Port Back link to new component generation

Author: gunndabad

src/GovUk.Frontend.AspNetCore/ComponentGeneration/DefaultComponentGenerator.BackLink.cs

@@ -0,0 +1,23 @@
+using System;
+using Microsoft.AspNetCore.Html;
+
+namespace GovUk.Frontend.AspNetCore.ComponentGeneration;
+
+public partial class DefaultComponentGenerator
+{
+    internal const string BackLinkElement = "a";
+
+    /// <inheritdoc/>
+    public virtual HtmlTagBuilder GenerateBackLink(BackLinkOptions options)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        options.Validate();
+
+        return new HtmlTagBuilder(BackLinkElement)
+            .WithAttribute("href", options.Href.NormalizeEmptyString() ?? new HtmlString("#"))
+            .WithCssClass("govuk-back-link")
+            .WithCssClasses(ExplodeClasses(options.Classes?.ToHtmlString()))
+            .WithAttributes(options.Attributes ?? [])
+            .WithAppendedHtml(GetEncodedTextOrHtml(options.Text, options.Html) ?? new HtmlString("Back"));
+    }
+}

src/GovUk.Frontend.AspNetCore/ComponentGeneration/IComponentGenerator.cs

@@ -5,6 +5,12 @@ namespace GovUk.Frontend.AspNetCore.ComponentGeneration;
 /// </summary>
 public interface IComponentGenerator
 {
+    /// <summary>
+    /// Generates a back link component.
+    /// </summary>
+    /// <returns>An <see cref="HtmlTagBuilder"/> with the component's HTML.</returns>
+    HtmlTagBuilder GenerateBackLink(BackLinkOptions options);
+
     /// <summary>
     /// Generates a breadcrumbs component.
     /// </summary>

src/GovUk.Frontend.AspNetCore/HtmlGeneration/ComponentGenerator.BackLink.cs

@@ -22,8 +22,6 @@ TagBuilder GenerateAccordion(
         string showSectionAriaLabelText,
         IEnumerable<AccordionItem> items);
 
-    TagBuilder GenerateBackLink(IHtmlContent content, AttributeDictionary attributes);
-
     TagBuilder GenerateButton(
         bool isStartButton,
         bool disabled,

src/GovUk.Frontend.AspNetCore/IGovUkHtmlGenerator.cs

@@ -1,8 +1,7 @@
-using System.Text.Encodings.Web;
+using System;
 using System.Threading.Tasks;
-using GovUk.Frontend.AspNetCore.HtmlGeneration;
+using GovUk.Frontend.AspNetCore.ComponentGeneration;
 using Microsoft.AspNetCore.Html;
-using Microsoft.AspNetCore.Mvc.TagHelpers;
 using Microsoft.AspNetCore.Razor.TagHelpers;
 
 namespace GovUk.Frontend.AspNetCore.TagHelpers;
@@ -11,32 +10,26 @@ namespace GovUk.Frontend.AspNetCore.TagHelpers;
 /// Generates a GDS back link component.
 /// </summary>
 [HtmlTargetElement(TagName)]
-[OutputElementHint(ComponentGenerator.BackLinkElement)]
+[OutputElementHint(DefaultComponentGenerator.BackLinkElement)]
 public class BackLinkTagHelper : TagHelper
 {
     internal const string TagName = "govuk-back-link";
 
-    private static readonly HtmlString _defaultContent = new HtmlString(HtmlEncoder.Default.Encode(ComponentGenerator.BackLinkDefaultContent));
-
-    private readonly IGovUkHtmlGenerator _htmlGenerator;
+    private readonly IComponentGenerator _componentGenerator;
 
     /// <summary>
     /// Creates a new <see cref="BackLinkTagHelper"/>.
     /// </summary>
-    public BackLinkTagHelper()
-        : this(htmlGenerator: null)
+    public BackLinkTagHelper(IComponentGenerator componentGenerator)
     {
-    }
-
-    internal BackLinkTagHelper(IGovUkHtmlGenerator? htmlGenerator)
-    {
-        _htmlGenerator = htmlGenerator ?? new ComponentGenerator();
+        ArgumentNullException.ThrowIfNull(componentGenerator);
+        _componentGenerator = componentGenerator;
     }
 
     /// <inheritdoc/>
     public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
     {
-        IHtmlContent content = _defaultContent;
+        IHtmlContent? content = null;
 
         if (output.TagMode == TagMode.StartTagAndEndTag)
         {
@@ -48,13 +41,18 @@ public override async Task ProcessAsync(TagHelperContext context, TagHelperOutpu
             content = output.Content;
         }
 
-        var tagBuilder = _htmlGenerator.GenerateBackLink(content, output.Attributes.ToAttributeDictionary());
+        var attributes = new EncodedAttributesDictionary(output.Attributes);
+        attributes.Remove("class", out var classes);
+        attributes.Remove("href", out var href);
 
-        output.TagName = tagBuilder.TagName;
-        output.TagMode = TagMode.StartTagAndEndTag;
+        var component = _componentGenerator.GenerateBackLink(new BackLinkOptions()
+        {
+            Html = content,
+            Href = href,
+            Classes = classes,
+            Attributes = attributes
+        });
 
