Use DI to implement battery detection, add BatteryCutoff property

- Removed the Xamarin.Essentials package from osu.Game and added it to osu.iOS and osu.Android only.
- iOS and Android implementations use Xamarin.Essentials.Battery, while the Desktop implementation
only returns 100% battery for now.
- Added a BatteryCutoff property to PowerStatus so it can be different for each platform (default 20%, 25% on iOS)

osu.Game/OsuGameBase.cs

@@ -40,6 +40,7 @@ using osu.Game.Rulesets;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Scoring;
 using osu.Game.Skinning;
+using osu.Game.Utils;
 using osuTK.Input;
 using RuntimeInfo = osu.Framework.RuntimeInfo;
 
@@ -95,6 +96,8 @@ namespace osu.Game
 
         protected Storage Storage { get; set; }
 
+        protected PowerStatus powerStatus;
+
         [Cached]
         [Cached(typeof(IBindable<RulesetInfo>))]
         protected readonly Bindable<RulesetInfo> Ruleset = new Bindable<RulesetInfo>();
@@ -329,6 +332,8 @@ namespace osu.Game
             dependencies.CacheAs(MusicController);
 
             Ruleset.BindValueChanged(onRulesetChanged);
+
+            dependencies.CacheAs(powerStatus);
         }
 
         private void onRulesetChanged(ValueChangedEvent<RulesetInfo> r)

osu.Game/Screens/Play/PlayerLoader.cs

@@ -24,9 +24,9 @@ using osu.Game.Overlays.Notifications;
 using osu.Game.Screens.Menu;
 using osu.Game.Screens.Play.PlayerSettings;
 using osu.Game.Users;
+using osu.Game.Utils;
 using osuTK;
 using osuTK.Graphics;
-using Xamarin.Essentials;
 
 namespace osu.Game.Screens.Play
 {
@@ -113,6 +113,9 @@ namespace osu.Game.Screens.Play
         [Resolved]
         private AudioManager audioManager { get; set; }
 
+        [Resolved]
+        private PowerStatus powerStatus { get; set; }
+
         public PlayerLoader(Func<Player> createPlayer)
         {
             this.createPlayer = createPlayer;
@@ -265,7 +268,6 @@ namespace osu.Game.Screens.Play
         }
 
         #endregion
-
         protected override void Update()
         {
             base.Update();
@@ -477,45 +479,18 @@ namespace osu.Game.Screens.Play
         #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)
+                // Checks if the notification has not been shown yet, device is unplugged and if device battery is at or below the cutoff
+                if (!powerStatus.IsCharging && powerStatus.ChargeLevel <= powerStatus.BatteryCutoff)
                 {
-                    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
         {

osu.Game/Tests/OsuTestBrowser.cs

@@ -7,11 +7,16 @@ using osu.Framework.Screens;
 using osu.Framework.Testing;
 using osu.Game.Graphics;
 using osu.Game.Screens.Backgrounds;
+using osu.Game.Utils;
 
 namespace osu.Game.Tests
 {
     public class OsuTestBrowser : OsuGameBase
     {
+        public OsuTestBrowser()
+        {
+            powerStatus = new DefaultPowerStatus();
+        }
         protected override void LoadComplete()
         {
             base.LoadComplete();

osu.Game/Utils/PowerStatus.cs

@@ -0,0 +1,22 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+namespace osu.Game.Utils
+{
+    public abstract class PowerStatus
+    {
+        /// <summary>
+        /// The maximum battery level before a warning notification
+        /// is sent.
+        /// </summary>
+        public virtual double BatteryCutoff { get; } = 0.2;
+        public virtual double ChargeLevel { get; set; }
+        public virtual bool IsCharging { get; set; }
+    }
+
+    public class DefaultPowerStatus : PowerStatus
+    {
+        public override double ChargeLevel { get; set; } = 1;
+        public override bool IsCharging { get; set; } = true;
+    }
+}