feat: Adds console commands (#1714)

### Summary
* Adds console command support.
* Adds `save`, `restart`, and `shutdown` commands.

Projects/Server/Console/ConsoleInputHandler.cs

@@ -0,0 +1,197 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2024 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: ConsoleInputHandler.cs                                          *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Threading;
+
+namespace Server;
+
+public static class ConsoleInputHandler
+{
+    private static readonly AutoResetEvent _receivedUserInput = new(false);
+    private static readonly AutoResetEvent _endUserInput = new(false);
+    private static bool _expectUserInput;
+    private static readonly Dictionary<string, ConsoleCommand> _inputCommands = new();
+    private static string[] _commandDescriptions;
+    private static string _input;
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void RegisterCommand(string command, string description, Action<string> function) =>
+        RegisterCommand([command], description, function);
+
+    // Note: Functions will be executed on a background thread!!
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void RegisterCommand(string[] commands, string description, Action<string> function)
+    {
+        if (commands is { Length: > 0 } && function != null)
+        {
+            var consoleCommand = new ConsoleCommand(commands, description, function);
+            lock (_inputCommands)
+            {
+                for (var i = 0; i < commands.Length; i++)
+                {
+                    var command = commands[i].ToLower();
+                    _inputCommands[command] = consoleCommand;
+                }
+            }
+
+            _commandDescriptions = null;
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static bool UnregisterInputCommand(string command)
+    {
+        lock (_inputCommands)
+        {
+            var removed = _inputCommands.Remove(command);
+            _commandDescriptions = null;
+            return removed;
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Action<string> GetInputCommand(string command)
+    {
+        lock (_inputCommands)
+        {
+            var action = _inputCommands.GetValueOrDefault(command)?.Function;
+            _commandDescriptions = null;
+            return action;
+        }
+    }
+
+    public static void Configure()
+    {
+        RegisterCommand(["help", "?"], "Displays this help screen.", DisplayHelp);
+    }
+
+    public static void Initialize()
+    {
+        new Thread(ProcessConsoleInput)
+        {
+            IsBackground = true,
+            Name = "Console Input Handler"
+        }.Start();
+    }
+
+    private static string[] GetHelpDescriptions()
+    {
+        if (_commandDescriptions != null)
+        {
+            return _commandDescriptions;
+        }
+
+        HashSet<ConsoleCommand> commands;
+        lock (_inputCommands)
+        {
+            commands = _inputCommands.Values.ToHashSet();
+        }
+
+        var longestCommand = 0;
+        var commandTuples = new (string Command, string Arguments)[commands.Count];
+
+        var index = 0;
+        foreach (var command in commands)
+        {
+            var commandAliases = string.Join("|", command.Commands);
+            longestCommand = Math.Max(longestCommand, commandAliases.Length);
+            commandTuples[index++] = (commandAliases, command.Description);
+        }
+
+        Array.Sort(commandTuples, (a, b) => a.Command.CompareOrdinal(b.Command));
+
+        _commandDescriptions = new string[commandTuples.Length];
+
+        for (var i = 0; i < commandTuples.Length; i++)
+        {
+            var (commandAliases, description) = commandTuples[i];
+            _commandDescriptions[i] = $"{commandAliases.PadRight(longestCommand + 1)} - {description}";
+        }
+
+        return _commandDescriptions;
+    }
+
+    private static void DisplayHelp(string arguments)
+    {
+        var commandDescriptions = GetHelpDescriptions();
+        if (commandDescriptions == null || commandDescriptions.Length == 0)
+        {
+            Console.WriteLine("No console commands registered.");
+            return;
+        }
+
+        Console.WriteLine("Available Commands:");
+        for (var i = 0; i < _commandDescriptions.Length; i++)
+        {
+            Console.WriteLine(_commandDescriptions[i]);
+        }
+    }
+
+    private static async void ProcessConsoleInput()
+    {
+        var token = Core.ClosingTokenSource.Token;
+
+        while (!token.IsCancellationRequested)
+        {
+            var input = Console.ReadLine()?.Trim();
+
+            if (Volatile.Read(ref _expectUserInput))
+            {
+                _input = input;
+                _receivedUserInput.Set();
+                _endUserInput.WaitOne();
+                continue;
+            }
+
+            if (string.IsNullOrEmpty(input))
+            {
+                continue;
+            }
+
+            var splitInput = input.Split(' ', 2);
+            var command = splitInput[0].ToLower();
+
+            Action<string> action;
+            lock (_inputCommands)
+            {
+                action = _inputCommands.GetValueOrDefault(command)?.Function;
+            }
+
+            action?.Invoke(splitInput.Length > 1 ? splitInput[1] : string.Empty);
+        }
+    }
+
+    public static string ReadLine()
+    {
+        Volatile.Write(ref _expectUserInput, true);
+        _receivedUserInput.WaitOne();
+        var line = _input;
+        Volatile.Write(ref _expectUserInput, false);
+        _endUserInput.Set();
+
+        return line;
+    }
+
+    private class ConsoleCommand(string[] commands, string description, Action<string> function)
+    {
+        public readonly string[] Commands = commands;
+        public readonly string Description = description;
+        public readonly Action<string> Function = function;
+    }
+}