Merge "Minimize a Task whenever we reach the Desktop Task limit" into main
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java b/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
index 1408ead..26e7acb 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/WMShellModule.java
@@ -29,6 +29,7 @@
 import com.android.internal.logging.UiEventLogger;
 import com.android.internal.statusbar.IStatusBarService;
 import com.android.launcher3.icons.IconProvider;
+import com.android.window.flags.Flags;
 import com.android.wm.shell.RootTaskDisplayAreaOrganizer;
 import com.android.wm.shell.ShellTaskOrganizer;
 import com.android.wm.shell.WindowManagerShellWrapper;
@@ -59,6 +60,7 @@
 import com.android.wm.shell.desktopmode.DesktopModeStatus;
 import com.android.wm.shell.desktopmode.DesktopModeTaskRepository;
 import com.android.wm.shell.desktopmode.DesktopTasksController;
+import com.android.wm.shell.desktopmode.DesktopTasksLimiter;
 import com.android.wm.shell.desktopmode.DesktopTasksTransitionObserver;
 import com.android.wm.shell.desktopmode.DragToDesktopTransitionHandler;
 import com.android.wm.shell.desktopmode.EnterDesktopTaskTransitionHandler;
@@ -517,23 +519,39 @@
             LaunchAdjacentController launchAdjacentController,
             RecentsTransitionHandler recentsTransitionHandler,
             MultiInstanceHelper multiInstanceHelper,
-            @ShellMainThread ShellExecutor mainExecutor
-    ) {
+            @ShellMainThread ShellExecutor mainExecutor,
+            Optional<DesktopTasksLimiter> desktopTasksLimiter) {
         return new DesktopTasksController(context, shellInit, shellCommandHandler, shellController,
                 displayController, shellTaskOrganizer, syncQueue, rootTaskDisplayAreaOrganizer,
                 dragAndDropController, transitions, enterDesktopTransitionHandler,
                 exitDesktopTransitionHandler, toggleResizeDesktopTaskTransitionHandler,
                 dragToDesktopTransitionHandler, desktopModeTaskRepository,
                 desktopModeLoggerTransitionObserver, launchAdjacentController,
-                recentsTransitionHandler, multiInstanceHelper, mainExecutor);
+                recentsTransitionHandler, multiInstanceHelper, mainExecutor, desktopTasksLimiter);
     }
 
     @WMSingleton
     @Provides
+    static Optional<DesktopTasksLimiter> provideDesktopTasksLimiter(
+            Transitions transitions,
+            @DynamicOverride DesktopModeTaskRepository desktopModeTaskRepository,
+            ShellTaskOrganizer shellTaskOrganizer) {
+        if (!DesktopModeStatus.isEnabled() || !Flags.enableDesktopWindowingTaskLimit()) {
+            return Optional.empty();
+        }
+        return Optional.of(
+                new DesktopTasksLimiter(
+                        transitions, desktopModeTaskRepository, shellTaskOrganizer));
+    }
+
+
+    @WMSingleton
+    @Provides
     static DragToDesktopTransitionHandler provideDragToDesktopTransitionHandler(
             Context context,
             Transitions transitions,
-            RootTaskDisplayAreaOrganizer rootTaskDisplayAreaOrganizer) {
+            RootTaskDisplayAreaOrganizer rootTaskDisplayAreaOrganizer,
+            Optional<DesktopTasksLimiter> desktopTasksLimiter) {
         return new DragToDesktopTransitionHandler(context, transitions,
                 rootTaskDisplayAreaOrganizer);
     }
@@ -541,7 +559,8 @@
     @WMSingleton
     @Provides
     static EnterDesktopTaskTransitionHandler provideEnterDesktopModeTaskTransitionHandler(
-            Transitions transitions) {
+            Transitions transitions,
+            Optional<DesktopTasksLimiter> desktopTasksLimiter) {
         return new EnterDesktopTaskTransitionHandler(transitions);
     }
 
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeStatus.java b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeStatus.java
index 32c22c0..fcddcad 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeStatus.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeStatus.java
@@ -77,6 +77,22 @@
             "persist.wm.debug.desktop_mode_enforce_device_restrictions", true);
 
     /**
+     * Default value for {@code MAX_TASK_LIMIT}.
+     */
+    @VisibleForTesting
+    public static final int DEFAULT_MAX_TASK_LIMIT = 4;
+
+    // TODO(b/335131008): add a config-overlay field for the max number of tasks in Desktop Mode
+    /**
+     * Flag declaring the maximum number of Tasks to show in Desktop Mode at any one time.
+     *
+     * <p> The limit does NOT affect Picture-in-Picture, Bubbles, or System Modals (like a screen
+     * recording window, or Bluetooth pairing window).
+     */
+    private static final int MAX_TASK_LIMIT = SystemProperties.getInt(
+            "persist.wm.debug.desktop_max_task_limit", DEFAULT_MAX_TASK_LIMIT);
+
+    /**
      * Return {@code true} if desktop windowing is enabled
      */
     public static boolean isEnabled() {
@@ -124,6 +140,13 @@
     }
 
     /**
+     * Return the maximum limit on the number of Tasks to show in Desktop Mode at any one time.
+     */
+    static int getMaxTaskLimit() {
+        return MAX_TASK_LIMIT;
+    }
+
+    /**
      * Return {@code true} if the current device supports desktop mode.
      */
     @VisibleForTesting
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepository.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepository.kt
index 50cea01..2d508b2 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepository.kt
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepository.kt
@@ -47,6 +47,7 @@
          */
         val activeTasks: ArraySet<Int> = ArraySet(),
         val visibleTasks: ArraySet<Int> = ArraySet(),
+        val minimizedTasks: ArraySet<Int> = ArraySet(),
         var stashed: Boolean = false
     )
 
@@ -202,6 +203,13 @@
         }
     }
 
+    /** Return whether the given Task is minimized. */
+    fun isMinimizedTask(taskId: Int): Boolean {
+        return displayData.valueIterator().asSequence().any { data ->
+            data.minimizedTasks.contains(taskId)
+        }
+    }
+
     /**
      *  Check if a task with the given [taskId] is the only active task on its display
      */
@@ -219,6 +227,25 @@
     }
 
     /**
+     * Returns whether Desktop Mode is currently showing any tasks, i.e. whether any Desktop Tasks
+     * are visible.
+     */
+    fun isDesktopModeShowing(displayId: Int): Boolean = getVisibleTaskCount(displayId) > 0
+
+    /**
+     * Returns a list of Tasks IDs representing all active non-minimized Tasks on the given display,
+     * ordered from front to back.
+     */
+    fun getActiveNonMinimizedTasksOrderedFrontToBack(displayId: Int): List<Int> {
+        val activeTasks = getActiveTasks(displayId)
+        val allTasksInZOrder = getFreeformTasksInZOrder()
+        return activeTasks
+                // Don't show already minimized Tasks
+                .filter { taskId -> !isMinimizedTask(taskId) }
+                .sortedBy { taskId -> allTasksInZOrder.indexOf(taskId) }
+    }
+
+    /**
      * Get a list of freeform tasks, ordered from top-bottom (top at index 0).
      */
      // TODO(b/278084491): pass in display id
@@ -255,6 +282,7 @@
         val prevCount = getVisibleTaskCount(displayId)
         if (visible) {
             displayData.getOrCreate(displayId).visibleTasks.add(taskId)
+            unminimizeTask(displayId, taskId)
         } else {
             displayData[displayId]?.visibleTasks?.remove(taskId)
         }
@@ -312,6 +340,24 @@
         freeformTasksInZOrder.add(0, taskId)
     }
 
