EphemeralView implementation

application-arrow/api/application-arrow.api

@@ -1,3 +1,7 @@
+public final class com/fraktalio/fmodel/application/EphemeralViewArrowExtensionKt {
+	public static final fun handleWithEffect (Lcom/fraktalio/fmodel/application/ViewStateComputation;Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+}
+
 public final class com/fraktalio/fmodel/application/EventSourcingAggregateArrowExtensionKt {
 	public static final fun handleOptimisticallyWithEffect (Lcom/fraktalio/fmodel/application/EventSourcingLockingAggregate;Ljava/lang/Object;)Lkotlinx/coroutines/flow/Flow;
 	public static final fun handleOptimisticallyWithEffect (Lcom/fraktalio/fmodel/application/EventSourcingLockingAggregate;Ljava/lang/Object;Ljava/util/Map;)Lkotlinx/coroutines/flow/Flow;

application-arrow/src/commonMain/kotlin/com/fraktalio/fmodel/application/EphemeralViewArrowExtension.kt

@@ -0,0 +1,42 @@
+package com.fraktalio.fmodel.application
+
+import arrow.core.Either
+import arrow.core.raise.catch
+import arrow.core.raise.either
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.fold
+
+/**
+ * Extension function - Handles the query of type [Q]
+ *
+ * @param query Query of type [Q] to be handled
+ * @return [Either] (either [Error] or State of type [S])
+ *
+ * @author Domenic Cassisi
+ */
+suspend fun <S, E, Q, EV> EV.handleWithEffect(query: Q): Either<Error, S>
+        where EV : ViewStateComputation<S, E>, EV : EphemeralViewRepository<E, Q> {
+
+    fun Q.fetchEventsWithEffect(): Either<Error, Flow<E>> =
+        either {
+            catch({
+                fetchEvents()
+            }) {
+                raise(Error.FetchingEventsFailed(query, it))
+            }
+        }
+
+    suspend fun Flow<E>.computeStateWithEffect(): Either<Error, S> =
+        either {
+            catch({
+                fold(initialState) { s, e -> evolve(s, e) }
+            }) {
+                raise(Error.CalculatingNewViewStateFailed(this@computeStateWithEffect, it))
+            }
+        }
+
+    return either {
+        query.fetchEventsWithEffect().bind()
+            .computeStateWithEffect().bind()
+    }
+}

application-arrow/src/commonTest/kotlin/com/fraktalio/fmodel/application/EphemeralViewTest.kt

@@ -0,0 +1,86 @@
+package com.fraktalio.fmodel.application
+
+import arrow.core.Either
+import com.fraktalio.fmodel.application.examples.numbers.even.query.EvenNumberEphemeralViewRepository
+import com.fraktalio.fmodel.application.examples.numbers.even.query.evenNumberEphemeralViewRepository
+import com.fraktalio.fmodel.domain.IView
+import com.fraktalio.fmodel.domain.examples.numbers.api.Description
+import com.fraktalio.fmodel.domain.examples.numbers.api.EvenNumberState
+import com.fraktalio.fmodel.domain.examples.numbers.api.NumberValue
+import com.fraktalio.fmodel.domain.examples.numbers.even.query.evenNumberView
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.shouldBe
+import io.kotest.matchers.types.shouldBeInstanceOf
+
+/**
+ * DSL - Given
+ */
+private suspend fun <S, E, Q> IView<S, E>.given(repository: EphemeralViewRepository<E, Q>, query: () -> Q): Either<Error, S> =
+    EphemeralView(
+        view = this,
+        ephemeralViewRepository = repository
+    ).handleWithEffect(query())
+
+/**
+ * DSL - When
+ */
+private fun <Q> whenQuery(query: Q): Q = query
+
+/**
+ * DSL - Then
+ */
+private infix fun <S> Either<Error, S>.thenState(expected: S) {
+    val state = when (this) {
+        is Either.Right -> value
+        is Either.Left -> throw AssertionError("Expected Either.Right, but found Either.Left with value $value")
+    }
+    state shouldBe expected
+}
+
+private fun <S> Either<Error, S>.thenError() {
+    val error = when (this) {
+        is Either.Right -> throw AssertionError("Expected Either.Left, but found Either.Right with value $value")
+        is Either.Left -> value
+    }
+    error.shouldBeInstanceOf<Error>()
+}
+
+/**
+ * Ephemeral View Test
+ */
+class EphemeralViewTest : FunSpec({
+    val evenView = evenNumberView()
+    val ephemeralViewRepository = evenNumberEphemeralViewRepository() as EvenNumberEphemeralViewRepository
+
+    test("Ephemeral View - load number flow 1") {
+        with(evenView) {
+            given(ephemeralViewRepository) {
+                whenQuery(1)
+            } thenState EvenNumberState(Description("Initial state, Number 2, Number 4"), NumberValue(6))
+        }
+    }
+
+    test("Ephemeral View - load number flow 2") {
+        with(evenView) {
+            given(ephemeralViewRepository) {
+                whenQuery(2)
+            } thenState EvenNumberState(Description("Initial state, Number 4, Number 2"), NumberValue(2))
+        }
+    }
+
+    test("Ephemeral View - load number flow 3 - with error") {
+        with(evenView) {
+            given(ephemeralViewRepository) {
+                whenQuery(3)
+            }.thenError()
+        }
+    }
+
+    test("Ephemeral View - load non-existing number flow") {
+        with(evenView) {
+            given(ephemeralViewRepository) {
+                whenQuery(4)
+            } thenState EvenNumberState(Description("Initial state"), NumberValue(0))
+        }
+    }
+})

