Implement RealDispatcher and Related Classes (#621)

* Implement RealDispatcher and Related Classes

Signed-off-by: mramotar <mramotar@dropbox.com>

* Implement RealOptionalInjector

Signed-off-by: mramotar <mramotar@dropbox.com>

* Implement DefaultLogger

Signed-off-by: mramotar <mramotar@dropbox.com>

---------

Signed-off-by: mramotar <mramotar@dropbox.com>

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/Logger.kt

@@ -0,0 +1,5 @@
+package org.mobilenativefoundation.paging.core
+
+interface Logger {
+    fun log(message: String)
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/Constants.kt

@@ -0,0 +1,5 @@
+package org.mobilenativefoundation.paging.core.impl
+
+internal object Constants {
+    const val UNCHECKED_CAST = "UNCHECKED_CAST"
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/DefaultLogger.kt

@@ -0,0 +1,22 @@
+package org.mobilenativefoundation.paging.core.impl
+
+import co.touchlab.kermit.CommonWriter
+import org.mobilenativefoundation.paging.core.Logger
+
+class DefaultLogger : Logger {
+    override fun log(message: String) {
+        logger.d(
+            """
+            
+            $message
+            
+            """.trimIndent(),
+        )
+    }
+
+    private val logger =
+        co.touchlab.kermit.Logger.apply {
+            setLogWriters(listOf(CommonWriter()))
+            setTag("org.mobilenativefoundation.paging")
+        }
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/Dispatcher.kt

@@ -0,0 +1,25 @@
+package org.mobilenativefoundation.paging.core.impl
+
+import org.mobilenativefoundation.paging.core.PagingAction
+
+/**
+ * A dispatcher for handling paging actions and dispatching them to the appropriate middleware and reducer.
+ *
+ * @param Id The type of the unique identifier for each item in the paged data.
+ * @param K The type of the key used for paging.
+ * @param P The type of the parameters associated with each page of data.
+ * @param D The type of the data items.
+ * @param E The type of errors that can occur during the paging process.
+ * @param A The type of custom actions that can be dispatched to modify the paging state.
+ */
+interface Dispatcher<Id : Comparable<Id>, K : Any, P : Any, D : Any, E : Any, A : Any> {
+
+    /**
+     * Dispatches a paging action to the middleware and reducer chain.
+     *
+     * @param PA The type of the paging action being dispatched.
+     * @param action The paging action to dispatch.
+     * @param index The index of the middleware to start dispatching from. Default is 0.
+     */
+    fun <PA : PagingAction<Id, K, P, D, E, A>> dispatch(action: PA, index: Int = 0)
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/EffectsHolder.kt

@@ -0,0 +1,79 @@
+package org.mobilenativefoundation.paging.core.impl
+
+import org.mobilenativefoundation.paging.core.Effect
+import org.mobilenativefoundation.paging.core.PagingAction
+import org.mobilenativefoundation.paging.core.PagingState
+import org.mobilenativefoundation.paging.core.impl.Constants.UNCHECKED_CAST
+import kotlin.reflect.KClass
+
+/**
+ * A type alias representing a mapping from a [PagingAction] to a list of [Effect]s.
+ */
+typealias PagingActionToEffects<Id, K, P, D, E, A> = MutableMap<KClass<out PagingAction<Id, K, P, D, E, A>>, MutableList<Effect<Id, K, P, D, E, A, *, *>>>
+
+/**
+ * A type alias representing a mapping from a [PagingState] to a [PagingActionToEffects] map.
+ */
+typealias PagingStateToPagingActionToEffects<Id, K, P, D, E, A> = MutableMap<KClass<out PagingState<Id, K, P, D, E>>, PagingActionToEffects<Id, K, P, D, E, A>>
+
+/**
+ * A class for holding and managing effects based on [PagingAction] and [PagingState] types.
+ *
+ * @param Id The type of the unique identifier for each item in the paged data.
+ * @param K The type of the key used for paging.
+ * @param P The type of the parameters associated with each page of data.
+ * @param D The type of the data items.
+ * @param E The type of errors that can occur during the paging process.
+ * @param A The type of custom actions that can be dispatched to modify the paging state.
+ */
+@Suppress(UNCHECKED_CAST)
+class EffectsHolder<Id : Comparable<Id>, K : Any, P : Any, D : Any, E : Any, A : Any> {
+    private val effects: PagingStateToPagingActionToEffects<Id, K, P, D, E, A> = mutableMapOf()
+
+    /**
+     * Retrieves the list of effects associated with the specified [PagingAction] and [PagingState] types.
+     *
+     * @param PA The type of the [PagingAction].
+     * @param S The type of the [PagingState].
+     * @param action The [KClass] of the [PagingAction].
+     * @param state The [KClass] of the [PagingState].
+     * @return The list of effects associated with the specified [PagingAction] and [PagingState] types.
+     */
+    fun <PA : PagingAction<Id, K, P, D, E, A>, S : PagingState<Id, K, P, D, E>> get(
+        action: KClass<out PagingAction<Id, K, P, D, E, A>>,
+        state: KClass<out PagingState<Id, K, P, D, E>>
+    ): List<Effect<Id, K, P, D, E, A, PA, S>> {
+        action as KClass<PA>
+        state as KClass<S>
+
+        return effects[state]?.get(action) as? List<Effect<Id, K, P, D, E, A, PA, S>> ?: emptyList()
+    }
+
+    /**
+     * Adds an effect to the list of effects associated with the specified [PagingAction] and [PagingState] types.
+     *
+     * @param PA The type of the [PagingAction].
+     * @param S The type of the [PagingState].
+     * @param action The [KClass] of the [PagingAction].
+     * @param state The [KClass] of the [PagingState].
+     * @param effect The effect to add.
+     */
+    fun <PA : PagingAction<Id, K, P, D, E, A>, S : PagingState<Id, K, P, D, E>> put(
+        action: KClass<out PagingAction<*, *, *, *, *, *>>,
+        state: KClass<out PagingState<*, *, *, *, *>>,
+        effect: Effect<Id, K, P, D, E, A, PA, S>
+    ) {
+        action as KClass<out PA>
+        state as KClass<out S>
+
+        if (state !in effects) {
+            effects[state] = mutableMapOf()
+        }
+
+        if (action !in effects[state]!!) {
+            effects[state]!![action] = mutableListOf()
+        }
+
+        effects[state]!![action]!!.add(effect)
+    }
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/EffectsLauncher.kt

