Guidebook links (#17162)

* Guidebook links

* warning!

Content.Client/Guidebook/Richtext/TextLinkTag.cs

@@ -0,0 +1,70 @@
+using System.Diagnostics.CodeAnalysis;
+using JetBrains.Annotations;
+using Robust.Client.UserInterface;
+using Robust.Client.UserInterface.Controls;
+using Robust.Client.UserInterface.RichText;
+using Robust.Shared.Input;
+using Robust.Shared.Utility;
+
+namespace Content.Client.Guidebook.RichText;
+
+[UsedImplicitly]
+public sealed class TextLinkTag : IMarkupTag
+{
+    public string Name => "textlink";
+
+    public Control? Control;
+
+    /// <inheritdoc/>
+    public bool TryGetControl(MarkupNode node, [NotNullWhen(true)] out Control? control)
+    {
+        if (!node.Value.TryGetString(out var text)
+            || !node.Attributes.TryGetValue("link", out var linkParameter)
+            || !linkParameter.TryGetString(out var link))
+        {
+            control = null;
+            return false;
+        }
+
+        var label = new Label();
+        label.Text = text;
+
+        label.MouseFilter = Control.MouseFilterMode.Stop;
+        label.FontColorOverride = Color.CornflowerBlue;
+        label.DefaultCursorShape = Control.CursorShape.Hand;
+
+        label.OnMouseEntered += _ => label.FontColorOverride = Color.LightSkyBlue;
+        label.OnMouseExited += _ => label.FontColorOverride = Color.CornflowerBlue;
+        label.OnKeyBindDown += args => OnKeybindDown(args, link);
+
+        control = label;
+        Control = label;
+        return true;
+    }
+
+    private void OnKeybindDown(GUIBoundKeyEventArgs args, string link)
+    {
+        if (args.Function != EngineKeyFunctions.UIClick)
+            return;
+
+        if (Control == null)
+            return;
+
+        var current = Control;
+        while (current != null)
+        {
+            current = current.Parent;
+
+            if (current is not ILinkClickHandler handler)
+                continue;
+            handler.HandleClick(link);
+            return;
+        }
+        Logger.Warning($"Warning! No valid ILinkClickHandler found.");
+    }
+}
+
+public interface ILinkClickHandler
+{
+    public void HandleClick(string link);
+}