Next piece of the puzzle

This probably breaks something.  I am sorry, grab me and I'll fix it

src/BizHawk.Client.Common/RomLoader.cs

@@ -423,7 +423,50 @@ namespace BizHawk.Client.Common
 			throw new NotImplementedException("M3U not supported!");
 		}
 
-		private void LoadOther(string path, CoreComm nextComm, bool forceAccurateCore, HawkFile file, out IEmulator nextEmulator, out RomGame rom, out GameInfo game, out bool cancel)
+		private static string ForcedCoreToCoreName(string forcedCore)
+		{
+			// TODO: Is this yet another list of core names really needed?  Let's just make the gamedb less dumb
+			return forcedCore switch
+			{
+				"snes9x" => CoreNames.Snes9X,
+				"bsnes" => CoreNames.Bsnes,
+				"quicknes" => CoreNames.QuickNes,
+				"pico" => CoreNames.PicoDrive,
+				_ => null
+			};
+		}
+
+		private IEmulator MakeCoreFromCoreInventory(string systemId, CoreInventoryParameters cip, string forcedCoreGameDb)
+		{
+			_config.PreferredCores.TryGetValue(systemId, out var preferredCore);
+			var forcedCore = ForcedCoreToCoreName(forcedCoreGameDb);
+			var cores = CoreInventory.Instance.GetCores(systemId)
+				.OrderBy(c =>
+				{
+					if (c.Name == preferredCore)
+						return (int)CorePriority.UserPreference;
+					else if (c.Name == forcedCore)
+						return (int)CorePriority.GameDbPreference;
+					else
+						return (int)c.Priority;
+				})
+				.ToList();
+			var exceptions = new List<Exception>();
+			foreach (var core in cores)
+			{
+				try
+				{
+					return core.Create(cip);
+				}
+				catch (Exception e)
+				{
+					exceptions.Add(e);
+				}
+			}
+			throw new AggregateException("No core could load the ROM", exceptions);
+		}
+
+		private void LoadOther(string path, CoreComm nextComm, HawkFile file, out IEmulator nextEmulator, out RomGame rom, out GameInfo game, out bool cancel)
 		{
 			cancel = false;
 			rom = new RomGame(file);
@@ -463,92 +506,17 @@ namespace BizHawk.Client.Common
 
 			game = rom.GameInfo;
 
-			var isXml = false;
-			if (file.Extension.ToLowerInvariant() == ".xml")
-			{
-				game.System = "SNES"; // other xml has already been handled
-				isXml = true;
-			}
-
 			nextEmulator = null;
 			if (game.System == null)
 				return; // The user picked nothing in the Core picker
 
