"""Enumeration metaclass.

XXX This is very much a work in progress.

"""

import string

class EnumMetaClass:
   """Metaclass for enumeration.

   To define your own enumeration, do something like

   class Color(Enum):
       red = 1
       green = 2
       blue = 3

   Now, Color.red, Color.green and Color.blue behave totally
   different: they are enumerated values, not integers.

   Enumerations cannot be instantiated; however they can be
   subclassed.

   """

   def __init__(self, name, bases, dict):
       """Constructor -- create an enumeration.

       Called at the end of the class statement.  The arguments are
       the name of the new class, a tuple containing the base
       classes, and a dictionary containing everything that was
       entered in the class' namespace during execution of the class
       statement.  In the above example, it would be {'red': 1,
       'green': 2, 'blue': 3}.

       """
       for base in bases:
           if base.__class__ is not EnumMetaClass:
               raise TypeError, "Enumeration base class must be enumeration"
       bases = filter(lambda x: x is not Enum, bases)
       self.__name__ = name
       self.__bases__ = bases
       self.__dict = {}
       for key, value in dict.items():
           self.__dict[key] = EnumInstance(name, key, value)

   def __getattr__(self, name):
       """Return an enumeration value.

       For example, Color.red returns the value corresponding to red.

       XXX Perhaps the values should be created in the constructor?

       This looks in the class dictionary and if it is not found
       there asks the base classes.

       The special attribute __members__ returns the list of names
       defined in this class (it does not merge in the names defined
       in base classes).

       """
       if name == '__members__':
           return self.__dict.keys()

       try:
           return self.__dict[name]
       except KeyError:
           for base in self.__bases__:
               try:
                   return getattr(base, name)
               except AttributeError:
                   continue

       raise AttributeError, name

   def __repr__(self):
       s = self.__name__
       if self.__bases__:
           s = s + '(' + string.join(map(lambda x: x.__name__,
                                         self.__bases__), ", ") + ')'
       if self.__dict:
           list = []
           for key, value in self.__dict.items():
               list.append("%s: %s" % (key, value))
           s = "%s: {%s}" % (s, string.join(list, ", "))
       return s


class EnumInstance:
   """Class to represent an enumeration value.

   EnumInstance('Color', 'red', 12) prints as 'Color.red' and behaves
   like the integer 12 when compared, but doesn't support arithmetic.

   XXX Should it record the actual enumeration rather than just its
   name?

   """

   def __init__(self, classname, enumname, value):
       self.__classname = classname
       self.__enumname = enumname
       self.__value = value

   def __int__(self):
       return self.__value

   def __repr__(self):
       return "EnumInstance(%s, %s, %s)" % (`self.__classname`,
                                            `self.__enumname`,
                                            `self.__value`)

   def __str__(self):
       return "%s" % self.__value

   def __cmp__(self, other):
       return cmp(self.__value, other)



# Create the base class for enumerations.
# It is an empty enumeration.
Enum = EnumMetaClass("Enum", (), {})

def _test():
   class Color(Enum):
       red = 1
       green = 2
       blue = 3

   print Color.red
   print dir(Color)

   print Color.red == Color.red
   print Color.red == Color.blue
   print Color.red == 1
   print Color.red == 2

   class ExtendedColor(Color):
       white = 0
       orange = 4
       yellow = 5
       purple = 6
       black = 7

   print ExtendedColor.orange
   print ExtendedColor.red

   print Color.red == ExtendedColor.red

   class OtherColor(Enum):
       white = 4
       blue = 5

   class MergedColor(Color, OtherColor):
       pass

   print MergedColor.red
   print MergedColor.white

   print Color
   print ExtendedColor
   print OtherColor
   print MergedColor

if __name__ == '__main__':
   _test()