# -*- coding: utf-8 -*-
#
# Copyright (C) 2007-2010 Edgewall Software
# All rights reserved.
#
# This software is licensed as described in the file COPYING, which
# you should have received as part of this distribution. The terms
# are also available at http://genshi.edgewall.org/wiki/License.
#
# This software consists of voluntary contributions made by many
# individuals. For the exact contribution history, see the revision
# history and logs, available at http://genshi.edgewall.org/log/.

"""Directives and utilities for internationalization and localization of
templates.

:since: version 0.4
:note: Directives support added since version 0.6
"""

from gettext import NullTranslations
import os
import re
from functools import partial
from types import FunctionType

import six

from genshi.core import Attrs, Namespace, QName, START, END, TEXT, \
                        XML_NAMESPACE, _ensure, StreamEventKind
from genshi.template.base import DirectiveFactory, EXPR, SUB, _apply_directives
from genshi.template.directives import Directive, StripDirective
from genshi.template.markup import MarkupTemplate, EXEC
from genshi.compat import ast, IS_PYTHON2, _ast_Str, _ast_Str_value

__all__ = ['Translator', 'extract']
__docformat__ = 'restructuredtext en'


I18N_NAMESPACE = Namespace('http://genshi.edgewall.org/i18n')

MSGBUF = StreamEventKind('MSGBUF')
SUB_START = StreamEventKind('SUB_START')
SUB_END = StreamEventKind('SUB_END')

GETTEXT_FUNCTIONS = ('_', 'gettext', 'ngettext', 'dgettext', 'dngettext',
                     'ugettext', 'ungettext')


class I18NDirective(Directive):
    """Simple interface for i18n directives to support messages extraction."""

    def __call__(self, stream, directives, ctxt, **vars):
        return _apply_directives(stream, directives, ctxt, vars)


class ExtractableI18NDirective(I18NDirective):
    """Simple interface for directives to support messages extraction."""

    def extract(self, translator, stream, gettext_functions=GETTEXT_FUNCTIONS,
                search_text=True, comment_stack=None, context_stack=None):
        raise NotImplementedError


contexted = {
    None: 'pgettext',
    'gettext': 'pgettext',
    'ngettext': 'pngettext',
    'dgettext': 'dpgettext',
    'dngettext': 'dnpgettext'
}


def contextify(line, func, msg, comment, context):
    if context:
        context = context[0]
        func = contexted.get(func)
        if func is None:
            raise ValueError("failure, bogus extraction method")
        if isinstance(msg, tuple):
            msg = (context, tuple[0], tuple[1])
        else:
            msg = (context, msg)
    return line, func, msg, comment


class CommentDirective(I18NDirective):
    """Implementation of the ``i18n:comment`` template directive which adds
    translation comments.

    >>> tmpl = MarkupTemplate('''<html xmlns:i18n="http://genshi.edgewall.org/i18n">
    ...   <p i18n:comment="As in Foo Bar">Foo</p>
    ... </html>''')
    >>> translator = Translator()
    >>> translator.setup(tmpl)
    >>> list(translator.extract(tmpl.stream))
    [(2, None, 'Foo', ['As in Foo Bar'])]
    """
    __slots__ = ['comment']

    def __init__(self, value, template=None, namespaces=None, lineno=-1,
                 offset=-1):
        Directive.__init__(self, None, template, namespaces, lineno, offset)
        self.comment = value


class MsgDirective(ExtractableI18NDirective):
    r"""Implementation of the ``i18n:msg`` directive which marks inner content
    as translatable. Consider the following examples:

    >>> tmpl = MarkupTemplate('''<html xmlns:i18n="http://genshi.edgewall.org/i18n">
    ...   <div i18n:msg="">
    ...     <p>Foo</p>
    ...     <p>Bar</p>
    ...   </div>
    ...   <p i18n:msg="">Foo <em>bar</em>!</p>
    ... </html>''')

    >>> translator = Translator()
    >>> translator.setup(tmpl)
    >>> list(translator.extract(tmpl.stream))
    [(2, None, '[1:Foo]\n    [2:Bar]', []), (6, None, 'Foo [1:bar]!', [])]
    >>> print(tmpl.generate().render())
    <html>
      <div><p>Foo</p>
        <p>Bar</p></div>
      <p>Foo <em>bar</em>!</p>
    </html>

