Fix #1468: Retain Drag and Drop state after an incorrect answer

app/src/main/java/org/oppia/android/app/player/state/itemviewmodel/DragAndDropSortInteractionViewModel.kt

@@ -3,9 +3,13 @@ package org.oppia.android.app.player.state.itemviewmodel
 import androidx.annotation.StringRes
 import androidx.databinding.Observable
 import androidx.databinding.ObservableField
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MediatorLiveData
+import androidx.lifecycle.Transformations
 import androidx.recyclerview.widget.RecyclerView
 import org.oppia.android.R
 import org.oppia.android.app.model.AnswerErrorCategory
+import org.oppia.android.app.model.EphemeralState
 import org.oppia.android.app.model.Interaction
 import org.oppia.android.app.model.InteractionObject
 import org.oppia.android.app.model.ListOfSetsOfHtmlStrings
@@ -24,7 +28,10 @@ import org.oppia.android.app.recyclerview.BindableAdapter
 import org.oppia.android.app.recyclerview.OnDragEndedListener
 import org.oppia.android.app.recyclerview.OnItemDragListener
 import org.oppia.android.app.translation.AppLanguageResourceHandler
+import org.oppia.android.domain.exploration.ExplorationProgressController
 import org.oppia.android.domain.translation.TranslationController
+import org.oppia.android.util.data.AsyncResult
+import org.oppia.android.util.data.DataProviders.Companion.toLiveData
 import javax.inject.Inject
 
 /** Represents the type of errors that can be thrown by drag and drop sort interaction. */
@@ -49,11 +56,13 @@ class DragAndDropSortInteractionViewModel private constructor(
   private val writtenTranslationContext: WrittenTranslationContext,
   private val resourceHandler: AppLanguageResourceHandler,
   private val translationController: TranslationController,
-  userAnswerState: UserAnswerState
+  userAnswerState: UserAnswerState,
+  private val explorationProgressController: ExplorationProgressController
 ) : StateItemViewModel(ViewType.DRAG_DROP_SORT_INTERACTION),
   InteractionAnswerHandler,
   OnItemDragListener,
   OnDragEndedListener {
+
   private val allowMultipleItemsInSamePosition: Boolean by lazy {
     interaction.customizationArgsMap["allowMultipleItemsInSamePosition"]?.boolValue ?: false
   }
@@ -72,19 +81,18 @@ class DragAndDropSortInteractionViewModel private constructor(
       subtitledHtml.contentId to translatedHtml
     }
 
-  private var answerErrorCetegory: AnswerErrorCategory = AnswerErrorCategory.NO_ERROR
+  private var answerErrorCategory: AnswerErrorCategory = AnswerErrorCategory.NO_ERROR
 
-  private val _originalChoiceItems: MutableList<DragDropInteractionContentViewModel> =
+  private var _originalChoiceItems: MutableList<DragDropInteractionContentViewModel> =
     computeOriginalChoiceItems(contentIdHtmlMap, choiceSubtitledHtmls, this, resourceHandler)
 
-  private val _choiceItems = computeSelectedChoiceItems(
-    contentIdHtmlMap,
-    choiceSubtitledHtmls,
-    this,
-    resourceHandler,
-    userAnswerState
-  )
-  val choiceItems: List<DragDropInteractionContentViewModel> = _choiceItems
+  lateinit var choiceItems: LiveData<List<DragDropInteractionContentViewModel>>
+  private var _choiceItems: MutableList<DragDropInteractionContentViewModel> =
+    computeSelectedChoiceItems(
+      contentIdHtmlMap,
+      this,
+      resourceHandler
+    )
 
   private var pendingAnswerError: String? = null
   private val isAnswerAvailable = ObservableField(false)
@@ -170,7 +178,7 @@ class DragAndDropSortInteractionViewModel private constructor(
    * updates the error string based on the specified error category.
    */
   override fun checkPendingAnswerError(category: AnswerErrorCategory): String? {
-    answerErrorCetegory = category
+    answerErrorCategory = category
     pendingAnswerError = when (category) {
       AnswerErrorCategory.REAL_TIME -> null
       AnswerErrorCategory.SUBMIT_TIME ->
@@ -252,7 +260,8 @@ class DragAndDropSortInteractionViewModel private constructor(
   /** Implementation of [StateItemViewModel.InteractionItemFactory] for this view model. */
   class FactoryImpl @Inject constructor(
     private val resourceHandler: AppLanguageResourceHandler,
-    private val translationController: TranslationController
+    private val translationController: TranslationController,
+    private val explorationProgressController: ExplorationProgressController
   ) : InteractionItemFactory {
     override fun create(
       entityId: String,
@@ -275,15 +284,16 @@ class DragAndDropSortInteractionViewModel private constructor(
         writtenTranslationContext,
         resourceHandler,
         translationController,
-        userAnswerState
+        userAnswerState,
+        explorationProgressController
       )
     }
   }
 
