Fix part of #4: Introduce domain module (#64)

* Migrate ListenableFuture to a Kotlin coroutine, and split HomeActivity
into both an activity and a fragment.

* Introduce the domain and testsupport modules.

The domain module includes a user app history controller that provides
instances of a new AsyncResult interface that's meant to be a potential
bridge between Kotlin coroutines and LiveData. The exact design of how
this should work needs to be determined as part of #6.

This also includes a new testsupport module that's required due to
robolectric/robolectric#4736. This is supporting a
new test for the app history controller that leverages an AndroidX
activity scenario to test the live data.

Note that the test does not yet work since there's a race condition
between the LiveData's coroutines completing and the test continuing to
verify the state of the activity. This needs to be resolved, likely by
waiting for test visual elements to change based on the LiveData result.

Additional tests need to be added for other new components, and some
slight cleaning up may be necessary.

* Fix binary build: testsupport should only be depended on for tests, not
for production configurations.

* Further attempts to try and test the asynchronous behavior of the new
LiveData + kotlin coroutine system.

This introduces a custom LiveData to mediate between Kotlin coroutines
in a way that allows tests to actually ensure the coroutines resolve
quickly, and ensure lifecycle safety through standard LiveData
mechanisms.

However, this doesn't actually fix the underlying tests (which have been
changed in a number of ways in this commit in an effort to try and get
them to pass). The kotlinx coroutine deps were downgraded to work around
a NoSuchMethodError (see
Kotlin/kotlinx.coroutines#1331). After
introducing a runBlockingTest structure and updating the user app
histoyr controller to use the test context, the operations seem to work
correctly. However, one job is hanging which is causing the test to
still fail (it appears to be deadlocked--no known amount of time allows
it to resolve).

This new NotifiableAsyncLiveData also appears to break the production
behavior, as well. The LiveData result is no longer being observed by
the data binding transformation function, so it seems the coroutines
aren't being executed, aren't completing, or something is deadlocking
somewhere. Further investigation is needed.

* Fix the app not properly binding to the live data by ensuring the data
binder had the view model set properly. Fix resource binding issues in
Robolectric tests by ensuring binary resources are provided to
Robolectric. Fix the controller tests not working by introducing a
temporary, custom CoroutineLiveData that ensures no long-living jobs
continue running after the live data is completed.

* Clean up tests (we no longer need a testsupport module for this module
introduction).

* Add test for AsyncResult. Set code style for Groovy files & clean up all
build gradle files. Add missing newlines at end of various files.

* Reformat top-level build.gradle file, as well.

* Address review comments: replace name-based TODOs with issues.

* Address review comments: add EOF new lines.

.gitignore

@@ -8,6 +8,7 @@
 /.idea/navEditor.xml
 /.idea/assetWizardSettings.xml
 app/build
+domain/build
 model/build
 utility/build
 .DS_Store

app/build.gradle

@@ -1,65 +1,71 @@
 apply plugin: 'com.android.application'
-
 apply plugin: 'kotlin-android'
-
 apply plugin: 'kotlin-android-extensions'
 
 android {
-    compileSdkVersion 29
-    buildToolsVersion "29.0.1"
-    defaultConfig {
-        applicationId "org.oppia.app"
-        minSdkVersion 16
-        targetSdkVersion 28
-        versionCode 1
-        versionName "1.0"
-        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+  compileSdkVersion 29
+  buildToolsVersion "29.0.1"
+  defaultConfig {
+    applicationId "org.oppia.app"
+    minSdkVersion 16
+    targetSdkVersion 28
+    versionCode 1
+    versionName "1.0"
+    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+  }
+  buildTypes {
+    release {
+      minifyEnabled false
+      proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
     }
-    buildTypes {
-        release {
-            minifyEnabled false
-            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
-        }
-    }
-    testOptions {
-        unitTests {
-            includeAndroidResources = true
-        }
+  }
+  dataBinding {
+    enabled = true
+  }
+  testOptions {
+    unitTests {
+      includeAndroidResources = true
     }
+  }
 
-    // https://proandroiddev.com/isolated-fragments-unit-tests-that-run-both-instrumented-and-on-the-jvm-with-the-same-source-code-283db2e9be5d
-    sourceSets {
-        androidTest {
-            java.srcDirs += "src/sharedTest/java"
-            kotlin.srcDirs += "src/sharedTest/java"
-        }
-        test {
-            java.srcDirs += "src/sharedTest/java"
-            kotlin.srcDirs += "src/sharedTest/java"
-        }
+  // https://proandroiddev.com/isolated-fragments-unit-tests-that-run-both-instrumented-and-on-the-jvm-with-the-same-source-code-283db2e9be5d
+  sourceSets {
+    androidTest {
+      java.srcDirs += "src/sharedTest/java"
+      kotlin.srcDirs += "src/sharedTest/java"
+    }
+    test {
+      java.srcDirs += "src/sharedTest/java"
+      kotlin.srcDirs += "src/sharedTest/java"
     }
+  }
 }
 
