Add valid merge strategies

This adds three merge startegies(overwrite, merge, deep-merge).
There can be a default merge startegy for an env or parameter
specific merge strategy. if none of the above is specified
then it defaults to 'overwrite'.

Change-Id: I05f56887d762342981e3cb9885872ef58ecd0ad8
Blueprint: environment-merging

heat/common/environment_util.py

@@ -0,0 +1,29 @@
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+ALLOWED_PARAM_MERGE_STRATEGIES = (OVERWRITE, MERGE, DEEP_MERGE) = (
+    'overwrite', 'merge', 'deep_merge')
+
+
+def get_param_merge_strategy(merge_strategies, param_key):
+
+    if merge_strategies is None:
+        return OVERWRITE
+
+    env_default = merge_strategies.get('default', OVERWRITE)
+
+    merge_strategy = merge_strategies.get(param_key, env_default)
+    if merge_strategy in ALLOWED_PARAM_MERGE_STRATEGIES:
+        return merge_strategy
+
+    return env_default

heat/tests/test_common_env_util.py

@@ -0,0 +1,50 @@
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from heat.common import environment_util as env_util
+from heat.tests import common
+
+
+class TestEnvironmentUtil(common.HeatTestCase):
+
+    def test_empty_merge_strategies(self):
+        merge_strategies = {}
+        param_strategy = env_util.get_param_merge_strategy(merge_strategies,
+                                                           'param1')
+        self.assertEqual(env_util.OVERWRITE, param_strategy)
+
+    def test_default_merge_strategy(self):
+        merge_strategies = {'default': 'deep_merge'}
+        param_strategy = env_util.get_param_merge_strategy(merge_strategies,
+                                                           'param1')
+        self.assertEqual(env_util.DEEP_MERGE, param_strategy)
+
+    def test_param_sepcific_merge_strategy(self):
+        merge_strategies = {'default': 'merge',
+                            'param1': 'deep_merge'}
+        param_strategy = env_util.get_param_merge_strategy(merge_strategies,
+                                                           'param1')
+        self.assertEqual(env_util.DEEP_MERGE, param_strategy)
+
+    def test_wrong_param_strategy(self):
+        merge_strategies = {'default': 'merge',
+                            'param1': 'unknown'}
+        param_strategy = env_util.get_param_merge_strategy(merge_strategies,
+                                                           'param1')
+        self.assertEqual(env_util.MERGE, param_strategy)
+
+    def test_merge_startegies_none(self):
+        merge_strategies = None
+        param_strategy = env_util.get_param_merge_strategy(merge_strategies,
+                                                           'param1')
+        self.assertEqual(env_util.OVERWRITE, param_strategy)