Split up factory objects and base data model objects.

Better to have a separate file for each class clearly addressing
it's purpose with it's filename.

  Source base data model -> source.py
  SourceFactory -> _sourcefactory.py
  Element base data model -> element.py
  ElementFactory -> _elementfactory.py

Also moved the _plugin.py to _plugincontext.py, since the object
is infact _PluginContext, lets follow this rule all around for
code clarity.

1 files changed, 94 insertions, 0 deletions

diff --git a/buildstream/_plugincontext.py b/buildstream/_plugincontext.py
new file mode 100644
index 000000000..040fe3ab6
--- /dev/null
+++ b/buildstream/_plugincontext.py
@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+#
+#  Copyright (C) 2016 Codethink Limited
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+#
+#  Authors:
+#        Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
+
+from .exceptions import PluginError
+
+# A Context for loading plugin types
+#
+# Args:
+#     plugin_base (PluginBase): The main PluginBase object to work with
+#     base_type (type):         A base object type for this context
+#     searchpath (list):        A list of paths to search for plugins
+#
+# Since multiple pipelines can be processed recursively
+# within the same interpretor, it's important that we have
+# one context associated to the processing of a given pipeline,
+# this way sources and element types which are particular to
+# a given BuildStream project are isolated to their respective
+# Pipelines.
+#
+class _PluginContext():
+
+    def __init__(self, plugin_base, base_type, searchpath=None):
+
+        if not searchpath:
+            raise PluginError ("Cannot create plugin context without any searchpath")
+
+        self.base_type = base_type; # The expected base class which plugins are to derive from
+        self.source    = None       # The PluginSource object
+        self.types     = {}         # Dictionary to lookup plugin types by their kind
+
+        self.load_plugins(plugin_base, searchpath)
+
+    # lookup():
+    #
+    # Fetches a type loaded from a plugin in this plugin context
+    #
+    # Args:
+    #     kind (str): The kind of Plugin to create
+    #
+    # Returns: the type associated with the given kind
+    #
+    # Raises: PluginError
+    #
+    def lookup(self, kind):
+        if not kind in self.types:
+            raise PluginError ("No %s type registered for kind '%s'" %
+                               (self.base_type.__name__, kind))
+
+        return self.types[kind]
+
+    def load_plugins(self, base, searchpath):
+        self.source = base.make_plugin_source(searchpath=searchpath)
+        for kind in self.source.list_plugins():
+            self.load_plugin(kind)
+
+    def load_plugin(self, kind):
+
+        plugin      = self.source.load_plugin(kind)
+        plugin_type = plugin.setup()
+
+        self.assert_plugin (kind, plugin_type)
+
+        print ("Registering %s plugin %s for kind %s" %
+               (self.base_type.__name__, plugin_type.__name__, kind))
+        self.types[kind] = plugin_type
+
+    def assert_plugin(self, kind, plugin_type):
+        if kind in self.types:
+            raise PluginError ("Tried to register %s plugin for existing kind '%s' (already registered %s)" %
+                               (self.base_type.__name__, kind, self.types[kind].__name__))
+        try:
+            if not issubclass(plugin_type, self.base_type):
+                raise PluginError ("%s plugin '%s' returned type '%s', which is not a subclass of Plugin" %
+                                   (self.base_type.__name__, kind, plugin_type.__name__))
+        except TypeError as e:
+            raise PluginError ("%s plugin '%s' returned something that is not an Plugin subclass" %
+                               (self.base_type.__name__, kind)) from e