@@ -0,0 +1,34 @@
+package org.mobilenativefoundation.paging.core.impl
+
+import org.mobilenativefoundation.paging.core.PagingAction
+import org.mobilenativefoundation.paging.core.PagingState
+import org.mobilenativefoundation.paging.core.impl.Constants.UNCHECKED_CAST
+import kotlin.reflect.KClass
+
+/**
+ * A class for launching effects based on dispatched [PagingAction]s and the current [PagingState].
+ *
+ * @param Id The type of the unique identifier for each item in the paged data.
+ * @param K The type of the key used for paging.
+ * @param P The type of the parameters associated with each page of data.
+ * @param D The type of the data items.
+ * @param E The type of errors that can occur during the paging process.
+ * @param A The type of custom actions that can be dispatched to modify the paging state.
+ * @property effectsHolder The [EffectsHolder] instance holding the effects.
+ */
+@Suppress(UNCHECKED_CAST)
+class EffectsLauncher<Id : Comparable<Id>, K : Any, P : Any, D : Any, E : Any, A : Any>(
+    private val effectsHolder: EffectsHolder<Id, K, P, D, E, A>
+) {
+
+    fun <PA : PagingAction<Id, K, P, D, E, A>, S : PagingState<Id, K, P, D, E>> launch(action: PA, state: S, dispatch: (PagingAction<Id, K, P, D, E, A>) -> Unit) {
+
+        effectsHolder.get<PA, S>(action::class, state::class).forEach { effect ->
+            effect(action, state, dispatch)
+        }
+
+        effectsHolder.get<PA, PagingState<Id, K, P, D, E>>(action::class, PagingState::class as KClass<out PagingState<Id, K, P, D, E>>).forEach { effect ->
+            effect(action, state, dispatch)
+        }
+    }
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/Injector.kt

@@ -0,0 +1,16 @@
+package org.mobilenativefoundation.paging.core.impl
+
+/**
+ * An interface representing an injector for providing instances of a specific type.
+ *
+ * @param T The type of the instance to be injected.
+ */
+interface Injector<T : Any> {
+
+    /**
+     * Injects an instance of type [T].
+     *
+     * @return The injected instance.
+     */
+    fun inject(): T
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/OptionalInjector.kt

@@ -0,0 +1,15 @@
+package org.mobilenativefoundation.paging.core.impl
+
+/**
+ * An interface representing an optional injector for providing instances of a specific type.
+ *
+ * @param T The type of the instance to be injected.
+ */
+interface OptionalInjector<T : Any> {
+    /**
+     * Injects an instance of type [T] if available, or returns null.
+     *
+     * @return The injected instance or null if not available.
+     */
+    fun inject(): T?
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/RealDispatcher.kt

