Add warning message when power save mode is enabled for attention settings fragment

Test: locally with flame, make RunSettingsRoboTests -j96 ROBOTEST_FILTER=AdaptiveSleepPreferenceControllerTest,AdaptiveSleepBatterySaverPreferenceControllerTest

Bug: 186690152
Change-Id: I42e018a8cf48166a8250fac9510a8882efb58568

src/com/android/settings/display/AdaptiveSleepBatterySaverPreferenceController.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2021 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.settings.display;
+
+import android.content.Context;
+import android.os.PowerManager;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.preference.PreferenceScreen;
+
+import com.android.settings.R;
+import com.android.settingslib.widget.BannerMessagePreference;
+
+/**
+ * The controller of Screen attention's battery saver warning preference.
+ * The preference appears when Screen Attention feature is disabled by battery saver mode.
+ */
+public class AdaptiveSleepBatterySaverPreferenceController {
+
+    @VisibleForTesting
+    final BannerMessagePreference mPreference;
+    private final PowerManager mPowerManager;
+
+    public AdaptiveSleepBatterySaverPreferenceController(Context context) {
+        mPreference = new BannerMessagePreference(context);
+        mPreference.setTitle(R.string.ambient_camera_summary_battery_saver_on);
+        mPreference.setPositiveButtonText(R.string.disable_text);
+        mPowerManager = context.getSystemService(PowerManager.class);
+        mPreference.setPositiveButtonOnClickListener(p -> {
+            mPowerManager.setPowerSaveModeEnabled(false);
+        });
+    }
+
+    /**
+     * Adds the controlled preference to the provided preference screen.
+     */
+    public void addToScreen(PreferenceScreen screen) {
+        screen.addPreference(mPreference);
+        updateVisibility();
+    }
+
+    /**
+     * Need this because all controller tests use RoboElectric. No easy way to mock this service,
+     * so we mock the call we need
+     */
+    @VisibleForTesting
+    boolean isPowerSaveMode() {
+        return mPowerManager.isPowerSaveMode();
+    }
+
+    /**
+     * Refreshes the visibility of the preference.
+     */
+    public void updateVisibility() {
+        mPreference.setVisible(isPowerSaveMode());
+    }
+}