VirtualProxyLoader : ProxyLoaderInterface {
+    private val proxyData: ProxyData by lazy {
+        ProxyData("PROXY DATA")
+    }
+
+    override fun fetch(): ProxyData {
+        return proxyData
+    }
+}

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

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+package com.example.algorithmstudy.design_pattern
+
+import com.example.algorithmstudy.pattern.structure.proxy.ProtectedProxyLoader
+import com.example.algorithmstudy.pattern.structure.proxy.User
+import com.example.algorithmstudy.pattern.structure.proxy.VirtualProxyLoader
+import org.junit.Test
+
+/**
+ *  ProxyTest Pattern
+ *
+ *  - Virtual proxy : 사용하는 객체가 이미 생성된 경우 재사용하는 패턴
+ *  - Protected proxy : 권한에 따라 객체 접근을 제어하는 패턴
+ */
+class ProxyTest {
+
+    @Test
+    fun testVirtualProxy() {
+        val proxyLoader = VirtualProxyLoader()
+
+        println(proxyLoader.fetch())
+        println(proxyLoader.fetch())
+        println(proxyLoader.fetch() === proxyLoader.fetch())
+    }
+
+    @Test
+    fun testProtectedProxy() {
+        val member = User(name = "choi", authorizeLevel = User.AuthorizeLevel.MEDIUM)
+        val guest = User(name = "steve", authorizeLevel = User.AuthorizeLevel.LOW)
+
+        val proxyLoader = ProtectedProxyLoader()
+
+        try {
+            println(proxyLoader.fetch(member))
+        } catch (e: IllegalAccessException) {
+            println(e.printStackTrace())
+        }
+
+        try {
+            println(proxyLoader.fetch(guest))
+        } catch (e: IllegalAccessException) {
+            println(e.printStackTrace())
+        }
+    }
+}