Admin filter factory

README.md

@@ -113,4 +113,43 @@ class MovieAdmin(GroupedActionAdminMixin, admin.ModelAdmin):
       # …
 ```
 
-The order of the groups is determined by the order of the individual actions: the first action for that group for each group determines how the groups are listed.
+The order of the groups is determined by the order of the individual actions: the first action for that group for each group determines how the groups are listed.
+
+## Simpler `SimpleListFilter`s
+
+Django allows to add extra filters on the Django admin, but even with a `SimpleListFilter`, they are cumbersome to make. We define a `ChoiceListFilter` which can be
+used to make these based on a dictionary, and add a function `adminfilter_factory(..)` to define such classes in a more convenient way.
+
+Once can define such simple list filter by working with a dict like:
+
+```python3
+from django.db.models import Q
+from django.db.models.functions import Now
+from django_adminlink.admin import ChoiceListFilter
+
+class ArchiveStatusFilter(ChoiceListFilter):
+    title = 'Archive status'
+    parameter_name = 'archive_status'
+    choices = {
+      'active': ('Active', ~Q(archived_at__lte=Now())),
+      'archived': ('Archived', Q(archived_at__lte=Now()))
+    }
+```
+
+so a dictionary that maps the key of the filter on a 2-tuple with the verbose name as first item, and the Django filter (a `Q` object) as second one. Because it is a dictionary, it is also impossible to specify the same key twice.
+
+We can also define this with the `adminfilter_factory(..)` as follows:
+
+
+```python3
+from django.db.models import Q
+from django_adminlink.admin import adminfilter_factory
+
+ARCHIVE_OPTIONS = [
+    ('active', 'Active', ~Q(archived_at__lte=Now())),
+    ('archived', 'Archived', Q(archived_at__lte=Now()))
+]
+ArchiveStatusFilter = adminfilter_factory('archive_status', ARCHIVE_OPTIONS)
+```
+
+here we can use the same dictionary structure, or any iterable of items with at least three items.

django_adminlink/admin.py

@@ -162,3 +162,31 @@ def get_action_choices(self, request, default_choices=models.BLANK_CHOICE_DASH):
 
 class GroupedActionAdmin(SingleItemActionMixin, admin.ModelAdmin):
     pass
+
+
+class ChoiceListFilter(admin.SimpleListFilter):
+    choices = {}
+
+    def lookups(self, request, model_admin):
+        return [(k, v) for k, (v, *__) in self.choices.items()]
+
+    def queryset(self, request, queryset):
+        val = self.choices.get(self.value())
+        if val and len(val) >= 2:
+            __, cond, *__ = val
+            return queryset.filter(cond)
+        return queryset
+
+
+def adminfilter_factory(parameter_name, choices, verbose_name=None):
+    default_verbose_name = parameter_name.replace("_", " ")
+    if verbose_name is None:
+        verbose_name = default_verbose_name.capitalize()
+    class_name = default_verbose_name.title().replace(" ", "")
+    if not isinstance(choices, dict):
+        choices = {k: vs for k, *vs in choices}
+    return type(
+        f"{class_name}Filter",
+        (ChoiceListFilter,),
+        {"title": verbose_name, "parameter_name": parameter_name, "choices": choices},
+    )