"""

Utilities for providing backwards compatibility for the maxlength argument,

which has been replaced by max_length. See ticket #2101.

"""

from warnings import warn

def get_maxlength(self):

    return self.max_length

def set_maxlength(self, value):

    self.max_length = value

def legacy_maxlength(max_length, maxlength):

    """

    Consolidates max_length and maxlength, providing backwards compatibilty

    for the legacy "maxlength" argument.

    If one of max_length or maxlength is given, then that value is returned.

    If both are given, a TypeError is raised. If maxlength is used at all, a

    deprecation warning is issued.

    """

    if maxlength is not None:

        warn("maxlength is deprecated. Use max_length instead.", DeprecationWarning, stacklevel=3)

        if max_length is not None:

            raise TypeError("Field cannot take both the max_length argument and the legacy maxlength argument.")

        max_length = maxlength

    return max_length

def remove_maxlength(func):

    """

    A decorator to be used on a class's __init__ that provides backwards

    compatibilty for the legacy "maxlength" keyword argument, i.e.

        name = models.CharField(maxlength=20)

    It does this by changing the passed "maxlength" keyword argument

    (if it exists) into a "max_length" keyword argument.

    """

    def inner(self, *args, **kwargs):

        max_length = kwargs.get('max_length', None)

        # pop maxlength because we don't want this going to __init__.

        maxlength = kwargs.pop('maxlength', None)

        max_length = legacy_maxlength(max_length, maxlength)

        # Only set the max_length keyword argument if we got a value back.

        if max_length is not None:

            kwargs['max_length'] = max_length

        func(self, *args, **kwargs)

    return inner

# This metaclass is used in two places, and should be removed when legacy

# support for maxlength is dropped.

#   * oldforms.FormField

#   * db.models.fields.Field

class LegacyMaxlength(type):

    """

    Metaclass for providing backwards compatibility support for the

    "maxlength" keyword argument.

    """

    def __init__(cls, name, bases, attrs):

        super(LegacyMaxlength, cls).__init__(name, bases, attrs)

        # Decorate the class's __init__ to remove any maxlength keyword.

        cls.__init__ = remove_maxlength(cls.__init__)

        # Support accessing and setting to the legacy maxlength attribute.

        cls.maxlength = property(get_maxlength, set_maxlength)