feat: parse content text (base case).

InkBlot/Visitor/Listener.cs

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+namespace InkBlot.Visitor;
+
+public partial class Listener : InkBlotAntlrGrammarBaseListener
+{
+}

InkBlot/Visitor/ListenerContentText.cs

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+using System.Text.RegularExpressions;
+using Antlr4.Runtime.Tree;
+
+namespace InkBlot.Visitor;
+
+public partial class Listener
+{
+    private readonly ParseTreeProperty<string> _contentTextValue = new();
+
+    private readonly Regex _escapeRegex = MyRegex();
+
+    [GeneratedRegex(@"\\(.)")]
+    private static partial Regex MyRegex();
+
+    private string GetContentText(InkBlotAntlrGrammarParser.ContentTextContext context)
+    {
+        return _contentTextValue.Get(context);
+    }
+
+    public override void ExitContentText(InkBlotAntlrGrammarParser.ContentTextContext context)
+    {
+        // escape sequences are captured by this node, but not interpreted
+        var contentWithEscapes = context.CONTENT_TEXT_NO_ESCAPE_SIMPLE().ToString();
+        if (contentWithEscapes == null)
+            // when does this happen? :?
+            throw new InvalidOperationException();
+
+        // replace \X with just X
+        var content = _escapeRegex.Replace(contentWithEscapes, match => match.Groups[1].Value);
+
+        // save the result
+        _contentTextValue.Put(context, content);
+    }
+}

InkBlot/Visitor/ListenerStory.cs

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+using InkBlot.ParseHierarchy;
+
+namespace InkBlot.Visitor;
+
+public partial class Listener
+{
+    private Story? _story;
+
+    public Story Story => _story ?? throw new InvalidOperationException("No story found yet.");
+
+    public override void ExitStory(InkBlotAntlrGrammarParser.StoryContext context)
+    {
+        var storyNodes = context.children.Select(child => child switch
+        {
+            InkBlotAntlrGrammarParser.ContentTextContext contentText => new Content(GetContentText(contentText)),
+            _ => throw new InvalidOperationException($"unknown context of type {child.GetType()}")
+        });
+        _story = new Story(storyNodes);
+    }
+}