From e0e3644ca98bb8cb95ee39049b1fefdc1f25dc81 Mon Sep 17 00:00:00 2001
From: "Chris S." <chrisasmall+github@gmail.com>
Date: Sun, 15 Jun 2025 00:36:25 +0100
Subject: [PATCH] Add nested template test and streamline input stream

---
 src/TextTemplate/Template.cs                  | 73 +++++++++++++++++++
 src/TextTemplate/TemplateEngine.cs            | 17 ++++-
 .../TextTemplate.Tests/TemplateClassTests.cs  | 41 +++++++++++
 3 files changed, 130 insertions(+), 1 deletion(-)
 create mode 100644 src/TextTemplate/Template.cs
 create mode 100644 tests/TextTemplate.Tests/TemplateClassTests.cs

diff --git a/src/TextTemplate/Template.cs b/src/TextTemplate/Template.cs
new file mode 100644
index 0000000..a4ed0fd
--- /dev/null
+++ b/src/TextTemplate/Template.cs
@@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using Antlr4.Runtime;
+
+namespace TextTemplate;
+
+/// <summary>
+/// Represents a text template similar to Go's template.Template.
+/// </summary>
+public class Template
+{
+    private string _templateString = string.Empty;
+
+    /// <summary>
+    /// The template name.
+    /// </summary>
+    public string Name { get; }
+
+    private Template(string name)
+    {
+        Name = name;
+    }
+
+    /// <summary>
+    /// Creates a new Template with the given name.
+    /// </summary>
+    public static Template New(string name) => new(name);
+
+    /// <summary>
+    /// Parses the supplied template string and returns the Template instance.
+    /// </summary>
+    public Template Parse(string templateString)
+    {
+        if (templateString == null) throw new ArgumentNullException(nameof(templateString));
+        // Validate using the TemplateEngine so parsing rules remain consistent.
+        TemplateEngine.Validate(templateString);
+        _templateString = templateString;
+        return this;
+    }
+
+    /// <summary>
+    /// Reads the given files, combines their contents, and parses the result.
+    /// </summary>
+    public Template ParseFiles(params string[] filenames)
+    {
+        if (filenames == null) throw new ArgumentNullException(nameof(filenames));
+        var sb = new StringBuilder();
+        foreach (var file in filenames)
+        {
+            sb.Append(File.ReadAllText(file));
+        }
+        return Parse(sb.ToString());
+    }
+
+    /// <summary>
+    /// Executes the template using the provided dictionary.
+    /// </summary>
+    public string Execute(IDictionary<string, object> data)
+    {
+        return TemplateEngine.Process(_templateString, data);
+    }
+
+    /// <summary>
+    /// Executes the template using the public properties of <typeparamref name="T"/>.
+    /// </summary>
+    public string Execute<T>(T model)
+    {
+        return TemplateEngine.Process(_templateString, model);
+    }
+
+}
diff --git a/src/TextTemplate/TemplateEngine.cs b/src/TextTemplate/TemplateEngine.cs
index 11d2cf0..d72dd81 100644
--- a/src/TextTemplate/TemplateEngine.cs
+++ b/src/TextTemplate/TemplateEngine.cs
@@ -24,7 +24,7 @@ public static string Process(string templateString, IDictionary<string, object>
     {
         templateString = PreprocessWhitespace(templateString);
         templateString = PreprocessComments(templateString);
-        AntlrInputStream inputStream = new(templateString);
+        var inputStream = new AntlrInputStream(templateString);
         var lexer = new GoTextTemplateLexer(inputStream);
         var tokens = new CommonTokenStream(lexer);
         var parser = new GoTextTemplateParser(tokens);
@@ -35,6 +35,21 @@ public static string Process(string templateString, IDictionary<string, object>
         return visitor.Visit(tree);
     }
 
+    /// <summary>
+    /// Parses <paramref name="templateString"/> to ensure it contains valid syntax.
+    /// </summary>
+    public static void Validate(string templateString)
+    {
+        if (templateString == null) throw new ArgumentNullException(nameof(templateString));
+        templateString = PreprocessWhitespace(templateString);
+        templateString = PreprocessComments(templateString);
+        var inputStream = new AntlrInputStream(templateString);
+        var lexer = new GoTextTemplateLexer(inputStream);
+        var tokens = new CommonTokenStream(lexer);
+        var parser = new GoTextTemplateParser(tokens);
+        parser.template();
+    }
+
     /// <summary>
     /// Processes <paramref name="templateString"/> using the public properties
     /// and fields of <paramref name="model"/> as template variables.
diff --git a/tests/TextTemplate.Tests/TemplateClassTests.cs b/tests/TextTemplate.Tests/TemplateClassTests.cs
new file mode 100644
index 0000000..9cdeef4
--- /dev/null
+++ b/tests/TextTemplate.Tests/TemplateClassTests.cs
@@ -0,0 +1,41 @@
+using Shouldly;
+using TextTemplate;
+using Xunit;
+using System.IO;
+
+namespace TextTemplate.Tests;
+
+public class TemplateClassTests
+{
+    [Fact]
+    public void NewParseExecutePattern_Works()
+    {
+        var tmpl = Template.New("t").Parse("Hello {{ .Name }}! {{ range .Items }}{{ . }} {{ end }}");
+        var result = tmpl.Execute(new { Name = "Bob", Items = new[] { "a", "b" } });
+        result.ShouldBe("Hello Bob! a b ");
+    }
+
+    [Fact]
+    public void ParseFiles_ReadsAndParsesAllFiles()
+    {
+        var f1 = Path.GetTempFileName();
+        var f2 = Path.GetTempFileName();
+        var f3 = Path.GetTempFileName();
+        try
+        {
+            File.WriteAllText(f1, "{{define \"header\"}}Hello {{.Name}}{{end}}");
+            File.WriteAllText(f2, "{{define \"exclaim\"}}!{{end}}");
+            File.WriteAllText(f3, "{{template \"header\" .}}{{template \"exclaim\"}}");
+
+            var tmpl = Template.New("t").ParseFiles(f1, f2, f3);
+            var result = tmpl.Execute(new { Name = "Ann" });
+            result.ShouldBe("Hello Ann!");
+        }
+        finally
+        {
+            File.Delete(f1);
+            File.Delete(f2);
+            File.Delete(f3);
+        }
+    }
+}