+    /** Mark a Task as minimized. */
+    fun minimizeTask(displayId: Int, taskId: Int) {
+        KtProtoLog.v(
+                WM_SHELL_DESKTOP_MODE,
+                "DesktopModeTaskRepository: minimize Task: display=%d, task=%d",
+                displayId, taskId)
+        displayData.getOrCreate(displayId).minimizedTasks.add(taskId)
+    }
+
+    /** Mark a Task as non-minimized. */
+    fun unminimizeTask(displayId: Int, taskId: Int) {
+        KtProtoLog.v(
+                WM_SHELL_DESKTOP_MODE,
+                "DesktopModeTaskRepository: unminimize Task: display=%d, task=%d",
+                displayId, taskId)
+        displayData[displayId]?.minimizedTasks?.remove(taskId)
+    }
+
     /**
      * Remove the task from the ordered list.
      */
@@ -325,7 +371,7 @@
         boundsBeforeMaximizeByTaskId.remove(taskId)
         KtProtoLog.d(
             WM_SHELL_DESKTOP_MODE,
-            "DesktopTaskRepo: remaining freeform tasks: " + freeformTasksInZOrder.toDumpString()
+            "DesktopTaskRepo: remaining freeform tasks: %s", freeformTasksInZOrder.toDumpString(),
         )
     }
 
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksController.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksController.kt
index 068661a..0a9e5d0 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksController.kt
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksController.kt
@@ -88,6 +88,7 @@
 import com.android.wm.shell.windowdecor.extension.isFreeform
 import com.android.wm.shell.windowdecor.extension.isFullscreen
 import java.io.PrintWriter
+import java.util.Optional
 import java.util.concurrent.Executor
 import java.util.function.Consumer
 
@@ -113,7 +114,8 @@
         private val launchAdjacentController: LaunchAdjacentController,
         private val recentsTransitionHandler: RecentsTransitionHandler,
         private val multiInstanceHelper: MultiInstanceHelper,
-        @ShellMainThread private val mainExecutor: ShellExecutor
+        @ShellMainThread private val mainExecutor: ShellExecutor,
+        private val desktopTasksLimiter: Optional<DesktopTasksLimiter>,
 ) : RemoteCallable<DesktopTasksController>, Transitions.TransitionHandler,
     DragAndDropController.DragAndDropListener {
 
@@ -341,11 +343,13 @@
         )
         exitSplitIfApplicable(wct, task)
         // Bring other apps to front first
-        bringDesktopAppsToFront(task.displayId, wct)
+        val taskToMinimize =
+                bringDesktopAppsToFrontBeforeShowingNewTask(task.displayId, wct, task.taskId)
         addMoveToDesktopChanges(wct, task)
 
         if (Transitions.ENABLE_SHELL_TRANSITIONS) {
-            enterDesktopTaskTransitionHandler.moveToDesktop(wct)
+            val transition = enterDesktopTaskTransitionHandler.moveToDesktop(wct)
+            addPendingMinimizeTransition(transition, taskToMinimize)
         } else {
             shellTaskOrganizer.applyTransaction(wct)
         }
@@ -382,10 +386,14 @@
         )
         val wct = WindowContainerTransaction()
         exitSplitIfApplicable(wct, taskInfo)
-        bringDesktopAppsToFront(taskInfo.displayId, wct)
+        moveHomeTaskToFront(wct)
+        val taskToMinimize =
+                bringDesktopAppsToFrontBeforeShowingNewTask(
+                        taskInfo.displayId, wct, taskInfo.taskId)
         addMoveToDesktopChanges(wct, taskInfo)
         wct.setBounds(taskInfo.token, freeformBounds)
-        dragToDesktopTransitionHandler.finishDragToDesktopTransition(wct)
+        val transition = dragToDesktopTransitionHandler.finishDragToDesktopTransition(wct)
+        transition?.let { addPendingMinimizeTransition(it, taskToMinimize) }
     }
 
     /**
@@ -507,8 +515,10 @@
 
         val wct = WindowContainerTransaction()
         wct.reorder(taskInfo.token, true)
+        val taskToMinimize = addAndGetMinimizeChangesIfNeeded(taskInfo.displayId, wct, taskInfo)
         if (Transitions.ENABLE_SHELL_TRANSITIONS) {
-            transitions.startTransition(TRANSIT_TO_FRONT, wct, null /* handler */)
+            val transition = transitions.startTransition(TRANSIT_TO_FRONT, wct, null /* handler */)
+            addPendingMinimizeTransition(transition, taskToMinimize)
         } else {
             shellTaskOrganizer.applyTransaction(wct)
         }
@@ -688,9 +698,20 @@
             ?: WINDOWING_MODE_UNDEFINED
     }
 
-    private fun bringDesktopAppsToFront(displayId: Int, wct: WindowContainerTransaction) {
-        KtProtoLog.v(WM_SHELL_DESKTOP_MODE, "DesktopTasksController: bringDesktopAppsToFront")
-        val activeTasks = desktopModeTaskRepository.getActiveTasks(displayId)
+    private fun bringDesktopAppsToFrontBeforeShowingNewTask(
+            displayId: Int,
+            wct: WindowContainerTransaction,
+            newTaskIdInFront: Int
+    ): RunningTaskInfo? = bringDesktopAppsToFront(displayId, wct, newTaskIdInFront)
+
+    private fun bringDesktopAppsToFront(
+            displayId: Int,
+            wct: WindowContainerTransaction,
+            newTaskIdInFront: Int? = null
+    ): RunningTaskInfo? {
+        KtProtoLog.v(WM_SHELL_DESKTOP_MODE,
+                "DesktopTasksController: bringDesktopAppsToFront, newTaskIdInFront=%s",
+                newTaskIdInFront ?: "null")
 
         if (Flags.enableDesktopWindowingWallpaperActivity()) {
             // Add translucent wallpaper activity to show the wallpaper underneath
@@ -700,13 +721,21 @@
             moveHomeTaskToFront(wct)
         }
 
-        // Then move other tasks on top of it
-        val allTasksInZOrder = desktopModeTaskRepository.getFreeformTasksInZOrder()
-        activeTasks
-            // Sort descending as the top task is at index 0. It should be ordered to top last
-            .sortedByDescending { taskId -> allTasksInZOrder.indexOf(taskId) }
-            .mapNotNull { taskId -> shellTaskOrganizer.getRunningTaskInfo(taskId) }
-            .forEach { task -> wct.reorder(task.token, true /* onTop */) }
+        val nonMinimizedTasksOrderedFrontToBack =
+                desktopModeTaskRepository.getActiveNonMinimizedTasksOrderedFrontToBack(displayId)
+        // If we're adding a new Task we might need to minimize an old one
+        val taskToMinimize: RunningTaskInfo? =
+                if (newTaskIdInFront != null && desktopTasksLimiter.isPresent) {
+                    desktopTasksLimiter.get().getTaskToMinimizeIfNeeded(
+                            nonMinimizedTasksOrderedFrontToBack, newTaskIdInFront)
+                } else { null }
+        nonMinimizedTasksOrderedFrontToBack
+                // If there is a Task to minimize, let it stay behind the Home Task
+                .filter { taskId -> taskId != taskToMinimize?.taskId }
+                .mapNotNull { taskId -> shellTaskOrganizer.getRunningTaskInfo(taskId) }
+                .reversed() // Start from the back so the front task is brought forward last
+                .forEach { task -> wct.reorder(task.token, true /* onTop */) }
+        return taskToMinimize
     }
 
     private fun moveHomeTaskToFront(wct: WindowContainerTransaction) {
@@ -824,13 +853,13 @@
             when {
                 request.type == TRANSIT_TO_BACK -> handleBackNavigation(task)
                 // If display has tasks stashed, handle as stashed launch
-                task.isStashed -> handleStashedTaskLaunch(task)
+                task.isStashed -> handleStashedTaskLaunch(task, transition)
                 // Check if the task has a top transparent activity
                 shouldLaunchAsModal(task) -> handleTransparentTaskLaunch(task)
                 // Check if fullscreen task should be updated
-                task.isFullscreen -> handleFullscreenTaskLaunch(task)
+                task.isFullscreen -> handleFullscreenTaskLaunch(task, transition)
                 // Check if freeform task should be updated
-                task.isFreeform -> handleFreeformTaskLaunch(task)
+                task.isFreeform -> handleFreeformTaskLaunch(task, transition)
                 else -> {
                     null
                 }
@@ -878,10 +907,12 @@
                 } ?: false
     }
 
