Add page.previous and page.next liquid variables (#22)

* sort pages

* rename tutorial files to enforce an order

* add prev next props to posts

* test previous next

* prevent nested recursive links between posts

* add a next/prev footer

* make prev/next work as expected for both pages and posts

* remove sort by index

* bold current section in nav

docs/includes/nav.html

@@ -1,7 +1,9 @@
 <nav>
     <a href="/">{{ site.config.name }}</a>
-    <a href="/tutorial/">tutorial</a>
-    <a href="/blog/">devlog</a>
+
+    {% assign section = page.path|split:"/" | first  %}
+    <a {% if section == "tutorial" %}style="font-weight:bold"{% endif %} href="/tutorial/">tutorial</a>
+    <a {% if section == "blog" %}style="font-weight:bold"{% endif %} href="/blog/">devlog</a>
 
     <div class="nav-right hidden-mobile">
         <a href="https://github.com/facundoolano/jorge">github</a>

docs/layouts/post.html

@@ -12,4 +12,29 @@ layout: base
         {% endif %}
     </header>
     {{ content }}
+
+    <br/>
+    <br/>
+
+    {% comment%}
+      if page.date then it's a post, and we want to invert the prev/next for the controls:
+      the next arrow should take you to the newer post, which appears fist in the site.posts list.
+    {%endcomment%}
+    {% if page.date %}
+    {% assign previous = page.next %}
+    {% assign next = page.previous %}
+    {% else %}
+    {% assign previous = page.previous %}
+    {% assign next = page.next %}
+    {% endif %}
+    <div class="pagination" style="display:flex">
+        {% if previous %}
+        <span>← <a class="title" href="{{previous.url}}"> {{ previous.subtitle | default:previous.title}}</a></span>
+        {% endif %}
+
+        {% if next %}
+        <span style="margin-left: auto"><a class="title" href="{{next.url}}">{{ next.subtitle | default:next.title}}</a> →</p>
+        {% endif %}
+    </div>
+
 </div>

docs/src/index.html

@@ -41,7 +41,7 @@ $ jorge serve
 
 <h2><a href="/tutorial" class="title" id="tutorial">Tutorial</a></h2>
 <ol start='0'>
-{% for page in site.pages|where:"dir", "/tutorial"|sort:"index" %}
+{% for page in site.pages|where:"dir", "/tutorial" %}
     <li>
         <a class="title" href="{{ page.url }}">{{ page.title }}{%if page.subtitle%}: {{page.subtitle|downcase}}{%endif%}</a>
     </li>

docs/src/tutorial/0-introduction.org

@@ -3,7 +3,6 @@ title: Introduction
 layout: post
 lang: en
 tags: [tutorial]
-index: 0
 ---
 #+OPTIONS: toc:nil num:nil
 #+LANGUAGE: en
@@ -14,10 +13,6 @@ jorge started as a Go learning project, aimed at streamlining my blogging workfl
 
 This tutorial covers the basics of using jorge, from starting a site to deploying it. I tried to keep it accessible, but you may need to consult with [[https://jekyllrb.com/docs/][Jekyll]] or [[https://gohugo.io/documentation/][Hugo]] documentation if you never used a static site generator, want to get the finer-grained details of template syntax, etc.
 
-#+HTML: <br>
-#+ATTR_HTML: :align right
-Next: [[file:installation][install jorge]].
-
 *** Notes
 
 [fn:1] Facundo Olano 👋

docs/src/tutorial/1-installation.org

@@ -1,9 +1,8 @@
 ---
-title: Installation
+title: Install jorge
 layout: post
 lang: en
 tags: [tutorial]
-index: 1
 ---
 #+OPTIONS: toc:nil num:nil
 #+LANGUAGE: en
@@ -48,7 +47,3 @@ Flags:
 
 Run "jorge <command> --help" for more information on a command.
 #+end_src
-
-#+HTML: <br>
-#+ATTR_HTML: :align right
-Next: [[file:jorge-init][start a website]].

docs/src/tutorial/2-jorge-init.org

@@ -4,7 +4,6 @@ subtitle: Start a website
 layout: post
 lang: en
 tags: [tutorial]
-index: 2
 ---
 #+OPTIONS: toc:nil num:nil
 #+LANGUAGE: en
@@ -60,8 +59,3 @@ Note how jorge assumes that the ~.html~ file extension will be omitted when serv
 and that index files represent URL directories (~src/blog/index.html~ will be served as ~/blog/)~.
 