    >>> tmpl = MarkupTemplate('''<html xmlns:i18n="http://genshi.edgewall.org/i18n">
    ...   <div i18n:msg="fname, lname">
    ...     <p>First Name: ${fname}</p>
    ...     <p>Last Name: ${lname}</p>
    ...   </div>
    ...   <p i18n:msg="">Foo <em>bar</em>!</p>
    ... </html>''')
    >>> translator.setup(tmpl)
    >>> list(translator.extract(tmpl.stream)) #doctest: +NORMALIZE_WHITESPACE
    [(2, None, '[1:First Name: %(fname)s]\n    [2:Last Name: %(lname)s]', []),
    (6, None, 'Foo [1:bar]!', [])]

    >>> tmpl = MarkupTemplate('''<html xmlns:i18n="http://genshi.edgewall.org/i18n">
    ...   <div i18n:msg="fname, lname">
    ...     <p>First Name: ${fname}</p>
    ...     <p>Last Name: ${lname}</p>
    ...   </div>
    ...   <p i18n:msg="">Foo <em>bar</em>!</p>
    ... </html>''')
    >>> translator.setup(tmpl)
    >>> print(tmpl.generate(fname='John', lname='Doe').render())
    <html>
      <div><p>First Name: John</p>
        <p>Last Name: Doe</p></div>
      <p>Foo <em>bar</em>!</p>
    </html>

    Starting and ending white-space is stripped of to make it simpler for
    translators. Stripping it is not that important since it's on the html
    source, the rendered output will remain the same.
    """
    __slots__ = ['params', 'lineno']

    def __init__(self, value, template=None, namespaces=None, lineno=-1,
                 offset=-1):
        Directive.__init__(self, None, template, namespaces, lineno, offset)
        self.params = [param.strip() for param in value.split(',') if param]
        self.lineno = lineno

    @classmethod
    def attach(cls, template, stream, value, namespaces, pos):
        if type(value) is dict:
            value = value.get('params', '').strip()
        return super(MsgDirective, cls).attach(template, stream, value.strip(),
                                               namespaces, pos)

    def __call__(self, stream, directives, ctxt, **vars):
        gettext = ctxt.get('_i18n.gettext')
        if ctxt.get('_i18n.domain') and ctxt.get('_i18n.context'):
            dpgettext = ctxt.get('_i18n.dpgettext')
            assert hasattr(dpgettext, '__call__'), \
                'No domain/context gettext function passed'
            gettext = lambda msg: dpgettext(ctxt.get('_i18n.domain'),
                                            ctxt.get('_i18n.context'),
                                            msg)
        elif ctxt.get('_i18n.domain'):
            dgettext = ctxt.get('_i18n.dgettext')
            assert hasattr(dgettext, '__call__'), \
                'No domain gettext function passed'
            gettext = lambda msg: dgettext(ctxt.get('_i18n.domain'), msg)
        elif ctxt.get('_i18n.context'):
            pgettext = ctxt.get('_i18n.pgettext')
            assert hasattr(pgettext, '__call__'), \
                'No context gettext function passed'
            gettext = lambda msg: pgettext(ctxt.get('_i18n.context'), msg)

        def _generate():
            msgbuf = MessageBuffer(self)
            previous = next(stream)
            if previous[0] is START:
                yield previous
            else:
                msgbuf.append(*previous)
            previous = next(stream)
            for kind, data, pos in stream:
                msgbuf.append(*previous)
                previous = kind, data, pos
            if previous[0] is not END:
                msgbuf.append(*previous)
                previous = None
            for event in msgbuf.translate(gettext(msgbuf.format())):
                yield event
            if previous:
                yield previous

        return _apply_directives(_generate(), directives, ctxt, vars)

    def extract(self, translator, stream, gettext_functions=GETTEXT_FUNCTIONS,
                search_text=True, comment_stack=None, context_stack=None):
        msgbuf = MessageBuffer(self)
        strip = False

        stream = iter(stream)
        previous = next(stream)
        if previous[0] is START:
            for message in translator._extract_attrs(previous,
                                                     gettext_functions,
                                                     search_text=search_text):
                yield message
            previous = next(stream)
            strip = True
        for event in stream:
            if event[0] is START:
                for message in translator._extract_attrs(event,
                                                         gettext_functions,
                                                         search_text=search_text):
                    yield message
            msgbuf.append(*previous)
            previous = event
        if not strip:
            msgbuf.append(*previous)