-    private fun handleFreeformTaskLaunch(task: RunningTaskInfo): WindowContainerTransaction? {
+    private fun handleFreeformTaskLaunch(
+            task: RunningTaskInfo,
+            transition: IBinder
+    ): WindowContainerTransaction? {
         KtProtoLog.v(WM_SHELL_DESKTOP_MODE, "DesktopTasksController: handleFreeformTaskLaunch")
-        val activeTasks = desktopModeTaskRepository.getActiveTasks(task.displayId)
-        if (activeTasks.none { desktopModeTaskRepository.isVisibleTask(it) }) {
+        if (!desktopModeTaskRepository.isDesktopModeShowing(task.displayId)) {
             KtProtoLog.d(
                     WM_SHELL_DESKTOP_MODE,
                     "DesktopTasksController: switch freeform task to fullscreen oon transition" +
@@ -892,13 +923,23 @@
                 addMoveToFullscreenChanges(wct, task)
             }
         }
+        // Desktop Mode is showing and we're launching a new Task - we might need to minimize
+        // a Task.
+        val wct = WindowContainerTransaction()
+        val taskToMinimize = addAndGetMinimizeChangesIfNeeded(task.displayId, wct, task)
+        if (taskToMinimize != null) {
+            addPendingMinimizeTransition(transition, taskToMinimize)
+            return wct
+        }
         return null
     }
 
-    private fun handleFullscreenTaskLaunch(task: RunningTaskInfo): WindowContainerTransaction? {
+    private fun handleFullscreenTaskLaunch(
+            task: RunningTaskInfo,
+            transition: IBinder
+    ): WindowContainerTransaction? {
         KtProtoLog.v(WM_SHELL_DESKTOP_MODE, "DesktopTasksController: handleFullscreenTaskLaunch")
-        val activeTasks = desktopModeTaskRepository.getActiveTasks(task.displayId)
-        if (activeTasks.any { desktopModeTaskRepository.isVisibleTask(it) }) {
+        if (desktopModeTaskRepository.isDesktopModeShowing(task.displayId)) {
             KtProtoLog.d(
                     WM_SHELL_DESKTOP_MODE,
                     "DesktopTasksController: switch fullscreen task to freeform on transition" +
@@ -907,21 +948,30 @@
             )
             return WindowContainerTransaction().also { wct ->
                 addMoveToDesktopChanges(wct, task)
+                // Desktop Mode is already showing and we're launching a new Task - we might need to
+                // minimize another Task.
+                val taskToMinimize = addAndGetMinimizeChangesIfNeeded(task.displayId, wct, task)
+                addPendingMinimizeTransition(transition, taskToMinimize)
             }
         }
         return null
     }
 
-    private fun handleStashedTaskLaunch(task: RunningTaskInfo): WindowContainerTransaction {
+    private fun handleStashedTaskLaunch(
+            task: RunningTaskInfo,
+            transition: IBinder
+    ): WindowContainerTransaction {
         KtProtoLog.d(
                 WM_SHELL_DESKTOP_MODE,
                 "DesktopTasksController: launch apps with stashed on transition taskId=%d",
                 task.taskId
         )
         val wct = WindowContainerTransaction()
-        bringDesktopAppsToFront(task.displayId, wct)
+        val taskToMinimize =
+                bringDesktopAppsToFrontBeforeShowingNewTask(task.displayId, wct, task.taskId)
         addMoveToDesktopChanges(wct, task)
         desktopModeTaskRepository.setStashed(task.displayId, false)
+        addPendingMinimizeTransition(transition, taskToMinimize)
         return wct
     }
 
@@ -1002,6 +1052,28 @@
         wct.setDensityDpi(taskInfo.token, getDefaultDensityDpi())
     }
 