@@ -0,0 +1,78 @@
+package org.mobilenativefoundation.paging.core.impl
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.launch
+import org.mobilenativefoundation.paging.core.Middleware
+import org.mobilenativefoundation.paging.core.PagingAction
+import org.mobilenativefoundation.paging.core.PagingState
+import org.mobilenativefoundation.paging.core.Reducer
+
+/**
+ * A real implementation of the [Dispatcher] interface for handling paging actions and managing the paging state.
+ *
+ * @param Id The type of the unique identifier for each item in the paged data.
+ * @param K The type of the key used for paging.
+ * @param P The type of the parameters associated with each page of data.
+ * @param D The type of the data items.
+ * @param E The type of errors that can occur during the paging process.
+ * @param A The type of custom actions that can be dispatched to modify the paging state.
+ * @property stateManager The [StateManager] instance for managing the paging state.
+ * @property middleware The list of [Middleware] instances to be applied to the dispatched actions.
+ * @property reducer The [Reducer] instance for reducing the paging state based on the dispatched actions.
+ * @property effectsLauncher The [EffectsLauncher] instance for launching effects based on the dispatched actions and the current state.
+ * @property childScope The [CoroutineScope] in which the dispatcher will operate.
+ */
+class RealDispatcher<Id : Comparable<Id>, K : Any, P : Any, D : Any, E : Any, A : Any>(
+    private val stateManager: StateManager<Id, K, P, D, E>,
+    private val middleware: List<Middleware<Id, K, P, D, E, A>>,
+    private val reducer: Reducer<Id, K, P, D, E, A>,
+    private val effectsLauncher: EffectsLauncher<Id, K, P, D, E, A>,
+    private val childScope: CoroutineScope,
+) : Dispatcher<Id, K, P, D, E, A> {
+
+    /**
+     * Dispatches a paging action to the middleware and reducer chain.
+     *
+     * @param PA The type of the paging action being dispatched.
+     * @param action The paging action to dispatch.
+     * @param index The index of the middleware to start dispatching from.
+     */
+    override fun <PA : PagingAction<Id, K, P, D, E, A>> dispatch(action: PA, index: Int) {
+        if (index < middleware.size) {
+
+            childScope.launch {
+                middleware[index].apply(action) { nextAction ->
+                    dispatch(nextAction, index + 1)
+                }
+            }
+
+        } else {
+            childScope.launch {
+                reduceAndLaunchEffects(action)
+            }
+        }
+    }
+
+    /**
+     * Reduces the paging state based on the dispatched action and launches the corresponding effects.
+     *
+     * @param PA The type of the paging action being dispatched.
+     * @param action The paging action to reduce and launch effects for.
+     */
+    private suspend fun <PA : PagingAction<Id, K, P, D, E, A>> reduceAndLaunchEffects(action: PA) {
+        val prevState = stateManager.state.value
+        val nextState = reducer.reduce(action, prevState)
+
+        stateManager.update(nextState)
+
+        when (nextState) {
+            is PagingState.Initial -> effectsLauncher.launch(action, nextState, ::dispatch)
+            is PagingState.Data.Idle -> effectsLauncher.launch(action, nextState, ::dispatch)
+            is PagingState.Data.ErrorLoadingMore<Id, K, P, D, E, *> -> effectsLauncher.launch(action, nextState, ::dispatch)
+            is PagingState.Data.LoadingMore -> effectsLauncher.launch(action, nextState, ::dispatch)
+            is PagingState.Error.Custom -> effectsLauncher.launch(action, nextState, ::dispatch)
+            is PagingState.Error.Exception -> effectsLauncher.launch(action, nextState, ::dispatch)
+            is PagingState.Loading -> effectsLauncher.launch(action, nextState, ::dispatch)
+        }
+    }
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/RealInjector.kt

@@ -0,0 +1,9 @@
+package org.mobilenativefoundation.paging.core.impl
+
+internal class RealInjector<T : Any> : Injector<T> {
+    var instance: T? = null
+
+    override fun inject(): T {
+        return instance!!
+    }
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/RealOptionalInjector.kt

@@ -0,0 +1,9 @@
+package org.mobilenativefoundation.paging.core.impl
+
+class RealOptionalInjector<T : Any> : OptionalInjector<T> {
+    var instance: T? = null
+
+    override fun inject(): T? {
+        return instance
+    }
+}

paging/core/src/commonMain/kotlin/org/mobilenativefoundation/paging/core/impl/StateManager.kt

@@ -0,0 +1,50 @@
+package org.mobilenativefoundation.paging.core.impl
+
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import org.mobilenativefoundation.paging.core.Logger
+import org.mobilenativefoundation.paging.core.PagingState
+
+/**
+ * A class for managing the state of the paging process.
+ *
+ * @param Id The type of the unique identifier for each item in the paged data.
+ * @param K The type of the key used for paging.
+ * @param P The type of the parameters associated with each page of data.
+ * @param D The type of the data items.
+ * @param E The type of errors that can occur during the paging process.
+ * @param initialState The initial [PagingState].
+ * @param loggerInjector The [OptionalInjector] for providing a [Logger] instance.
+ */
+class StateManager<Id : Comparable<Id>, K : Any, P : Any, D : Any, E : Any>(
+    initialState: PagingState<Id, K, P, D, E>,
+    loggerInjector: OptionalInjector<Logger>
+) {
+
+    private val logger = lazy { loggerInjector.inject() }
+
+    private val _state = MutableStateFlow(initialState)
+    val state = _state.asStateFlow()
+
+    /**
+     * Updates the state with the specified [PagingState].
+     *
+     * @param nextState The next [PagingState] to update the state with.
+     */
+    fun update(nextState: PagingState<Id, K, P, D, E>) {
+
+        log(nextState)
+
+        _state.value = nextState
+    }
+
+    private fun log(nextState: PagingState<Id, K, P, D, E>) {
+        logger.value?.log(
+            """
+            Updating state:
+                Previous state: ${_state.value}
+                Next state: $nextState
+        """.trimIndent()
+        )
+    }
+}