-			CoreInventory.Core core;
 			switch (game.System)
 			{
-				case "SNES":
-					var name = game.ForcedCore?.ToLower() switch
-					{
-						"snes9x" => CoreNames.Snes9X,
-						"bsnes" => CoreNames.Bsnes,
-						_ => _config.PreferredCores["SNES"]
-					};
-					try
-					{
-						core = CoreInventory.Instance["SNES", name];
-					}
-					catch // TODO: CoreInventory should support some sort of trygetvalue
-					{
-						// need to get rid of this hack at some point
-						nextEmulator = new LibsnesCore(
-							game,
-							isXml ? null : rom.FileData,
-							isXml ? rom.FileData : null,
-							Path.GetDirectoryName(path.SubstringBefore('|')),
-							nextComm,
-							GetCoreSettings<LibsnesCore, LibsnesCore.SnesSettings>(),
-							GetCoreSyncSettings<LibsnesCore, LibsnesCore.SnesSyncSettings>()
-						);
-						return;
-					}
-					break;
-				case "NES":
-					// apply main spur-of-the-moment switcheroo as lowest priority
-					var preference = _config.PreferredCores["NES"];
-
-					// if user has saw fit to override in gamedb, apply that
-					if (!string.IsNullOrEmpty(game.ForcedCore))
-					{
-						preference = game.ForcedCore.ToLower() switch
-						{
-							"quicknes" => CoreNames.QuickNes,
-							_ => CoreNames.NesHawk
-						};
-					}
-
-					// but only neshawk is accurate
-					if (forceAccurateCore)
-					{
-						preference = CoreNames.NesHawk;
-					}
-
-					core = CoreInventory.Instance["NES", preference];
-					break;
 				case "GB":
 				case "GBC":
 					if (_config.GbAsSgb)
 					{
-						if (_config.SgbUseBsnes)
+						game.System = "SGB";
-						{
-							game.System = "SNES";
-							game.AddOption("SGB", "");
-							nextEmulator = new LibsnesCore(
-								game,
-								rom.FileData,
-								null,
-								null,
-								nextComm,
-								GetCoreSettings<LibsnesCore, LibsnesCore.SnesSettings>(),
-								GetCoreSyncSettings<LibsnesCore, LibsnesCore.SnesSyncSettings>()
-							);
-							return;
-						}
-						core = CoreInventory.Instance["SGB", CoreNames.SameBoy];
-					}
-					else
-					{
-						core = CoreInventory.Instance["GB", _config.PreferredCores["GB"]];
 					}
 					break;
 				case "ChannelF":
@@ -567,17 +535,10 @@ namespace BizHawk.Client.Common
 					);
 					rom.GameInfo.Name = gameName;
 					return;
-				case "GEN":
-					core = CoreInventory.Instance["GEN", game.ForcedCore?.ToLower() == "pico" ? CoreNames.PicoDrive : CoreNames.Gpgx];
-					break;
 				default:
-					core = _config.PreferredCores.TryGetValue(game.System, out var coreName)
-						? CoreInventory.Instance[game.System, coreName]
-						: CoreInventory.Instance[game.System];
 					break;
 			}
-
+			var cip = new CoreInventoryParameters(this)
-			nextEmulator = core.Create(new CoreInventoryParameters(this)
 			{
 				Comm = nextComm,
 				Game = game,
@@ -593,7 +554,8 @@ namespace BizHawk.Client.Common
 				},
 				DeterministicEmulationRequested = Deterministic
 
-			});
+			};
+			nextEmulator = MakeCoreFromCoreInventory(game.System, cip, game.ForcedCore);
 		}
 
 		private void LoadPSF(string path, CoreComm nextComm, HawkFile file, out IEmulator nextEmulator, out RomGame rom, out GameInfo game)
@@ -747,7 +709,7 @@ namespace BizHawk.Client.Common
 			}
 		}
 
-		public bool LoadRom(string path, CoreComm nextComm, string launchLibretroCore, bool forceAccurateCore = false, int recursiveCount = 0)
+		public bool LoadRom(string path, CoreComm nextComm, string launchLibretroCore, int recursiveCount = 0)
 		{
 			if (path == null) return false;
 
@@ -862,7 +824,7 @@ namespace BizHawk.Client.Common
 							}
 							else
 							{
-								LoadOther(path, nextComm, forceAccurateCore, file, out nextEmulator, out rom, out game, out cancel); // must be called after LoadXML because of SNES hacks
+								LoadOther(path, nextComm, file, out nextEmulator, out rom, out game, out cancel); // must be called after LoadXML because of SNES hacks
 							}
 							break;
 					}
@@ -894,7 +856,7 @@ namespace BizHawk.Client.Common
 						DoMessageCallback("Unable to use quicknes, using NESHawk instead");
 					}
 