+    /** Returns the ID of the Task that will be minimized, or null if no task will be minimized. */
+    private fun addAndGetMinimizeChangesIfNeeded(
+            displayId: Int,
+            wct: WindowContainerTransaction,
+            newTaskInfo: RunningTaskInfo
+    ): RunningTaskInfo? {
+        if (!desktopTasksLimiter.isPresent) return null
+        return desktopTasksLimiter.get().addAndGetMinimizeTaskChangesIfNeeded(
+                displayId, wct, newTaskInfo)
+    }
+
+    private fun addPendingMinimizeTransition(
+            transition: IBinder,
+            taskToMinimize: RunningTaskInfo?
+    ) {
+        if (taskToMinimize == null) return
+        desktopTasksLimiter.ifPresent {
+            it.addPendingMinimizeChange(
+                    transition, taskToMinimize.displayId, taskToMinimize.taskId)
+        }
+    }
+
     /** Enter split by using the focused desktop task in given `displayId`. */
     fun enterSplit(
         displayId: Int,
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksLimiter.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksLimiter.kt
new file mode 100644
index 0000000..3404d37
--- /dev/null
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DesktopTasksLimiter.kt
@@ -0,0 +1,217 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * 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 com.android.wm.shell.desktopmode
+
+import android.app.ActivityManager.RunningTaskInfo
+import android.os.IBinder
+import android.view.SurfaceControl
+import android.view.WindowManager.TRANSIT_TO_BACK
+import android.window.TransitionInfo
+import android.window.WindowContainerTransaction
+import androidx.annotation.VisibleForTesting
+import com.android.wm.shell.ShellTaskOrganizer
+import com.android.wm.shell.protolog.ShellProtoLogGroup
+import com.android.wm.shell.transition.Transitions
+import com.android.wm.shell.transition.Transitions.TransitionObserver
+import com.android.wm.shell.util.KtProtoLog
+
+/**
+ * Limits the number of tasks shown in Desktop Mode.
+ *
+ * This class should only be used if
+ * [com.android.window.flags.Flags.enableDesktopWindowingTaskLimit()] is true.
+ */
+class DesktopTasksLimiter (
+        transitions: Transitions,
+        private val taskRepository: DesktopModeTaskRepository,
+        private val shellTaskOrganizer: ShellTaskOrganizer,
+) {
+    private val minimizeTransitionObserver = MinimizeTransitionObserver()
+
+    init {
+        transitions.registerObserver(minimizeTransitionObserver)
+    }
+
+    private data class TaskDetails (val displayId: Int, val taskId: Int)
+
+    // TODO(b/333018485): replace this observer when implementing the minimize-animation
+    private inner class MinimizeTransitionObserver : TransitionObserver {
+        private val mPendingTransitionTokensAndTasks = mutableMapOf<IBinder, TaskDetails>()
+
+        fun addPendingTransitionToken(transition: IBinder, taskDetails: TaskDetails) {
+            mPendingTransitionTokensAndTasks[transition] = taskDetails
+        }
+
+        override fun onTransitionReady(
+                transition: IBinder,
+                info: TransitionInfo,
+                startTransaction: SurfaceControl.Transaction,
+                finishTransaction: SurfaceControl.Transaction
+        ) {
+            val taskToMinimize = mPendingTransitionTokensAndTasks.remove(transition) ?: return
+
+            if (!taskRepository.isActiveTask(taskToMinimize.taskId)) return
+
+            if (!isTaskReorderedToBackOrInvisible(info, taskToMinimize)) {
+                KtProtoLog.v(
+                        ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE,
+                        "DesktopTasksLimiter: task %d is not reordered to back nor invis",
+                        taskToMinimize.taskId)
+                return
+            }
+            this@DesktopTasksLimiter.markTaskMinimized(
+                    taskToMinimize.displayId, taskToMinimize.taskId)
+        }
+
+        /**
+         * Returns whether the given Task is being reordered to the back in the given transition, or
+         * is already invisible.
+         *
+         * <p> This check can be used to double-check that a task was indeed minimized before
+         * marking it as such.
+         */
+        private fun isTaskReorderedToBackOrInvisible(
+                info: TransitionInfo,
+                taskDetails: TaskDetails
+        ): Boolean {
+            val taskChange = info.changes.find { change ->
+                change.taskInfo?.taskId == taskDetails.taskId }
+            if (taskChange == null) {
+                return !taskRepository.isVisibleTask(taskDetails.taskId)
+            }
+            return taskChange.mode == TRANSIT_TO_BACK
+        }
+
+        override fun onTransitionStarting(transition: IBinder) {}
+
+        override fun onTransitionMerged(merged: IBinder, playing: IBinder) {
+            mPendingTransitionTokensAndTasks.remove(merged)?.let { taskToTransfer ->
+                mPendingTransitionTokensAndTasks[playing] = taskToTransfer
+            }
+        }
+
+        override fun onTransitionFinished(transition: IBinder, aborted: Boolean) {
+            KtProtoLog.v(
+                    ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE,
+                    "DesktopTasksLimiter: transition %s finished", transition)
+            mPendingTransitionTokensAndTasks.remove(transition)
+        }
+    }
+
+    /**
+     * Mark a task as minimized, this should only be done after the corresponding transition has
+     * finished so we don't minimize the task if the transition fails.
+     */
+    private fun markTaskMinimized(displayId: Int, taskId: Int) {
+        KtProtoLog.v(
+                ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE,
+                "DesktopTasksLimiter: marking %d as minimized", taskId)
+        taskRepository.minimizeTask(displayId, taskId)
+    }
+
+    /**
+     * Add a minimize-transition to [wct] if adding [newFrontTaskInfo] brings us over the task
+     * limit.
+     *
+     * @param transition the transition that the minimize-transition will be appended to, or null if
+     * the transition will be started later.
+     * @return the ID of the minimized task, or null if no task is being minimized.
+     */
+    fun addAndGetMinimizeTaskChangesIfNeeded(
+            displayId: Int,
+            wct: WindowContainerTransaction,
+            newFrontTaskInfo: RunningTaskInfo,
+    ): RunningTaskInfo? {
+        KtProtoLog.v(
+                ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE,
+                "DesktopTasksLimiter: addMinimizeBackTaskChangesIfNeeded, newFrontTask=%d",
+                newFrontTaskInfo.taskId)
+        val newTaskListOrderedFrontToBack = createOrderedTaskListWithGivenTaskInFront(
+                taskRepository.getActiveNonMinimizedTasksOrderedFrontToBack(displayId),
+                newFrontTaskInfo.taskId)
+        val taskToMinimize = getTaskToMinimizeIfNeeded(newTaskListOrderedFrontToBack)
+        if (taskToMinimize != null) {
+            wct.reorder(taskToMinimize.token, false /* onTop */)
+            return taskToMinimize
+        }
+        return null
+    }
+
+    /**
+     * Add a pending minimize transition change, to update the list of minimized apps once the
+     * transition goes through.
+     */
+    fun addPendingMinimizeChange(transition: IBinder, displayId: Int, taskId: Int) {
+        minimizeTransitionObserver.addPendingTransitionToken(
+                transition, TaskDetails(displayId, taskId))
+    }
+
+    /**
+     * Returns the maximum number of tasks that should ever be displayed at the same time in Desktop
+     * Mode.
+     */
+    fun getMaxTaskLimit(): Int = DesktopModeStatus.getMaxTaskLimit()
+
+    /**
+     * Returns the Task to minimize given 1. a list of visible tasks ordered from front to back and
+     * 2. a new task placed in front of all the others.
+     */
+    fun getTaskToMinimizeIfNeeded(
+            visibleFreeformTaskIdsOrderedFrontToBack: List<Int>,
+            newTaskIdInFront: Int
+    ): RunningTaskInfo? {
+        return getTaskToMinimizeIfNeeded(
+                createOrderedTaskListWithGivenTaskInFront(
+                        visibleFreeformTaskIdsOrderedFrontToBack, newTaskIdInFront))
+    }
+
+    /** Returns the Task to minimize given a list of visible tasks ordered from front to back. */
+    fun getTaskToMinimizeIfNeeded(
+            visibleFreeformTaskIdsOrderedFrontToBack: List<Int>
+    ): RunningTaskInfo? {
+        if (visibleFreeformTaskIdsOrderedFrontToBack.size <= getMaxTaskLimit()) {
+            KtProtoLog.v(
+                    ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE,
+                    "DesktopTasksLimiter: no need to minimize; tasks below limit")
+            // No need to minimize anything
+            return null
+        }
+        val taskToMinimize =
+                shellTaskOrganizer.getRunningTaskInfo(
+                        visibleFreeformTaskIdsOrderedFrontToBack.last())
+        if (taskToMinimize == null) {
+            KtProtoLog.e(
+                    ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE,
+                    "DesktopTasksLimiter: taskToMinimize == null")
+            return null
+        }
+        return taskToMinimize
+    }
+
+    private fun createOrderedTaskListWithGivenTaskInFront(
+            existingTaskIdsOrderedFrontToBack: List<Int>,
+            newTaskId: Int
+    ): List<Int> {
+        return listOf(newTaskId) +
+                existingTaskIdsOrderedFrontToBack.filter { taskId -> taskId != newTaskId }
+    }
+
+    @VisibleForTesting
+    fun getTransitionObserver(): TransitionObserver {
+        return minimizeTransitionObserver
+    }
+}
\ No newline at end of file
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DragToDesktopTransitionHandler.kt b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DragToDesktopTransitionHandler.kt
index 0061d03..e341f2d 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DragToDesktopTransitionHandler.kt
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/DragToDesktopTransitionHandler.kt
@@ -150,20 +150,20 @@
      * windowing mode changes to the dragged task. This is called when the dragged task is released
      * inside the desktop drop zone.
      */
-    fun finishDragToDesktopTransition(wct: WindowContainerTransaction) {
+    fun finishDragToDesktopTransition(wct: WindowContainerTransaction): IBinder? {
         if (!inProgress) {
             // Don't attempt to finish a drag to desktop transition since there is no transition in
             // progress which means that the drag to desktop transition was never successfully
             // started.
-            return
+            return null
         }
         if (requireTransitionState().startAborted) {
             // Don't attempt to complete the drag-to-desktop since the start transition didn't
             // succeed as expected. Just reset the state as if nothing happened.
             clearState()
-            return
+            return null
         }
-        transitions.startTransition(TRANSIT_DESKTOP_MODE_END_DRAG_TO_DESKTOP, wct, this)
+        return transitions.startTransition(TRANSIT_DESKTOP_MODE_END_DRAG_TO_DESKTOP, wct, this)
     }
 
