##############################################################################
#
# Copyright (c) 2004 Zope Corporation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE.
#
##############################################################################
"""Locale Inheritance Support

This module provides support for locale inheritance.

Note: In many respects this is similar to Zope 2's acquisition model, since
locale inheritance is not inheritance in the programming sense. 

$Id: inheritance.py 27048 2004-08-12 14:11:31Z srichter $
"""
from zope.interface import implements
from zope.i18n.interfaces.locales import \
     ILocaleInheritance, IAttributeInheritance, IDictionaryInheritance

class NoParentException(AttributeError):
    pass

class Inheritance(object):
    """A simple base version of locale inheritance.

    This object contains some shared code amongst the various
    'ILocaleInheritance' implementations.
    """

    implements(ILocaleInheritance)

    # See zope.i18n.interfaces.locales.ILocaleInheritance
    __parent__ = None

    # See zope.i18n.interfaces.locales.ILocaleInheritance
    __name__ = None

    def getInheritedSelf(self):
        """See zope.i18n.interfaces.locales.ILocaleInheritance"""
        if self.__parent__ is None:
            raise NoParentException, 'No parent was specified.'
        parent = self.__parent__.getInheritedSelf()
        if isinstance(parent, dict):
            return parent[self.__name__]
        return getattr(parent, self.__name__)


class AttributeInheritance(Inheritance):
    r"""Implementation of locale inheritance for attributes.

    Example::

      >>> from zope.i18n.locales.tests.test_docstrings import \
      ...     LocaleInheritanceStub

      >>> root = LocaleInheritanceStub()
      >>> root.data = 'value'
      >>> root.attr = 'bar value'
      >>> root.data2 = AttributeInheritance()
      >>> root.data2.attr = 'value2' 

      >>> locale = LocaleInheritanceStub(root)
      >>> locale.attr = 'foo value'
      >>> locale.data2 = AttributeInheritance()

      Here is an attribute lookup directly from the locale ...

      >>> locale.data
      'value'
      >>> locale.attr
      'foo value'

      ... however, we can also have any amount of nesting.

      >>> locale.data2.attr
      'value2'

      Once we have looked up a particular attribute, it should be cached,
      i.e. exist in the dictionary of this inheritance object.

      >>> 'attr' in locale.data2.__dict__
      True
      >>> locale.data2.__dict__['attr']
      'value2'

      Make sure that None can be assigned as value as well.

      >>> locale.data2.attr = None
      >>> locale.data2.attr is None
      True
    """

    implements(IAttributeInheritance)

    def __setattr__(self, name, value):
        """See zope.i18n.interfaces.locales.ILocaleInheritance"""
        # If we have a value that can also inherit data from other locales, we
        # set its parent and name, so that we know how to get to it. 
        if (ILocaleInheritance.providedBy(value) and 
            not name.startswith('__')):
            value.__parent__ = self
            value.__name__ = name
        super(AttributeInheritance, self).__setattr__(name, value)


    def __getattr__(self, name):
        """See zope.i18n.interfaces.locales.ILocaleInheritance"""
        try:
            selfUp = self.getInheritedSelf()
        except NoParentException:
            # There was simply no parent anymore, so let's raise an error
            # for good
            raise AttributeError, \
                "'%s' object (or any of its parents) has no attribute '%s'" %(
                self.__class__.__name__, name)
        else:
            value = getattr(selfUp, name)
            # Since a locale hierarchy never changes after startup, we can
            # cache the value locally, saving the time to ever look it up
            # again.
            # Note that we cannot use the normal setattr function, since
            # __setattr__ of this class tries to assign a parent and name,
            # which we do not want to override.
            super(AttributeInheritance, self).__setattr__(name, value)
            return value
        


class InheritingDictionary(Inheritance, dict):
    """Implementation of a dictionary that can also inherit values.

    Example::

      >>> from zope.i18n.locales.tests.test_docstrings import \\
      ...     LocaleInheritanceStub

      >>> root = LocaleInheritanceStub()
      >>> root.data = InheritingDictionary({1: 'one', 2: 'two', 3: 'three'})
      >>> root.data2 = AttributeInheritance()
      >>> root.data2.dict = InheritingDictionary({1: 'i', 2: 'ii', 3: 'iii'})

      >>> locale = LocaleInheritanceStub(root)
      >>> locale.data = InheritingDictionary({1: 'eins'})
      >>> locale.data2 = AttributeInheritance()
      >>> locale.data2.dict = InheritingDictionary({1: 'I'})

      Here is a dictionary lookup directly from the locale ...

      >>> locale.data[1]
      'eins'
      >>> locale.data[2]
      'two'

      ... however, we can also have any amount of nesting.

      >>> locale.data2.dict[1]
      'I'
      >>> locale.data2.dict[2]
      'ii'

      We also have to overwrite 'get()', 'keys()' and 'items()' since we want
      to make sure that all upper locales are consulted before returning the
      default or to construct the list of elements, respectively.

      >>> locale.data2.dict.get(2)
      'ii'
      >>> locale.data2.dict.get(4) is None
      True
      >>> locale.data.keys()
      [1, 2, 3]
      >>> locale.data.items()
      [(1, 'eins'), (2, 'two'), (3, 'three')]
    """

    implements(IDictionaryInheritance)

    def __setitem__(self, name, value):
        """See zope.i18n.interfaces.locales.ILocaleInheritance"""
        if ILocaleInheritance.providedBy(value):
            value.__parent__ = self
            value.__name__ = name
        super(InheritingDictionary, self).__setitem__(name, value)

    def __getitem__(self, name):
        """See zope.i18n.interfaces.locales.ILocaleInheritance"""
        if not self.has_key(name):
            try: 
                selfUp = self.getInheritedSelf()
            except NoParentException:
                pass
            else:
                return selfUp.__getitem__(name)
        return super(InheritingDictionary, self).__getitem__(name)

    def get(self, name, default=None):
        """See zope.i18n.interfaces.locales.ILocaleInheritance"""
        try:
            return self[name]
        except KeyError:
            return default

    def items(self):
        try:
            d = dict(self.getInheritedSelf())
        except NoParentException:
            d = {}
        d.update(self)
        return d.items()

    def keys(self):
        return [item[0] for item in self.items()]

    def value(self):
        return [item[1] for item in self.items()]
        
        