-					return LoadRom(path, nextComm, launchLibretroCore, true, recursiveCount + 1);
+					return LoadRom(path, nextComm, launchLibretroCore, recursiveCount + 1);
 				}
 				else if (ex is MissingFirmwareException)
 				{
@@ -906,7 +868,7 @@ namespace BizHawk.Client.Common
 					// To avoid catch-22, disable SGB mode
 					_config.GbAsSgb = false;
 					DoMessageCallback("Failed to load a GB rom in SGB mode.  Disabling SGB Mode.");
-					return LoadRom(path, nextComm, launchLibretroCore, false, recursiveCount + 1);
+					return LoadRom(path, nextComm, launchLibretroCore, recursiveCount + 1);
 				}
 				else if (ex is NoAvailableCoreException)
 				{

src/BizHawk.Emulation.Cores/Consoles/NEC/PCE/HyperNyma.cs

@@ -16,7 +16,8 @@ namespace BizHawk.Emulation.Cores.Consoles.NEC.PCE
 	{
 		private readonly LibHyperNyma _hyperNyma;
 
-		[CoreConstructor(new[] { "PCE", "SGX" })]
+		[CoreConstructor("PCE", Priority = CorePriority.Low)]
+		[CoreConstructor("SGX", Priority = CorePriority.Low)]
 		public HyperNyma(GameInfo game, byte[] rom, CoreComm comm, string extension,
 			NymaSettings settings, NymaSyncSettings syncSettings, bool deterministic)
 			: base(comm, "PCE", "PC Engine Controller", settings, syncSettings)

src/BizHawk.Emulation.Cores/Consoles/NEC/PCE/TurboNyma.cs

@@ -16,7 +16,8 @@ namespace BizHawk.Emulation.Cores.Consoles.NEC.PCE
 	{
 		private readonly LibTurboNyma _turboNyma;
 
-		[CoreConstructor(new[] { "PCE", "SGX" })]
+		[CoreConstructor("PCE")]
+		[CoreConstructor("SGX")]
 		public TurboNyma(GameInfo game, byte[] rom, CoreComm comm, string extension,
 			NymaSettings settings, NymaSyncSettings syncSettings, bool deterministic)
 			: base(comm, "PCE", "PC Engine Controller", settings, syncSettings)

src/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/GBHawk.cs

@@ -93,7 +93,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 		private static byte[] GBA_override = { 0xFF, 0x00, 0xCD, 0x03, 0x35, 0xAA, 0x31, 0x90, 0x94, 0x00, 0x00, 0x00, 0x00 };
 
-		[CoreConstructor(new[] { "GB", "GBC" })]
+		[CoreConstructor("GB")]
+		[CoreConstructor("GBC")]
 		public GBHawk(CoreComm comm, GameInfo game, byte[] rom, /*string gameDbFn,*/ GBSettings settings, GBSyncSettings syncSettings)
 		{
 			var ser = new BasicServiceProvider(this);

src/BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/Gambatte.cs

@@ -23,7 +23,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 		IBoardInfo, IRomInfo, IDebuggable, ISettable<Gameboy.GambatteSettings, Gameboy.GambatteSyncSettings>,
 		IGameboyCommon, ICycleTiming, ILinkable
 	{
-		[CoreConstructor(new[] { "GB", "GBC" })]
+		[CoreConstructor("GB")]
+		[CoreConstructor("GBC")]
 		public Gameboy(CoreComm comm, GameInfo game, byte[] file, Gameboy.GambatteSettings settings, Gameboy.GambatteSyncSettings syncSettings, bool deterministic)
 		{
 			var ser = new BasicServiceProvider(this);

src/BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/Sameboy.cs

@@ -41,6 +41,7 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.Gameboy
 		{ }
 
 		[CoreConstructor("GB")]
+		[CoreConstructor("GBC")]
 		public Sameboy(CoreComm comm, byte[] rom, Settings settings, SyncSettings syncSettings, bool deterministic)
 			: this(rom, comm, false, settings, syncSettings, deterministic)
 		{ }

src/BizHawk.Emulation.Cores/Consoles/Nintendo/QuickNES/QuickNES.cs

@@ -33,7 +33,7 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.QuickNES
 			QN.qn_setup_mappers();
 		}
 
