From cd6bbec1a52045ed4c2d0e1f5cf21b286eb42e97 Mon Sep 17 00:00:00 2001
From: Oliver Booth <git@olivr.me>
Date: Sat, 27 Apr 2024 15:36:13 +0100
Subject: [PATCH] feat: add <meta> tag creation abstraction

---
 OliverBooth/Extensions/HtmlUtility.cs   | 118 ++++++++++++++++++++++++
 OliverBooth/Pages/Shared/_Layout.cshtml |  11 +--
 2 files changed, 120 insertions(+), 9 deletions(-)
 create mode 100644 OliverBooth/Extensions/HtmlUtility.cs

diff --git a/OliverBooth/Extensions/HtmlUtility.cs b/OliverBooth/Extensions/HtmlUtility.cs
new file mode 100644
index 0000000..7139ac5
--- /dev/null
+++ b/OliverBooth/Extensions/HtmlUtility.cs
@@ -0,0 +1,118 @@
+using System.Web;
+using Cysharp.Text;
+using OliverBooth.Data.Blog;
+using OliverBooth.Services;
+
+namespace OliverBooth.Extensions;
+
+/// <summary>
+///     Provides helper methods for generating HTML tags 
+/// </summary>
+public static class HtmlUtility
+{
+    /// <summary>
+    ///     Creates <c>&lt;meta&gt;</c> embed tags by pulling data from the specified blog post.
+    /// </summary>
+    /// <param name="post">The blog post whose metadata should be retrieved.</param>
+    /// <param name="blogPostService">The <see cref="IBlogPostService" /> injected by the page.</param>
+    /// <returns>A string containing a collection of <c>&lt;meta&gt;</c> embed tags.</returns>
+    /// <exception cref="ArgumentNullException">
+    ///     <para><paramref name="post" /> is <see langword="null" />.</para>
+    ///     -or-
+    ///     <para><paramref name="blogPostService" /> is <see langword="null" />.</para>
+    /// </exception>
+    public static string CreateMetaTagsFromPost(IBlogPost post, IBlogPostService blogPostService)
+    {
+        if (post is null)
+        {
+            throw new ArgumentNullException(nameof(post));
+        }
+
+        if (blogPostService is null)
+        {
+            throw new ArgumentNullException(nameof(blogPostService));
+        }
+
+
+        string excerpt = blogPostService.RenderExcerpt(post, out _);
+        var tags = new Dictionary<string, string>
+        {
+            ["title"] = post.Title,
+            ["description"] = excerpt,
+            ["author"] = post.Author.DisplayName
+        };
+        return CreateMetaTags(tags);
+    }
+
+    /// <summary>
+    ///     Creates <c>&lt;meta&gt;</c> embed tags by pulling data from the specified dictionary.
+    /// </summary>
+    /// <param name="tags">
+    ///     A dictionary containing the tag values. This dictionary should be in the form:
+    ///
+    ///     <list type="table">
+    ///         <listheader>
+    ///             <term>Key</term>
+    ///             <description>Description</description>
+    ///         </listheader>
+    ///
+    ///         <item>
+    ///             <term>description</term>
+    ///             <description>
+    ///                 The value to apply to the <c>description</c>, <c>og:description</c>, and <c>twitter:description</c>, tags.
+    ///             </description>
+    ///         </item>
+    ///
+    ///         <item>
+    ///             <term>author</term>
+    ///             <description>The value to apply to the <c>og:site_name</c>, and <c>twitter:creator</c>, tags.</description>
+    ///         </item>
+    ///
+    ///         <item>
+    ///             <term>title</term>
+    ///             <description>
+    ///                 The value to apply to the <c>title</c>, <c>og:title</c>, and <c>twitter:title</c>, tags.
+    ///             </description>
+    ///         </item>
+    ///     </list>
+    ///
+    ///     Any other values contained with the dictionary are ignored.
+    /// </param>
+    /// <returns>A string containing a collection of <c>&lt;meta&gt;</c> embed tags.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="tags" /> is <see langword="null" />.</exception>
+    public static string CreateMetaTags(IReadOnlyDictionary<string, string> tags)
+    {
+        if (tags is null)
+        {
+            throw new ArgumentNullException(nameof(tags));
+        }
+
+        using Utf8ValueStringBuilder builder = ZString.CreateUtf8StringBuilder();
+        builder.AppendLine("""<meta property="og:type" content="article">""");
+
+        if (tags.TryGetValue("description", out string? description))
+        {
+            description = HttpUtility.HtmlEncode(description);
+            builder.AppendLine($"""<meta name="description" content="{description}">""");
+            builder.AppendLine($"""<meta property="og:description" content="{description}">""");
+            builder.AppendLine($"""<meta property="twitter:description" content="{description}">""");
+        }
+
+        if (tags.TryGetValue("author", out string? author))
+        {
+            author = HttpUtility.HtmlEncode(author);
+            builder.AppendLine($"""<meta property="og:site_name" content="{author}">""");
+            builder.AppendLine($"""<meta property="twitter:creator" content="{author}">""");
+        }
+
+        if (tags.TryGetValue("title", out string? title))
+        {
+            title = HttpUtility.HtmlEncode(title);
+            builder.AppendLine($"""<meta name="title" content="{title}">""");
+            builder.AppendLine($"""<meta property="og:title" content="{title}">""");
+            builder.AppendLine($"""<meta property="twitter:title" content="{title}">""");
+        }
+
+        return builder.ToString();
+    }
+}
diff --git a/OliverBooth/Pages/Shared/_Layout.cshtml b/OliverBooth/Pages/Shared/_Layout.cshtml
index 2ee6fe0..4ed9767 100644
--- a/OliverBooth/Pages/Shared/_Layout.cshtml
+++ b/OliverBooth/Pages/Shared/_Layout.cshtml
@@ -1,4 +1,5 @@
 @using OliverBooth.Data.Blog
+@using OliverBooth.Extensions
 @using OliverBooth.Services
 @inject IBlogPostService BlogPostService
 @{
@@ -28,15 +29,7 @@
     }
     @if (ViewData["Post"] is IBlogPost post)
     {
-        string excerpt = BlogPostService.RenderExcerpt(post, out bool trimmed);
-        <meta name="title" content="@post.Title">
-        <meta name="description" content="@excerpt">
-        <meta property="og:title" content="@post.Title">
-        <meta property="og:description" content="@excerpt">
-        <meta property="og:type" content="article">
-        <meta property="twitter:title" content="@post.Title">
-        <meta property="twitter:creator" content="@post.Author.DisplayName">
-        <meta property="twitter:description" content="@excerpt">
+        @Html.Raw(HtmlUtility.CreateMetaTagsFromPost(post, BlogPostService))
     }
     else
     {