Adds extensions implementation for WindowAreaComponent and rear display status listeners

This cl includes the functionality of adding/removing
listeners for Rear Display status.

Bug: 207686851
Test: ExtensionWindowAreaComponentTest
Change-Id: I2d4d519a5e4933cd2b1319f2da99845f647006eb

core/res/res/values/config.xml

@@ -5884,4 +5884,10 @@
 
     <!-- The number of tasks to scan to get the visibility of Home -->
     <integer name="config_maxScanTasksForHomeVisibility">10</integer>
+
+    <!-- Device state that corresponds to rear display mode, feature provided
+         through Jetpack WindowManager
+         TODO(b/236022708) Move rear display state to device state config file
+    -->
+    <integer name="config_deviceStateRearDisplay">-1</integer>
 </resources>

core/res/res/values/symbols.xml

@@ -4812,6 +4812,7 @@
   <java-symbol type="drawable" name="ic_swap_horiz" />
   <java-symbol type="array" name="config_deviceStatesAvailableForAppRequests" />
   <java-symbol type="array" name="config_serviceStateLocationAllowedPackages" />
+  <java-symbol type="integer" name="config_deviceStateRearDisplay"/>
 
   <!-- For app language picker -->
   <java-symbol type="string" name="system_locale_title" />

libs/WindowManager/Jetpack/src/androidx/window/extensions/WindowExtensionsImpl.java

@@ -20,11 +20,14 @@ import android.app.ActivityThread;
 import android.content.Context;
 
 import androidx.annotation.NonNull;
+import androidx.window.extensions.area.WindowAreaComponent;
+import androidx.window.extensions.area.WindowAreaComponentImpl;
 import androidx.window.extensions.embedding.ActivityEmbeddingComponent;
 import androidx.window.extensions.embedding.SplitController;
 import androidx.window.extensions.layout.WindowLayoutComponent;
 import androidx.window.extensions.layout.WindowLayoutComponentImpl;
 
+
 /**
  * The reference implementation of {@link WindowExtensions} that implements the initial API version.
  */
@@ -33,6 +36,7 @@ public class WindowExtensionsImpl implements WindowExtensions {
     private final Object mLock = new Object();
     private volatile WindowLayoutComponent mWindowLayoutComponent;
     private volatile SplitController mSplitController;
+    private volatile WindowAreaComponent mWindowAreaComponent;
 
     @Override
     public int getVendorApiLevel() {
@@ -75,4 +79,23 @@ public class WindowExtensionsImpl implements WindowExtensions {
         }
         return mSplitController;
     }
+
+    /**
+     * Returns a reference implementation of {@link WindowAreaComponent} if available,
+     * {@code null} otherwise. The implementation must match the API level reported in
+     * {@link WindowExtensions#getWindowAreaComponent()}.
+     * @return {@link WindowAreaComponent} OEM implementation.
+     */
+    public WindowAreaComponent getWindowAreaComponent() {
+        if (mWindowAreaComponent == null) {
+            synchronized (mLock) {
+                if (mWindowAreaComponent == null) {
+                    Context context = ActivityThread.currentApplication();
+                    mWindowAreaComponent =
+                            new WindowAreaComponentImpl(context);
+                }
+            }
+        }
+        return mWindowAreaComponent;
+    }
 }

libs/WindowManager/Jetpack/src/androidx/window/extensions/area/WindowAreaComponentImpl.java

