Send a warning notification if device is unplugged and low battery

- Uses Xamarin.Essentials in osu.Game.PlayerLoader to check battery level
- Encapsulated battery checking in the public BatteryManager class so battery level and plugged in status can be accessed and edited in TestPlayerLoader
- When checking battery level, catch NotImplementedException thrown by Xamarin.Essentials.Battery on non-mobile platforms
- Added visual unit tests for battery notification
  To mock battery status and level, we had to define a batteryManager object in TestPlayerLoader and add a new function ResetPlayerWithBattery()

Co-Authored-By: Marlina José <marlina@umich.edu>

osu.Android/Properties/AndroidManifest.xml

@@ -6,5 +6,6 @@
 	<uses-permission android:name="android.permission.WAKE_LOCK" />
 	<uses-permission android:name="android.permission.READ_FRAME_BUFFER" />
 	<uses-permission android:name="android.permission.INTERNET" />
+	<uses-permission android:name="android.permission.BATTERY_STATS" />
 	<application android:allowBackup="true" android:supportsRtl="true" android:label="osu!" android:icon="@drawable/lazer" />
 </manifest>

osu.Game.Tests/Visual/Gameplay/TestScenePlayerLoader.cs

@@ -93,6 +93,26 @@ namespace osu.Game.Tests.Visual.Gameplay
             LoadScreen(loader = new TestPlayerLoader(() => player = new TestPlayer(interactive, interactive)));
         }
 
+        /// <summary>
+        /// Sets the input manager child to a new test player loader container instance with a custom battery level
+        /// </summary>
+        /// <param name="interactive">If the test player should behave like the production one.</param>
+        /// <param name="pluggedIn">If the player's device is plugged in.</param>
+        /// <param name="batteryLevel">A custom battery level for the test player.</param>
+        private void resetPlayerWithBattery(bool interactive, bool pluggedIn, double batteryLevel)
+        {
+            Beatmap.Value = CreateWorkingBeatmap(new OsuRuleset().RulesetInfo);
+            Beatmap.Value.BeatmapInfo.EpilepsyWarning = epilepsyWarning;
+
+            foreach (var mod in SelectedMods.Value.OfType<IApplicableToTrack>())
+                mod.ApplyToTrack(Beatmap.Value.Track);
+
+            loader = new TestPlayerLoader(() => player = new TestPlayer(interactive, interactive));
+            loader.batteryManager.ChargeLevel = batteryLevel;
+            loader.batteryManager.PluggedIn = pluggedIn;
+            LoadScreen(loader);
+        }
+
         [Test]
         public void TestEarlyExitBeforePlayerConstruction()
         {
@@ -270,6 +290,32 @@ namespace osu.Game.Tests.Visual.Gameplay
             AddUntilStep("wait for player load", () => player.IsLoaded);
         }
 
+        [TestCase(false, 1.0)] // not plugged in, full battery, no notification
+        [TestCase(false, 0.2)] // not plugged in, at warning level, no notification
+        [TestCase(true, 0.1)] // plugged in, charging, below warning level, no notification
+        [TestCase(false, 0.1)] // not plugged in, below warning level, notification
+        public void TestLowBatteryNotification(bool pluggedIn, double batteryLevel)
+        {
+            AddStep("reset notification lock", () => sessionStatics.GetBindable<bool>(Static.BatteryLowNotificationShownOnce).Value = false);
+
+            // mock phone on battery
+            AddStep("load player", () => resetPlayerWithBattery(false, pluggedIn, batteryLevel));
+            AddUntilStep("wait for player", () => player?.LoadState == LoadState.Ready);
+            int notificationCount = !pluggedIn && batteryLevel < PlayerLoader.battery_tolerance ? 1 : 0;
+            AddAssert("check for notification", () => notificationOverlay.UnreadCount.Value == notificationCount);
+            AddStep("click notification", () =>
+                {
+                    var scrollContainer = (OsuScrollContainer)notificationOverlay.Children.Last();
+                    var flowContainer = scrollContainer.Children.OfType<FillFlowContainer<NotificationSection>>().First();
+                    var notification = flowContainer.First();
+
+                    InputManager.MoveMouseTo(notification);
+                    InputManager.Click(MouseButton.Left);
+                });
+
+            AddUntilStep("wait for player load", () => player.IsLoaded);
+        }
+
         [TestCase(true)]
         [TestCase(false)]
         public void TestEpilepsyWarning(bool warning)
@@ -310,6 +356,8 @@ namespace osu.Game.Tests.Visual.Gameplay
 
             public IReadOnlyList<Mod> DisplayedMods => MetadataInfo.Mods.Value;
 
