fix post-nav button order

Navigation now follows newer/older logic. click right to go older, left
to go newer.

src/zona/builder.py

@@ -99,6 +99,8 @@ class ZonaBuilder:
 
     def _build(self):
         assert self.items
+        # sort according to date
+        # descending order
         post_list: list[Item] = sorted(
             [item for item in self.items if item.post],
             key=lambda item: item.metadata.date
@@ -106,12 +108,16 @@ class ZonaBuilder:
             else date.min,
             reverse=True,
         )
+        # number of posts
         posts = len(post_list)
+        # link post chronology
         for i, item in enumerate(post_list):
-            prev = post_list[i - 1] if i > 0 else None
-            next = post_list[i + 1] if i < posts - 2 else None
-            item.previous = prev
-            item.next = next
+            # prev: older post
+            older = post_list[i + 1] if i + 1 < posts else None
+            # next: newer post
+            newer = post_list[i - 1] if i > 0 else None
+            item.older = older
+            item.newer = newer
 
         templater = Templater(
             config=self.config,

src/zona/data/templates/post_nav.html

@@ -1,9 +1,11 @@
 <div class="post-nav">
   <center>
-    <span class="symbol">&lt;</span>{% if previous %}<a
-      href="{{ previous }}"
-    >prev</a>{% endif %}{% if previous and next %}<span class="symbol"
-    >|</span>{% endif %}{% if next %}<a href="{{ next }}">next</a>{% endif
-    %}<span class="symbol">&gt;</span>
+    <span class="symbol">&lt;</span>{% if newer %}<a href="{{ newer }}">newr</a>{%
+    else %}<span class="placeholder">null</span>{% endif %}<span
+      class="symbol"
+    ><span class="bar"></span></span>{% if older %}<a href="{{ older }}"
+    >oldr</a>{% else %}<span class="placeholder">null</span>{% endif %}<span
+      class="symbol"
+    >&gt;</span>
   </center>
 </div>

src/zona/models.py

@@ -23,8 +23,8 @@ class Item:
     type: ItemType | None = None
     copy: bool = True
     post: bool = False
-    next: Item | None = None
-    previous: Item | None = None
+    newer: Item | None = None
+    older: Item | None = None
 
 
 # @dataclass

src/zona/templates.py

@@ -27,7 +27,6 @@ def get_footer(template_dir: Path) -> str | None:
         return html_footer.read_text()
 
 
-# TODO: add next/prev post button logic to posts
 # TODO: add a recent posts element that can be included elsewhere?
 class Templater:
     def __init__(
@@ -79,11 +78,11 @@ class Templater:
             header=header,
             footer=footer,
             is_post=item.post,
-            next=util.normalize_url(item.next.url)
-            if item.next
+            newer=util.normalize_url(item.newer.url)
+            if item.newer
             else None,
-            previous=util.normalize_url(item.previous.url)
-            if item.previous
+            older=util.normalize_url(item.older.url)
+            if item.older
             else None,
             post_list=self.post_list,
         )