   override fun getUserAnswerState(): UserAnswerState {
     if (_choiceItems == _originalChoiceItems) {
       return UserAnswerState.newBuilder().apply {
-        this.answerErrorCategory = answerErrorCetegory
+        this.answerErrorCategory = answerErrorCategory
       }.build()
     }
     return UserAnswerState.newBuilder().apply {
@@ -292,7 +302,7 @@ class DragAndDropSortInteractionViewModel private constructor(
         ListOfSetsOfTranslatableHtmlContentIds.newBuilder().apply {
           addAllContentIdLists(htmlContentIds)
         }.build()
-      answerErrorCategory = answerErrorCetegory
+      answerErrorCategory = answerErrorCategory
     }.build()
   }
 
@@ -324,25 +334,69 @@ class DragAndDropSortInteractionViewModel private constructor(
 
   private fun computeSelectedChoiceItems(
     contentIdHtmlMap: Map<String, String>,
-    choiceStrings: List<SubtitledHtml>,
     dragAndDropSortInteractionViewModel: DragAndDropSortInteractionViewModel,
-    resourceHandler: AppLanguageResourceHandler,
-    userAnswerState: UserAnswerState
+    resourceHandler: AppLanguageResourceHandler
   ): MutableList<DragDropInteractionContentViewModel> {
-    return if (userAnswerState.listOfSetsOfTranslatableHtmlContentIds.contentIdListsCount == 0) {
-      _originalChoiceItems.toMutableList()
-    } else {
-      userAnswerState.listOfSetsOfTranslatableHtmlContentIds.contentIdListsList
-        .mapIndexed { index, contentId ->
-          DragDropInteractionContentViewModel(
-            contentIdHtmlMap = contentIdHtmlMap,
-            htmlContent = contentId,
-            itemIndex = index,
-            listSize = choiceStrings.size,
-            dragAndDropSortInteractionViewModel = dragAndDropSortInteractionViewModel,
-            resourceHandler = resourceHandler
+    val explorationEphemeralStateLiveData = MediatorLiveData<AsyncResult<EphemeralState>>().apply {
+      value = AsyncResult.Pending()
+      addSource(explorationProgressController.getCurrentState().toLiveData()) { result ->
+        value = result
+      }
+    }
+
+    choiceItems = Transformations.map(explorationEphemeralStateLiveData) { result ->
+      when (result) {
+        is AsyncResult.Failure, is AsyncResult.Pending -> {
+          _originalChoiceItems
+        }
+        is AsyncResult.Success -> {
+          _choiceItems = processEphemeralStateResult(
+            result.value,
+            contentIdHtmlMap,
+            dragAndDropSortInteractionViewModel,
+            resourceHandler
           )
-        }.toMutableList()
+          _originalChoiceItems = _choiceItems.toMutableList()
+          _choiceItems
+        }
+        else -> _originalChoiceItems
+      }
+    }
+
+    return _choiceItems.takeIf { !it.isNullOrEmpty() }
+      ?: _originalChoiceItems.toMutableList()
+  }
+
+  private fun processEphemeralStateResult(
+    state: EphemeralState,
+    contentIdHtmlMap: Map<String, String>,
+    dragAndDropSortInteractionViewModel: DragAndDropSortInteractionViewModel,
+    resourceHandler: AppLanguageResourceHandler
+  ): MutableList<DragDropInteractionContentViewModel> {
+    val wrongAnswerList = state.pendingState.wrongAnswerList
+    return if (wrongAnswerList.isNotEmpty()) {
+      val latestWrongAnswerContentIdList = wrongAnswerList.last()
+        .userAnswer.answer.listOfSetsOfTranslatableHtmlContentIds.contentIdListsList
+      latestWrongAnswerContentIdList.mapIndexed { index, setOfTranslatableHtmlContentIds ->
+        DragDropInteractionContentViewModel(
+          contentIdHtmlMap = contentIdHtmlMap,
+          htmlContent = SetOfTranslatableHtmlContentIds.newBuilder().apply {
+            for (contentIds in setOfTranslatableHtmlContentIds.contentIdsList) {
+              addContentIds(
+                TranslatableHtmlContentId.newBuilder().apply {
+                  contentId = contentIds.contentId
+                }
+              )
+            }
+          }.build(),
+          itemIndex = index,
+          listSize = latestWrongAnswerContentIdList.size,
+          dragAndDropSortInteractionViewModel = dragAndDropSortInteractionViewModel,
+          resourceHandler = resourceHandler
+        )
+      }.toMutableList()
+    } else {
+      _originalChoiceItems.toMutableList()
     }
   }
 }