-        output.Attributes.Clear();
-        output.MergeAttributes(tagBuilder);
-        output.Content.SetHtmlContent(tagBuilder.InnerHtml);
+        component.WriteTo(output);
     }
 }

src/GovUk.Frontend.AspNetCore/TagHelpers/BackLinkTagHelper.cs

@@ -15,6 +15,13 @@ public ComponentTests()
         _componentGenerator = new DefaultComponentGenerator();
     }
 
+    [Theory]
+    [ComponentFixtureData("back-link", typeof(BackLinkOptions))]
+    public void BackLink(ComponentTestCaseData<BackLinkOptions> data) =>
+        CheckComponentHtmlMatchesExpectedHtml(
+            data,
+            (generator, options) => generator.GenerateBackLink(options).ToHtmlString());
+
     [Theory]
     [ComponentFixtureData("breadcrumbs", typeof(BreadcrumbsOptions))]
     public void Breadcrumbs(ComponentTestCaseData<BreadcrumbsOptions> data) =>

tests/GovUk.Frontend.AspNetCore.ConformanceTests/ComponentTests.BackLink.cs

@@ -1,53 +1,26 @@
 using System.Collections.Generic;
+using System.Text.Encodings.Web;
 using System.Threading.Tasks;
+using GovUk.Frontend.AspNetCore.ComponentGeneration;
 using GovUk.Frontend.AspNetCore.TagHelpers;
-using GovUk.Frontend.AspNetCore.TestCommon;
+using Microsoft.AspNetCore.Html;
 using Microsoft.AspNetCore.Razor.TagHelpers;
+using Moq;
 using Xunit;
 
 namespace GovUk.Frontend.AspNetCore.Tests.TagHelpers;
 
 public class BackLinkTagHelperTests
 {
     [Fact]
-    public async Task ProcessAsync_WithContent_GeneratesExpectedOutput()
+    public async Task ProcessAsync_InvokesComponentGeneratorWithExpectedOptions()
     {
         // Arrange
-        var context = new TagHelperContext(
-            tagName: "govuk-back-link",
-            allAttributes: new TagHelperAttributeList(),
-            items: new Dictionary<object, object>(),
-            uniqueId: "test");
+        var href = "http://foo.com";
+        var classes = "custom-class";
+        var dataFooAttrValue = "bar";
+        var content = "My custom link content";
 
-        var output = new TagHelperOutput(
-            "govuk-back-link",
-            attributes: new TagHelperAttributeList()
-            {
-                { "href", "http://foo.com" }
-            },
-            getChildContentAsync: (useCachedResult, encoder) =>
-            {
-                var tagHelperContent = new DefaultTagHelperContent();
-                tagHelperContent.SetContent("My custom link content");
-                return Task.FromResult<TagHelperContent>(tagHelperContent);
-            });
-
-        var tagHelper = new BackLinkTagHelper();
-
-        // Act
-        await tagHelper.ProcessAsync(context, output);
-
-        // Assert
-        var expectedHtml = @"
-<a class=""govuk-back-link"" href=""http://foo.com"">My custom link content</a>";
-
-        AssertEx.HtmlEqual(@expectedHtml, output.ToHtmlString());
-    }
-
-    [Fact]
-    public async Task ProcessAsync_WithNoContent_GeneratesExpectedOutput()
-    {
-        // Arrange
         var context = new TagHelperContext(
             tagName: "govuk-back-link",
             allAttributes: new TagHelperAttributeList(),
@@ -58,24 +31,37 @@ public async Task ProcessAsync_WithNoContent_GeneratesExpectedOutput()
             "govuk-back-link",
             attributes: new TagHelperAttributeList()
             {
-                { "href", "http://foo.com" }
+                { "href", href },
+                { "class", classes },
+                { "data-foo", dataFooAttrValue }
             },
             getChildContentAsync: (useCachedResult, encoder) =>
             {
                 var tagHelperContent = new DefaultTagHelperContent();
+                tagHelperContent.SetHtmlContent(content);
                 return Task.FromResult<TagHelperContent>(tagHelperContent);
             });
-        output.TagMode = TagMode.SelfClosing;
 
-        var tagHelper = new BackLinkTagHelper();
+        var componentGeneratorMock = new Mock<DefaultComponentGenerator>() { CallBase = true };
+        BackLinkOptions? actualOptions = null;
+        componentGeneratorMock.Setup(mock => mock.GenerateBackLink(It.IsAny<BackLinkOptions>())).Callback<BackLinkOptions>(o => actualOptions = o);
+
+        var tagHelper = new BackLinkTagHelper(componentGeneratorMock.Object);
 
         // Act
         await tagHelper.ProcessAsync(context, output);
 
         // Assert
-        var expectedHtml = @"
-<a class=""govuk-back-link"" href=""http://foo.com"">Back</a>";
-
-        AssertEx.HtmlEqual(@expectedHtml, output.ToHtmlString());
+        Assert.NotNull(actualOptions);
+        Assert.Equal(content, actualOptions!.Html?.ToHtmlString());
+        Assert.Null(actualOptions.Text);
+        Assert.Equal(href, actualOptions.Href?.ToHtmlString());
+        Assert.Equal(classes, actualOptions.Classes?.ToHtmlString());
+        Assert.NotNull(actualOptions.Attributes);
+        Assert.Collection(actualOptions.Attributes, kvp =>
+        {
+            Assert.Equal("data-foo", kvp.Key);
+            Assert.Equal(dataFooAttrValue, kvp.Value);
+        });
     }
 }