-		[CoreConstructor("NES")]
+		[CoreConstructor("NES", Priority = CorePriority.Low)]
 		public QuickNES(byte[] file, QuickNESSettings settings, QuickNESSyncSettings syncSettings)
 		{
 			FP = OSTailoredCode.IsUnixHost

src/BizHawk.Emulation.Cores/Consoles/Nintendo/SNES/LibsnesCore.cs

@@ -29,6 +29,13 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES
 	public unsafe partial class LibsnesCore : IEmulator, IVideoProvider, ISaveRam, IStatable, IInputPollable, IRegionable, ICodeDataLogger,
 		IDebuggable, ISettable<LibsnesCore.SnesSettings, LibsnesCore.SnesSyncSettings>
 	{
+		[CoreConstructor("SGB")]
+		[CoreConstructor("SNES")]
+		public LibsnesCore(GameInfo game, byte[] rom, CoreComm comm,
+			LibsnesCore.SnesSettings settings, LibsnesCore.SnesSyncSettings syncSettings)
+			:this(game, rom, null, null, comm, settings, syncSettings)
+		{}
+		
 		public LibsnesCore(GameInfo game, byte[] romData, byte[] xmlData, string baseRomPath, CoreComm comm,
 			LibsnesCore.SnesSettings settings, LibsnesCore.SnesSyncSettings syncSettings)
 		{
@@ -47,7 +54,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES
 			CoreComm = comm;
 			byte[] sgbRomData = null;
 
-			if (game["SGB"])
+			if (game.System == "SGB")
 			{
 				if ((romData[0x143] & 0xc0) == 0xc0)
 				{
@@ -112,7 +119,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES
 				romData = newData;
 			}
 
-			if (game["SGB"])
+			if (game.System == "SGB")
 			{
 				IsSGB = true;
 				SystemId = "SNES";

src/BizHawk.Emulation.Cores/Consoles/Nintendo/SubGBHawk/SubGBHawk.cs

@@ -14,7 +14,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.SubGBHawk
 	public partial class SubGBHawk : IEmulator, IStatable, IInputPollable,
 		ISettable<GBHawk.GBHawk.GBSettings, GBHawk.GBHawk.GBSyncSettings>, IDebuggable
 	{
-		[CoreConstructor(new[] { "GB", "GBC" })]
+		[CoreConstructor("GB", Priority = CorePriority.SuperLow)]
+		[CoreConstructor("GBC", Priority = CorePriority.SuperLow)]
 		public SubGBHawk(CoreComm comm, GameInfo game, byte[] rom, /*string gameDbFn,*/ GBHawk.GBHawk.GBSettings settings, GBHawk.GBHawk.GBSyncSettings syncSettings)
 		{
 			

src/BizHawk.Emulation.Cores/Consoles/Nintendo/SubNESHawk/SubNESHawk.cs

@@ -12,7 +12,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.SubNESHawk
 	public partial class SubNESHawk : IEmulator, IStatable, IInputPollable,
 		ISettable<NES.NES.NESSettings, NES.NES.NESSyncSettings>
 	{
-		[CoreConstructor("NES")]
+		[CoreConstructor("NES", Priority = CorePriority.SuperLow)]
 		public SubNESHawk(CoreComm comm, GameInfo game, byte[] rom, /*string gameDbFn,*/ NES.NES.NESSettings settings, NES.NES.NESSyncSettings syncSettings)
 		{
 			var subNesSettings = (NES.NES.NESSettings)settings ?? new NES.NES.NESSettings();