     /**
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/EnterDesktopTaskTransitionHandler.java b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/EnterDesktopTaskTransitionHandler.java
index 79bb540..74b8f83 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/EnterDesktopTaskTransitionHandler.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/EnterDesktopTaskTransitionHandler.java
@@ -78,10 +78,12 @@
     /**
      * Starts Transition of type TRANSIT_MOVE_TO_DESKTOP
      * @param wct WindowContainerTransaction for transition
+     * @return the token representing the started transition
      */
-    public void moveToDesktop(@NonNull WindowContainerTransaction wct) {
+    public IBinder moveToDesktop(@NonNull WindowContainerTransaction wct) {
         final IBinder token = mTransitions.startTransition(TRANSIT_MOVE_TO_DESKTOP, wct, this);
         mPendingTransitionTokens.add(token);
+        return token;
     }
 
     @Override
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/freeform/FreeformTaskListener.java b/libs/WindowManager/Shell/src/com/android/wm/shell/freeform/FreeformTaskListener.java
index f2bdcae..6fea203 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/freeform/FreeformTaskListener.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/freeform/FreeformTaskListener.java
@@ -95,6 +95,7 @@
         if (DesktopModeStatus.isEnabled()) {
             mDesktopModeTaskRepository.ifPresent(repository -> {
                 repository.addOrMoveFreeformTaskToTop(taskInfo.taskId);
+                repository.unminimizeTask(taskInfo.displayId, taskInfo.taskId);
                 if (taskInfo.isVisible) {
                     if (repository.addActiveTask(taskInfo.displayId, taskInfo.taskId)) {
                         ProtoLog.v(ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE,
@@ -116,6 +117,7 @@
         if (DesktopModeStatus.isEnabled()) {
             mDesktopModeTaskRepository.ifPresent(repository -> {
                 repository.removeFreeformTask(taskInfo.taskId);
+                repository.unminimizeTask(taskInfo.displayId, taskInfo.taskId);
                 if (repository.removeActiveTask(taskInfo.taskId)) {
                     ProtoLog.v(ShellProtoLogGroup.WM_SHELL_DESKTOP_MODE,
                             "Removing active freeform task: #%d", taskInfo.taskId);
@@ -162,6 +164,7 @@
         if (DesktopModeStatus.isEnabled() && taskInfo.isFocused) {
             mDesktopModeTaskRepository.ifPresent(repository -> {
                 repository.addOrMoveFreeformTaskToTop(taskInfo.taskId);
+                repository.unminimizeTask(taskInfo.displayId, taskInfo.taskId);
             });
         }
     }
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepositoryTest.kt b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepositoryTest.kt
index b2b54ac..dca7be1 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepositoryTest.kt
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopModeTaskRepositoryTest.kt
@@ -483,6 +483,102 @@
         assertThat(repo.removeBoundsBeforeMaximize(taskId)).isNull()
     }
 
+    @Test
+    fun minimizeTaskNotCalled_noTasksMinimized() {
+        assertThat(repo.isMinimizedTask(taskId = 0)).isFalse()
+        assertThat(repo.isMinimizedTask(taskId = 1)).isFalse()
+    }
+
+    @Test
+    fun minimizeTask_onlyThatTaskIsMinimized() {
+        repo.minimizeTask(displayId = 0, taskId = 0)
+
+        assertThat(repo.isMinimizedTask(taskId = 0)).isTrue()
+        assertThat(repo.isMinimizedTask(taskId = 1)).isFalse()
+        assertThat(repo.isMinimizedTask(taskId = 2)).isFalse()
+    }
+
+    @Test
+    fun unminimizeTask_taskNoLongerMinimized() {
+        repo.minimizeTask(displayId = 0, taskId = 0)
+        repo.unminimizeTask(displayId = 0, taskId = 0)
+
+        assertThat(repo.isMinimizedTask(taskId = 0)).isFalse()
+        assertThat(repo.isMinimizedTask(taskId = 1)).isFalse()
+        assertThat(repo.isMinimizedTask(taskId = 2)).isFalse()
+    }
+
+    @Test
+    fun unminimizeTask_nonExistentTask_doesntCrash() {
+        repo.unminimizeTask(displayId = 0, taskId = 0)
+
+        assertThat(repo.isMinimizedTask(taskId = 0)).isFalse()
+        assertThat(repo.isMinimizedTask(taskId = 1)).isFalse()
+        assertThat(repo.isMinimizedTask(taskId = 2)).isFalse()
+    }
+
+
+    @Test
+    fun updateVisibleFreeformTasks_toVisible_taskIsUnminimized() {
+        repo.minimizeTask(displayId = 10, taskId = 2)
+
+        repo.updateVisibleFreeformTasks(displayId = 10, taskId = 2, visible = true)
+
+        assertThat(repo.isMinimizedTask(taskId = 2)).isFalse()
+    }
+
+    @Test
+    fun isDesktopModeShowing_noActiveTasks_returnsFalse() {
+        assertThat(repo.isDesktopModeShowing(displayId = 0)).isFalse()
+    }
+
+    @Test
+    fun isDesktopModeShowing_noTasksVisible_returnsFalse() {
+        repo.addActiveTask(displayId = 0, taskId = 1)
+        repo.addActiveTask(displayId = 0, taskId = 2)
+
+        assertThat(repo.isDesktopModeShowing(displayId = 0)).isFalse()
+    }
+
+    @Test
+    fun isDesktopModeShowing_tasksActiveAndVisible_returnsTrue() {
+        repo.addActiveTask(displayId = 0, taskId = 1)
+        repo.addActiveTask(displayId = 0, taskId = 2)
+        repo.updateVisibleFreeformTasks(displayId = 0, taskId = 1, visible = true)
+
+        assertThat(repo.isDesktopModeShowing(displayId = 0)).isTrue()
+    }
+
+    @Test
+    fun getActiveNonMinimizedTasksOrderedFrontToBack_returnsFreeformTasksInCorrectOrder() {
+        repo.addActiveTask(displayId = 0, taskId = 1)
+        repo.addActiveTask(displayId = 0, taskId = 2)
+        repo.addActiveTask(displayId = 0, taskId = 3)
+        // The front-most task will be the one added last through addOrMoveFreeformTaskToTop
+        repo.addOrMoveFreeformTaskToTop(taskId = 3)
+        repo.addOrMoveFreeformTaskToTop(taskId = 2)
+        repo.addOrMoveFreeformTaskToTop(taskId = 1)
+
+        assertThat(repo.getActiveNonMinimizedTasksOrderedFrontToBack(displayId = 0)).isEqualTo(
+                listOf(1, 2, 3))
+    }
+
+    @Test
+    fun getActiveNonMinimizedTasksOrderedFrontToBack_minimizedTaskNotIncluded() {
+        repo.addActiveTask(displayId = 0, taskId = 1)
+        repo.addActiveTask(displayId = 0, taskId = 2)
+        repo.addActiveTask(displayId = 0, taskId = 3)
+        // The front-most task will be the one added last through addOrMoveFreeformTaskToTop
+        repo.addOrMoveFreeformTaskToTop(taskId = 3)
+        repo.addOrMoveFreeformTaskToTop(taskId = 2)
+        repo.addOrMoveFreeformTaskToTop(taskId = 1)
+        repo.minimizeTask(displayId = 0, taskId = 2)
+
+        assertThat(repo.getActiveNonMinimizedTasksOrderedFrontToBack(displayId = 0)).isEqualTo(
+                listOf(1, 3))
+    }
+
+
     class TestListener : DesktopModeTaskRepository.ActiveTasksListener {
         var activeChangesOnDefaultDisplay = 0
         var activeChangesOnSecondaryDisplay = 0
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksControllerTest.kt b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksControllerTest.kt
index 64f6041..ad4b720 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksControllerTest.kt
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksControllerTest.kt
@@ -105,6 +105,7 @@
 import org.mockito.kotlin.atLeastOnce
 import org.mockito.kotlin.capture
 import org.mockito.quality.Strictness
+import java.util.Optional
 import org.mockito.Mockito.`when` as whenever
 
