Improve Open Graph data for books and add it for lists

bookwyrm/templates/book/book.html

@@ -8,7 +8,7 @@
 {% block title %}{{ book|book_title }}{% endblock %}
 
 {% block opengraph %}
-    {% include 'snippets/opengraph.html' with image=book.preview_image %}
+    {% include 'snippets/opengraph.html' with title=book.title description=book|book_description image=book.preview_image %}
 {% endblock %}
 
 {% block content %}

bookwyrm/templates/lists/layout.html

@@ -1,8 +1,13 @@
 {% extends 'layout.html' %}
 {% load i18n %}
+{% load list_page_tags %}
 
 {% block title %}{{ list.name }}{% endblock %}
 
+{% block opengraph %}
+    {% include 'snippets/opengraph.html' with title=list|opengraph_title description=list|opengraph_description %}
+{% endblock %}
+
 {% block content %}
 <header class="columns content is-mobile">
     <div class="column">

bookwyrm/templatetags/list_page_tags.py

@@ -0,0 +1,25 @@
+""" template filters for list page """
+from django import template
+from django.utils.translation import gettext_lazy as _, ngettext
+
+from bookwyrm import models
+
+
+register = template.Library()
+
+
+@register.filter(name="opengraph_title")
+def get_opengraph_title(book_list: models.List) -> str:
+    """Construct title for Open Graph"""
+    return _("Book List: %(name)s") % {"name": book_list.name}
+
+
+@register.filter(name="opengraph_description")
+def get_opengraph_description(book_list: models.List) -> str:
+    """Construct description for Open Graph"""
+    num_books = book_list.books.all().count()
+    num_books_str = ngettext(
+        "%(num)d book - by %(user)s", "%(num)d books - by %(user)s", num_books
+    ) % {"num": num_books, "user": book_list.user}
+
+    return f"{book_list.description} {num_books_str}"