SS14-17313 Chatfactor: Chat Censorship Systems (#25908)

* SS14-17313 Chat Censorship Systems

Adds some systems to manage chat censorship:

1. No-op: does nothing
2. SimpleCensor: a regex-free censor with a variety of rules to use
3. RegexCensor: a censor that uses regex.

This exposes a singleton backed by a builder pattern (ChatCensor) that
is set up, probably during the code init phase, and then globally available
for your censorship needs.

* Migrate to Shared

* Add a reset function to the builder.

* Resolve PJB's feedback; add unit tests

Content.Shared/Chat/V2/Moderation/ChatCensor.cs

@@ -0,0 +1,59 @@
+using System.Linq;
+
+namespace Content.Shared.Chat.V2.Moderation;
+
+public interface IChatCensor
+{
+    public bool Censor(string input, out string output, char replaceWith = '*');
+}
+
+public sealed class CompoundChatCensor(IEnumerable<IChatCensor> censors) : IChatCensor
+{
+    public bool Censor(string input, out string output, char replaceWith = '*')
+    {
+        var censored = false;
+
+        foreach (var censor in censors)
+        {
+            if (censor.Censor(input, out output, replaceWith))
+            {
+                censored = true;
+            }
+        }
+
+        output = input;
+
+        return censored;
+    }
+}
+
+public sealed class ChatCensorFactory
+{
+    private List<IChatCensor> _censors = new();
+
+    public void With(IChatCensor censor)
+    {
+        _censors.Add(censor);
+    }
+
+    /// <summary>
+    /// Builds a ChatCensor that combines all the censors that have been added to this.
+    /// </summary>
+    public IChatCensor Build()
+    {
+        return new CompoundChatCensor(_censors.ToArray());
+    }
+
+    /// <summary>
+    /// Resets the build state to zero, allowing for different rules to be provided to the next censor(s) built.
+    /// </summary>
+    /// <returns>True if the builder had any setup prior to the reset.</returns>
+    public bool Reset()
+    {
+        var notEmpty = _censors.Count > 0;
+
+        _censors = new List<IChatCensor>();
+
+        return notEmpty;
+    }
+}

Content.Shared/Chat/V2/Moderation/RegexCensor.cs

@@ -0,0 +1,15 @@
+using System.Text.RegularExpressions;
+
+namespace Content.Shared.Chat.V2.Moderation;
+
+public sealed class RegexCensor(Regex censorInstruction) : IChatCensor
+{
+    private readonly Regex _censorInstruction = censorInstruction;
+
+    public bool Censor(string input, out string output, char replaceWith = '*')
+    {
+        output = _censorInstruction.Replace(input, replaceWith.ToString());
+
+        return !string.Equals(input, output);
+    }
+}