backend: Add pagination for blog entries

Related ticket: Instanssi#52

Author: jpot

backend/Instanssi/ext_blog/templates/ext_blog/blog_messages.html

@@ -2,11 +2,23 @@
 <div id="blog">
 {% for entry in entries %}
     <div class="message" id="{{ entry.id }}">
+        {# TODO These links won't work if entry is not on currently shown page. Fix by adding a separate view. #}
         <a style="text-decoration: none;" href="#{{ entry.id }}"><h2>{{ entry.title }}</h2></a>
         <time datetime="{{ entry.date|date:"Y-m-d\TH:i" }}" class="date">{{ entry.date|date:"d.m.Y H:i" }}</time>
         <div class="content">{{ entry.text|safe }}</div>
     </div>
 {% endfor %}
+{% if needs_pagination %}
+    <ul class="pagination">
+        {% for i in page_range %}
+            {% if i == page_number %}
+                <li class="active" aria-label="Nykyinen sivu: {{ i }}/{{ num_pages }}"><a>{{ i }}</a></li>
+            {% else %}
+                <li><a href="?p={{ i }}" aria-label="Siirry sivulle: {{ i }}/{{ num_pages }}">{{ i }}</a></li>
+            {% endif %}
+        {% endfor %}
+    </ul>
+{% endif %}
 </div>
 {% else %}
 <p>Blogissa ei ole entryjä!</p>

backend/Instanssi/ext_blog/templatetags/blog_tags.py

@@ -1,10 +1,25 @@
 from django import template
+from django.core.paginator import Paginator
 
 from Instanssi.ext_blog.models import BlogEntry
 
 register = template.Library()
 
 
-@register.inclusion_tag("ext_blog/blog_messages.html")
-def render_blog(event_id: int, max_posts: int = 10) -> dict:
-    return {"entries": BlogEntry.get_latest().filter(event_id=event_id)[:max_posts]}
+@register.inclusion_tag("ext_blog/blog_messages.html", takes_context=True)
+def render_blog(context, event_id: int, max_posts: int = 10) -> dict:
+    request = context["request"]
+    page_number = request.GET.get('p', 1) # Default to page 1 if get parameter is missing
+    # Make sure the page number from the get parameter is a valid integer:
+    try:
+        page_number = int(page_number)
+    except ValueError:
+        page_number = 1
+    full_entries_list = BlogEntry.get_latest().filter(event_id=event_id)
+    paginator = Paginator(full_entries_list, max_posts)
+    current_page = paginator.get_page(page_number)
+    entries = current_page.object_list
+    # We will pass this boolean as extra data to the template for simplicity
+    # It's used to determine whether to render pagination links or not:
+    needs_pagination = paginator.count > paginator.per_page
+    return {"entries": entries, "needs_pagination": needs_pagination, "page_range": paginator.page_range, "page_number": current_page.number, "num_pages": paginator.num_pages}