Port Skip link to IComponentGenerator

Author: gunndabad

docs/components/skip-link.md

@@ -20,6 +20,6 @@
 
 The content is the HTML to use within the generated link.
 
-| Attribute | Type | Description |
-| --- | --- | --- |
-| `href` | `string` | The 'href' attribute for the link. The default is '#content'. Cannot be `null` or empty. |
+| Attribute | Type | Description                                                                   |
+| --- | --- |-------------------------------------------------------------------------------|
+| `href` | `string` | The 'href' attribute for the link. If not specified, '#content' will be used. |

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

@@ -0,0 +1,25 @@
+using System;
+using Microsoft.AspNetCore.Html;
+
+namespace GovUk.Frontend.AspNetCore.ComponentGeneration;
+
+public partial class DefaultComponentGenerator
+{
+    internal const string SkipLinkDefaultHref = "#content";
+    internal const string SkipLinkElement = "a";
+
+    /// <inheritdoc/>
+    public virtual HtmlTagBuilder GenerateSkipLink(SkipLinkOptions options)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        options.Validate();
+
+        return new HtmlTagBuilder(SkipLinkElement)
+            .WithAttribute("href", options.Href ?? new HtmlString(SkipLinkDefaultHref))
+            .WithCssClass("govuk-skip-link")
+            .WithCssClasses(ExplodeClasses(options.Classes?.ToHtmlString()))
+            .WithAttributes(options.Attributes)
+            .WithAttribute("data-module", "govuk-skip-link", encodeValue: false)
+            .WithAppendedHtml(GetEncodedTextOrHtml(options.Text, options.Html)!);
+    }
+}

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

@@ -95,6 +95,12 @@ public interface IComponentGenerator
     /// <returns>An <see cref="HtmlTagBuilder"/> with the component's HTML.</returns>
     HtmlTagBuilder GeneratePhaseBanner(PhaseBannerOptions options);
 
+    /// <summary>
+    /// Generates a skip link component.
+    /// </summary>
+    /// <returns>An <see cref="HtmlTagBuilder"/> with the component's HTML.</returns>
+    HtmlTagBuilder GenerateSkipLink(SkipLinkOptions options);
+
     /// <summary>
     /// Generates a tag component.
     /// </summary>

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

@@ -11,4 +11,12 @@ public class SkipLinkOptions
     public IHtmlContent? Href { get; set; }
     public IHtmlContent? Classes { get; set; }
     public EncodedAttributesDictionary? Attributes { get; set; }
+
+    internal void Validate()
+    {
+        if (Html.NormalizeEmptyString() is null && Text.NormalizeEmptyString() is null)
+        {
+            throw new InvalidOptionsException(GetType(), $"{nameof(Html)} or {nameof(Text)} must be specified.");
+        }
+    }
 }

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

@@ -115,8 +115,6 @@ TagBuilder GenerateSelect(
         IEnumerable<SelectItem> items,
         AttributeDictionary attributes);
 
-    TagBuilder GenerateSkipLink(string href, IHtmlContent content, AttributeDictionary attributes);
-
     TagBuilder GenerateSummaryCard(SummaryCardTitle title, SummaryListActions actions, IHtmlContent summaryList, AttributeDictionary attributes);
 
     TagBuilder GenerateSummaryList(IEnumerable<SummaryListRow> rows, AttributeDictionary attributes);

src/GovUk.Frontend.AspNetCore/IGovUkHtmlGenerator.cs

@@ -1,6 +1,6 @@
+using System;
 using System.Threading.Tasks;
-using GovUk.Frontend.AspNetCore.HtmlGeneration;
-using Microsoft.AspNetCore.Mvc.TagHelpers;
+using GovUk.Frontend.AspNetCore.ComponentGeneration;
 using Microsoft.AspNetCore.Razor.TagHelpers;
 
 namespace GovUk.Frontend.AspNetCore.TagHelpers;
@@ -9,61 +9,54 @@ namespace GovUk.Frontend.AspNetCore.TagHelpers;
 /// Generates a GDS skip link component.
 /// </summary>
 [HtmlTargetElement(TagName)]
-[OutputElementHint(ComponentGenerator.SkipLinkElement)]
+[OutputElementHint(DefaultComponentGenerator.SkipLinkElement)]
 public class SkipLinkTagHelper : TagHelper
 {
     internal const string TagName = "govuk-skip-link";
 
     private const string HrefAttributeName = "href";
 
-    private readonly IGovUkHtmlGenerator _htmlGenerator;
-
-    private string _href = ComponentGenerator.SkipLinkDefaultHref;
+    private readonly IComponentGenerator _componentGenerator;
 
     /// <summary>
     /// Creates a new <see cref="BackLinkTagHelper"/>.
     /// </summary>
-    public SkipLinkTagHelper()
-        : this(htmlGenerator: null)
-    {
-    }
-
-    internal SkipLinkTagHelper(IGovUkHtmlGenerator? htmlGenerator)
+    public SkipLinkTagHelper(IComponentGenerator componentGenerator)
     {
-        _htmlGenerator = htmlGenerator ?? new ComponentGenerator();
+        ArgumentNullException.ThrowIfNull(componentGenerator);
+        _componentGenerator = componentGenerator;
     }
 
     /// <summary>
     /// The <c>href</c> attribute for the link.
     /// </summary>
     /// <remarks>
-    /// The default is <c>&quot;#content&quot;</c>.
-    /// Cannot be <c>null</c> or empty.
+    /// If not specified, <c>#content</c> will be used.
     /// </remarks>
     [HtmlAttributeName(HrefAttributeName)]
-    public string Href
-    {
-        get => _href;
-        set => _href = Guard.ArgumentNotNullOrEmpty(nameof(value), value);
-    }
+    public string? Href { get; set; }
 