        yield contextify(
            self.lineno, None, msgbuf.format(), comment_stack[-1:], context_stack[-1:])


class ChooseBranchDirective(I18NDirective):
    __slots__ = ['params']

    def __call__(self, stream, directives, ctxt, **vars):
        self.params = ctxt.get('_i18n.choose.params', [])[:]
        msgbuf = MessageBuffer(self)
        stream = _apply_directives(stream, directives, ctxt, vars)

        previous = next(stream)
        if previous[0] is START:
            yield previous
        else:
            msgbuf.append(*previous)

        try:
            previous = next(stream)
        except StopIteration:
            # For example <i18n:singular> or <i18n:plural> directives
            yield MSGBUF, (), -1 # the place holder for msgbuf output
            ctxt['_i18n.choose.%s' % self.tagname] = msgbuf
            return

        for event in stream:
            msgbuf.append(*previous)
            previous = event
        yield MSGBUF, (), -1 # the place holder for msgbuf output

        if previous[0] is END:
            yield previous # the outer end tag
        else:
            msgbuf.append(*previous)
        ctxt['_i18n.choose.%s' % self.tagname] = msgbuf

    def extract(self, translator, stream, gettext_functions=GETTEXT_FUNCTIONS,
                search_text=True, comment_stack=None, context_stack=None,
                msgbuf=None):
        stream = iter(stream)
        previous = next(stream)

        if previous[0] is START:
            # skip the enclosing element
            for message in translator._extract_attrs(previous,
                                                     gettext_functions,
                                                     search_text=search_text):
                yield message
            previous = next(stream)

        for event in stream:
            if previous[0] is START:
                for message in translator._extract_attrs(previous,
                                                         gettext_functions,
                                                         search_text=search_text):
                    yield message
            msgbuf.append(*previous)
            previous = event

        if previous[0] is not END:
            msgbuf.append(*previous)


class SingularDirective(ChooseBranchDirective):
    """Implementation of the ``i18n:singular`` directive to be used with the
    ``i18n:choose`` directive."""


class PluralDirective(ChooseBranchDirective):
    """Implementation of the ``i18n:plural`` directive to be used with the
    ``i18n:choose`` directive."""


class ChooseDirective(ExtractableI18NDirective):
    """Implementation of the ``i18n:choose`` directive which provides plural
    internationalisation of strings.

    This directive requires at least one parameter, the one which evaluates to
    an integer which will allow to choose the plural/singular form. If you also
    have expressions inside the singular and plural version of the string you
    also need to pass a name for those parameters. Consider the following
    examples:

    >>> tmpl = MarkupTemplate('''<html xmlns:i18n="http://genshi.edgewall.org/i18n">
    ...   <div i18n:choose="num; num">
    ...     <p i18n:singular="">There is $num coin</p>
    ...     <p i18n:plural="">There are $num coins</p>
    ...   </div>
    ... </html>''')
    >>> translator = Translator()
    >>> translator.setup(tmpl)
    >>> list(translator.extract(tmpl.stream)) #doctest: +NORMALIZE_WHITESPACE
    [(2, 'ngettext', ('There is %(num)s coin',
                      'There are %(num)s coins'), [])]

    >>> tmpl = MarkupTemplate('''<html xmlns:i18n="http://genshi.edgewall.org/i18n">
    ...   <div i18n:choose="num; num">
    ...     <p i18n:singular="">There is $num coin</p>
    ...     <p i18n:plural="">There are $num coins</p>
    ...   </div>
    ... </html>''')
    >>> translator.setup(tmpl)
    >>> print(tmpl.generate(num=1).render())
    <html>
      <div>
        <p>There is 1 coin</p>
      </div>
    </html>
    >>> print(tmpl.generate(num=2).render())
    <html>
      <div>
        <p>There are 2 coins</p>
      </div>
    </html>

    When used as a element and not as an attribute:

    >>> tmpl = MarkupTemplate('''<html xmlns:i18n="http://genshi.edgewall.org/i18n">
    ...   <i18n:choose numeral="num" params="num">
    ...     <p i18n:singular="">There is $num coin</p>
    ...     <p i18n:plural="">There are $num coins</p>
    ...   </i18n:choose>
    ... </html>''')
    >>> translator.setup(tmpl)
    >>> list(translator.extract(tmpl.stream)) #doctest: +NORMALIZE_WHITESPACE
    [(2, 'ngettext', ('There is %(num)s coin',
                      'There are %(num)s coins'), [])]
    """
    __slots__ = ['numeral', 'params', 'lineno']

    def __init__(self, value, template=None, namespaces=None, lineno=-1,
                 offset=-1):
        Directive.__init__(self, None, template, namespaces, lineno, offset)
        params = [v.strip() for v in value.split(';')]
        self.numeral = self._parse_expr(params.pop(0), template, lineno, offset)
        self.params = params and [name.strip() for name in
                                  params[0].split(',') if name] or []
        self.lineno = lineno

    @classmethod
    def attach(cls, template, stream, value, namespaces, pos):
        if type(value) is dict:
            numeral = value.get('numeral', '').strip()
            assert numeral != '', "at least pass the numeral param"
            params = [v.strip() for v in value.get('params', '').split(',')]
            value = '%s; ' % numeral + ', '.join(params)
        return super(ChooseDirective, cls).attach(template, stream, value,
                                                  namespaces, pos)

    def __call__(self, stream, directives, ctxt, **vars):
        ctxt.push({'_i18n.choose.params': self.params,
                   '_i18n.choose.singular': None,
                   '_i18n.choose.plural': None})

        ngettext = ctxt.get('_i18n.ngettext')
        assert hasattr(ngettext, '__call__'), 'No ngettext function available'
        npgettext = ctxt.get('_i18n.npgettext')
        if not npgettext:
            npgettext = lambda c, s, p, n: ngettext(s, p, n)
        dngettext = ctxt.get('_i18n.dngettext')
        if not dngettext:
            dngettext = lambda d, s, p, n: ngettext(s, p, n)
        dnpgettext = ctxt.get('_i18n.dnpgettext')
        if not dnpgettext:
            dnpgettext = lambda d, c, s, p, n: dngettext(d, s, p, n)

        new_stream = []
        singular_stream = None
        singular_msgbuf = None
        plural_stream = None
        plural_msgbuf = None

        numeral = self.numeral.evaluate(ctxt)
        is_plural = self._is_plural(numeral, ngettext)

        for event in stream:
            if event[0] is SUB and any(isinstance(d, ChooseBranchDirective)
                                       for d in event[1][0]):
                subdirectives, substream = event[1]

                if isinstance(subdirectives[0], SingularDirective):
                    singular_stream = list(_apply_directives(substream,
                                                             subdirectives,
                                                             ctxt, vars))
                    new_stream.append((MSGBUF, None, (None, -1, -1)))

                elif isinstance(subdirectives[0], PluralDirective):
                    if is_plural:
                        plural_stream = list(_apply_directives(substream,
                                                               subdirectives,
                                                               ctxt, vars))

            else:
                new_stream.append(event)

        if ctxt.get('_i18n.context') and ctxt.get('_i18n.domain'):
            ngettext = lambda s, p, n: dnpgettext(ctxt.get('_i18n.domain'),
                                                  ctxt.get('_i18n.context'),
                                                  s, p, n)
        elif ctxt.get('_i18n.context'):
            ngettext = lambda s, p, n: npgettext(ctxt.get('_i18n.context'),
                                                 s, p, n)
        elif ctxt.get('_i18n.domain'):
            ngettext = lambda s, p, n: dngettext(ctxt.get('_i18n.domain'),
                                                 s, p, n)

        singular_msgbuf = ctxt.get('_i18n.choose.singular')
        if is_plural:
            plural_msgbuf = ctxt.get('_i18n.choose.plural')
            msgbuf, choice = plural_msgbuf, plural_stream
        else:
            msgbuf, choice = singular_msgbuf, singular_stream
            plural_msgbuf = MessageBuffer(self)

        for kind, data, pos in new_stream:
            if kind is MSGBUF:
                for event in choice:
                    if event[0] is MSGBUF:
                        translation = ngettext(singular_msgbuf.format(),
                                               plural_msgbuf.format(),
                                               numeral)
                        for subevent in msgbuf.translate(translation):
                            yield subevent
                    else:
                        yield event
            else:
                yield kind, data, pos

        ctxt.pop()

