/*
 *  Unreal Engine .NET 6 integration 
 *  Copyright (c) 2021 Stanislav Denisov
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to deal
 *  in the Software without restriction, including without limitation the rights
 *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *  copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 *
 *  The above copyright notice and this permission notice shall be included in all
 *  copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 *  SOFTWARE.
 */

using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Reflection.Emit;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Loader;
using UnrealEngine.Plugins;

namespace UnrealEngine.Runtime {
	internal enum LogLevel : int {
		Display,
		Warning,
		Error,
		Fatal
	}

	internal enum CallbackType : int {
		ActorOverlapDelegate,
		ActorHitDelegate,
		ActorCursorDelegate,
		ActorKeyDelegate,
		ComponentOverlapDelegate,
		ComponentHitDelegate,
		ComponentCursorDelegate,
		ComponentKeyDelegate,
		CharacterLandedDelegate
	}

	internal enum ArgumentType : int {
		None,
		Single,
		Integer,
		Pointer,
		Callback
	}

	internal enum CommandType : int {
		Initialize = 1,
		LoadAssemblies = 2,
		UnloadAssemblies = 3,
		Find = 4,
		Execute = 5
	}

	[StructLayout(LayoutKind.Explicit, Size = 16)]
	internal unsafe struct Callback {
		[FieldOffset(0)]
		internal IntPtr* parameters;
		[FieldOffset(8)]
		internal CallbackType type;
	}

	[StructLayout(LayoutKind.Explicit, Size = 24)]
	internal unsafe struct Argument {
		[FieldOffset(0)]
		internal float single;
		[FieldOffset(0)]
		internal uint integer;
		[FieldOffset(0)]
		internal IntPtr pointer;
		[FieldOffset(0)]
		internal Callback callback;
		[FieldOffset(16)]
		internal ArgumentType type;
	}

	[StructLayout(LayoutKind.Explicit, Size = 40)]
	internal unsafe struct Command {
		// Initialize
		[FieldOffset(0)]
		internal IntPtr* buffer;
		[FieldOffset(8)]
		internal int checksum;
		// Find
		[FieldOffset(0)]
		internal IntPtr method;
		[FieldOffset(8)]
		internal int optional;
		// Execute
		[FieldOffset(0)]
		internal IntPtr function;
		[FieldOffset(8)]
		internal Argument value;
		[FieldOffset(32)]
		internal CommandType type;
	}

	internal sealed class Plugin {
		internal PluginLoader loader;
		internal Assembly assembly;
		internal Dictionary<int, IntPtr> userFunctions;
	}

	internal sealed class AssembliesContextManager {
		internal AssemblyLoadContext assembliesContext;

		[MethodImpl(MethodImplOptions.NoInlining)]
		internal WeakReference CreateAssembliesContext() {
			assembliesContext = new("UnrealEngine", true);

			return new(assembliesContext, trackResurrection: true);
		}

		[MethodImpl(MethodImplOptions.NoInlining)]
		internal void UnloadAssembliesContext() => assembliesContext?.Unload();
	}

	internal static unsafe class Core {
		private static AssembliesContextManager assembliesContextManager;
		private static WeakReference assembliesContextWeakReference;
		private static Plugin plugin;
		private static IntPtr sharedEvents;
		private static IntPtr sharedFunctions;
		private static int sharedChecksum;

		private static delegate* unmanaged[Cdecl]<string, void> Exception;
		private static delegate* unmanaged[Cdecl]<LogLevel, string, void> Log;

		[UnmanagedCallersOnly]
		internal static unsafe IntPtr ManagedCommand(Command command) {
			if (command.type == CommandType.Execute) {
				try {
					switch (command.value.type) {
						case ArgumentType.None: {
							((delegate* unmanaged[Cdecl]<void>)command.function)();
							break;
						}

						case ArgumentType.Single: {
							((delegate* unmanaged[Cdecl]<float, void>)command.function)(command.value.single);
							break;
						}

						case ArgumentType.Integer: {
							((delegate* unmanaged[Cdecl]<uint, void>)command.function)(command.value.integer);
							break;
						}

						case ArgumentType.Pointer: {
							((delegate* unmanaged[Cdecl]<IntPtr, void>)command.function)(command.value.pointer);
							break;
						}

						case ArgumentType.Callback: {
							if (command.value.callback.type == CallbackType.ActorOverlapDelegate || command.value.callback.type == CallbackType.ComponentOverlapDelegate || command.value.callback.type == CallbackType.ActorKeyDelegate || command.value.callback.type == CallbackType.ComponentKeyDelegate)
								((delegate* unmanaged[Cdecl]<IntPtr, IntPtr, void>)command.function)(command.value.callback.parameters[0], command.value.callback.parameters[1]);
							else if (command.value.callback.type == CallbackType.ActorHitDelegate || command.value.callback.type == CallbackType.ComponentHitDelegate)
								((delegate* unmanaged[Cdecl]<IntPtr, IntPtr, IntPtr, IntPtr, void>)command.function)(command.value.callback.parameters[0], command.value.callback.parameters[1], command.value.callback.parameters[2], command.value.callback.parameters[3]);
							else if (command.value.callback.type == CallbackType.ActorCursorDelegate || command.value.callback.type == CallbackType.ComponentCursorDelegate || command.value.callback.type == CallbackType.CharacterLandedDelegate)
								((delegate* unmanaged[Cdecl]<IntPtr, void>)command.function)(command.value.callback.parameters[0]);
							else
								throw new Exception("Unknown callback type");
							break;
						}