 /**
@@ -145,6 +146,7 @@
     private lateinit var controller: DesktopTasksController
     private lateinit var shellInit: ShellInit
     private lateinit var desktopModeTaskRepository: DesktopModeTaskRepository
+    private lateinit var desktopTasksLimiter: DesktopTasksLimiter
     private lateinit var recentsTransitionStateListener: RecentsTransitionStateListener
 
     private val shellExecutor = TestShellExecutor()
@@ -160,9 +162,12 @@
 
         shellInit = Mockito.spy(ShellInit(testExecutor))
         desktopModeTaskRepository = DesktopModeTaskRepository()
+        desktopTasksLimiter =
+                DesktopTasksLimiter(transitions, desktopModeTaskRepository, shellTaskOrganizer)
 
         whenever(shellTaskOrganizer.getRunningTasks(anyInt())).thenAnswer { runningTasks }
         whenever(transitions.startTransition(anyInt(), any(), isNull())).thenAnswer { Binder() }
+        whenever(enterDesktopTransitionHandler.moveToDesktop(any())).thenAnswer { Binder() }
         whenever(displayController.getDisplayLayout(anyInt())).thenReturn(displayLayout)
         whenever(displayLayout.getStableBounds(any())).thenAnswer { i ->
                 (i.arguments.first() as Rect).set(STABLE_BOUNDS)
@@ -203,7 +208,8 @@
             launchAdjacentController,
             recentsTransitionHandler,
             multiInstanceHelper,
-            shellExecutor
+            shellExecutor,
+            Optional.of(desktopTasksLimiter),
         )
     }
 
@@ -409,6 +415,25 @@
     }
 
     @Test
+    fun showDesktopApps_dontReorderMinimizedTask() {
+        val homeTask = setUpHomeTask()
+        val freeformTask = setUpFreeformTask()
+        val minimizedTask = setUpFreeformTask()
+        markTaskHidden(freeformTask)
+        markTaskHidden(minimizedTask)
+        desktopModeTaskRepository.minimizeTask(DEFAULT_DISPLAY, minimizedTask.taskId)
+
+        controller.showDesktopApps(DEFAULT_DISPLAY, RemoteTransition(TestRemoteTransition()))
+
+        val wct = getLatestWct(
+                type = TRANSIT_TO_FRONT, handlerClass = OneShotRemoteHandler::class.java)
+        assertThat(wct.hierarchyOps).hasSize(2)
+        // Reorder home and freeform task to top, don't reorder the minimized task
+        wct.assertReorderAt(index = 0, homeTask, toTop = true)
+        wct.assertReorderAt(index = 1, freeformTask, toTop = true)
+    }
+
+    @Test
     fun getVisibleTaskCount_noTasks_returnsZero() {
         assertThat(controller.getVisibleTaskCount(DEFAULT_DISPLAY)).isEqualTo(0)
     }
@@ -606,6 +631,24 @@
     }
 
     @Test
+    fun moveToDesktop_bringsTasksOverLimit_dontShowBackTask() {
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        val homeTask = setUpHomeTask()
+        val freeformTasks = (1..taskLimit).map { _ -> setUpFreeformTask() }
+        val newTask = setUpFullscreenTask()
+
+        controller.moveToDesktop(newTask)
+
+        val wct = getLatestMoveToDesktopWct()
+        assertThat(wct.hierarchyOps.size).isEqualTo(taskLimit + 1) // visible tasks + home
+        wct.assertReorderAt(0, homeTask)
+        for (i in 1..<taskLimit) { // Skipping freeformTasks[0]
+            wct.assertReorderAt(index = i, task = freeformTasks[i])
+        }
+        wct.assertReorderAt(taskLimit, newTask)
+    }
+
+    @Test
     fun moveToFullscreen_tdaFullscreen_windowingModeSetToUndefined() {
         val task = setUpFreeformTask()
         val tda = rootTaskDisplayAreaOrganizer.getDisplayAreaInfo(DEFAULT_DISPLAY)!!
@@ -659,6 +702,20 @@
     }
 
     @Test
+    fun moveTaskToFront_bringsTasksOverLimit_minimizesBackTask() {
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        setUpHomeTask()
+        val freeformTasks = (1..taskLimit + 1).map { _ -> setUpFreeformTask() }
+
+        controller.moveTaskToFront(freeformTasks[0])
+
+        val wct = getLatestWct(type = TRANSIT_TO_FRONT)
+        assertThat(wct.hierarchyOps.size).isEqualTo(2) // move-to-front + minimize
+        wct.assertReorderAt(0, freeformTasks[0], toTop = true)
+        wct.assertReorderAt(1, freeformTasks[1], toTop = false)
+    }
+
+    @Test
     fun moveToNextDisplay_noOtherDisplays() {
         whenever(rootTaskDisplayAreaOrganizer.displayIds).thenReturn(intArrayOf(DEFAULT_DISPLAY))
         val task = setUpFreeformTask(displayId = DEFAULT_DISPLAY)
@@ -777,6 +834,38 @@
     }
 
     @Test
+    fun handleRequest_fullscreenTaskToFreeform_underTaskLimit_dontMinimize() {
+        assumeTrue(ENABLE_SHELL_TRANSITIONS)
+
+        val freeformTask = setUpFreeformTask()
+        markTaskVisible(freeformTask)
+        val fullscreenTask = createFullscreenTask()
+
+        val wct = controller.handleRequest(Binder(), createTransition(fullscreenTask))
+
+        // Make sure we only reorder the new task to top (we don't reorder the old task to bottom)
+        assertThat(wct?.hierarchyOps?.size).isEqualTo(1)
+        wct!!.assertReorderAt(0, fullscreenTask, toTop = true)
+    }
+
+    @Test
+    fun handleRequest_fullscreenTaskToFreeform_bringsTasksOverLimit_otherTaskIsMinimized() {
+        assumeTrue(ENABLE_SHELL_TRANSITIONS)
+
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        val freeformTasks = (1..taskLimit).map { _ -> setUpFreeformTask() }
+        freeformTasks.forEach { markTaskVisible(it) }
+        val fullscreenTask = createFullscreenTask()
+
+        val wct = controller.handleRequest(Binder(), createTransition(fullscreenTask))
+
+        // Make sure we reorder the new task to top, and the back task to the bottom
+        assertThat(wct!!.hierarchyOps.size).isEqualTo(2)
+        wct!!.assertReorderAt(0, fullscreenTask, toTop = true)
+        wct!!.assertReorderAt(1, freeformTasks[0], toTop = false)
+    }
+
+    @Test
     fun handleRequest_fullscreenTask_freeformNotVisible_returnNull() {
         assumeTrue(ENABLE_SHELL_TRANSITIONS)
 