    def extract(self, translator, stream, gettext_functions=GETTEXT_FUNCTIONS,
                search_text=True, comment_stack=None, context_stack=None):
        strip = False
        stream = iter(stream)
        previous = next(stream)

        if previous[0] is START:
            # skip the enclosing element
            for message in translator._extract_attrs(previous,
                                                     gettext_functions,
                                                     search_text=search_text):
                yield message
            previous = next(stream)
            strip = True

        singular_msgbuf = MessageBuffer(self)
        plural_msgbuf = MessageBuffer(self)

        for event in stream:
            if previous[0] is SUB:
                directives, substream = previous[1]
                for directive in directives:
                    if isinstance(directive, SingularDirective):
                        for message in directive.extract(translator,
                                substream, gettext_functions, search_text,
                                comment_stack, context_stack, msgbuf=singular_msgbuf):
                            yield message
                    elif isinstance(directive, PluralDirective):
                        for message in directive.extract(translator,
                                substream, gettext_functions, search_text,
                                comment_stack, context_stack, msgbuf=plural_msgbuf):
                            yield message
                    elif not isinstance(directive, StripDirective):
                        singular_msgbuf.append(*previous)
                        plural_msgbuf.append(*previous)
            else:
                if previous[0] is START:
                    for message in translator._extract_attrs(previous,
                                                             gettext_functions,
                                                             search_text):
                        yield message
                singular_msgbuf.append(*previous)
                plural_msgbuf.append(*previous)
            previous = event

        if not strip:
            singular_msgbuf.append(*previous)
            plural_msgbuf.append(*previous)

        yield contextify(self.lineno, 'ngettext', \
            (singular_msgbuf.format(), plural_msgbuf.format()), \
            comment_stack[-1:], context_stack[-1:])

    def _is_plural(self, numeral, ngettext):
        # XXX: should we test which form was chosen like this!?!?!?
        # There should be no match in any catalogue for these singular and
        # plural test strings
        singular = u'O\x85\xbe\xa9\xa8az\xc3?\xe6\xa1\x02n\x84\x93'
        plural = u'\xcc\xfb+\xd3Pn\x9d\tT\xec\x1d\xda\x1a\x88\x00'
        return ngettext(singular, plural, numeral) == plural


class DomainDirective(I18NDirective):
    """Implementation of the ``i18n:domain`` directive which allows choosing
    another i18n domain(catalog) to translate from.

    >>> from genshi.filters.tests.i18n import DummyTranslations
    >>> tmpl = MarkupTemplate('''<html xmlns:i18n="http://genshi.edgewall.org/i18n">
    ...   <p i18n:msg="">Bar</p>
    ...   <div i18n:domain="foo">
    ...     <p i18n:msg="">FooBar</p>
    ...     <p>Bar</p>
    ...     <p i18n:domain="bar" i18n:msg="">Bar</p>
    ...     <p i18n:domain="">Bar</p>
    ...   </div>
    ...   <p>Bar</p>
    ... </html>''')

    >>> translations = DummyTranslations({'Bar': 'Voh'})
    >>> translations.add_domain('foo', {'FooBar': 'BarFoo', 'Bar': 'foo_Bar'})
    >>> translations.add_domain('bar', {'Bar': 'bar_Bar'})
    >>> translator = Translator(translations)
    >>> translator.setup(tmpl)

    >>> print(tmpl.generate().render())
    <html>
      <p>Voh</p>
      <div>
        <p>BarFoo</p>
        <p>foo_Bar</p>
        <p>bar_Bar</p>
        <p>Voh</p>
      </div>
      <p>Voh</p>
    </html>
    """
    __slots__ = ['domain']

    def __init__(self, value, template=None, namespaces=None, lineno=-1,
                 offset=-1):
        Directive.__init__(self, None, template, namespaces, lineno, offset)
        self.domain = value and value.strip() or '__DEFAULT__'

    @classmethod
    def attach(cls, template, stream, value, namespaces, pos):
        if type(value) is dict:
            value = value.get('name')
        return super(DomainDirective, cls).attach(template, stream, value,
                                                  namespaces, pos)

    def __call__(self, stream, directives, ctxt, **vars):
        ctxt.push({'_i18n.domain': self.domain})
        for event in _apply_directives(stream, directives, ctxt, vars):
            yield event
        ctxt.pop()


class ContextDirective(I18NDirective):
    __slots__ = ['context']

    def __init__(self, value, template=None, namespaces=None, lineno=-1,
                 offset=-1):
        Directive.__init__(self, None, template, namespaces, lineno, offset)
        self.context = value