application-arrow/src/commonTest/kotlin/com/fraktalio/fmodel/application/examples/numbers/even/query/EvenNumberEphemeralViewRepository.kt

@@ -0,0 +1,44 @@
+package com.fraktalio.fmodel.application.examples.numbers.even.query
+
+import com.fraktalio.fmodel.application.EphemeralViewRepository
+import com.fraktalio.fmodel.domain.examples.numbers.api.Description
+import com.fraktalio.fmodel.domain.examples.numbers.api.NumberEvent
+import com.fraktalio.fmodel.domain.examples.numbers.api.NumberValue
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.emptyFlow
+import kotlinx.coroutines.flow.flowOf
+
+/**
+ * Simple flows of events to represent previously stored events in the event store
+ */
+private var numberFlow1 = flowOf(
+    NumberEvent.EvenNumberEvent.EvenNumberAdded(Description("Number 2"), NumberValue(2)),
+    NumberEvent.EvenNumberEvent.EvenNumberAdded(Description("Number 4"), NumberValue(4))
+)
+
+private var numberFlow2 = flowOf(
+    NumberEvent.EvenNumberEvent.EvenNumberAdded(Description("Number 4"), NumberValue(4)),
+    NumberEvent.EvenNumberEvent.EvenNumberSubtracted(Description("Number 2"), NumberValue(2))
+)
+
+/**
+ * Even number ephemeral view implementation
+ */
+class EvenNumberEphemeralViewRepository : EphemeralViewRepository<NumberEvent.EvenNumberEvent?, Int> {
+
+    override fun Int.fetchEvents(): Flow<NumberEvent.EvenNumberEvent?> {
+        return when (this) {
+            1 -> numberFlow1
+            2 -> numberFlow2
+            3 -> throw RuntimeException("Some fake error while fetching events.")
+            else -> emptyFlow()
+        }
+    }
+
+}
+
+/**
+ * Helper function to create an [EvenNumberEphemeralViewRepository]
+ */
+fun evenNumberEphemeralViewRepository(): EphemeralViewRepository<NumberEvent.EvenNumberEvent?, Int> =
+    EvenNumberEphemeralViewRepository()

application-vanilla/api/application-vanilla.api

@@ -1,3 +1,7 @@
+public final class com/fraktalio/fmodel/application/EphemeralViewExtensionKt {
+	public static final fun handle (Lcom/fraktalio/fmodel/application/ViewStateComputation;Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
+}
+
 public final class com/fraktalio/fmodel/application/EventSourcingAggregateActorExtensionKt {
 	public static final fun handleConcurrently (Lcom/fraktalio/fmodel/application/EventSourcingAggregate;Lkotlinx/coroutines/flow/Flow;IILkotlinx/coroutines/CoroutineStart;Lkotlin/coroutines/CoroutineContext;Lkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
 	public static final fun handleConcurrently (Lcom/fraktalio/fmodel/application/EventSourcingAggregate;Lkotlinx/coroutines/flow/Flow;IILkotlinx/coroutines/CoroutineStart;Lkotlin/coroutines/CoroutineContext;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;

application-vanilla/src/commonMain/kotlin/com/fraktalio/fmodel/application/EphemeralViewExtension.kt

@@ -0,0 +1,14 @@
+package com.fraktalio.fmodel.application
+
+import kotlinx.coroutines.flow.fold
+
+/**
+ * Extension function - Handles the query of type [Q]
+ *
+ * @param query Query of type [Q] to be handled
+ * @return State of type [S]
+ *
+ * @author Domenic Cassisi
+ */
+suspend fun <S, E, Q, EV> EV.handle(query: Q): S where EV : ViewStateComputation<S, E>, EV : EphemeralViewRepository<E, Q> =
+    query.fetchEvents().fold(initialState) { s, e -> evolve(s, e) }

application-vanilla/src/commonTest/kotlin/com/fraktalio/fmodel/application/EphemeralViewTest.kt