 If you prefer to build your site from scratch, you can skip running ~jorge init~ altogether; the rest of the commands only expect a ~src/~ directory to work with.
-
-
-#+HTML: <br>
-#+ATTR_HTML: :align right
-Next: [[file:jorge-serve][browse the site locally]].

docs/src/tutorial/3-jorge-serve.org

@@ -4,7 +4,6 @@ subtitle: Browse the site locally
 layout: post
 lang: en
 tags: [tutorial]
-index: 3
 ---
 #+OPTIONS: toc:nil num:nil
 #+LANGUAGE: en
@@ -61,7 +60,3 @@ If you update the code in ~src/index.html~, you should see your browser tab refr
 #+end_src
 
 The new title should show up on the browser page.
-
-#+HTML: <br>
-#+ATTR_HTML: :align right
-Next: [[file:jorge-post][add a blog post]].

docs/src/tutorial/4-jorge-post.org

@@ -4,7 +4,6 @@ subtitle: Add a blog post
 layout: post
 lang: en
 tags: [tutorial]
-index: 4
 ---
 #+OPTIONS: toc:nil num:nil
 #+LANGUAGE: en
@@ -83,10 +82,6 @@ $ jorge post "Another kind of post"
 added src/2024-02-23-another-kind-of-post.md
 #+end_src
 
-#+HTML: <br>
-#+ATTR_HTML: :align right
-Next: [[file:jorge-build][prepare for production]].
-
 *** Notes
 
 [fn:1] Both a blog archive and the RSS feed (technically [[https://en.wikipedia.org/wiki/Atom_(web_standard)][Atom]]) are already implemented in the default site generated by ~jorge init~.

docs/src/tutorial/5-jorge-build.org

@@ -4,7 +4,6 @@ subtitle: Prepare for production
 layout: post
 lang: en
 tags: [tutorial]
-index: 5
 ---
 #+OPTIONS: toc:nil num:nil
 #+LANGUAGE: en

docs/src/tutorial/index.html

@@ -4,7 +4,7 @@ title: Tutorial
 ---
 
 <ol start='0'>
-    {% for page in site.pages|where:"dir", "/tutorial"|sort:"index" %}
+    {% for page in site.pages|where:"dir", "/tutorial" %}
     <li>
         <a class="title" href="{{ page.url }}">{{ page.title }}{%if page.subtitle%}: {{page.subtitle|downcase}}{%endif%}</a>
     </li>

site/site.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"io/fs"
+	"maps"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -181,21 +182,56 @@ func (site *Site) loadTemplates() error {
 		return err
 	}
 
-	// sort posts by reverse chronological order
-	Compare := func(a map[string]interface{}, b map[string]interface{}) int {
-		return b["date"].(time.Time).Compare(a["date"].(time.Time))
+	// sort by reverse chronological order when date is present
+	// otherwise by path alphabetical
+	CompareTemplates := func(a map[string]interface{}, b map[string]interface{}) int {
+		if bdate, ok := b["date"]; ok {
+			if adate, ok := a["date"]; ok {
+				return bdate.(time.Time).Compare(adate.(time.Time))
 			}
-	slices.SortFunc(site.posts, Compare)
+		}
+		return strings.Compare(a["path"].(string), b["path"].(string))
+	}
+	slices.SortFunc(site.posts, CompareTemplates)
+	slices.SortFunc(site.pages, CompareTemplates)
 	for _, posts := range site.tags {
-		slices.SortFunc(posts, Compare)
+		slices.SortFunc(posts, CompareTemplates)
 	}
+
+	// populate previous and next in template index
+	site.addPrevNext(site.pages)
+	site.addPrevNext(site.posts)
+
 	return nil
 }
 
+func (site *Site) addPrevNext(posts []map[string]interface{}) {
+	for i, post := range posts {
+		path := filepath.Join(site.Config.RootDir, post["src_path"].(string))
+
+		// only consider them part of the same collection if they share the directory
+		if i > 0 && post["dir"] == posts[i-1]["dir"] {
+			// make a copy of the map, without prev/next (to avoid weird recursion)
+			previous := maps.Clone(posts[i-1])
+			delete(previous, "previous")
+			delete(previous, "next")
+			site.templates[path].Metadata["previous"] = previous
+		}
+
+		if i < len(posts)-1 && post["dir"] == posts[i+1]["dir"] {
+			next := maps.Clone(posts[i+1])
+			delete(next, "previous")
+			delete(next, "next")
+			site.templates[path].Metadata["next"] = next
+		}
+	}
+}
+
 func (site *Site) Build() error {
 	// clear previous target contents
 	os.RemoveAll(site.Config.TargetDir)
-	os.Mkdir(site.Config.SrcDir, DIR_RWE_MODE)
+	os.Mkdir(site.Config.
+		SrcDir, DIR_RWE_MODE)
 
 	wg, files := spawnBuildWorkers(site)
 	defer wg.Wait()

