Add back osu.Desktop project

While it was nice having less projects to deal with, it meant hacks to get around circular dependencies between rulesets and osu.Game. For now, let's just restore the osu.Desktop project and call it a day.

This allows for the project to build again with default visual studio settings.

osu.Desktop/OsuGameDesktop.cs

@@ -0,0 +1,142 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Drawing;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Threading.Tasks;
+using System.Windows.Forms;
+using Microsoft.Win32;
+using osu.Desktop.Overlays;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Platform;
+using osu.Game;
+using osu.Game.Screens.Menu;
+
+namespace osu.Desktop
+{
+    internal class OsuGameDesktop : OsuGame
+    {
+        private VersionManager versionManager;
+
+        public OsuGameDesktop(string[] args = null)
+            : base(args)
+        {
+        }
+
+        public override Storage GetStorageForStableInstall()
+        {
+            try
+            {
+                return new StableStorage();
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
+        /// <summary>
+        /// A method of accessing an osu-stable install in a controlled fashion.
+        /// </summary>
+        private class StableStorage : DesktopStorage
+        {
+            protected override string LocateBasePath()
+            {
+                Func<string, bool> checkExists = p => Directory.Exists(Path.Combine(p, "Songs"));
+
+                string stableInstallPath;
+
+                try
+                {
+                    using (RegistryKey key = Registry.ClassesRoot.OpenSubKey("osu"))
+                        stableInstallPath = key?.OpenSubKey(@"shell\open\command")?.GetValue(String.Empty).ToString().Split('"')[1].Replace("osu!.exe", "");
+
+                    if (checkExists(stableInstallPath))
+                        return stableInstallPath;
+                }
+                catch
+                {
+                }
+
+                stableInstallPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), @"osu!");
+                if (checkExists(stableInstallPath))
+                    return stableInstallPath;
+
+                stableInstallPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile), ".osu");
+                if (checkExists(stableInstallPath))
+                    return stableInstallPath;
+
+                return null;
+            }
+
+            public StableStorage()
+                : base(string.Empty)
+            {
+            }
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            LoadComponentAsync(versionManager = new VersionManager { Depth = int.MinValue });
+
+            ScreenChanged += s =>
+            {
+                if (s is Intro && s.ChildScreen == null)
+                {
+                    Add(versionManager);
+                    versionManager.State = Visibility.Visible;
+                }
+            };
+        }
+
+        public override void SetHost(GameHost host)
+        {
+            base.SetHost(host);
+            var desktopWindow = host.Window as DesktopGameWindow;
+            if (desktopWindow != null)
+            {
+                desktopWindow.CursorState |= CursorState.Hidden;
+
+                desktopWindow.Icon = new Icon(Assembly.GetExecutingAssembly().GetManifestResourceStream(GetType(), "lazer.ico"));
+                desktopWindow.Title = Name;
+
+                desktopWindow.DragEnter += dragEnter;
+                desktopWindow.DragDrop += dragDrop;
+            }
+        }
+
+        private void dragDrop(DragEventArgs e)
+        {
+            // this method will only be executed if e.Effect in dragEnter gets set to something other that None.
+            var dropData = (object[])e.Data.GetData(DataFormats.FileDrop);
+            var filePaths = dropData.Select(f => f.ToString()).ToArray();
+
+            if (filePaths.All(f => Path.GetExtension(f) == @".osz"))
+                Task.Run(() => BeatmapManager.Import(filePaths));
+            else if (filePaths.All(f => Path.GetExtension(f) == @".osr"))
+                Task.Run(() =>
+                {
+                    var score = ScoreStore.ReadReplayFile(filePaths.First());
+                    Schedule(() => LoadScore(score));
+                });
+        }
+
+        private static readonly string[] allowed_extensions = { @".osz", @".osr" };
+
+        private void dragEnter(DragEventArgs e)
+        {
+            // dragDrop will only be executed if e.Effect gets set to something other that None in this method.
+            bool isFile = e.Data.GetDataPresent(DataFormats.FileDrop);
+            if (isFile)
+            {
+                var paths = ((object[])e.Data.GetData(DataFormats.FileDrop)).Select(f => f.ToString()).ToArray();
+                e.Effect = allowed_extensions.Any(ext => paths.All(p => p.EndsWith(ext))) ? DragDropEffects.Copy : DragDropEffects.None;
+            }
+        }
+    }
+}