@@ -0,0 +1,60 @@
+package com.fraktalio.fmodel.application
+
+import com.fraktalio.fmodel.application.examples.numbers.even.query.EvenNumberEphemeralViewRepository
+import com.fraktalio.fmodel.application.examples.numbers.even.query.evenNumberEphemeralViewRepository
+import com.fraktalio.fmodel.domain.IView
+import com.fraktalio.fmodel.domain.examples.numbers.api.Description
+import com.fraktalio.fmodel.domain.examples.numbers.api.EvenNumberState
+import com.fraktalio.fmodel.domain.examples.numbers.api.NumberValue
+import com.fraktalio.fmodel.domain.examples.numbers.even.query.evenNumberView
+import io.kotest.core.spec.style.FunSpec
+import io.kotest.matchers.shouldBe
+
+/**
+ * DSL - Given
+ */
+private suspend fun <S, E, Q> IView<S, E>.given(repository: EphemeralViewRepository<E, Q>, query: () -> Q): S =
+    EphemeralView(
+        view = this,
+        ephemeralViewRepository = repository
+    ).handle(query())
+
+/**
+ * DSL - When
+ */
+private fun <Q> whenQuery(query: Q): Q = query
+
+/**
+ * DSL - Then
+ */
+private infix fun <S> S.thenState(expected: S) = shouldBe(expected)
+
+class EphemeralViewTest : FunSpec({
+    val evenView = evenNumberView()
+    val ephemeralViewRepository = evenNumberEphemeralViewRepository() as EvenNumberEphemeralViewRepository
+
+    test("Ephemeral View - load number flow 1") {
+        with(evenView) {
+            given(ephemeralViewRepository) {
+                whenQuery(1)
+            } thenState EvenNumberState(Description("Initial state, Number 2, Number 4"), NumberValue(6))
+        }
+    }
+
+    test("Ephemeral View - load number flow 2") {
+        with(evenView) {
+            given(ephemeralViewRepository) {
+                whenQuery(2)
+            } thenState EvenNumberState(Description("Initial state, Number 4, Number 2"), NumberValue(2))
+        }
+    }
+
+    test("Ephemeral View - load non-existing number flow") {
+        with(evenView) {
+            given(ephemeralViewRepository) {
+                whenQuery(3)
+            } thenState EvenNumberState(Description("Initial state"), NumberValue(0))
+        }
+    }
+
+})

application-vanilla/src/commonTest/kotlin/com/fraktalio/fmodel/application/examples/numbers/even/query/EvenNumberEphemeralViewRepository.kt

@@ -0,0 +1,43 @@
+package com.fraktalio.fmodel.application.examples.numbers.even.query
+
+import com.fraktalio.fmodel.application.EphemeralViewRepository
+import com.fraktalio.fmodel.domain.examples.numbers.api.Description
+import com.fraktalio.fmodel.domain.examples.numbers.api.NumberEvent
+import com.fraktalio.fmodel.domain.examples.numbers.api.NumberValue
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.emptyFlow
+import kotlinx.coroutines.flow.flowOf
+
+/**
+ * Simple flows of events to represent previously stored events in the event store
+ */
+private var numberFlow1 = flowOf(
+    NumberEvent.EvenNumberEvent.EvenNumberAdded(Description("Number 2"), NumberValue(2)),
+    NumberEvent.EvenNumberEvent.EvenNumberAdded(Description("Number 4"), NumberValue(4))
+)
+
+private var numberFlow2 = flowOf(
+    NumberEvent.EvenNumberEvent.EvenNumberAdded(Description("Number 4"), NumberValue(4)),
+    NumberEvent.EvenNumberEvent.EvenNumberSubtracted(Description("Number 2"), NumberValue(2))
+)
+
+/**
+ * Even number ephemeral view implementation
+ */
+class EvenNumberEphemeralViewRepository : EphemeralViewRepository<NumberEvent.EvenNumberEvent?, Int> {
+
+    override fun Int.fetchEvents(): Flow<NumberEvent.EvenNumberEvent?> {
+        return when (this) {
+            1 -> numberFlow1
+            2 -> numberFlow2
+            else -> emptyFlow()
+        }
+    }
+
+}
+
+/**
+ * Helper function to create an [EvenNumberEphemeralViewRepository]
+ */
+fun evenNumberEphemeralViewRepository(): EphemeralViewRepository<NumberEvent.EvenNumberEvent?, Int> =
+    EvenNumberEphemeralViewRepository()

application/api/application.api

@@ -7,6 +7,21 @@ public final class com/fraktalio/fmodel/application/ActionPublisher$DefaultImpls
 	public static fun publish (Lcom/fraktalio/fmodel/application/ActionPublisher;Lkotlinx/coroutines/flow/Flow;Ljava/util/Map;)Lkotlinx/coroutines/flow/Flow;
 }
 