 dependencies {
-    implementation fileTree(dir: 'libs', include: ['*.jar'])
-    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
-    implementation 'androidx.appcompat:appcompat:1.0.2'
-    implementation 'androidx.core:core-ktx:1.0.2'
-    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
-    api 'com.google.guava:guava:28.0-android'
-
-    testImplementation 'androidx.test:core:1.2.0'
-    testImplementation 'androidx.test.ext:junit:1.1.1'
-    testImplementation 'org.robolectric:robolectric:4.3'
-    testImplementation "com.google.truth:truth:0.43"
-    testImplementation 'androidx.test.espresso:espresso-core:3.2.0'
-
-    androidTestImplementation 'androidx.test:core:1.2.0'
-    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
-    androidTestImplementation 'androidx.test:runner:1.2.0'
-    androidTestImplementation "com.google.truth:truth:0.43"
-    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
-
-    implementation project(":model")
-    implementation project(":utility")
+  implementation fileTree(dir: 'libs', include: ['*.jar'])
+  implementation(
+      'android.arch.lifecycle:extensions:1.1.1',
+      'androidx.appcompat:appcompat:1.0.2',
+      'androidx.constraintlayout:constraintlayout:1.1.3',
+      'androidx.core:core-ktx:1.0.2',
+      'androidx.lifecycle:lifecycle-runtime-ktx:2.2.0-alpha03',
+      "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version",
+  )
+  testImplementation(
+      'androidx.test:core:1.2.0',
+      'androidx.test.espresso:espresso-core:3.2.0',
+      'androidx.test.ext:junit:1.1.1',
+      'com.google.truth:truth:0.43',
+      'org.robolectric:robolectric:4.3',
+  )
+  androidTestImplementation(
+      'androidx.test:core:1.2.0',
+      'androidx.test.espresso:espresso-core:3.2.0',
+      'androidx.test.ext:junit:1.1.1',
+      'androidx.test:runner:1.2.0',
+      'com.google.truth:truth:0.43',
+  )
+  implementation project(":model")
+  implementation project(":domain")
+  implementation project(":utility")
 }

app/src/main/java/org/oppia/app/HomeActivity.kt

@@ -1,52 +1,14 @@
 package org.oppia.app
 
-import androidx.appcompat.app.AppCompatActivity
 import android.os.Bundle
-import android.util.Log
-import android.widget.TextView
-import com.google.common.util.concurrent.FutureCallback
-import com.google.common.util.concurrent.Futures
-import com.google.common.util.concurrent.ListenableFuture
-import com.google.common.util.concurrent.MoreExecutors.directExecutor
-import org.oppia.app.model.UserAppHistory
-import org.oppia.util.data.AsyncDataSource
+import androidx.appcompat.app.AppCompatActivity
 
 /** The central activity for all users entering the app. */
 class HomeActivity : AppCompatActivity() {
 
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     setContentView(R.layout.home_activity)
-  }
-
-  override fun onStart() {
-    super.onStart()
-    // TODO(BenHenning): Convert this to LiveData rather than risk an async operation completing outside of the
-    // activity's lifecycle. Also, a directExecutor() in this context could be a really bad idea if it isn't the main
-    // thread.
-    Futures.addCallback(getUserAppHistory().pendingOperation, object: FutureCallback<UserAppHistory> {
-      override fun onSuccess(result: UserAppHistory?) {
-        if (result != null && result.alreadyOpenedApp) {
-          getWelcomeTextView().setText(R.string.welcome_back_text)
-        }
-      }
-
-      override fun onFailure(t: Throwable) {
-        // TODO(BenHenning): Replace this log statement with a clearer logging API.
-        Log.e("HomeActivity", "Failed to retrieve user app history", t)
-      }
-    }, directExecutor())
-  }
-
-  private fun getWelcomeTextView(): TextView {
-    return findViewById(R.id.welcome_text_view)
-  }
-
-  private fun getUserAppHistory(): AsyncDataSource<UserAppHistory> {
-    // TODO(BenHenning): Retrieve this from a domain provider.
-    return object: AsyncDataSource<UserAppHistory> {
-      override val pendingOperation: ListenableFuture<UserAppHistory>
-        get() = Futures.immediateFuture(UserAppHistory.newBuilder().setAlreadyOpenedApp(false).build())
-    }
+    supportFragmentManager.beginTransaction().add(R.id.home_fragment_placeholder, HomeFragment()).commitNow()
   }
 }