site/site_test.go

@@ -117,6 +117,112 @@ title: about
 
 }
 
+func TestPreviousNext(t *testing.T) {
+	config := newProject()
+	defer os.RemoveAll(config.RootDir)
+
+	// prev next distinguish between series in different dirs
+	// add two different blog dirs and two different page dirs (tutorials)
+	blog1 := filepath.Join(config.SrcDir, "blog1")
+	blog2 := filepath.Join(config.SrcDir, "blog2")
+	tutorial1 := filepath.Join(config.SrcDir, "tutorial1")
+	tutorial2 := filepath.Join(config.SrcDir, "tutorial2")
+	os.Mkdir(blog1, DIR_RWE_MODE)
+	os.Mkdir(blog2, DIR_RWE_MODE)
+	os.Mkdir(tutorial1, DIR_RWE_MODE)
+	os.Mkdir(tutorial2, DIR_RWE_MODE)
+
+	newFile(blog1, "p1-1.html", `---
+date: 2024-01-01
+---`)
+	newFile(blog1, "p1-2.html", `---
+date: 2024-01-02
+---`)
+	newFile(blog1, "p1-3.html", `---
+date: 2024-01-03
+---`)
+
+	newFile(blog2, "p2-1.html", `---
+date: 2024-02-01
+---`)
+	newFile(blog2, "p2-2.html", `---
+date: 2024-02-02
+---`)
+	newFile(blog2, "p2-3.html", `---
+date: 2024-02-03
+---`)
+
+	newFile(tutorial1, "1-first-part.html", `---
+---`)
+	newFile(tutorial1, "2-another-entry.html", `---
+---`)
+	newFile(tutorial1, "3-goodbye.html", `---
+---`)
+
+	newFile(tutorial2, "index.html", `---
+---`)
+	newFile(tutorial2, "the-end.html", `---
+---`)
+	newFile(tutorial2, "another-entry.html", `---
+---`)
+
+	site, err := Load(*config)
+	// helper method to map a filename to its prev next keys (if any)
+	getPrevNext := func(dir string, filename string) (interface{}, interface{}) {
+		path := filepath.Join(dir, filename)
+		templ := site.templates[path]
+		return templ.Metadata["previous"], templ.Metadata["next"]
+	}
+	// tests for posts (sorted reverse chronologically, most recent one first)
+	assertEqual(t, err, nil)
+	prev, next := getPrevNext(blog1, "p1-3.html")
+	assertEqual(t, prev, nil)
+	assertEqual(t, next.(map[string]interface{})["url"], "/blog1/p1-2")
+
+	prev, next = getPrevNext(blog1, "p1-2.html")
+	assertEqual(t, prev.(map[string]interface{})["url"], "/blog1/p1-3")
+	assertEqual(t, next.(map[string]interface{})["url"], "/blog1/p1-1")
+
+	prev, next = getPrevNext(blog1, "p1-1.html")
+	assertEqual(t, prev.(map[string]interface{})["url"], "/blog1/p1-2")
+	assertEqual(t, next, nil)
+
+	assertEqual(t, err, nil)
+	prev, next = getPrevNext(blog2, "p2-3.html")
+	assertEqual(t, prev, nil)
+	assertEqual(t, next.(map[string]interface{})["url"], "/blog2/p2-2")
+
+	prev, next = getPrevNext(blog2, "p2-2.html")
+	assertEqual(t, prev.(map[string]interface{})["url"], "/blog2/p2-3")
+	assertEqual(t, next.(map[string]interface{})["url"], "/blog2/p2-1")
+
+	prev, next = getPrevNext(blog2, "p2-1.html")
+	assertEqual(t, prev.(map[string]interface{})["url"], "/blog2/p2-2")
+	assertEqual(t, next, nil)
+
+	// test for pages based on filename
+	prev, next = getPrevNext(tutorial1, "1-first-part.html")
+	assertEqual(t, prev, nil)
+	assertEqual(t, next.(map[string]interface{})["url"], "/tutorial1/2-another-entry")
+
+	prev, next = getPrevNext(tutorial1, "2-another-entry.html")
+	assertEqual(t, prev.(map[string]interface{})["url"], "/tutorial1/1-first-part")
+	assertEqual(t, next.(map[string]interface{})["url"], "/tutorial1/3-goodbye")
+
+	prev, next = getPrevNext(tutorial1, "3-goodbye.html")
+	assertEqual(t, prev.(map[string]interface{})["url"], "/tutorial1/2-another-entry")
+	assertEqual(t, next, nil)
+
+	// ensure alphabetical and index skipped
+	prev, next = getPrevNext(tutorial2, "another-entry.html")
+	assertEqual(t, prev, nil)
+	assertEqual(t, next.(map[string]interface{})["url"], "/tutorial2/the-end")
+
+	prev, next = getPrevNext(tutorial2, "the-end.html")
+	assertEqual(t, prev.(map[string]interface{})["url"], "/tutorial2/another-entry")
+	assertEqual(t, next, nil)
+}
+
 func TestRenderArchive(t *testing.T) {
 	config := newProject()
 	defer os.RemoveAll(config.RootDir)