source: wokkel/compat.py @ 218:71cba82a4b8b

# -*- test-case-name: wokkel.test.test_compat -*-
#
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Compatibility module to provide backwards compatibility with Twisted features.
"""

__all__ = ['BootstrapMixin', 'XmlStreamServerFactory', 'IQ',
           'NamedConstant', 'ValueConstant', 'Names', 'Values']

from itertools import count

from twisted.python.deprecate import deprecatedModuleAttribute
from twisted.python.versions import Version
from twisted.words.protocols.jabber import xmlstream
from twisted.words.protocols.jabber.xmlstream import XmlStreamServerFactory
from twisted.words.xish.xmlstream import BootstrapMixin

deprecatedModuleAttribute(
        Version("Wokkel", 0, 7, 0),
        "Use twisted.words.xish.xmlstream.BootstrapMixin instead.",
        __name__,
        "BootstrapMixin")

deprecatedModuleAttribute(
        Version("Wokkel", 0, 7, 0),
        "Use twisted.words.protocols.jabber.xmlstream.XmlStreamServerFactory "
                "instead.",
        __name__,
        "XmlStreamServerFactory")

class IQ(xmlstream.IQ):
    def __init__(self, *args, **kwargs):
        # Make sure we have a reactor parameter
        try:
            reactor = kwargs['reactor']
        except KeyError:
            from twisted.internet import reactor
        kwargs['reactor'] = reactor

        # Check if IQ's init accepts the reactor parameter
        try:
            xmlstream.IQ.__init__(self, *args, **kwargs)
        except TypeError:
            # Guess not. Remove the reactor parameter and try again.
            del kwargs['reactor']
            xmlstream.IQ.__init__(self, *args, **kwargs)

            # Patch the XmlStream instance so that it has a _callLater
            self._xmlstream._callLater = reactor.callLater



_unspecified = object()
_constantOrder = count().next


class _Constant(object):
    """
    @ivar _index: A C{int} allocated from a shared counter in order to keep
        track of the order in which L{_Constant}s are instantiated.

    @ivar name: A C{str} giving the name of this constant; only set once the
        constant is initialized by L{_ConstantsContainer}.

    @ivar _container: The L{_ConstantsContainer} subclass this constant belongs
        to; only set once the constant is initialized by that subclass.

    @since: Twisted 12.0.0.
    """
    def __init__(self):
        self._index = _constantOrder()


    def __get__(self, oself, cls):
        """
        Ensure this constant has been initialized before returning it.
        """
        cls._initializeEnumerants()
        return self


    def __repr__(self):
        """
        Return text identifying both which constant this is and which collection
        it belongs to.
        """
        return "<%s=%s>" % (self._container.__name__, self.name)


    def _realize(self, container, name, value):
        """
        Complete the initialization of this L{_Constant}.

        @param container: The L{_ConstantsContainer} subclass this constant is
            part of.

        @param name: The name of this constant in its container.

        @param value: The value of this constant; not used, as named constants
            have no value apart from their identity.
        """
        self._container = container
        self.name = name



class _EnumerantsInitializer(object):
    """
    L{_EnumerantsInitializer} is a descriptor used to initialize a cache of
    objects representing named constants for a particular L{_ConstantsContainer}
    subclass.

    @since: Twisted 12.0.0.
    """
    def __get__(self, oself, cls):
        """
        Trigger the initialization of the enumerants cache on C{cls} and then
        return it.
        """
        cls._initializeEnumerants()
        return cls._enumerants



class _ConstantsContainer(object):
    """
    L{_ConstantsContainer} is a class with attributes used as symbolic
    constants.  It is up to subclasses to specify what kind of constants are
    allowed.

    @cvar _constantType: Specified by a L{_ConstantsContainer} subclass to
        specify the type of constants allowed by that subclass.

    @cvar _enumerantsInitialized: A C{bool} tracking whether C{_enumerants} has
        been initialized yet or not.

    @cvar _enumerants: A C{dict} mapping the names of constants (eg
        L{NamedConstant} instances) found in the class definition to those
        instances.  This is initialized via the L{_EnumerantsInitializer}
        descriptor the first time it is accessed.

