Add command history to single-player and multiplayer

The last 50 valid commands starting with / are saved to memory.
Regular chat messages are not saved to prevent spam.
The command history persists across single-player and multiplayer games.
Press arrow up/down to show the previously typed commands within the current OpenRA session.

OpenRA.Mods.Common/Widgets/Logic/CommandHistory.cs

@@ -0,0 +1,89 @@
+#region Copyright & License Information
+/*
+ * Copyright (c) The OpenRA Developers and Contributors
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you 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. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System.Collections.Generic;
+
+namespace OpenRA.Mods.Common.Widgets.Logic
+{
+	public sealed class CommandHistory
+	{
+		const int MaxHistorySize = 50;
+		static CommandHistory instance;
+		static readonly object LockObject = new();
+		readonly List<string> history = [];
+		int currentIndex = -1;
+
+		CommandHistory() { }
+
+		public static CommandHistory Instance
+		{
+			get
+			{
+				if (instance == null)
+				{
+					lock (LockObject)
+					{
+						instance ??= new CommandHistory();
+					}
+				}
+
+				return instance;
+			}
+		}
+
+		public void AddCommand(string command)
+		{
+			if (string.IsNullOrWhiteSpace(command) || !command.StartsWith('/'))
+				return;
+
+			var trimmedCommand = command.Trim();
+			history.RemoveAll(c => c == trimmedCommand);
+			history.Insert(0, trimmedCommand);
+			if (history.Count > MaxHistorySize)
+				history.RemoveAt(history.Count - 1);
+
+			currentIndex = -1;
+		}
+
+		public string GetPrevious()
+		{
+			if (history.Count == 0)
+				return null;
+
+			if (currentIndex < history.Count - 1)
+				currentIndex++;
+
+			return history[currentIndex];
+		}
+
+		public string GetNext()
+		{
+			if (history.Count == 0)
+				return null;
+
+			if (currentIndex > 0)
+			{
+				currentIndex--;
+				return history[currentIndex];
+			}
+
+			if (currentIndex == 0)
+				currentIndex = -1;
+
+			return null;
+		}
+
+		public void Reset()
+		{
+			currentIndex = -1;
+		}
+	}
+}

OpenRA.Mods.Common/Widgets/Logic/Ingame/IngameChatLogic.cs

@@ -49,6 +49,7 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 		readonly Dictionary<TextNotificationPool, Widget> templates = [];
 
 		readonly TabCompletionLogic tabCompletion = new();
+		readonly CommandHistory commandHistory = CommandHistory.Instance;
 
 		readonly string chatLineSound = ChromeMetrics.Get<string>("ChatLineSound");
 
@@ -159,11 +160,18 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 					{
 						var text = chatText.Text.Trim();
 						var from = world.IsReplay ? null : orderManager.LocalClient.Name;
+						var commandName = text[1..].Split(' ')[0].ToLowerInvariant();
+						var isValidCommand = !string.IsNullOrEmpty(commandName) &&
+							chatTraits.OfType<ChatCommands>().Any(trait => trait.Commands.ContainsKey(commandName));
 						foreach (var trait in chatTraits)
 							trait.OnChat(from, text);
+
+						if (isValidCommand)
+							commandHistory.AddCommand(text);
 					}
 				}
 
+				commandHistory.Reset();
 				chatText.Text = "";
 				if (!isMenuChat)
 					CloseChat();
@@ -191,9 +199,40 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 				else
 					chatText.YieldKeyboardFocus();
 
+				commandHistory.Reset();
 				return true;
 			};
 
+			chatText.OnArrowUp = _ =>
+			{
+				var previousCommand = commandHistory.GetPrevious();
+				if (previousCommand != null)
+				{
+					chatText.Text = previousCommand;
+					chatText.CursorPosition = chatText.Text.Length;
+					return true;
+				}
+
+				return false;
+			};
+
+			chatText.OnArrowDown = _ =>
+			{
+				var nextCommand = commandHistory.GetNext();
+				if (nextCommand != null)
+				{
+					chatText.Text = nextCommand;
+					chatText.CursorPosition = chatText.Text.Length;
+					return true;
+				}
+				else
+				{
+					chatText.Text = "";
+					commandHistory.Reset();
+					return true;
+				}
+			};
+
 			chatAvailableIn = new CachedTransform<int, string>(x => FluentProvider.GetMessage(ChatAvailability, "seconds", x));
 
 			if (!isMenuChat)
@@ -265,6 +304,7 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 		public void OpenChat()
 		{
 			chatText.Text = "";
+			commandHistory.Reset();
 			chatChrome.Visible = true;
 			chatScrollPanel.ScrollToBottom();
 			if (!chatText.IsDisabled())

OpenRA.Mods.Common/Widgets/TextFieldWidget.cs

@@ -57,6 +57,8 @@ namespace OpenRA.Mods.Common.Widgets
 		public Func<KeyInput, bool> OnEnterKey = _ => false;
 		public Func<KeyInput, bool> OnTabKey = _ => false;
 		public Func<KeyInput, bool> OnEscKey = _ => false;
+		public Func<KeyInput, bool> OnArrowUp = _ => false;
+		public Func<KeyInput, bool> OnArrowDown = _ => false;
 		public Func<bool> OnAltKey = () => false;
 		public Action OnLoseFocus = () => { };
 		public Action OnTextEdited = () => { };
@@ -282,6 +284,16 @@ namespace OpenRA.Mods.Common.Widgets
 
 					break;
 
+				case Keycode.UP:
+					if (OnArrowUp(e))
+						return true;
+					break;
+
+				case Keycode.DOWN:
+					if (OnArrowDown(e))
+						return true;
+					break;
+
 				case Keycode.HOME:
 					ResetBlinkCycle();
 					if (e.Modifiers.HasModifier(Modifiers.Shift))