Closes #33: Add ability to clone objects (pre-populate form fields)

netbox/utilities/templates/buttons/clone.html

@@ -0,0 +1,3 @@
+<a href="{{ url }}" class="btn btn-success">
+    <span class="fa fa-plus" aria-hidden="true"></span> Clone
+</a>

netbox/utilities/templatetags/buttons.py

@@ -1,4 +1,5 @@
 from django import template
+from django.urls import reverse
 
 from extras.models import ExportTemplate
 
@@ -7,12 +8,47 @@ register = template.Library()
 
 @register.inclusion_tag('buttons/add.html')
 def add_button(url):
-    return {'add_url': url}
+    return {
+        'add_url': url,
+    }
 
 
 @register.inclusion_tag('buttons/import.html')
 def import_button(url):
-    return {'import_url': url}
+    return {
+        'import_url': url,
+    }
+
+
+@register.inclusion_tag('buttons/clone.html')
+def clone_button(url, instance):
+
+    url = reverse(url)
+
+    # Populate form field values
+    params = {}
+    for field_name in getattr(instance, 'clone_fields', []):
+        field = instance._meta.get_field(field_name)
+        field_value = field.value_from_object(instance)
+
+        # Swap out False with URL-friendly value
+        if field_value is False:
+            field_value = ''
+
+        # Omit empty values
+        if field_value not in (None, ''):
+            params[field_name] = field_value
+
+        # TODO: Tag replication
+
+    # Append parameters to URL
+    param_string = '&'.join(['{}={}'.format(k, v) for k, v in params.items()])
+    if param_string:
+        url = '{}?{}'.format(url, param_string)
+
+    return {
+        'url': url,
+    }
 
 
 @register.inclusion_tag('buttons/export.html', takes_context=True)