app/src/main/java/org/oppia/app/HomeFragment.kt

@@ -0,0 +1,55 @@
+package org.oppia.app
+
+import android.os.Bundle
+import android.util.Log
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import androidx.fragment.app.Fragment
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.Transformations
+import androidx.lifecycle.ViewModelProviders
+import org.oppia.app.databinding.HomeFragmentBinding
+import org.oppia.app.model.UserAppHistory
+import org.oppia.domain.UserAppHistoryController
+import org.oppia.util.data.AsyncResult
+
+/** Fragment that contains an introduction to the app. */
+class HomeFragment : Fragment() {
+  private val userAppHistoryController = UserAppHistoryController()
+
+  override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
+    val binding = HomeFragmentBinding.inflate(inflater, container, /* attachToRoot= */ false)
+    val viewModel = getUserAppHistoryViewModel()
+    val appUserHistory = getUserAppHistory()
+    viewModel.userAppHistoryLiveData = appUserHistory
+    // NB: Both the view model and lifecycle owner must be set in order to correctly bind LiveData elements to
+    // data-bound view models.
+    binding.let {
+      it.viewModel = viewModel
+      it.lifecycleOwner = this
+    }
+
+    // TODO(#70): Mark that the user opened the app once it's persisted to disk.
+
+    return binding.root
+  }
+
+  private fun getUserAppHistoryViewModel(): UserAppHistoryViewModel {
+    return ViewModelProviders.of(this).get(UserAppHistoryViewModel::class.java)
+  }
+
+  private fun getUserAppHistory(): LiveData<UserAppHistory> {
+    // If there's an error loading the data, assume the default.
+    return Transformations.map(
+      userAppHistoryController.getUserAppHistory()
+    ) { result: AsyncResult<UserAppHistory> -> processUserAppHistoryResult(result) }
+  }
+
+  private fun processUserAppHistoryResult(appHistoryResult: AsyncResult<UserAppHistory>): UserAppHistory {
+    if (appHistoryResult.isFailure()) {
+      Log.e("HomeFragment", "Failed to retrieve user app history", appHistoryResult.error)
+    }
+    return appHistoryResult.getOrDefault(UserAppHistory.getDefaultInstance())
+  }
+}

app/src/main/java/org/oppia/app/UserAppHistoryViewModel.kt

@@ -0,0 +1,10 @@
+package org.oppia.app
+
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.ViewModel
+import org.oppia.app.model.UserAppHistory
+
+/** [ViewModel] for user app usage history. */
+class UserAppHistoryViewModel: ViewModel() {
+  var userAppHistoryLiveData: LiveData<UserAppHistory>? = null
+}

app/src/main/res/layout/home_activity.xml

@@ -1,20 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
-<androidx.constraintlayout.widget.ConstraintLayout
+<FrameLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
-  xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
+  android:id="@+id/home_fragment_placeholder"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
-  tools:context=".HomeActivity">
-
-  <TextView
-    android:id="@+id/welcome_text_view"
-    android:layout_width="wrap_content"
-    android:layout_height="wrap_content"
-    android:text="@string/welcome_text"
-    app:layout_constraintBottom_toBottomOf="parent"
-    app:layout_constraintLeft_toLeftOf="parent"
-    app:layout_constraintRight_toRightOf="parent"
-    app:layout_constraintTop_toTopOf="parent" />
-
-</androidx.constraintlayout.widget.ConstraintLayout>
+  tools:context=".HomeActivity" />

app/src/main/res/layout/home_fragment.xml

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layout
+  xmlns:android="http://schemas.android.com/apk/res/android"
+  xmlns:app="http://schemas.android.com/apk/res-auto">
+
+  <data>
+    <import type="org.oppia.app.R"/>
+    <variable
+      name="viewModel"
+      type="org.oppia.app.UserAppHistoryViewModel"/>
+  </data>
+
+  <androidx.constraintlayout.widget.ConstraintLayout
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+
+    <TextView
+      android:id="@+id/welcome_text_view"
+      android:layout_width="wrap_content"
+      android:layout_height="wrap_content"
+      android:text="@{viewModel.userAppHistoryLiveData.getAlreadyOpenedApp() ? R.string.welcome_back_text : R.string.welcome_text}"
+      app:layout_constraintBottom_toBottomOf="parent"
+      app:layout_constraintLeft_toLeftOf="parent"
+      app:layout_constraintRight_toRightOf="parent"
+      app:layout_constraintTop_toTopOf="parent"/>
+
+  </androidx.constraintlayout.widget.ConstraintLayout>
+</layout>

build.gradle

@@ -1,27 +1,27 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
-    ext.kotlin_version = '1.3.41'
-    repositories {
-        google()
-        jcenter()
-    }
-    dependencies {
-        classpath 'com.android.tools.build:gradle:3.4.2'
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-        classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.10'
-        // NOTE: Do not place your application dependencies here; they belong
-        // in the individual module build.gradle files
-    }
+  ext.kotlin_version = '1.3.41'
+  repositories {
+    google()
+    jcenter()
+  }
+  dependencies {
+    classpath 'com.android.tools.build:gradle:3.4.2'
+    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.10'
+    // NOTE: Do not place your application dependencies here; they belong
+    // in the individual module build.gradle files
+  }
 }
 
 allprojects {
-    repositories {
-        google()
-        jcenter()
-    }
+  repositories {
+    google()
+    jcenter()
+  }
 }
 
 task clean(type: Delete) {
-    delete rootProject.buildDir
+  delete rootProject.buildDir
 }