     /// <inheritdoc/>
     public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
     {
-        var childContent = await output.GetChildContentAsync();
+        var childContent = (await output.GetChildContentAsync()).Snapshot();
 
         if (output.Content.IsModified)
         {
             childContent = output.Content;
         }
 
-        var tagBuilder = _htmlGenerator.GenerateSkipLink(Href, childContent, output.Attributes.ToAttributeDictionary());
+        var attributes = new EncodedAttributesDictionary(output.Attributes);
+        attributes.Remove("class", out var classes);
 
-        output.TagName = tagBuilder.TagName;
-        output.TagMode = TagMode.StartTagAndEndTag;
+        var component = _componentGenerator.GenerateSkipLink(new SkipLinkOptions
+        {
+            Html = childContent,
+            Href = Href.ToHtmlContent(),
+            Classes = classes,
+            Attributes = attributes
+        });
 
-        output.Attributes.Clear();
-        output.MergeAttributes(tagBuilder);
-        output.Content.SetHtmlContent(tagBuilder.InnerHtml);
+        component.WriteTo(output);
     }
 }

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

@@ -135,6 +135,13 @@ public void Pagination(ComponentTestCaseData<PaginationOptions> data) =>
             data,
             (generator, options) => generator.GeneratePagination(options).ToHtmlString());
 
+    [Theory]
+    [ComponentFixtureData("skip-link", typeof(SkipLinkOptions))]
+    public void SkipLink(ComponentTestCaseData<SkipLinkOptions> data) =>
+        CheckComponentHtmlMatchesExpectedHtml(
+            data,
+            (generator, options) => generator.GenerateSkipLink(options).ToHtmlString());
+
     [Theory]
     [ComponentFixtureData("task-list", typeof(TaskListOptions))]
     public void TaskList(ComponentTestCaseData<TaskListOptions> data) =>

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

@@ -1,18 +1,23 @@
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using GovUk.Frontend.AspNetCore.ComponentGeneration;
 using GovUk.Frontend.AspNetCore.TagHelpers;
 using GovUk.Frontend.AspNetCore.TestCommon;
 using Microsoft.AspNetCore.Razor.TagHelpers;
+using Moq;
 using Xunit;
 
 namespace GovUk.Frontend.AspNetCore.Tests.TagHelpers;
 
 public class SkipLinkTagHelperTests
 {
     [Fact]
-    public async Task ProcessAsync_WithHrefSpecified_GeneratesExpectedOutput()
+    public async Task ProcessAsync_InvokesComponentGeneratorWithExpectedOptions()
     {
         // Arrange
+        var href = "#main";
+        var content = "Link content";
+
         var context = new TagHelperContext(
             tagName: "govuk-skip-link",
             allAttributes: new TagHelperAttributeList(),
@@ -25,53 +30,25 @@ public async Task ProcessAsync_WithHrefSpecified_GeneratesExpectedOutput()
             getChildContentAsync: (useCachedResult, encoder) =>
             {
                 var tagHelperContent = new DefaultTagHelperContent();
-                tagHelperContent.SetContent("Link content");
+                tagHelperContent.SetContent(content);
                 return Task.FromResult<TagHelperContent>(tagHelperContent);
             });
 
-        var tagHelper = new SkipLinkTagHelper()
+        var componentGeneratorMock = new Mock<DefaultComponentGenerator>() { CallBase = true };
+        SkipLinkOptions? actualOptions = null;
+        componentGeneratorMock.Setup(mock => mock.GenerateSkipLink(It.IsAny<SkipLinkOptions>())).Callback<SkipLinkOptions>(o => actualOptions = o);
+
+        var tagHelper = new SkipLinkTagHelper(componentGeneratorMock.Object)
         {
-            Href = "#main"
+            Href = href
         };
 
         // Act
         await tagHelper.ProcessAsync(context, output);
 
         // Assert
-        var expectedHtml = @"
-<a class=""govuk-skip-link"" href=""#main"" data-module=""govuk-skip-link"">Link content</a>";
-
-        AssertEx.HtmlEqual(expectedHtml, output.ToHtmlString());
-    }
-
-    [Fact]
-    public async Task ProcessAsync_WithNoHrefSpecified_UsesDefaultHref()
-    {
-        // Arrange
-        var context = new TagHelperContext(
-            tagName: "govuk-skip-link",
-            allAttributes: new TagHelperAttributeList(),
-            items: new Dictionary<object, object>(),
-            uniqueId: "test");
-
-        var output = new TagHelperOutput(
-            "govuk-skip-link",
-            attributes: new TagHelperAttributeList(),
-            getChildContentAsync: (useCachedResult, encoder) =>
-            {
-                var tagHelperContent = new DefaultTagHelperContent();
-                tagHelperContent.SetContent("Link content");
-                return Task.FromResult<TagHelperContent>(tagHelperContent);
-            });
-
-        var tagHelper = new SkipLinkTagHelper();
-
-        // Act
-        await tagHelper.ProcessAsync(context, output);
-
-        // Assert
-        var element = output.RenderToElement();
-
-        Assert.Equal("#content", element.GetAttribute("href"));
+        Assert.NotNull(actualOptions);
+        Assert.Equal(href, actualOptions.Href?.ToHtmlString());
+        Assert.Equal(content, actualOptions.Html?.ToHtmlString());
     }
 }