@@ -0,0 +1,189 @@
+/*
+ * Copyright (C) 2022 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 androidx.window.extensions.area;
+
+import static android.hardware.devicestate.DeviceStateManager.INVALID_DEVICE_STATE;
+
+import android.app.Activity;
+import android.content.Context;
+import android.hardware.devicestate.DeviceStateManager;
+import android.util.ArraySet;
+
+import androidx.annotation.NonNull;
+
+import com.android.internal.R;
+import com.android.internal.annotations.GuardedBy;
+
+import java.util.concurrent.Executor;
+import java.util.function.Consumer;
+
+/**
+ * Reference implementation of androidx.window.extensions.area OEM interface for use with
+ * WindowManager Jetpack.
+ *
+ * This component currently supports Rear Display mode with the ability to add and remove
+ * status listeners for this mode.
+ *
+ * The public methods in this class are thread-safe.
+ **/
+public class WindowAreaComponentImpl implements WindowAreaComponent,
+        DeviceStateManager.DeviceStateCallback {
+
+    private final Object mLock = new Object();
+
+    private final DeviceStateManager mDeviceStateManager;
+    private final Executor mExecutor;
+
+    @GuardedBy("mLock")
+    private final ArraySet<Consumer<Integer>> mRearDisplayStatusListeners = new ArraySet<>();
+    private final int mRearDisplayState;
+
+    @GuardedBy("mLock")
+    private int mCurrentDeviceState = INVALID_DEVICE_STATE;
+    @GuardedBy("mLock")
+    private int mCurrentDeviceBaseState = INVALID_DEVICE_STATE;
+
+    public WindowAreaComponentImpl(@NonNull Context context) {
+        mDeviceStateManager = context.getSystemService(DeviceStateManager.class);
+        mExecutor = context.getMainExecutor();
+
+        // TODO(b/236022708) Move rear display state to device state config file
+        mRearDisplayState = context.getResources().getInteger(
+                R.integer.config_deviceStateRearDisplay);
+
+        mDeviceStateManager.registerCallback(mExecutor, this);
+    }
+
+    /**
+     * Adds a listener interested in receiving updates on the RearDisplayStatus
+     * of the device. Because this is being called from the OEM provided
+     * extensions, we will post the result of the listener on the executor
+     * provided by the developer at the initial call site.
+     *
+     * Depending on the initial state of the device, we will return either
+     * {@link WindowAreaComponent#STATUS_AVAILABLE} or
+     * {@link WindowAreaComponent#STATUS_UNAVAILABLE} if the feature is supported or not in that
+     * state respectively. When the RearDisplay feature is triggered, we update the status to be
+     * {@link WindowAreaComponent#STATUS_UNAVAILABLE}.
+     *
+     * TODO(b/239833099) Add a STATUS_ACTIVE option to let apps know if a feature is currently
+     * enabled.
+     *
+     * @param consumer {@link Consumer} interested in receiving updates to the status of
+     * rear display mode.
+     */
+    public void addRearDisplayStatusListener(
+            @NonNull Consumer<@WindowAreaStatus Integer> consumer) {
+        synchronized (mLock) {
+            mRearDisplayStatusListeners.add(consumer);
+
+            // If current device state is still invalid, we haven't gotten our initial value yet
+            if (mCurrentDeviceState == INVALID_DEVICE_STATE) {
+                return;
+            }
+            consumer.accept(getCurrentStatus());
+        }
+    }
+
+    /**
+     * Removes a listener no longer interested in receiving updates.
+     * @param consumer no longer interested in receiving updates to RearDisplayStatus
+     */
+    public void removeRearDisplayStatusListener(
+            @NonNull Consumer<@WindowAreaStatus Integer> consumer) {
+        synchronized (mLock) {
+            mRearDisplayStatusListeners.remove(consumer);
+        }
+    }
+
+    /**
+     * Creates and starts a RearDisplaySession and provides updates to the
+     * callback provided. Because this is being called from the OEM provided
+     * extensions, we will post the result of the listener on the executor
+     * provided by the developer at the initial call site.
+     *
+     * When we enable rear display mode, we submit a request to {@link DeviceStateManager}
+     * to override the device state to the state that corresponds to RearDisplay
+     * mode. When the {@link DeviceStateRequest} is activated, we let the
+     * consumer know that the session is active by sending
+     * {@link WindowAreaComponent#SESSION_STATE_ACTIVE}.
+     *
+     * @param activity to provide updates to the client on
+     * the status of the Session
+     * @param rearDisplaySessionCallback to provide updates to the client on
+     * the status of the Session
+     */
+    public void startRearDisplaySession(@NonNull Activity activity,
+            @NonNull Consumer<@WindowAreaSessionState Integer> rearDisplaySessionCallback) {
+        // Todo("Adding in chained cl")
+    }
+
+    /**
+     * Ends the current RearDisplaySession and provides updates to the
+     * callback provided. Because this is being called from the OEM provided
+     * extensions, we will post the result of the listener on the executor
+     * provided by the developer.
+     */
+    public void endRearDisplaySession() {
+        // Todo("Adding in chained cl")
+    }
+
+    @Override
+    public void onBaseStateChanged(int state) {
+        synchronized (mLock) {
+            mCurrentDeviceBaseState = state;
+        }
+    }
+
+    @Override
+    public void onStateChanged(int state) {
+        synchronized (mLock) {
+            mCurrentDeviceState = state;
+            updateStatusConsumers(getCurrentStatus());
+        }
+    }
+
+    @GuardedBy("mLock")
+    private int getCurrentStatus() {
+        if (isRearDisplayActive()) {
+            return WindowAreaComponent.STATUS_UNAVAILABLE;
+        }
+        return WindowAreaComponent.STATUS_AVAILABLE;
+    }
+
+    /**
+     * Helper method to determine if a rear display session is currently active by checking
+     * if the current device configuration matches that of rear display. This would be true
+     * if there is a device override currently active (base state != current state) and the current
+     * state is that which corresponds to {@code mRearDisplayState}
+     * @return {@code true} if the device is in rear display mode and {@code false} if not
+     */
+    @GuardedBy("mLock")
+    private boolean isRearDisplayActive() {
+        return (mCurrentDeviceState != mCurrentDeviceBaseState) && (mCurrentDeviceState
+                == mRearDisplayState);
+    }
+
+    @GuardedBy("mLock")
+    private void updateStatusConsumers(@WindowAreaStatus int windowAreaStatus) {
+        synchronized (mLock) {
+            for (int i = 0; i < mRearDisplayStatusListeners.size(); i++) {
+                mRearDisplayStatusListeners.valueAt(i).accept(windowAreaStatus);
+            }
+        }
+    }
+}