Move SQLite connections out of database classes; make abstract Database.

osu.Game/Database/Database.cs

@@ -0,0 +1,44 @@
+// 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 osu.Framework.Logging;
+using osu.Framework.Platform;
+using SQLite.Net;
+
+namespace osu.Game.Database
+{
+    public abstract class Database
+    {
+        protected SQLiteConnection Connection { get; }
+        protected Storage Storage { get; }
+
+        protected Database(Storage storage, SQLiteConnection connection)
+        {
+            Storage = storage;
+            Connection = connection;
+
+            try
+            {
+                Prepare();
+            }
+            catch (Exception e)
+            {
+                Logger.Error(e, @"Failed to initialise the beatmap database! Trying again with a clean database...");
+                storage.DeleteDatabase(@"beatmaps");
+                Reset();
+                Prepare();
+            }
+        }
+
+        /// <summary>
+        /// Prepare this database for use.
+        /// </summary>
+        protected abstract void Prepare();
+
+        /// <summary>
+        /// Reset this database to a default state. Undo all changes to database and storage backings.
+        /// </summary>
+        public abstract void Reset();
+    }
+}