add missing component.py

diff --git a/component.py b/component.py
new file mode 100644 (file)
index 0000000..a789528
--- /dev/null
+++ b/component.py
@@ -0,0 +1,99 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (c) 2009 Olivier Guilyardi <olivier@samalyse.com>
+#
+# This file is part of TimeSide.
+
+# TimeSide is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 2 of the License, or
+# (at your option) any later version.
+
+# TimeSide 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 General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with TimeSide.  If not, see <http://www.gnu.org/licenses/>.
+
+
+# This file defines a generic object interface mechanism and 
+# a way to determine which components implements a given interface.
+#
+# For example, the following defines the Music class as implementing the
+# listenable interface.
+#
+# class Listenable(Interface):
+#     pass
+#
+# class Music(Component):
+#    implements(Listenable)
+#
+# Several class can implements a such interface, and it is possible to 
+# discover which class implements it with implementations():
+#
+# list_of_classes = implementations(Listenable)
+#
+# This mechanism support inheritance of interfaces: a class implementing a given 
+# interface is also considered to implement all the ascendants of this interface.
+#
+# However, inheritance is not supported for components. The descendants of a class 
+# implementing a given interface are not automatically considered to implement this 
+# interface too. 
+
+__all__ = ['Component', 'MetaComponent', 'implements', 'Interface', 'implementations']
+
+class Interface(object):
+    """Marker base class for interfaces."""
+
+def implements(*interfaces):
+    """Registers the interfaces implemented by a component when placed in the
+    class header"""
+    _implements.extend(interfaces)
+
+def implementations(interface, recurse=True):
+    """Returns the components implementing interface, and if recurse, any of 
+    the descendants of interface."""
+    result = []
+    find_implementations(interface, recurse, result)
+    return result
+
+_implementations = []
+_implements = []
+
+class MetaComponent(type):
+    """Metaclass of the Component class, used mainly to register the interface
+    declared to be implemented by a component."""
+    def __new__(cls, name, bases, d):
+        new_class = type.__new__(cls, name, bases, d)
+        if _implements:
+            for i in _implements:
+                _implementations.append((i, new_class))
+        del _implements[:]
+        return new_class
+
+class Component(object):
+    """Base class of all components"""
+    __metaclass__ = MetaComponent
+
+def extend_unique(list1, list2):
+    """Extend list1 with list2 as list.extend(), but doesn't append duplicates
+    to list1"""
+    for item in list2:
+        if item not in list1:
+            list1.append(item)
+
+def find_implementations(interface, recurse, result):
+    """Find implementations of an interface or of one of its descendants and
+    extend result with the classes found."""
+    for i, cls in _implementations:
+        if (i == interface):
+            extend_unique(result, [cls])
+
+    if recurse:
+        subinterfaces = interface.__subclasses__()
+        if subinterfaces:
+            for i in subinterfaces:
+                find_implementations(i, recurse, result)
+