src/BizHawk.Emulation.Cores/Consoles/PC Engine/PCEngine.cs

@@ -21,7 +21,8 @@ namespace BizHawk.Emulation.Cores.PCEngine
 		IDebuggable, ISettable<PCEngine.PCESettings, PCEngine.PCESyncSettings>, IDriveLight, ICodeDataLogger,
 		IPceGpuView
 	{
-		[CoreConstructor(new[] { "PCE", "SGX" })]
+		[CoreConstructor("PCE", Priority = CorePriority.Low)]
+		[CoreConstructor("SGX", Priority = CorePriority.Low)]
 		public PCEngine(GameInfo game, byte[] rom, PCEngine.PCESettings settings, PCEngine.PCESyncSettings syncSettings)
 		{
 			switch (game.System)

src/BizHawk.Emulation.Cores/Consoles/Sega/PicoDrive/PicoDrive.cs

@@ -19,7 +19,8 @@ namespace BizHawk.Emulation.Cores.Consoles.Sega.PicoDrive
 		private DiscSectorReader _cdReader;
 		private bool _isPal;
 
-		[CoreConstructor(new[] { "GEN", "32X" })]
+		[CoreConstructor("GEN", Priority = CorePriority.Low)]
+		[CoreConstructor("32X")]
 		public PicoDrive(CoreComm comm, GameInfo game, byte[] rom, bool deterministic, SyncSettings syncSettings)
 			: this(comm, game, rom, null, deterministic, syncSettings)
 		{ }

src/BizHawk.Emulation.Cores/Consoles/Sega/SMS/SMS.cs

@@ -23,7 +23,9 @@ namespace BizHawk.Emulation.Cores.Sega.MasterSystem
 	public partial class SMS : IEmulator, ISoundProvider, ISaveRam, IInputPollable, IRegionable,
 		IDebuggable, ISettable<SMS.SmsSettings, SMS.SmsSyncSettings>, ICodeDataLogger
 	{
-		[CoreConstructor(new[] { "SMS", "SG", "GG" })]
+		[CoreConstructor("SMS")]
+		[CoreConstructor("SG")]
+		[CoreConstructor("GG")]
 		public SMS(CoreComm comm, GameInfo game, byte[] rom, SmsSettings settings, SmsSyncSettings syncSettings)
 		{
 			var ser = new BasicServiceProvider(this);

src/BizHawk.Emulation.Cores/CoreInventory.cs

@@ -28,11 +28,12 @@ namespace BizHawk.Emulation.Cores
 			// If true, this is a new style constructor that takes a CoreLoadParameters object
 			private readonly bool _useCoreLoadParameters;
 
-			public Core(string name, Type type, ConstructorInfo ctor)
+			public Core(string name, Type type, ConstructorInfo ctor, CorePriority priority)
 			{
 				Name = name;
 				Type = type;
 				CTor = ctor;
+				Priority = priority;
 
 				var pp = CTor.GetParameters();
 				if (pp.Length == 1
@@ -65,9 +66,14 @@ namespace BizHawk.Emulation.Cores
 				}
 			}
 
+			/// <summary>
+			/// (hopefully) a CoreNames value
+			/// </summary>
+			/// <value></value>
 			public string Name { get; }
 			public Type Type { get; }
 			public ConstructorInfo CTor { get; }
+			public CorePriority Priority { get; }
 			public Type SettingsType { get; } = typeof(object);
 			public Type SyncSettingsType { get; } = typeof(object);
 
@@ -116,53 +122,22 @@ namespace BizHawk.Emulation.Cores
 			}
 		}
 
-		private void ProcessConstructor(Type type, string system, CoreAttribute coreAttr, ConstructorInfo cons)
+		private void ProcessConstructor(Type type, CoreConstructorAttribute consAttr, CoreAttribute coreAttr, ConstructorInfo cons)
 		{
-			Core core = new Core(coreAttr.CoreName, type, cons);
+			Core core = new Core(coreAttr.CoreName, type, cons, consAttr.Priority);
-			if (!_systems.TryGetValue(system, out var ss))
+			if (!_systems.TryGetValue(consAttr.System, out var ss))
 			{
 				ss = new List<Core>();
-				_systems.Add(system, ss);
+				_systems.Add(consAttr.System, ss);
 			}
 
