# shallowutil.py -- remotefilelog utilities
#
# Copyright 2014 Facebook, Inc.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

def interposeclass(container, classname):
    '''Interpose a class into the hierarchies of all loaded subclasses. This
    function is intended for use as a decorator.

      import mymodule
      @replaceclass(mymodule, 'myclass')
      class mysubclass(mymodule.myclass):
          def foo(self):
              f = super(mysubclass, self).foo()
              return f + ' bar'

    Existing instances of the class being replaced will not have their
    __class__ modified, so call this function before creating any
    objects of the target type. Note that this doesn't actually replace the
    class in the module -- that can cause problems when using e.g. super()
    to call a method in the parent class. Instead, new instances should be
    created using a factory of some sort that this extension can override.
    '''
    def wrap(cls):
        oldcls = getattr(container, classname)
        oldbases = (oldcls,)
        newbases = (cls,)
        for subcls in oldcls.__subclasses__():
            if subcls is not cls:
                assert subcls.__bases__ == oldbases
                subcls.__bases__ = newbases
        return cls
    return wrap