+            public new BatteryManager batteryManager => base.batteryManager;
+
             public TestPlayerLoader(Func<Player> createPlayer)
                 : base(createPlayer)
             {

osu.Game.Tests/osu.Game.Tests.csproj

@@ -22,4 +22,4 @@
     <ProjectReference Include="..\osu.Game.Rulesets.Mania\osu.Game.Rulesets.Mania.csproj" />
     <ProjectReference Include="..\osu.Game.Rulesets.Taiko\osu.Game.Rulesets.Taiko.csproj" />
   </ItemGroup>
-</Project>
+</Project>

osu.Game/Configuration/SessionStatics.cs

@@ -16,6 +16,7 @@ namespace osu.Game.Configuration
         {
             SetDefault(Static.LoginOverlayDisplayed, false);
             SetDefault(Static.MutedAudioNotificationShownOnce, false);
+            SetDefault(Static.BatteryLowNotificationShownOnce, false);
             SetDefault(Static.LastHoverSoundPlaybackTime, (double?)null);
             SetDefault<APISeasonalBackgrounds>(Static.SeasonalBackgrounds, null);
         }
@@ -25,6 +26,7 @@ namespace osu.Game.Configuration
     {
         LoginOverlayDisplayed,
         MutedAudioNotificationShownOnce,
+        BatteryLowNotificationShownOnce,
 
         /// <summary>
         /// Info about seasonal backgrounds available fetched from API - see <see cref="APISeasonalBackgrounds"/>.

osu.Game/Screens/Play/PlayerLoader.cs

@@ -26,6 +26,7 @@ using osu.Game.Screens.Play.PlayerSettings;
 using osu.Game.Users;
 using osuTK;
 using osuTK.Graphics;
+using Xamarin.Essentials;
 
 namespace osu.Game.Screens.Play
 {
@@ -121,6 +122,7 @@ namespace osu.Game.Screens.Play
         private void load(SessionStatics sessionStatics)
         {
             muteWarningShownOnce = sessionStatics.GetBindable<bool>(Static.MutedAudioNotificationShownOnce);
+            batteryWarningShownOnce = sessionStatics.GetBindable<bool>(Static.BatteryLowNotificationShownOnce);
 
             InternalChild = (content = new LogoTrackingContainer
             {
@@ -196,6 +198,7 @@ namespace osu.Game.Screens.Play
             Scheduler.Add(new ScheduledDelegate(pushWhenLoaded, Clock.CurrentTime + 1800, 0));
 
             showMuteWarningIfNeeded();
+            showBatteryWarningIfNeeded();
         }
 
         public override void OnResuming(IScreen last)
@@ -470,5 +473,73 @@ namespace osu.Game.Screens.Play
         }
 
         #endregion
+
+        #region Low battery warning
+        private Bindable<bool> batteryWarningShownOnce;
+
+        // Send a warning if battery is less than 20%
+        public const double battery_tolerance = 0.2;
+
+        private void showBatteryWarningIfNeeded()
+        {
+            if (!batteryWarningShownOnce.Value)
+            {
+                // Checks if the notification has not been shown yet, device is unplugged and if device battery is low.
+                if (!batteryManager.PluggedIn && batteryManager.ChargeLevel < battery_tolerance)
+                {
+                    Console.WriteLine("Battery level: {0}", batteryManager.ChargeLevel);
+                    notificationOverlay?.Post(new BatteryWarningNotification());
+                    batteryWarningShownOnce.Value = true;
+                }
+            }
+        }
+        public BatteryManager batteryManager = new BatteryManager();
+        public class BatteryManager
+        {
+            public double ChargeLevel;
+            public bool PluggedIn;
+            public BatteryManager()
+            {
+                // Attempt to get battery information using Xamarin.Essentials
+                // Xamarin.Essentials throws a NotSupportedOrImplementedException on .NET standard so this only works on iOS/Android
+                // https://github.com/xamarin/Essentials/blob/7218ab88f7fbe00ec3379bd54e6c0ce35ffc0c22/Xamarin.Essentials/Battery/Battery.netstandard.tvos.cs
+                try
+                {
+                    ChargeLevel = Battery.ChargeLevel;
+                    PluggedIn = Battery.PowerSource == BatteryPowerSource.Battery;
+                }
+                catch (NotImplementedException e)
+                {
+                    Console.WriteLine("Could not access battery info: {0}", e);
+                    ChargeLevel = 1.0;
+                    PluggedIn = false;
+                }
+            }
+        }
+
+        private class BatteryWarningNotification : SimpleNotification
+        {
+            public override bool IsImportant => true;
+
+            public BatteryWarningNotification()
+            {
+                Text = "Your battery level is low! Charge your device to prevent interruptions.";
+            }
+
+            [BackgroundDependencyLoader]
+            private void load(OsuColour colours, NotificationOverlay notificationOverlay)
+            {
+                Icon = FontAwesome.Solid.BatteryQuarter;
+                IconBackgound.Colour = colours.RedDark;
+
+                Activated = delegate
+                {
+                    notificationOverlay.Hide();
+                    return true;
+                };
+            }
+        }
+
+        #endregion
     }
 }

osu.Game/osu.Game.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup Label="Project">
     <TargetFramework>netstandard2.1</TargetFramework>
     <OutputType>Library</OutputType>
@@ -35,5 +35,6 @@
     <PackageReference Include="SharpCompress" Version="0.28.1" />
     <PackageReference Include="NUnit" Version="3.13.1" />
     <PackageReference Include="System.ComponentModel.Annotations" Version="5.0.0" />
+    <PackageReference Include="Xamarin.Essentials" Version="1.6.1" />
   </ItemGroup>
 </Project>