[feature] Add possibility to change list handling behaviour

Closes #153

netjsonconfig/backends/base/backend.py

@@ -26,7 +26,8 @@ class BaseBackend(object):
     FILE_SECTION_DELIMITER = '# ---------- files ---------- #'
     list_identifiers = []
 
-    def __init__(self, config=None, native=None, templates=None, context=None):
+    def __init__(self, config=None, native=None, templates=None,
+                 templates_list_handling=None, context=None):
         """
         :param config: ``dict`` containing a valid **NetJSON** configuration dictionary
         :param native: ``str`` or file object representing a native configuration that will
@@ -44,7 +45,8 @@ def __init__(self, config=None, native=None, templates=None, context=None):
         if config is not None:
             # perform deepcopy to avoid modifying the original config argument
             config = deepcopy(self._load(config))
-            self.config = self._merge_config(config, templates)
+            self.config = self._merge_config(config, templates,
+                                             templates_list_handling)
             self.config = self._evaluate_vars(self.config, context)
         # backward conversion (native configuration > NetJSON)
         elif native is not None:
@@ -70,7 +72,7 @@ def _load(self, config):
             )
         return config
 
-    def _merge_config(self, config, templates):
+    def _merge_config(self, config, templates, templates_list_handling):
         """
         Merges config with templates
         """
@@ -82,8 +84,14 @@ def _merge_config(self, config, templates):
         # merge templates with main configuration
         result = {}
         config_list = templates + [config]
-        for merging in config_list:
-            result = merge_config(result, self._load(merging), self.list_identifiers)
+        for i, merging in enumerate(config_list):
+            if i < len(templates):
+                result = merge_config(result, self._load(merging),
+                                      self.list_identifiers,
+                                      templates_list_handling[i])
+            else:
+                result = merge_config(result, self._load(merging),
+                                      self.list_identifiers)
         return result
 
     def _evaluate_vars(self, config, context):

netjsonconfig/backends/openwrt/openwrt.py

@@ -36,7 +36,8 @@ class OpenWrt(BaseBackend):
     list_identifiers = ['name', 'config_value', 'id']
 
     def __init__(
-        self, config=None, native=None, templates=None, context=None, dsa=True
+        self, config=None, native=None, templates=None,
+        templates_list_handling=None, context=None, dsa=True
     ):
         """
         :param config: ``dict`` containing a valid **NetJSON** configuration dictionary
@@ -52,7 +53,8 @@ def __init__(
                            ``templates`` is not of type ``list``
         """
         self.dsa = dsa
-        super().__init__(config, native, templates, context)
+        super().__init__(config, native, templates,
+                         templates_list_handling, context)
 
     def _generate_contents(self, tar):
         """

netjsonconfig/utils.py

@@ -3,7 +3,8 @@
 from copy import deepcopy
 
 
-def merge_config(template, config, list_identifiers=None):
+def merge_config(template, config, list_identifiers=None,
+                 list_handling='append_at_end'):
     """
     Merges ``config`` on top of ``template``.
 
@@ -24,15 +25,17 @@ def merge_config(template, config, list_identifiers=None):
     for key, value in config.items():
         if isinstance(value, dict):
             node = result.get(key, OrderedDict())
-            result[key] = merge_config(node, value)
+            result[key] = merge_config(node, value,
+                                       list_handling=list_handling)
         elif isinstance(value, list) and isinstance(result.get(key), list):
-            result[key] = merge_list(result[key], value, list_identifiers)
+            result[key] = merge_list(result[key], value, list_identifiers,
+                                     list_handling)
         else:
             result[key] = value
     return result
 
 
-def merge_list(list1, list2, identifiers=None):
+def merge_list(list1, list2, identifiers=None, list_handling='append_at_end'):
     """
     Merges ``list2`` on top of ``list1``.
 
@@ -47,6 +50,8 @@ def merge_list(list1, list2, identifiers=None):
     :param identifiers: ``list`` or ``None``
     :returns: merged ``list``
     """
+    if list_handling == 'override':
+        return list2
     identifiers = identifiers or []
     dict_map = {'list1': OrderedDict(), 'list2': OrderedDict()}
     counter = 1
@@ -74,7 +79,12 @@ def merge_list(list1, list2, identifiers=None):
                 key = tuple(key)
             container[key] = deepcopy(el)
         counter += 1
-    merged = merge_config(dict_map['list1'], dict_map['list2'])
+    if list_handling == 'insert_at_beginning':
+        merged = merge_config(dict_map['list2'], dict_map['list1'],
+                              list_handling=list_handling)
+    else:
+        merged = merge_config(dict_map['list1'], dict_map['list2'],
+                              list_handling=list_handling)
     return list(merged.values())