# 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


def is_persistent(item):
  prop = item[1]
  return type(prop) is property and \
         hasattr(prop.fget, 'decorator') and \
         prop.fget.decorator is PersistentProperty


class Persistent(type):
  def __init__(cls, name, bases, dct):
    # is_dirty
    setattr(cls, '__dirty__', False)
    
    # properties
    setattr(cls, '__properties__', filter(is_persistent, dct.iteritems()))
    
    super(Persistent, cls).__init__(name, bases, dct)
    

def PersistentProperty(function):
  function.decorator = PersistentProperty
  
  keys = 'fset', 'fdel'
  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)
    return setter(obj, value)
  
  def probe_function(frame, event, arg):
    if event == 'return':
      locals = frame.f_locals
      func_locals.update(dict((k,locals.get(k)) for k in keys))
      
      if locals.has_key('fset'):
        func_locals['fset'] = lambda obj, value : fsetter(obj, function.__name__, locals['fset'], value)
      
      if locals.has_key('fdef'):
        f = lambda obj : fgetter(obj, function.__name__, locals['fget'], locals['fdef'])
      else:
        f = lambda obj : fgetter(obj, function.__name__, locals['fget'], lambda x : None)
      f.decorator = PersistentProperty # tag the getter
      func_locals['fget'] = f
      
      sys.settrace(None)
    return probe_function
  sys.settrace(probe_function)
  function()
  return property(**func_locals)