Resurrect SimpleUpdateManager as MobileUpdateNotifier

While removing the desktop specific logic from it

osu.Android/OsuGameAndroid.cs

@@ -80,7 +80,7 @@ namespace osu.Android
             host.Window.CursorState |= CursorState.Hidden;
         }
 
-        protected override UpdateManager CreateUpdateManager() => new SimpleUpdateManager();
+        protected override UpdateManager CreateUpdateManager() => new MobileUpdateNotifier();
 
         protected override BatteryInfo CreateBatteryInfo() => new AndroidBatteryInfo();
 

osu.Game/Updater/MobileUpdateNotifier.cs

@@ -0,0 +1,102 @@
+// 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.
+
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using System.Threading.Tasks;
+using osu.Framework;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics.Sprites;
+using osu.Framework.Platform;
+using osu.Game.Online.API;
+using osu.Game.Overlays.Notifications;
+
+namespace osu.Game.Updater
+{
+    /// <summary>
+    /// An update manager that shows notifications if a newer release is detected for mobile platforms.
+    /// Installation is left up to the user.
+    /// </summary>
+    public partial class MobileUpdateNotifier : UpdateManager
+    {
+        private string version = null!;
+
+        [Resolved]
+        private GameHost host { get; set; } = null!;
+
+        [BackgroundDependencyLoader]
+        private void load(OsuGameBase game)
+        {
+            version = game.Version;
+        }
+
+        protected override async Task<bool> PerformUpdateCheck()
+        {
+            try
+            {
+                var releases = new OsuJsonWebRequest<GitHubRelease>("https://api.github.com/repos/ppy/osu/releases/latest");
+
+                await releases.PerformAsync().ConfigureAwait(false);
+
+                var latest = releases.ResponseObject;
+
+                // avoid any discrepancies due to build suffixes for now.
+                // eventually we will want to support release streams and consider these.
+                version = version.Split('-').First();
+                string latestTagName = latest.TagName.Split('-').First();
+
+                if (latestTagName != version && tryGetBestUrl(latest, out string? url))
+                {
+                    Notifications.Post(new SimpleNotification
+                    {
+                        Text = $"A newer release of osu! has been found ({version} → {latestTagName}).\n\n"
+                               + "Click here to download the new version, which can be installed over the top of your existing installation",
+                        Icon = FontAwesome.Solid.Download,
+                        Activated = () =>
+                        {
+                            host.OpenUrlExternally(url);
+                            return true;
+                        }
+                    });
+
+                    return true;
+                }
+            }
+            catch
+            {
+                // we shouldn't crash on a web failure. or any failure for the matter.
+                return true;
+            }
+
+            return false;
+        }
+
+        private bool tryGetBestUrl(GitHubRelease release, [NotNullWhen(true)] out string? url)
+        {
+            url = null;
+            GitHubAsset? bestAsset = null;
+
+            switch (RuntimeInfo.OS)
+            {
+                case RuntimeInfo.Platform.iOS:
+                    if (release.Assets?.Exists(f => f.Name.EndsWith(".ipa", StringComparison.Ordinal)) == true)
+                        // iOS releases are available via testflight. this link seems to work well enough for now.
+                        // see https://stackoverflow.com/a/32960501
+                        url = "itms-beta://beta.itunes.apple.com/v1/app/1447765923";
+
+                    break;
+
+                case RuntimeInfo.Platform.Android:
+                    if (release.Assets?.Exists(f => f.Name.EndsWith(".apk", StringComparison.Ordinal)) == true)
+                        // on our testing device using the .apk URL causes the download to magically disappear.
+                        url = release.HtmlUrl;
+
+                    break;
+            }
+
+            url ??= bestAsset?.BrowserDownloadUrl;
+            return url != null;
+        }
+    }
+}

osu.iOS/OsuGameIOS.cs

@@ -15,7 +15,7 @@ namespace osu.iOS
     {
         public override Version AssemblyVersion => new Version(NSBundle.MainBundle.InfoDictionary["CFBundleVersion"].ToString());
 
-        protected override UpdateManager CreateUpdateManager() => new SimpleUpdateManager();
+        protected override UpdateManager CreateUpdateManager() => new MobileUpdateNotifier();
 
         protected override BatteryInfo CreateBatteryInfo() => new IOSBatteryInfo();