Async API improvements "v2" (#672)

* Async API improvements "v2"

**NB: This PR actually changes only 3 files in `libraries/architecture/`. All the other changes are automated refactors to fix the calling code.**

This is a proposal for improvements to our `Async` type as discussed in: https://github.com/vector-im/element-x-android/pull/598/files#r1230664392 and in other chats.

Please bear in mind it is just a proposal, I'd love to hear your feedback about it, especially when it comes to naming: I've tried to make parameter and function names use a terminology similar to what we find in the Kotlin stdlib and its `Result` type.

I'm inclined to like more the non-extension flavours of the new `run*` APIs, though I'd also like your feedback about what API shape you prefer.

### Summary of the changes:
#### Functional
- Adds `exceptionOrNull()` API to complement the existing `dataOrNull()` API.
- Adds `isFailure()`, `isLoading()`, `isSuccess()` and `isUninitialized()` courtesy APIs.
- Renames `executeResult()` to `runUpdatingState()`:
	- Becomes the base API to which all the other similarly named APIs call into.
	- Makes it inline.
	- Adds contract.
	- Passes over any `prevData` to newre Async states.
	- Passes through the `block`s return value.
	- Adds unit tests.
- Renames `execute` to `runCatchingUpdatingState()` and makes it just call into `runUpdatingState()`
- Adds extension function overloads to the `run*` functions to accept `MutableState` as receiver

#### Cosmetics
- Reorders classes and methods in alphabetic order.
- Reorder parameter names to mimic conventions in Kotlin stdlib.
- Adds docstrings where useful.

* Use `fold()`

* rename pop to popFirst

* Add docstrings

* Please Detekt

* Rename exception to error.

* Please detekt

* Update existing usages.

libraries/architecture/build.gradle.kts

@@ -26,4 +26,8 @@ dependencies {
     api(libs.dagger)
     api(libs.appyx.core)
     api(libs.androidx.lifecycle.runtime)
+
+    testImplementation(libs.test.junit)
+    testImplementation(libs.coroutines.test)
+    testImplementation(libs.test.truth)
 }

libraries/architecture/src/main/kotlin/io/element/android/libraries/architecture/Async.kt

@@ -18,51 +18,152 @@ package io.element.android.libraries.architecture
 
 import androidx.compose.runtime.MutableState
 import androidx.compose.runtime.Stable
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 
+/**
+ * Sealed type that allows to model an asynchronous operation.
+ */
 @Stable
 sealed interface Async<out T> {
+
+    /**
+     * Represents a failed operation.
+     *
+     * @param T the type of data returned by the operation.
+     * @property error the error that caused the operation to fail.
+     * @property prevData the data returned by a previous successful run of the operation if any.
+     */
+    data class Failure<out T>(
+        val error: Throwable,
+        val prevData: T? = null,
+    ) : Async<T>
+
+    /**
+     * Represents an operation that is currently ongoing.
+     *
+     * @param T the type of data returned by the operation.
+     * @property prevData the data returned by a previous successful run of the operation if any.
+     */
+    data class Loading<out T>(
+        val prevData: T? = null,
+    ) : Async<T>
+
+    /**
+     * Represents a successful operation.
+     *
+     * @param T the type of data returned by the operation.
+     * @property data the data returned by the operation.
+     */
+    data class Success<out T>(
+        val data: T,
+    ) : Async<T>
+
+    /**
+     * Represents an uninitialized operation (i.e. yet to be run).
+     */
     object Uninitialized : Async<Nothing>
-    data class Loading<out T>(val prevState: T? = null) : Async<T>
-    data class Failure<out T>(val error: Throwable, val prevState: T? = null) : Async<T>
-    data class Success<out T>(val state: T) : Async<T>
 
-    fun dataOrNull(): T? {
-        return when (this) {
-            is Failure -> prevState
-            is Loading -> prevState
-            is Success -> state
-            Uninitialized -> null
+    /**
+     * Returns the data returned by the operation, or null otherwise.
+     *
+     * Please note this method may return stale data if the operation is not [Success].
+     */
+    fun dataOrNull(): T? = when (this) {
+        is Failure -> prevData
+        is Loading -> prevData
+        is Success -> data
+        Uninitialized -> null
+    }
+
+    /**
+     * Returns the error that caused the operation to fail, or null otherwise.
+     */
+    fun errorOrNull(): Throwable? = when (this) {
+        is Failure -> error
+        else -> null
+    }
+
+    fun isFailure(): Boolean = this is Failure<T>
+
+    fun isLoading(): Boolean = this is Loading<T>
+
+    fun isSuccess(): Boolean = this is Success<T>
+
+    fun isUninitialized(): Boolean = this == Uninitialized
+}
+
+suspend inline fun <T> MutableState<Async<T>>.runCatchingUpdatingState(
+    errorTransform: (Throwable) -> Throwable = { it },
+    block: () -> T,
+): Result<T> = runUpdatingState(
+    state = this,
+    errorTransform = errorTransform,
+    resultBlock = {
+        runCatching {
+            block()
         }
-    }
-}
+    },
+)
 
-suspend inline fun <T> (suspend () -> T).execute(
+suspend inline fun <T> (suspend () -> T).runCatchingUpdatingState(
     state: MutableState<Async<T>>,
-    errorMapping: ((Throwable) -> Throwable) = { it },
-) {
-    try {
-        state.value = Async.Loading()
-        val result = this()
-        state.value = Async.Success(result)
-    } catch (error: Throwable) {
-        state.value = Async.Failure(errorMapping.invoke(error))
-    }
-}
+    errorTransform: (Throwable) -> Throwable = { it },
+): Result<T> = runUpdatingState(
+    state = state,
+    errorTransform = errorTransform,
+    resultBlock = {
+        runCatching {
+            this()
+        }
+    },
+)
 
