From b271fd32bdadd6f9cbd5e2261554f70837cd06ac Mon Sep 17 00:00:00 2001
From: Jeremy Stretch <stretch@packetlife.net>
Date: Fri, 7 Feb 2020 11:36:22 -0500
Subject: [PATCH] Introduce NaturalOrderingField

---
 netbox/utilities/fields.py   | 33 +++++++++++++++++++++++++++++++++
 netbox/utilities/ordering.py | 31 +++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 netbox/utilities/ordering.py

diff --git a/netbox/utilities/fields.py b/netbox/utilities/fields.py
index d2165aea6..6181a7ca1 100644
--- a/netbox/utilities/fields.py
+++ b/netbox/utilities/fields.py
@@ -1,6 +1,7 @@
 from django.core.validators import RegexValidator
 from django.db import models
 
+from utilities.ordering import naturalize
 from .forms import ColorSelect
 
 ColorValidator = RegexValidator(
@@ -35,3 +36,35 @@ class ColorField(models.CharField):
     def formfield(self, **kwargs):
         kwargs['widget'] = ColorSelect
         return super().formfield(**kwargs)
+
+
+class NaturalOrderingField(models.CharField):
+    """
+    A field which stores a naturalized representation of its target field, to be used for ordering its parent model.
+
+    :param target_field: Name of the field of the parent model to be naturalized
+    :param naturalize_function: The function used to generate a naturalized value (optional)
+    """
+    description = "Stores a representation of its target field suitable for natural ordering"
+
+    def __init__(self, target_field, naturalize_function=naturalize, *args, **kwargs):
+        self.target_field = target_field
+        self.naturalize_function = naturalize_function
+        super().__init__(*args, **kwargs)
+
+    def pre_save(self, model_instance, add):
+        """
+        Generate a naturalized value from the target field
+        """
+        value = getattr(model_instance, self.target_field)
+        return self.naturalize_function(value, max_length=self.max_length)
+
+    def deconstruct(self):
+        kwargs = super().deconstruct()[3]  # Pass kwargs from CharField
+        kwargs['naturalize_function'] = self.naturalize_function
+        return (
+            self.name,
+            'utilities.fields.NaturalOrderingField',
+            ['target_field'],
+            kwargs,
+        )
diff --git a/netbox/utilities/ordering.py b/netbox/utilities/ordering.py
new file mode 100644
index 000000000..2d6c06f63
--- /dev/null
+++ b/netbox/utilities/ordering.py
@@ -0,0 +1,31 @@
+import re
+
+
+def naturalize(value, max_length=None, integer_places=8):
+    """
+    Take an alphanumeric string and prepend all integers to `integer_places` places to ensure the strings
+    are ordered naturally. For example:
+
+        site9router21
+        site10router4
+        site10router19
+
+    becomes:
+
+        site00000009router00000021
+        site00000010router00000004
+        site00000010router00000019
+
+    :param value: The value to be naturalized
+    :param max_length: The maximum length of the returned string. Characters beyond this length will be stripped.
+    :param integer_places: The number of places to which each integer will be expanded. (Default: 8)
+    """
+    output = []
+    for segment in re.split(r'(\d+)', value):
+        if segment.isdigit():
+            output.append(segment.rjust(integer_places, '0'))
+        elif segment:
+            output.append(segment)
+    ret = ''.join(output)
+
+    return ret[:max_length] if max_length else ret