Introduces base class and interface for the factories

Created by: stefanoborini

Introduces a base class for the factories.

Fixes #49 (closed)

force_bdss/core/base_factory.py

+from envisage.plugin import Plugin
+from traits.api import HasStrictTraits, Str, Instance
+
+from force_bdss.ids import factory_id
+
+
+class BaseFactory(HasStrictTraits):
+    #: Unique identifier that identifies the factory uniquely in the
+    #: universe of factories. Create one with the function factory_id()
+    id = Str()
+
+    #: A human readable name of the factory. Spaces allowed
+    name = Str()
+
+    #: Reference to the plugin that carries this factory
+    #: This is automatically set by the system. you should not define it
+    #: in your subclass.
+    plugin = Instance(Plugin, allow_none=False)
+
+    def __init__(self, plugin):
+        super(BaseFactory, self).__init__(plugin=plugin)
+
+        self.name = self.get_name()
+        identifier = self.get_identifier()
+        try:
+            id = self._global_id(identifier)
+        except ValueError:
+            raise ValueError(
+                "Invalid identifier {} returned by "
+                "{}.get_identifier()".format(
+                    identifier,
+                    self.__class__.__name__
+                )
+            )
+        self.id = id
+
+    def get_name(self):
+        """Must be reimplemented to return a user-visible name of the
+        data source.
+        """
+        raise NotImplementedError(
+            "get_name was not implemented in factory {}".format(
+                self.__class__))
+
+    def get_identifier(self):
+        """Must be reimplemented to return a unique string identifying
+        the factory. The provider is responsible to guarantee this identifier
+        to be unique across the plugin data sources.
+        """
+        raise NotImplementedError(
+            "get_identifier was not implemented in factory {}".format(
+                self.__class__))
+
+    def _global_id(self, identifier):
+        return factory_id(self.plugin.id, identifier)