@@ -841,6 +930,22 @@
     }
 
     @Test
+    fun handleRequest_freeformTask_freeformVisible_aboveTaskLimit_minimize() {
+        assumeTrue(ENABLE_SHELL_TRANSITIONS)
+
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        val freeformTasks = (1..taskLimit).map { _ -> setUpFreeformTask() }
+        freeformTasks.forEach { markTaskVisible(it) }
+        val newFreeformTask = createFreeformTask()
+
+        val wct =
+                controller.handleRequest(Binder(), createTransition(newFreeformTask, TRANSIT_OPEN))
+
+        assertThat(wct?.hierarchyOps?.size).isEqualTo(1)
+        wct!!.assertReorderAt(0, freeformTasks[0], toTop = false) // Reorder to the bottom
+    }
+
+    @Test
     fun handleRequest_freeformTask_freeformNotVisible_returnSwitchToFullscreenWCT() {
         assumeTrue(ENABLE_SHELL_TRANSITIONS)
 
@@ -1352,11 +1457,16 @@
         .isGreaterThan(index)
 }
 
-private fun WindowContainerTransaction.assertReorderAt(index: Int, task: RunningTaskInfo) {
+private fun WindowContainerTransaction.assertReorderAt(
+        index: Int,
+        task: RunningTaskInfo,
+        toTop: Boolean? = null
+) {
     assertIndexInBounds(index)
     val op = hierarchyOps[index]
     assertThat(op.type).isEqualTo(HIERARCHY_OP_TYPE_REORDER)
     assertThat(op.container).isEqualTo(task.token.asBinder())
+    toTop?.let { assertThat(op.toTop).isEqualTo(it) }
 }
 
