Accept argument in naturalday_partial, downcast format if necessary

bookwyrm/templatetags/date_ext.py

@@ -8,15 +8,23 @@ from bookwyrm.utils.partial_date import PartialDate
 register = template.Library()
 
 
-@register.filter(expects_localtime=True, is_safe=False)
-def naturalday_partial(date):
-    """allow templates to easily format PartialDate objects"""
+@register.filter(expects_localtime=True)
+def naturalday_partial(date, arg=None):
+    """chooses appropriate precision if date is a PartialDate object
+
+    If arg is a Django-defined format such as "DATE_FORMAT", it will be adjusted
+    so that the precision of the PartialDate object is honored.
+    """
+    django_formats = ("DATE_FORMAT", "SHORT_DATE_FORMAT", "YEAR_MONTH_FORMAT")
     if not isinstance(date, PartialDate):
-        return defaultfilters.date(date)
+        return defaultfilters.date(date, arg)
+    if arg is None:
+        arg = "DATE_FORMAT"
     if date.has_day:
-        fmt = "DATE_FORMAT"
+        fmt = arg
     elif date.has_month:
-        fmt = "YEAR_MONTH_FORMAT"
+        # there is no SHORT_YEAR_MONTH_FORMAT, so we ignore SHORT_DATE_FORMAT :(
+        fmt = "YEAR_MONTH_FORMAT" if arg == "DATE_FORMAT" else arg
     else:
-        fmt = "Y"
+        fmt = "Y" if arg in django_formats else arg
     return naturalday(date, fmt)

bookwyrm/tests/templatetags/test_date_ext.py

@@ -29,3 +29,34 @@ class PartialDateTags(TestCase):
         self.assertEqual("2023", date_ext.naturalday_partial(self._partial_year))
         self.assertEqual("June 2023", date_ext.naturalday_partial(self._partial_month))
         self.assertEqual("30 Jun 2023", date_ext.naturalday_partial(self._partial_day))
+
+    def test_format_arg_is_used(self):
+        """the provided format should be used by default"""
+        self.assertEqual("Dec.31", date_ext.naturalday_partial(self._dt, "M.j"))
+        self.assertEqual("Dec.31", date_ext.naturalday_partial(self._date, "M.j"))
+        self.assertEqual("June", date_ext.naturalday_partial(self._partial_day, "F"))
+
+    def test_month_precision_downcast(self):
+        """precision is adjusted for well-known date formats"""
+        self.assertEqual(
+            "June 2023", date_ext.naturalday_partial(self._partial_month, "DATE_FORMAT")
+        )
+
+    def test_year_precision_downcast(self):
+        """precision is adjusted for well-known date formats"""
+        for fmt in "DATE_FORMAT", "SHORT_DATE_FORMAT", "YEAR_MONTH_FORMAT":
+            with self.subTest(desc=fmt):
+                self.assertEqual(
+                    "2023", date_ext.naturalday_partial(self._partial_year, fmt)
+                )
+
+    def test_nonstandard_formats_passthru(self):
+        """garbage-in, garbage-out: we don't mess with unknown date formats"""
+        # Expected because there is no SHORT_YEAR_MONTH_FORMAT in Django that we can use
+        self.assertEqual(
+            "30/06/2023",
+            date_ext.naturalday_partial(self._partial_month, "SHORT_DATE_FORMAT"),
+        )
+        self.assertEqual(
+            "December.31", date_ext.naturalday_partial(self._partial_year, "F.j")
+        )