1 files changed, 81 insertions, 0 deletions
diff --git a/util/persistence.py b/util/persistence.py
new file mode 100644
index 0000000..e73879b
--- /dev/null
+++ b/util/persistence.py
@@ -0,0 +1,81 @@
+# This program 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.
+#
+# This program 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 this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#
+
+import sys
+
+
+class Persistent(type):
+  '''Metaclass providing object persistence'''
+  def __init__(cls, name, bases, dct):
+    super(Persistent, cls).__init__(name, bases, dct)
+    
+    setattr(cls, '__dirty__', False)
+    setattr(cls, '__properties__', filter(_is_persistent, dct.iteritems()))
+
+    from util.journalpickler import dumps, loads
+    setattr(cls, 'dumps', dumps)
+    setattr(cls, 'loads', loads)
+
+
+
+def PersistentProperty(function):
+  '''Decorator to set up persistent properties
+     Adapted from: http://wiki.python.org/moin/PythonDecoratorLibrary
+  '''
+  
+  func_locals = {'doc':function.__doc__}
+
+  def fgetter(obj, name, getter, fdef):
+    attr_name = '_' + obj.__class__.__name__ + '__' + name
+    if not hasattr(obj, attr_name):
+      setattr(obj, attr_name, fdef(obj))
+    return getter(obj)
+  
+  def fsetter(obj, name, setter, value):
+    setattr(obj, '__dirty__', True) # TODO -> Propogate dirty flag up to any
+                                    #         parent objects ?
+    return setter(obj, value)
+  
+  def introspect(frame, event, arg):
+    if event == 'return':
+      locals = frame.f_locals
+      if locals.has_key('delete'):
+        func_locals['fdel'] = locals['delete']
+      if locals.has_key('set'):
+        func_locals['fset'] = \
+          lambda obj, value : fsetter(obj, function.__name__, locals['set'], value)
+      if locals.has_key('default'):
+        get_function = lambda obj : fgetter(obj, function.__name__, locals['get'], locals['default'])
+      else:
+        get_function = lambda obj : fgetter(obj, function.__name__, locals['get'], lambda x : None)
+      get_function.__decorator__ = PersistentProperty # tag the getter so we can id the
+                                                      # decorator. Yeah, it's ugly.
+      func_locals['fget'] = get_function
+      sys.settrace(None)
+    return introspect
+  sys.settrace(introspect)
+  function()
+  return property(**func_locals)
+
+
+# a wee bit ugly
+def _is_persistent(item):
+  '''check if property is decorated with PersistentProperty decorator'''
+  prop = item[1]
+  return type(prop) is property and \
+         hasattr(prop.fget, '__decorator__') and \
+         prop.fget.__decorator__ is PersistentProperty
+
+