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Commit 3197243

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added Mediator design pattern
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package design_patterns
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/**
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*
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* Mediator is a behavioral design pattern that reduces the coupling of many classes among themselves
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*
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* by moving these couplings into one mediator class
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*
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*/
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// SoftwareDevelopmentManager is a mediator for the customer, designer, programmer and tester
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class SoftwareDevelopmentManager {
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private lateinit var customer: SoftwareDevelopmentMember
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private lateinit var designer: SoftwareDevelopmentMember
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private lateinit var programmer: SoftwareDevelopmentMember
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private lateinit var tester: SoftwareDevelopmentMember
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fun changeCustomer(member: SoftwareDevelopmentMember) { customer = member }
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fun changeDesigner(member: SoftwareDevelopmentMember) { designer = member }
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fun changeProgrammer(member: SoftwareDevelopmentMember) { programmer = member }
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fun changeTester(member: SoftwareDevelopmentMember) { tester = member }
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private val stages = mutableListOf<String>()
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val stagesAsString: String
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get() = stages.joinToString("\n")
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// members do not interact directly with each other because the mediator does it
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// which reduces the coupling between them
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fun nextStage(work: String, member: SoftwareDevelopmentMember) {
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val finishedStage = when (member) {
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is CustomerSoftwareDevelopmentMember -> designer.receiveWork(work)
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is DesignerSoftwareDevelopmentMember -> programmer.receiveWork(work)
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is ProgrammerSoftwareDevelopmentMember -> tester.receiveWork(work)
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is TesterSoftwareDevelopmentMember -> customer.receiveWork(work)
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else -> ""
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}
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stages.add(finishedStage)
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}
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}
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// SoftwareDevelopmentMember works with other members through the mediator
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abstract class SoftwareDevelopmentMember(protected val mediator: SoftwareDevelopmentManager) {
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abstract fun receiveWork(work: String): String
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abstract fun finishWork()
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}
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class CustomerSoftwareDevelopmentMember(mediator: SoftwareDevelopmentManager) : SoftwareDevelopmentMember(mediator) {
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override fun receiveWork(work: String) = "Customer accepted the work: $work"
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override fun finishWork() {
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mediator.nextStage("design development", this)
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}
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}
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class DesignerSoftwareDevelopmentMember(mediator: SoftwareDevelopmentManager) : SoftwareDevelopmentMember(mediator) {
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override fun receiveWork(work: String) = "Designer accepted the work: $work"
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override fun finishWork() {
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mediator.nextStage("writing code", this)
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}
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}
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class ProgrammerSoftwareDevelopmentMember(mediator: SoftwareDevelopmentManager) : SoftwareDevelopmentMember(mediator) {
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override fun receiveWork(work: String) = "Programmer accepted the work: $work"
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override fun finishWork() {
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mediator.nextStage("application testing", this)
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}
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}
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class TesterSoftwareDevelopmentMember(mediator: SoftwareDevelopmentManager) : SoftwareDevelopmentMember(mediator) {
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override fun receiveWork(work: String) = "Tester accepted the work: $work"
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override fun finishWork() {
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mediator.nextStage("business valuation", this)
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}
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}
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package design_patterns
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import org.junit.Test
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import org.junit.Assert.assertEquals
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class MediatorTest {
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@Test
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fun test() {
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val manager = SoftwareDevelopmentManager()
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val customer = CustomerSoftwareDevelopmentMember(manager)
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manager.changeCustomer(customer)
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val designer = DesignerSoftwareDevelopmentMember(manager)
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manager.changeDesigner(designer)
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val programmer = ProgrammerSoftwareDevelopmentMember(manager)
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manager.changeProgrammer(programmer)
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val tester = TesterSoftwareDevelopmentMember(manager)
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manager.changeTester(tester)
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customer.finishWork()
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designer.finishWork()
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programmer.finishWork()
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tester.finishWork()
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assertEquals("""
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Designer accepted the work: design development
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Programmer accepted the work: writing code
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Tester accepted the work: application testing
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Customer accepted the work: business valuation
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""".trimIndent(), manager.stagesAsString)
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}
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}

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