Add createSynchronizedStoreEnhancer function

`createSynchronizedStoreEnhancer` generates a store enhancer that wraps a Redux store in a synchronization object, causing access to store methods to be synchronized. Recommended usecase is when using a thread-safe store with enhancers or middleware that require access to store methods.

Author: Jenn Kao

redux-kotlin-threadsafe/src/commonMain/kotlin/org/reduxkotlin/Enhancers.kt

@@ -0,0 +1,22 @@
+package org.reduxkotlin
+
+/**
+ * Creates a store enhancer that wraps a Redux store in a synchronization object,
+ * causing access to store methods to be synchronized.
+ *
+ * See `SynchronizedStore` for implementation of synchronization.
+ *
+ * This enhancer should be placed after all other enhancers that involve access to store methods in
+ * the composition chain, as this will result in those enhancers receiving the synchronized store object.
+
+ * @returns {StoreEnhancer} A store enhancer that synchronizes the store.
+ */
+fun <State> createSynchronizedStoreEnhancer(): StoreEnhancer<State> {
+    return { storeCreator ->
+        { reducer, initialState, en: Any? ->
+            val store = storeCreator(reducer, initialState, en)
+            val synchronizedStore = SynchronizedStore(store)
+            synchronizedStore
+        }
+    }
+}

redux-kotlin-threadsafe/src/jvmTest/kotlin/org/reduxkotlin/util/CreateThreadSafeStoreSpec.kt

@@ -7,48 +7,101 @@ import kotlinx.coroutines.runBlocking
 import kotlinx.coroutines.withContext
 import org.junit.Test
 import org.reduxkotlin.createThreadSafeStore
+import org.reduxkotlin.applyMiddleware
+import org.reduxkotlin.createStore
+import org.reduxkotlin.createSynchronizedStoreEnhancer
+import org.reduxkotlin.compose
+import org.reduxkotlin.Dispatcher
+import org.reduxkotlin.GetState
+import org.reduxkotlin.Middleware
+import java.util.Timer
+import kotlin.concurrent.timerTask
 import kotlin.system.measureTimeMillis
 import kotlin.test.assertEquals
 
 class MultiThreadedClass {
-    @Test
-    fun multithreadedIncrementsMassively() {
-        suspend fun massiveRun(action: suspend () -> Unit) {
-            val n = 100 // number of coroutines to launch
-            val k = 1000 // times an action is repeated by each coroutine
-            val time = measureTimeMillis {
-                coroutineScope {
-                    // scope for coroutines
-                    repeat(n) {
-                        launch {
-                            repeat(k) { action() }
-                        }
+    private suspend fun massiveRun(numCoroutines: Int, numRepeats: Int, action: suspend () -> Unit) {
+        val time = measureTimeMillis {
+            coroutineScope {
+                repeat(numCoroutines) {
+                    launch {
+                        repeat(numRepeats) { action() }
                     }
                 }
             }
-            println("Completed ${n * k} actions in $time ms")
         }
+        println("Completed ${numCoroutines * numRepeats} actions in $time ms")
+    }
 
+    @Test
+    fun multithreadedIncrementsMassively() {
         // NOTE: changing this to createStore() breaks the tests
-        val store = createThreadSafeStore(counterReducer, TestCounterState())
+        val store = createThreadSafeStore(counterReducer, TestState())
         runBlocking {
             withContext(Dispatchers.Default) {
-                massiveRun {
+                massiveRun(100, 1000) {
                     store.dispatch(Increment())
                 }
             }
             assertEquals(100000, store.state.counter)
         }
     }
+
+    @Test
+    fun multithreadedIncrementsMassivelyWithEnhancer() {
+        val store = createStore(counterReducer, TestState(), compose(
+            applyMiddleware(createTestThunkMiddleware()),
+                createSynchronizedStoreEnhancer() // needs to be placed after enhancers that requires synchronized store methods
+        ))
+        runBlocking {
+            withContext(Dispatchers.Default) {
+                massiveRun(10, 100) {
+                    store.dispatch(incrementThunk())
+                }
+            }
+            // wait to assert to account for the last of thunk delays
+            Timer().schedule(timerTask {
+                assertEquals(10000, store.state.counter)
+            }, 50)
+        }
+    }
 }
 
 class Increment
 
-data class TestCounterState(val counter: Int = 0)
+data class TestState(val counter: Int = 0)
 
-val counterReducer = { state: TestCounterState, action: Any ->
+val counterReducer = { state: TestState, action: Any ->
     when (action) {
         is Increment -> state.copy(counter = state.counter + 1)
         else -> state
     }
 }
+
+// Enhancer mimics the behavior of `createThunkMiddleware` provided by the redux-kotlin-thunk library
+typealias TestThunk<State> = (dispatch: Dispatcher, getState: GetState<State>, extraArg: Any?) -> Any
+fun <State> createTestThunkMiddleware(): Middleware<State> =
+    { store ->
+        { next: Dispatcher ->
+            { action: Any ->
+                if (action is Function<*>) {
+                    @Suppress("UNCHECKED_CAST")
+                    val thunk = try {
+                        (action as TestThunk<*>)
+                    } catch (e: ClassCastException) {
+                        throw IllegalArgumentException("Require type TestThunk", e)
+                    }
+                    thunk(store.dispatch, store.getState, null)
+                } else {
+                    next(action)
+                }
+            }
+        }
+    }
+
+fun incrementThunk(): TestThunk<TestState> = { dispatch, getState, _ ->
+    Timer().schedule(timerTask {
+        dispatch(Increment())
+    }, 50)
+    getState()
+}