Add bundle instantiation helpers

Add some helper functions for use by upcoming changes in the Sugar shell.

src/sugar3/bundle/__init__.py

@@ -14,3 +14,37 @@
 # License along with this library; if not, write to the
 # Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 # Boston, MA 02111-1307, USA.
+
+import os
+
+from gi.repository import Gio
+
+from sugar3.bundle.activitybundle import ActivityBundle
+from sugar3.bundle.contentbundle import ContentBundle
+
+
+def bundle_from_archive(path, mime_type=None):
+    """
+    Return an appropriate Bundle object for a given file path.
+    The bundle type is identified by mime_type, which is guessed if not
+    provided.
+    """
+    if mime_type is None:
+        mime_type, certainty = Gio.content_type_guess(path, data=None)
+    if mime_type == ActivityBundle.MIME_TYPE:
+        return ActivityBundle(path)
+    elif mime_type == ContentBundle.MIME_TYPE:
+        return ContentBundle(path)
+    return None
+
+
+def bundle_from_dir(path):
+    """
+    Return an appropriate Bundle object for a given directory containing
+    an unzipped bundle.
+    """
+    if os.path.exists(os.path.join(path, 'activity', 'activity.info')):
+        return ActivityBundle(path)
+    elif os.path.exists(os.path.join(path, 'library', 'library.info')):
+        return ContentBundle(path)
+    return None