implement configurable default values for parameters

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>

cdist/core/cdist_type.py

@@ -62,6 +62,7 @@ class CdistType(object):
         self.__optional_parameters = None
         self.__optional_multiple_parameters = None
         self.__boolean_parameters = None
+        self.__parameter_defaults = None
 
     @classmethod
     def list_types(cls, base_path):
@@ -190,3 +191,19 @@ class CdistType(object):
             finally:
                 self.__boolean_parameters = parameters
         return self.__boolean_parameters
+
+    @property
+    def parameter_defaults(self):
+        if not self.__parameter_defaults:
+            defaults = {}
+            try:
+                defaults_dir = os.path.join(self.absolute_path, "parameter", "default")
+                for name in os.listdir(defaults_dir):
+                    with open(os.path.join(defaults_dir, name)) as fd:
+                        defaults[name] = fd.read().strip()
+            except EnvironmentError:
+                # error ignored
+                pass
+            finally:
+                self.__parameter_defaults = defaults
+        return self.__parameter_defaults

cdist/emulator.py

@@ -96,10 +96,12 @@ class Emulator(object):
             parser.add_argument(argument, dest=parameter, action='append', required=True)
         for parameter in self.cdist_type.optional_parameters:
             argument = "--" + parameter
-            parser.add_argument(argument, dest=parameter, action='store', required=False)
+            parser.add_argument(argument, dest=parameter, action='store', required=False,
+                default=self.cdist_type.parameter_defaults.get(parameter, None))
         for parameter in self.cdist_type.optional_multiple_parameters:
             argument = "--" + parameter
-            parser.add_argument(argument, dest=parameter, action='append', required=False)
+            parser.add_argument(argument, dest=parameter, action='append', required=False,
+                default=self.cdist_type.parameter_defaults.get(parameter, None))
         for parameter in self.cdist_type.boolean_parameters:
             argument = "--" + parameter
             parser.add_argument(argument, dest=parameter, action='store_const', const='')