+public abstract interface class com/fraktalio/fmodel/application/EphemeralView : com/fraktalio/fmodel/application/EphemeralViewRepository, com/fraktalio/fmodel/application/ViewStateComputation {
+}
+
+public final class com/fraktalio/fmodel/application/EphemeralView$DefaultImpls {
+	public static fun computeNewState (Lcom/fraktalio/fmodel/application/EphemeralView;Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
+}
+
+public final class com/fraktalio/fmodel/application/EphemeralViewKt {
+	public static final fun EphemeralView (Lcom/fraktalio/fmodel/domain/IView;Lcom/fraktalio/fmodel/application/EphemeralViewRepository;)Lcom/fraktalio/fmodel/application/EphemeralView;
+}
+
+public abstract interface class com/fraktalio/fmodel/application/EphemeralViewRepository {
+	public abstract fun fetchEvents (Ljava/lang/Object;)Lkotlinx/coroutines/flow/Flow;
+}
+
 public abstract class com/fraktalio/fmodel/application/Error : com/fraktalio/fmodel/application/Result {
 	public abstract fun getThrowable ()Ljava/lang/Throwable;
 }
@@ -110,6 +125,19 @@ public final class com/fraktalio/fmodel/application/Error$EventPublishingFailed
 	public fun toString ()Ljava/lang/String;
 }
 
+public final class com/fraktalio/fmodel/application/Error$FetchingEventsFailed : com/fraktalio/fmodel/application/Error {
+	public fun <init> (Ljava/lang/Object;Ljava/lang/Throwable;)V
+	public final fun component1 ()Ljava/lang/Object;
+	public final fun component2 ()Ljava/lang/Throwable;
+	public final fun copy (Ljava/lang/Object;Ljava/lang/Throwable;)Lcom/fraktalio/fmodel/application/Error$FetchingEventsFailed;
+	public static synthetic fun copy$default (Lcom/fraktalio/fmodel/application/Error$FetchingEventsFailed;Ljava/lang/Object;Ljava/lang/Throwable;ILjava/lang/Object;)Lcom/fraktalio/fmodel/application/Error$FetchingEventsFailed;
+	public fun equals (Ljava/lang/Object;)Z
+	public final fun getId ()Ljava/lang/Object;
+	public fun getThrowable ()Ljava/lang/Throwable;
+	public fun hashCode ()I
+	public fun toString ()Ljava/lang/String;
+}
+
 public final class com/fraktalio/fmodel/application/Error$FetchingStateFailed : com/fraktalio/fmodel/application/Error {
 	public fun <init> (Ljava/lang/Object;Ljava/lang/Throwable;)V
 	public synthetic fun <init> (Ljava/lang/Object;Ljava/lang/Throwable;ILkotlin/jvm/internal/DefaultConstructorMarker;)V

application/src/commonMain/kotlin/com/fraktalio/fmodel/application/EphemeralView.kt

@@ -0,0 +1,39 @@
+package com.fraktalio.fmodel.application
+
+import com.fraktalio.fmodel.domain.IView
+
+/**
+ * EphemeralView is using/delegating a `view` / [ViewStateComputation]<[S], [E]> to handle events of type [E] without maintaining a state of projection(s).
+ *
+ * [EphemeralView] extends [ViewStateComputation] and [EphemeralViewRepository] interfaces,
+ * clearly communicating that it is composed out of these two behaviours.
+ *
+ * @param S Ephemeral View state of type [S]
+ * @param E Events of type [E] that are handled by this Ephemeral View
+ * @param Q Query of type [Q]
+ *
+ * @author Domenic Cassisi
+ */
+interface EphemeralView<S, E, Q> : ViewStateComputation<S, E>, EphemeralViewRepository<E, Q>
+
+/**
+ * Ephemeral View constructor-like function.
+ *
+ * The Delegation pattern has proven to be a good alternative to implementation inheritance, and Kotlin supports it natively requiring zero boilerplate code.
+ *
+ * @param S Ephemeral View state of type [S]
+ * @param E Events of type [E] that are used internally to build/fold new state
+ * @param Q Identifier of type [Q]
+ * @property view A view component of type [IView]<[S], [E]>
+ * @property ephemeralViewRepository Interface for fetching events for [Q] - dependencies by delegation
+ * @return An object/instance of type [EphemeralView]<[S], [E], [Q]>
+ *
+ * @author Domenic Cassisi
+ */
+fun <S, E, Q> EphemeralView(
+    view: IView<S, E>,
+    ephemeralViewRepository: EphemeralViewRepository<E, Q>
+): EphemeralView<S, E, Q> =
+    object : EphemeralView<S, E, Q>,
+        EphemeralViewRepository<E, Q> by ephemeralViewRepository,
+        IView<S, E> by view {}