From 8b11327a2f4763f75917e7425fa55a79c73abd87 Mon Sep 17 00:00:00 2001
From: Taavi Teska <taaviteska@gmail.com>
Date: Tue, 24 Apr 2018 11:59:00 +0300
Subject: [PATCH] Add mixin for easier implementation of ordering in Django's
 generic ListView

---
 AUTHORS.rst             |  2 +-
 README.rst              |  1 +
 tests/test_importing.py |  1 +
 tg_utils/mixins.py      | 58 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 61 insertions(+), 1 deletion(-)
 create mode 100644 tg_utils/mixins.py

diff --git a/AUTHORS.rst b/AUTHORS.rst
index d4d0ab3..66e699f 100644
--- a/AUTHORS.rst
+++ b/AUTHORS.rst
@@ -10,4 +10,4 @@ Development Lead
 Contributors
 ------------
 
-None yet. Why not be the first?
+* Taavi Teska <taavi@thorgate.eu>
diff --git a/README.rst b/README.rst
index f7ffe74..f57e1e5 100644
--- a/README.rst
+++ b/README.rst
@@ -30,6 +30,7 @@ Features
 * Unique filename generation for uploads.
 * Using hashids for models (instead of exposing primary keys).
 * System checks for email and Sentry configuration.
+* Mixin for easier implementation of ordering in Django's generic ListView.
 * JS/CSS compressors for `Django Compressor <https://django-compressor.readthedocs.org/en/latest/>`_.
 
 
diff --git a/tests/test_importing.py b/tests/test_importing.py
index 9e2d3e2..7ebaed6 100644
--- a/tests/test_importing.py
+++ b/tests/test_importing.py
@@ -13,6 +13,7 @@ def test_imports():
     from tg_utils import files
     from tg_utils import hashmodels
     from tg_utils import managers
+    from tg_utils import mixins
     from tg_utils import models
     from tg_utils import profiling
     from tg_utils import signals
diff --git a/tg_utils/mixins.py b/tg_utils/mixins.py
new file mode 100644
index 0000000..5ab3221
--- /dev/null
+++ b/tg_utils/mixins.py
@@ -0,0 +1,58 @@
+import re
+
+from django.utils.html import escape
+from django.utils.safestring import mark_safe
+
+
+class OrderingOptionsMixin:
+    """
+    Mixin for easier implementation of ordering in Django's generic ListView.
+
+    Add `ordering_options` to your subclass and you should be ready to go.
+    Note that the user-passed query parameters are validated and you should have ascending as well as descending (with a
+    starting minus-sign (-)) listed in the ordering_options.
+
+    Use `{{ view.ordering_query_<field_name> }}` in the template to get the corresponding parameters for a header link.
+    """
+    ordering_query_param = 'order'
+    ordering_options = ()
+    discard_params = ('page',)
+
+    @staticmethod
+    def ordering_to_str(ordering: tuple):
+        return mark_safe(','.join(map(escape, ordering)))
+
+    def get_ordering(self):
+        requested_ordering = self.request.GET.get(self.ordering_query_param)
+        if requested_ordering is not None:
+            requested_ordering = tuple(o for o in requested_ordering.split(','))
+            if all(map(lambda o: o in self.ordering_options, requested_ordering)):
+                return requested_ordering
+        return super().get_ordering()
+
+    def __getitem__(self, item):
+        current_ordering = tuple(self.get_ordering())
+        if item == 'ordering_query_current':
+            if current_ordering is not None:
+                return self.ordering_to_str(current_ordering)
+            return ''
+
+        match = re.search('^ordering_query_([_a-zA-Z]+)$', item)
+        if match is not None:
+            ordering = match.group(1)
+            if ordering in self.ordering_options:
+                if current_ordering is None or not current_ordering:
+                    resulting_ordering = ordering
+                else:
+                    reverse = ordering == current_ordering[0]
+                    ordering_possibilities = (ordering, '-{}'.format(ordering))
+                    filtered_ordering = tuple(co for co in current_ordering if co not in ordering_possibilities)
+                    resulting_ordering = (ordering if not reverse else '-{}'.format(ordering),) + filtered_ordering
+                query_params = self.request.GET.copy()
+                for param in self.discard_params:
+                    if param in query_params:
+                        del query_params[param]
+                query_params[self.ordering_query_param] = self.ordering_to_str(resulting_ordering)
+                return query_params.urlencode()
+
+        return super()[item]