 private fun WindowContainerTransaction.assertReorderSequence(vararg tasks: RunningTaskInfo) {
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksLimiterTest.kt b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksLimiterTest.kt
new file mode 100644
index 0000000..38ea034
--- /dev/null
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/desktopmode/DesktopTasksLimiterTest.kt
@@ -0,0 +1,317 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * 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 com.android.wm.shell.desktopmode
+
+import android.app.ActivityManager.RunningTaskInfo
+import android.os.Binder
+import android.platform.test.flag.junit.SetFlagsRule
+import android.testing.AndroidTestingRunner
+import android.view.Display.DEFAULT_DISPLAY
+import android.view.WindowManager.TRANSIT_OPEN
+import android.view.WindowManager.TRANSIT_TO_BACK
+import android.window.WindowContainerTransaction
+import android.window.WindowContainerTransaction.HierarchyOp.HIERARCHY_OP_TYPE_REORDER
+import androidx.test.filters.SmallTest
+import com.android.dx.mockito.inline.extended.ExtendedMockito
+import com.android.dx.mockito.inline.extended.StaticMockitoSession
+import com.android.wm.shell.ShellTaskOrganizer
+import com.android.wm.shell.ShellTestCase
+import com.android.wm.shell.desktopmode.DesktopTestHelpers.Companion.createFreeformTask
+import com.android.wm.shell.transition.TransitionInfoBuilder
+import com.android.wm.shell.transition.Transitions
+import com.android.wm.shell.util.StubTransaction
+import com.google.common.truth.Truth.assertThat
+import org.junit.After
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.Mock
+import org.mockito.Mockito.`when`
+import org.mockito.quality.Strictness
+
+
+/**
+ * Test class for {@link DesktopTasksLimiter}
+ *
+ * Usage: atest WMShellUnitTests:DesktopTasksLimiterTest
+ */
+@SmallTest
+@RunWith(AndroidTestingRunner::class)
+class DesktopTasksLimiterTest : ShellTestCase() {
+
+    @JvmField
+    @Rule
+    val setFlagsRule = SetFlagsRule()
+
+    @Mock lateinit var shellTaskOrganizer: ShellTaskOrganizer
+    @Mock lateinit var transitions: Transitions
+
+    private lateinit var mockitoSession: StaticMockitoSession
+    private lateinit var desktopTasksLimiter: DesktopTasksLimiter
+    private lateinit var desktopTaskRepo: DesktopModeTaskRepository
+
+    @Before
+    fun setUp() {
+        mockitoSession = ExtendedMockito.mockitoSession().strictness(Strictness.LENIENT)
+                .spyStatic(DesktopModeStatus::class.java).startMocking()
+        `when`(DesktopModeStatus.isEnabled()).thenReturn(true)
+
+        desktopTaskRepo = DesktopModeTaskRepository()
+
+        desktopTasksLimiter = DesktopTasksLimiter(
+                transitions, desktopTaskRepo, shellTaskOrganizer)
+    }
+
+    @After
+    fun tearDown() {
+        mockitoSession.finishMocking()
+    }
+
+    // Currently, the task limit can be overridden through an adb flag. This test ensures the limit
+    // hasn't been overridden.
+    @Test
+    fun getMaxTaskLimit_isSameAsConstant() {
+        assertThat(desktopTasksLimiter.getMaxTaskLimit()).isEqualTo(
+            DesktopModeStatus.DEFAULT_MAX_TASK_LIMIT)
+    }
+
+    @Test
+    fun addPendingMinimizeTransition_taskIsNotMinimized() {
+        val task = setUpFreeformTask()
+        markTaskHidden(task)
+
+        desktopTasksLimiter.addPendingMinimizeChange(Binder(), displayId = 1, taskId = task.taskId)
+
+        assertThat(desktopTaskRepo.isMinimizedTask(taskId = task.taskId)).isFalse()
+    }
+
+    @Test
+    fun onTransitionReady_noPendingTransition_taskIsNotMinimized() {
+        val task = setUpFreeformTask()
+        markTaskHidden(task)
+
+        desktopTasksLimiter.getTransitionObserver().onTransitionReady(
+                Binder() /* transition */,
+                TransitionInfoBuilder(TRANSIT_OPEN).addChange(TRANSIT_TO_BACK, task).build(),
+                StubTransaction() /* startTransaction */,
+                StubTransaction() /* finishTransaction */)
+
+        assertThat(desktopTaskRepo.isMinimizedTask(taskId = task.taskId)).isFalse()
+    }
+
+    @Test
+    fun onTransitionReady_differentPendingTransition_taskIsNotMinimized() {
+        val pendingTransition = Binder()
+        val taskTransition = Binder()
+        val task = setUpFreeformTask()
+        markTaskHidden(task)
+        desktopTasksLimiter.addPendingMinimizeChange(
+            pendingTransition, displayId = DEFAULT_DISPLAY, taskId = task.taskId)
+
+        desktopTasksLimiter.getTransitionObserver().onTransitionReady(
+            taskTransition /* transition */,
+            TransitionInfoBuilder(TRANSIT_OPEN).addChange(TRANSIT_TO_BACK, task).build(),
+            StubTransaction() /* startTransaction */,
+            StubTransaction() /* finishTransaction */)
+
+        assertThat(desktopTaskRepo.isMinimizedTask(taskId = task.taskId)).isFalse()
+    }
+
+    @Test
+    fun onTransitionReady_pendingTransition_noTaskChange_taskVisible_taskIsNotMinimized() {
+        val transition = Binder()
+        val task = setUpFreeformTask()
+        markTaskVisible(task)
+        desktopTasksLimiter.addPendingMinimizeChange(
+                transition, displayId = DEFAULT_DISPLAY, taskId = task.taskId)
+
+        desktopTasksLimiter.getTransitionObserver().onTransitionReady(
+                transition,
+                TransitionInfoBuilder(TRANSIT_OPEN).build(),
+                StubTransaction() /* startTransaction */,
+                StubTransaction() /* finishTransaction */)
+
+        assertThat(desktopTaskRepo.isMinimizedTask(taskId = task.taskId)).isFalse()
+    }
+
+    @Test
+    fun onTransitionReady_pendingTransition_noTaskChange_taskInvisible_taskIsMinimized() {
+        val transition = Binder()
+        val task = setUpFreeformTask()
+        markTaskHidden(task)
+        desktopTasksLimiter.addPendingMinimizeChange(
+                transition, displayId = DEFAULT_DISPLAY, taskId = task.taskId)
+
+        desktopTasksLimiter.getTransitionObserver().onTransitionReady(
+                transition,
+                TransitionInfoBuilder(TRANSIT_OPEN).build(),
+                StubTransaction() /* startTransaction */,
+                StubTransaction() /* finishTransaction */)
+
+        assertThat(desktopTaskRepo.isMinimizedTask(taskId = task.taskId)).isTrue()
+    }
+
+    @Test
+    fun onTransitionReady_pendingTransition_changeTaskToBack_taskIsMinimized() {
+        val transition = Binder()
+        val task = setUpFreeformTask()
+        desktopTasksLimiter.addPendingMinimizeChange(
+                transition, displayId = DEFAULT_DISPLAY, taskId = task.taskId)
+
+        desktopTasksLimiter.getTransitionObserver().onTransitionReady(
+                transition,
+                TransitionInfoBuilder(TRANSIT_OPEN).addChange(TRANSIT_TO_BACK, task).build(),
+                StubTransaction() /* startTransaction */,
+                StubTransaction() /* finishTransaction */)
+
+        assertThat(desktopTaskRepo.isMinimizedTask(taskId = task.taskId)).isTrue()
+    }
+
+    @Test
+    fun onTransitionReady_transitionMergedFromPending_taskIsMinimized() {
+        val mergedTransition = Binder()
+        val newTransition = Binder()
+        val task = setUpFreeformTask()
+        desktopTasksLimiter.addPendingMinimizeChange(
+            mergedTransition, displayId = DEFAULT_DISPLAY, taskId = task.taskId)
+        desktopTasksLimiter.getTransitionObserver().onTransitionMerged(
+            mergedTransition, newTransition)
+
+        desktopTasksLimiter.getTransitionObserver().onTransitionReady(
+            newTransition,
+            TransitionInfoBuilder(TRANSIT_OPEN).addChange(TRANSIT_TO_BACK, task).build(),
+            StubTransaction() /* startTransaction */,
+            StubTransaction() /* finishTransaction */)
+
+        assertThat(desktopTaskRepo.isMinimizedTask(taskId = task.taskId)).isTrue()
+    }
+
+    @Test
+    fun addAndGetMinimizeTaskChangesIfNeeded_tasksWithinLimit_noTaskMinimized() {
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        (1..<taskLimit).forEach { _ -> setUpFreeformTask() }
+
+        val wct = WindowContainerTransaction()
+        val minimizedTaskId =
+                desktopTasksLimiter.addAndGetMinimizeTaskChangesIfNeeded(
+                        displayId = DEFAULT_DISPLAY,
+                        wct = wct,
+                        newFrontTaskInfo = setUpFreeformTask())
+
+        assertThat(minimizedTaskId).isNull()
+        assertThat(wct.hierarchyOps).isEmpty() // No reordering operations added
+    }
+
+    @Test
+    fun addAndGetMinimizeTaskChangesIfNeeded_tasksAboveLimit_backTaskMinimized() {
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        // The following list will be ordered bottom -> top, as the last task is moved to top last.
+        val tasks = (1..taskLimit).map { setUpFreeformTask() }
+
+        val wct = WindowContainerTransaction()
+        val minimizedTaskId =
+                desktopTasksLimiter.addAndGetMinimizeTaskChangesIfNeeded(
+                        displayId = DEFAULT_DISPLAY,
+                        wct = wct,
+                        newFrontTaskInfo = setUpFreeformTask())
+
+        assertThat(minimizedTaskId).isEqualTo(tasks.first())
+        assertThat(wct.hierarchyOps.size).isEqualTo(1)
+        assertThat(wct.hierarchyOps[0].type).isEqualTo(HIERARCHY_OP_TYPE_REORDER)
+        assertThat(wct.hierarchyOps[0].toTop).isFalse() // Reorder to bottom
+    }
+
+    @Test
+    fun addAndGetMinimizeTaskChangesIfNeeded_nonMinimizedTasksWithinLimit_noTaskMinimized() {
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        val tasks = (1..taskLimit).map { setUpFreeformTask() }
+        desktopTaskRepo.minimizeTask(displayId = DEFAULT_DISPLAY, taskId = tasks[0].taskId)
+
+        val wct = WindowContainerTransaction()
+        val minimizedTaskId =
+                desktopTasksLimiter.addAndGetMinimizeTaskChangesIfNeeded(
+                        displayId = 0,
+                        wct = wct,
+                        newFrontTaskInfo = setUpFreeformTask())
+
+        assertThat(minimizedTaskId).isNull()
+        assertThat(wct.hierarchyOps).isEmpty() // No reordering operations added
+    }
+
+    @Test
+    fun getTaskToMinimizeIfNeeded_tasksWithinLimit_returnsNull() {
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        val tasks = (1..taskLimit).map { setUpFreeformTask() }
+
+        val minimizedTask = desktopTasksLimiter.getTaskToMinimizeIfNeeded(
+                visibleFreeformTaskIdsOrderedFrontToBack = tasks.map { it.taskId })
+
+        assertThat(minimizedTask).isNull()
+    }
+
+    @Test
+    fun getTaskToMinimizeIfNeeded_tasksAboveLimit_returnsBackTask() {
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        val tasks = (1..taskLimit + 1).map { setUpFreeformTask() }
+
+        val minimizedTask = desktopTasksLimiter.getTaskToMinimizeIfNeeded(
+                visibleFreeformTaskIdsOrderedFrontToBack = tasks.map { it.taskId })
+
+        // first == front, last == back
+        assertThat(minimizedTask).isEqualTo(tasks.last())
+    }
+
+    @Test
+    fun getTaskToMinimizeIfNeeded_withNewTask_tasksAboveLimit_returnsBackTask() {
+        val taskLimit = desktopTasksLimiter.getMaxTaskLimit()
+        val tasks = (1..taskLimit).map { setUpFreeformTask() }
+
+        val minimizedTask = desktopTasksLimiter.getTaskToMinimizeIfNeeded(
+                visibleFreeformTaskIdsOrderedFrontToBack = tasks.map { it.taskId },
+                newTaskIdInFront = setUpFreeformTask().taskId)
+
+        // first == front, last == back
+        assertThat(minimizedTask).isEqualTo(tasks.last())
+    }
+
+    private fun setUpFreeformTask(
+            displayId: Int = DEFAULT_DISPLAY,
+    ): RunningTaskInfo {
+        val task = createFreeformTask(displayId)
+        `when`(shellTaskOrganizer.getRunningTaskInfo(task.taskId)).thenReturn(task)
+        desktopTaskRepo.addActiveTask(displayId, task.taskId)
+        desktopTaskRepo.addOrMoveFreeformTaskToTop(task.taskId)
+        return task
+    }
+
+    private fun markTaskVisible(task: RunningTaskInfo) {
+        desktopTaskRepo.updateVisibleFreeformTasks(
+                task.displayId,
+                task.taskId,
+                visible = true
+        )
+    }
+
+    private fun markTaskHidden(task: RunningTaskInfo) {
+        desktopTaskRepo.updateVisibleFreeformTasks(
+                task.displayId,
+                task.taskId,
+                visible = false
+        )
+    }
+}