-suspend inline fun <T> (suspend () -> Result<T>).executeResult(state: MutableState<Async<T>>) {
-    if (state.value !is Async.Success) {
-        state.value = Async.Loading()
+suspend inline fun <T> MutableState<Async<T>>.runUpdatingState(
+    errorTransform: (Throwable) -> Throwable = { it },
+    resultBlock: () -> Result<T>,
+): Result<T> = runUpdatingState(
+    state = this,
+    errorTransform = errorTransform,
+    resultBlock = resultBlock,
+)
+
+/**
+ * Calls the specified [Result]-returning function [resultBlock]
+ * encapsulating its progress and return value into an [Async] while
+ * posting its updates to the MutableState [state].
+ *
+ * @param T the type of data returned by the operation.
+ * @param state the [MutableState] to post updates to.
+ * @param errorTransform a function to transform the error before posting it.
+ * @param resultBlock a suspending function that returns a [Result].
+ * @return the [Result] returned by [resultBlock].
+ */
+@OptIn(ExperimentalContracts::class)
+@Suppress("REDUNDANT_INLINE_SUSPEND_FUNCTION_TYPE")
+suspend inline fun <T> runUpdatingState(
+    state: MutableState<Async<T>>,
+    errorTransform: (Throwable) -> Throwable = { it },
+    resultBlock: suspend () -> Result<T>,
+): Result<T> {
+    contract {
+        callsInPlace(resultBlock, InvocationKind.EXACTLY_ONCE)
     }
-    this().fold(
+    val prevData = state.value.dataOrNull()
+    state.value = Async.Loading(prevData = prevData)
+    return resultBlock().fold(
         onSuccess = {
             state.value = Async.Success(it)
+            Result.success(it)
         },
         onFailure = {
-            state.value = Async.Failure(it)
+            val error = errorTransform(it)
+            state.value = Async.Failure(
+                error = error,
+                prevData = prevData,
+            )
+            Result.failure(error)
         }
     )
 }
-
-fun <T> Async<T>.isLoading(): Boolean {
-    return this is Async.Loading<T>
-}

libraries/architecture/src/test/kotlin/io/element/android/libraries/architecture/AsyncKtTest.kt

@@ -0,0 +1,113 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.element.android.libraries.architecture
+
+import androidx.compose.runtime.MutableState
+import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.test.runTest
+import org.junit.Test
+
+class AsyncKtTest {
+    @Test
+    fun `updates state when block returns success`() = runTest {
+        val state = TestableMutableState<Async<Int>>(Async.Uninitialized)
+
+        val result = runUpdatingState(state) {
+            delay(1)
+            Result.success(1)
+        }
+
+        assertThat(result.isSuccess).isTrue()
+        assertThat(result.getOrNull()).isEqualTo(1)
+
+        assertThat(state.popFirst()).isEqualTo(Async.Uninitialized)
+        assertThat(state.popFirst()).isEqualTo(Async.Loading(null))
+        assertThat(state.popFirst()).isEqualTo(Async.Success(1))
+        state.assertNoMoreValues()
+    }
+
+    @Test
+    fun `updates state when block returns failure`() = runTest {
+        val state = TestableMutableState<Async<Int>>(Async.Uninitialized)
+
+        val result = runUpdatingState(state) {
+            delay(1)
+            Result.failure(MyThrowable("hello"))
+        }
+
+        assertThat(result.isFailure).isTrue()
+        assertThat(result.exceptionOrNull()).isEqualTo(MyThrowable("hello"))
+
+        assertThat(state.popFirst()).isEqualTo(Async.Uninitialized)
+        assertThat(state.popFirst()).isEqualTo(Async.Loading(null))
+        assertThat(state.popFirst()).isEqualTo(Async.Failure<Int>(MyThrowable("hello")))
+        state.assertNoMoreValues()
+    }
+
+    @Test
+    fun `updates state when block returns failure transforming the error`() = runTest {
+        val state = TestableMutableState<Async<Int>>(Async.Uninitialized)
+
+        val result = runUpdatingState(state, { MyThrowable(it.message + " world") }) {
+            delay(1)
+            Result.failure(MyThrowable("hello"))
+        }
+
+        assertThat(result.isFailure).isTrue()
+        assertThat(result.exceptionOrNull()).isEqualTo(MyThrowable("hello world"))
+
+        assertThat(state.popFirst()).isEqualTo(Async.Uninitialized)
+        assertThat(state.popFirst()).isEqualTo(Async.Loading(null))
+        assertThat(state.popFirst()).isEqualTo(Async.Failure<Int>(MyThrowable("hello world")))
+        state.assertNoMoreValues()
+    }
+}
+
+/**
+ * A fake [MutableState] that allows to record all the states that were set.
+ */
+private class TestableMutableState<T>(
+    value: T
+) : MutableState<T> {
+
+    private val _deque = ArrayDeque<T>(listOf(value))
+
+    override var value: T
+        get() = _deque.last()
+        set(value) {
+            _deque.addLast(value)
+        }
+
+    /**
+     * Returns the states that were set in the order they were set.
+     */
+    fun popFirst(): T = _deque.removeFirst()
+
+    fun assertNoMoreValues() {
+        assertThat(_deque).isEmpty()
+    }
+
+    override operator fun component1(): T = value
+
+    override operator fun component2(): (T) -> Unit = { value = it }
+}
+
+/**
+ * An exception that is also a data class so we can compare it using equals.
+ */
+private data class MyThrowable(val myMessage: String) : Throwable(myMessage)