// Copyright Epic Games, Inc. All Rights Reserved.

using EpicGames.Core;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace UnrealBuildBase
{
	public class ProcessSingleton
	{
		public static string GetUniqueMutexForPath(string Name, string UniquePath)
		{
			// generate a md5 hash of the path, as GetHashCode is not guaranteed to generate a stable hash
			return string.Format("Global\\{0}_{1}", Name, ContentHash.MD5(UniquePath.ToUpperInvariant()));
		}

		/// <summary>
		/// Returns true/false based on whether this is the only instance
		/// running (checked at startup).
		/// </summary>
		public static bool IsSoleInstance { get; private set; }

		/// <summary>
		/// Runs the specified delegate checking if this is the only instance of the application.
		/// </summary>
		/// <param name="Main"></param>
		/// <param name="bWaitForUATMutex"></param>
		public static async Task<ExitCode> RunSingleInstanceAsync(Func<Task<ExitCode>> Main, bool bWaitForUATMutex, ILogger Logger)
		{
			// Need to execute this logic on a background thread, since mutex ownership on Linux has thread affinity (ie. mutexes be released on the
			// same thread that acquires it, which is not guaranteed through an async continuation)
			TaskCompletionSource<ExitCode> Result = new TaskCompletionSource<ExitCode>();
			Thread Thread = new Thread(() => RunSingleInstanceThread(Main, Result, bWaitForUATMutex, Logger));
			Thread.Start();
			return await Result.Task;
		}

		public static void RunSingleInstanceThread(Func<Task<ExitCode>> Main, TaskCompletionSource<ExitCode> Result, bool bWaitForUATMutex, ILogger Logger)
		{
			try
			{
				bool AllowMultipleInsances = (Environment.GetEnvironmentVariable("uebp_UATMutexNoWait") == "1");

				string EntryAssemblyLocation = Assembly.GetEntryAssembly()!.GetOriginalLocation();

				string MutexName = GetUniqueMutexForPath(Path.GetFileNameWithoutExtension(EntryAssemblyLocation), EntryAssemblyLocation);
				using (Mutex SingleInstanceMutex = new Mutex(true, MutexName, out bool bCreatedMutex))
				{
					IsSoleInstance = bCreatedMutex;

					if (!IsSoleInstance && AllowMultipleInsances == false)
					{
						if (bWaitForUATMutex)
						{
							Logger.LogWarning("Another instance of UAT at '{File}' is running, and the -WaitForUATMutex parameter has been used. Waiting for other UAT to finish...", EntryAssemblyLocation);
							int Seconds = 0;
							while (WaitMutexNoExceptions(SingleInstanceMutex, 15 * 1000) == false)
							{
								Seconds += 15;
								Logger.LogInformation("Still waiting for Mutex. {TimeSeconds} seconds has passed...", Seconds);
							}
						}
						else
						{
							throw new Exception($"A conflicting instance of AutomationTool is already running. Current location: {EntryAssemblyLocation}. A process manager may be used to determine the conflicting process and what tool may have launched it");
						}
					}

					ExitCode ExitCode = Task.Run(() => Main()).Result;

					if (IsSoleInstance)
					{
						SingleInstanceMutex.ReleaseMutex();
					}

					Result.SetResult(ExitCode);
				}
			}
			catch (Exception Ex)
			{
				Result.TrySetException(Ex);
			}
		}

		static bool WaitMutexNoExceptions(Mutex Mutex, int TimeoutMs)
		{
			try
			{
				return Mutex.WaitOne(15 * 1000);
			}
			catch (AbandonedMutexException)
			{
				return true;
			}
		}
	}
}