						default:
							throw new Exception("Unknown function type");
					}
				}

				catch (Exception exception) {
					try {
						Exception(exception.ToString());
					}

					catch (FileNotFoundException fileNotFoundException) {
						Exception("One of the project dependencies is missed! Please, publish the project instead of building it\r\n" + fileNotFoundException.ToString());
					}
				}

				return default;
			}

			if (command.type == CommandType.Find) {
				IntPtr function = IntPtr.Zero;

				try {
					string method = Marshal.PtrToStringAnsi(command.method);

					if (!plugin.userFunctions.TryGetValue(method.GetHashCode(StringComparison.Ordinal), out function) && command.optional != 1)
						Log(LogLevel.Error, "Managed function was not found \"" + method + "\"");
				}

				catch (Exception exception) {
					Exception(exception.ToString());
				}

				return function;
			}

			if (command.type == CommandType.Initialize) {
				try {
					assembliesContextManager = new();
					assembliesContextWeakReference = assembliesContextManager.CreateAssembliesContext();

					int position = 0;
					IntPtr* buffer = command.buffer;

					unchecked {
						int head = 0;
						IntPtr* runtimeFunctions = (IntPtr*)buffer[position++];

						Exception = (delegate* unmanaged[Cdecl]<string, void>)runtimeFunctions[head++];
						Log = (delegate* unmanaged[Cdecl]<LogLevel, string, void>)runtimeFunctions[head++];
					}

					sharedEvents = buffer[position++];
					sharedFunctions = buffer[position++];
					sharedChecksum = command.checksum;
				}

				catch (Exception exception) {
					Exception("Runtime initialization failed\r\n" + exception.ToString());
				}

				return new(0xF);
			}

			if (command.type == CommandType.LoadAssemblies) {
				try {
					const string frameworkAssemblyName = "UnrealEngine.Framework";
					string assemblyPath = Assembly.GetExecutingAssembly().Location;
					string managedFolder = assemblyPath.Substring(0, assemblyPath.IndexOf("Plugins", StringComparison.Ordinal)) + "Managed";
					string[] folders = Directory.GetDirectories(managedFolder);

					Array.Resize(ref folders, folders.Length + 1);

					folders[folders.Length - 1] = managedFolder;

					foreach (string folder in folders) {
						IEnumerable<string> assemblies = Directory.EnumerateFiles(folder, "*.dll", SearchOption.AllDirectories);

						foreach (string assembly in assemblies) {
							AssemblyName name = null;
							bool loadingFailed = false;

							try {
								name = AssemblyName.GetAssemblyName(assembly);
							}

							catch (BadImageFormatException) {
								continue;
							}

							if (name?.Name != frameworkAssemblyName) {
								plugin = new();
								plugin.loader = PluginLoader.CreateFromAssemblyFile(assembly, config => { config.DefaultContext = assembliesContextManager.assembliesContext; config.IsUnloadable = true; config.LoadInMemory = true; });
								plugin.assembly = plugin.loader.LoadAssemblyFromPath(assembly);

								AssemblyName[] referencedAssemblies = plugin.assembly.GetReferencedAssemblies();

								foreach (AssemblyName referencedAssembly in referencedAssemblies) {
									if (referencedAssembly.Name == frameworkAssemblyName) {
										Assembly framework = plugin.loader.LoadAssembly(referencedAssembly);

										using (assembliesContextManager.assembliesContext.EnterContextualReflection()) {
											Type sharedClass = framework.GetType(frameworkAssemblyName + ".Shared");

											if ((int)sharedClass.GetField("checksum", BindingFlags.NonPublic | BindingFlags.Static).GetValue(null) == sharedChecksum) {
												plugin.userFunctions = (Dictionary<int, IntPtr>)sharedClass.GetMethod("Load", BindingFlags.NonPublic | BindingFlags.Static).Invoke(null, new object[] { sharedEvents, sharedFunctions, plugin.assembly });

												Log(LogLevel.Display, "Framework loaded succesfuly for " + assembly);

												return default;
											} else {
												Log(LogLevel.Fatal, "Framework loading failed, version is incompatible with the runtime, please, recompile the project with an updated version referenced in " + assembly);

												loadingFailed = true;
											}
										}
									}
								}

								UnloadAssemblies();

								if (loadingFailed)
									return default;
							}
						}
					}
				}

				catch (Exception exception) {
					Exception("Loading of assemblies failed\r\n" + exception.ToString());
				}

				return default;
			}

			if (command.type == CommandType.UnloadAssemblies)
				UnloadAssemblies();

			return default;
		}

		[MethodImpl(MethodImplOptions.NoInlining)]
		private static void UnloadAssemblies() {
			try {
				plugin?.loader.Dispose();
				plugin = null;

				assembliesContextManager.UnloadAssembliesContext();
				assembliesContextManager = null;

				if (assembliesContextWeakReference.IsAlive) {
					GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);
					GC.WaitForPendingFinalizers();
				}

				assembliesContextManager = new();
				assembliesContextWeakReference = assembliesContextManager.CreateAssembliesContext();
			}

			catch (Exception exception) {
				Exception("Unloading of assemblies failed\r\n" + exception.ToString());
			}
		}
	}
}