From d114870f87fa9573eba4c783a1dd0e1aacbe366d Mon Sep 17 00:00:00 2001
From: Oliver Booth <git@olivr.me>
Date: Tue, 19 Sep 2023 19:29:21 +0100
Subject: [PATCH] feat: add links to next and prev articles

---
 OliverBooth/Pages/Blog/Article.cshtml    | 37 ++++++++++++++++++++++++
 OliverBooth/Services/BlogPostService.cs  | 20 +++++++++++++
 OliverBooth/Services/IBlogPostService.cs | 14 +++++++++
 3 files changed, 71 insertions(+)

diff --git a/OliverBooth/Pages/Blog/Article.cshtml b/OliverBooth/Pages/Blog/Article.cshtml
index 0cd7b79..798a4c1 100644
--- a/OliverBooth/Pages/Blog/Article.cshtml
+++ b/OliverBooth/Pages/Blog/Article.cshtml
@@ -1,6 +1,8 @@
 @page "/blog/{year:int}/{month:int}/{day:int}/{slug}"
 @using Humanizer
 @using OliverBooth.Data.Blog
+@using OliverBooth.Services
+@inject IBlogPostService BlogPostService
 @model Article
 
 @if (Model.Post is not { } post)
@@ -54,6 +56,41 @@
 
 <hr>
 
+<div class="row">
+    <div class="col-sm-12 col-md-6">
+        @if (BlogPostService.GetPreviousPost(post) is { } previousPost)
+        {
+            <small>Previous Post</small>
+            <p class="lead">
+                <a asp-page="Article"
+                   asp-route-year="@previousPost.Published.Year.ToString("0000")"
+                   asp-route-month="@previousPost.Published.Month.ToString("00")"
+                   asp-route-day="@previousPost.Published.Day.ToString("00")"
+                   asp-route-slug="@previousPost.Slug">
+                    @previousPost.Title
+                </a>
+            </p>
+        }
+    </div>
+    <div class="col-sm-12 col-md-6" style="text-align: right;">
+        @if (BlogPostService.GetNextPost(post) is { } nextPost)
+        {
+            <small>Next Post</small>
+            <p class="lead">
+                <a asp-page="Article"
+                   asp-route-year="@nextPost.Published.Year.ToString("0000")"
+                   asp-route-month="@nextPost.Published.Month.ToString("00")"
+                   asp-route-day="@nextPost.Published.Day.ToString("00")"
+                   asp-route-slug="@nextPost.Slug">
+                    @nextPost.Title
+                </a>
+            </p>
+        }
+    </div>
+</div>
+
+<hr>
+
 @if (post.EnableComments)
 {
     <div id="disqus_thread"></div>
diff --git a/OliverBooth/Services/BlogPostService.cs b/OliverBooth/Services/BlogPostService.cs
index 77da54a..aa2a4a1 100644
--- a/OliverBooth/Services/BlogPostService.cs
+++ b/OliverBooth/Services/BlogPostService.cs
@@ -66,6 +66,26 @@ internal sealed class BlogPostService : IBlogPostService
             .ToArray().Select(CacheAuthor).ToArray();
     }
 
+    /// <inheritdoc />
+    public IBlogPost? GetNextPost(IBlogPost blogPost)
+    {
+        using BlogContext context = _dbContextFactory.CreateDbContext();
+        return context.BlogPosts
+            .Where(p => p.Visibility == BlogPostVisibility.Published)
+            .OrderBy(post => post.Published)
+            .FirstOrDefault(post => post.Published > blogPost.Published);
+    }
+
+    /// <inheritdoc />
+    public IBlogPost? GetPreviousPost(IBlogPost blogPost)
+    {
+        using BlogContext context = _dbContextFactory.CreateDbContext();
+        return context.BlogPosts
+            .Where(p => p.Visibility == BlogPostVisibility.Published)
+            .OrderByDescending(post => post.Published)
+            .FirstOrDefault(post => post.Published < blogPost.Published);
+    }
+
     /// <inheritdoc />
     public string RenderExcerpt(IBlogPost post, out bool wasTrimmed)
     {
diff --git a/OliverBooth/Services/IBlogPostService.cs b/OliverBooth/Services/IBlogPostService.cs
index a7ac372..bcb48ee 100644
--- a/OliverBooth/Services/IBlogPostService.cs
+++ b/OliverBooth/Services/IBlogPostService.cs
@@ -34,6 +34,20 @@ public interface IBlogPostService
     /// <returns>A collection of blog posts.</returns>
     IReadOnlyList<IBlogPost> GetBlogPosts(int page, int pageSize = 10);
 
+    /// <summary>
+    ///     Returns the next blog post from the specified blog post.
+    /// </summary>
+    /// <param name="blogPost">The blog post whose next post to return.</param>
+    /// <returns>The next blog post from the specified blog post.</returns>
+    IBlogPost? GetNextPost(IBlogPost blogPost);
+
+    /// <summary>
+    ///     Returns the previous blog post from the specified blog post.
+    /// </summary>
+    /// <param name="blogPost">The blog post whose previous post to return.</param>
+    /// <returns>The previous blog post from the specified blog post.</returns>
+    IBlogPost? GetPreviousPost(IBlogPost blogPost);
+
     /// <summary>
     ///     Renders the excerpt of the specified blog post.
     /// </summary>