 			ss.Add(core);
 		}
 
-		/// <summary>
+		public IEnumerable<Core> GetCores(string system)
-		/// find a core matching a particular game.system
-		/// </summary>
-		public Core this[string system]
 		{
-			get
+			_systems.TryGetValue(system, out var cores);
-			{
+			return cores ?? Enumerable.Empty<Core>();
-				List<Core> ss = _systems[system];
-				if (ss.Count != 1)
-				{
-					throw new InvalidOperationException("Ambiguous core selection!");
-				}
-
-				return ss[0];
-			}
-		}
-
-		/// <summary>
-		/// find a core matching a particular game.system with a particular CoreAttributes.Name
-		/// </summary>
-		public Core this[string system, string core]
-		{
-			get
-			{
-				List<Core> ss = _systems[system];
-				foreach (Core c in ss)
-				{
-					if (c.Name == core)
-					{
-						return c;
-					}
-				}
-
-				throw new InvalidOperationException("No such core!");
-			}
 		}
 
 		/// <summary>
@@ -183,9 +158,9 @@ namespace BizHawk.Emulation.Cores
 							.Where(c => c.GetCustomAttributes(typeof(CoreConstructorAttribute), false).Length > 0);
 						foreach(var con in cons)
 						{
-							foreach (string system in ((CoreConstructorAttribute)con.GetCustomAttributes(typeof(CoreConstructorAttribute), false)[0]).Systems)
+							foreach (var consAttr in con.GetCustomAttributes(typeof(CoreConstructorAttribute), false).Cast<CoreConstructorAttribute>())
 							{
-								ProcessConstructor(typ, system, (CoreAttribute)coreAttr[0], con);
+								ProcessConstructor(typ, consAttr, (CoreAttribute)coreAttr[0], con);
 							}
 						}
 					}
@@ -196,23 +171,45 @@ namespace BizHawk.Emulation.Cores
 		public static readonly CoreInventory Instance = new CoreInventory(new[] { typeof(CoreInventory).Assembly });
 	}
 
-	[AttributeUsage(AttributeTargets.Constructor)]
+	public enum CorePriority
+	{
+		/// <summary>
+		/// The gamedb has requested this core for this game
+		/// </summary>
+		GameDbPreference = -300,
+		/// <summary>
+		/// The user has indicated in preferences that this is their favourite core
+		/// </summary>
+		UserPreference = -200,
+		
+		/// <summary>
+		/// A very good core that should be prefered over normal cores.  Don't use this?
+		/// </summary>
+		High = -100,
+
+		/// <summary>
+		/// Most cores should use this
+		/// </summary>
+		Normal = 0,
+		/// <summary>
+		/// Experimental, special use, or garbage core
+		/// </summary>
+		Low = 100,
+		/// <summary>
+		/// TODO:  Do we need this?  Does it need a better name?
+		/// </summary>
+		SuperLow = 200,
+	}
+
+	[AttributeUsage(AttributeTargets.Constructor, AllowMultiple = true)]
 	public sealed class CoreConstructorAttribute : Attribute
 	{
-		private readonly List<string> _systems = new List<string>();
+		public string System { get; }
-
-		/// <remarks>TODO neither array nor <see cref="IEnumerable{T}"/> is the correct collection to be using here, try <see cref="IReadOnlyList{T}"/>/<see cref="IReadOnlyCollection{T}"/> instead</remarks>
-		public CoreConstructorAttribute(string[] systems)
-		{
-			_systems.AddRange(systems);
-		}
-
 		public CoreConstructorAttribute(string system)
 		{
-			_systems.Add(system);
+			System = system;
 		}
-
+		public CorePriority Priority { get; set; }
-		public IEnumerable<string> Systems => _systems;
 	}
 
 	/// <summary>