    @since: Twisted 12.0.0.
    """
    _constantType = None

    _enumerantsInitialized = False
    _enumerants = _EnumerantsInitializer()

    def __new__(cls):
        """
        Classes representing constants containers are not intended to be
        instantiated.

        The class object itself is used directly.
        """
        raise TypeError("%s may not be instantiated." % (cls.__name__,))


    def _initializeEnumerants(cls):
        """
        Find all of the L{NamedConstant} instances in the definition of C{cls},
        initialize them with constant values, and build a mapping from their
        names to them to attach to C{cls}.
        """
        if not cls._enumerantsInitialized:
            constants = []
            for (name, descriptor) in cls.__dict__.iteritems():
                if isinstance(descriptor, cls._constantType):
                    constants.append((descriptor._index, name, descriptor))
            enumerants = {}
            for (index, enumerant, descriptor) in constants:
                value = cls._constantFactory(enumerant)
                descriptor._realize(cls, enumerant, value)
                enumerants[enumerant] = descriptor
            # Replace the _enumerants descriptor with the result so future
            # access will go directly to the values.  The _enumerantsInitialized
            # flag is still necessary because NamedConstant.__get__ may also
            # call this method.
            cls._enumerants = enumerants
            cls._enumerantsInitialized = True
    _initializeEnumerants = classmethod(_initializeEnumerants)


    def _constantFactory(cls, name):
        """
        Construct the value for a new constant to add to this container.

        @param name: The name of the constant to create.

        @return: L{NamedConstant} instances have no value apart from identity,
            so return a meaningless dummy value.
        """
        return _unspecified
    _constantFactory = classmethod(_constantFactory)


    def lookupByName(cls, name):
        """
        Retrieve a constant by its name or raise a C{ValueError} if there is no
        constant associated with that name.

        @param name: A C{str} giving the name of one of the constants defined by
            C{cls}.

        @raise ValueError: If C{name} is not the name of one of the constants
            defined by C{cls}.

        @return: The L{NamedConstant} associated with C{name}.
        """
        if name in cls._enumerants:
            return getattr(cls, name)
        raise ValueError(name)
    lookupByName = classmethod(lookupByName)


    def iterconstants(cls):
        """
        Iteration over a L{Names} subclass results in all of the constants it
        contains.

        @return: an iterator the elements of which are the L{NamedConstant}
            instances defined in the body of this L{Names} subclass.
        """
        constants = cls._enumerants.values()
        constants.sort(key=lambda descriptor: descriptor._index)
        return iter(constants)
    iterconstants = classmethod(iterconstants)



class NamedConstant(_Constant):
    """
    L{NamedConstant} defines an attribute to be a named constant within a
    collection defined by a L{Names} subclass.

    L{NamedConstant} is only for use in the definition of L{Names}
    subclasses.  Do not instantiate L{NamedConstant} elsewhere and do not
    subclass it.

    @since: Twisted 12.0.0.
    """



class Names(_ConstantsContainer):
    """
    A L{Names} subclass contains constants which differ only in their names and
    identities.

    @since: Twisted 12.0.0.
    """
    _constantType = NamedConstant



class ValueConstant(_Constant):
    """
    L{ValueConstant} defines an attribute to be a named constant within a
    collection defined by a L{Values} subclass.

    L{ValueConstant} is only for use in the definition of L{Values} subclasses.
    Do not instantiate L{ValueConstant} elsewhere and do not subclass it.

    @since: Twisted 12.0.0.
    """
    def __init__(self, value):
        _Constant.__init__(self)
        self.value = value



class Values(_ConstantsContainer):
    """
    A L{Values} subclass contains constants which are associated with arbitrary
    values.

    @since: Twisted 12.0.0.
    """
    _constantType = ValueConstant

    def lookupByValue(cls, value):
        """
        Retrieve a constant by its value or raise a C{ValueError} if there is no
        constant associated with that value.

        @param value: The value of one of the constants defined by C{cls}.

        @raise ValueError: If C{value} is not the value of one of the constants
            defined by C{cls}.

        @return: The L{ValueConstant} associated with C{value}.
        """
        for constant in cls.iterconstants():
            if constant.value == value:
                return constant
        raise ValueError(value)
    lookupByValue = classmethod(lookupByValue)