    @classmethod
    def attach(cls, template, stream, value, namespaces, pos):
        if type(value) is dict:
            value = value.get('name')
        return super(ContextDirective, cls).attach(template, stream, value,
                                                   namespaces, pos)

    def __call__(self, stream, directives, ctxt, **vars):
        ctxt.push({'_i18n.context': self.context})
        for event in _apply_directives(stream, directives, ctxt, vars):
            yield event
        ctxt.pop()


class Translator(DirectiveFactory):
    """Can extract and translate localizable strings from markup streams and
    templates.

    For example, assume the following template:

    >>> tmpl = MarkupTemplate('''<html xmlns:py="http://genshi.edgewall.org/">
    ...   <head>
    ...     <title>Example</title>
    ...   </head>
    ...   <body>
    ...     <h1>Example</h1>
    ...     <p>${_("Hello, %(name)s") % dict(name=username)}</p>
    ...   </body>
    ... </html>''', filename='example.html')

    For demonstration, we define a dummy ``gettext``-style function with a
    hard-coded translation table, and pass that to the `Translator` initializer:

    >>> def pseudo_gettext(string):
    ...     return {
    ...         'Example': 'Beispiel',
    ...         'Hello, %(name)s': 'Hallo, %(name)s'
    ...     }[string]
    >>> translator = Translator(pseudo_gettext)

    Next, the translator needs to be prepended to any already defined filters
    on the template:

    >>> tmpl.filters.insert(0, translator)

    When generating the template output, our hard-coded translations should be
    applied as expected:

    >>> print(tmpl.generate(username='Hans', _=pseudo_gettext))
    <html>
      <head>
        <title>Beispiel</title>
      </head>
      <body>
        <h1>Beispiel</h1>
        <p>Hallo, Hans</p>
      </body>
    </html>

    Note that elements defining ``xml:lang`` attributes that do not contain
    variable expressions are ignored by this filter. That can be used to
    exclude specific parts of a template from being extracted and translated.
    """

    directives = [
        ('domain', DomainDirective),
        ('comment', CommentDirective),
        ('ctxt', ContextDirective),
        ('msg', MsgDirective),
        ('choose', ChooseDirective),
        ('singular', SingularDirective),
        ('plural', PluralDirective)
    ]

    IGNORE_TAGS = frozenset([
        QName('script'), QName('http://www.w3.org/1999/xhtml}script'),
        QName('style'), QName('http://www.w3.org/1999/xhtml}style')
    ])
    INCLUDE_ATTRS = frozenset([
        'abbr', 'alt', 'label', 'prompt', 'standby', 'summary', 'title',
        'placeholder',
    ])
    NAMESPACE = I18N_NAMESPACE

    def __init__(self, translate=NullTranslations(), ignore_tags=IGNORE_TAGS,
                 include_attrs=INCLUDE_ATTRS, extract_text=True):
        """Initialize the translator.

        :param translate: the translation function, for example ``gettext`` or
                          ``ugettext``.
        :param ignore_tags: a set of tag names that should not be localized
        :param include_attrs: a set of attribute names should be localized
        :param extract_text: whether the content of text nodes should be
                             extracted, or only text in explicit ``gettext``
                             function calls

        :note: Changed in 0.6: the `translate` parameter can now be either
               a ``gettext``-style function, or an object compatible with the
               ``NullTransalations`` or ``GNUTranslations`` interface
        """
        self.translate = translate
        self.ignore_tags = ignore_tags
        self.include_attrs = include_attrs
        self.extract_text = extract_text

    def __call__(self, stream, ctxt=None, translate_text=True,
                 translate_attrs=True):
        """Translate any localizable strings in the given stream.

        This function shouldn't be called directly. Instead, an instance of
        the `Translator` class should be registered as a filter with the
        `Template` or the `TemplateLoader`, or applied as a regular stream
        filter. If used as a template filter, it should be inserted in front of
        all the default filters.

        :param stream: the markup event stream
        :param ctxt: the template context (not used)
        :param translate_text: whether text nodes should be translated (used
                               internally)
        :param translate_attrs: whether attribute values should be translated
                                (used internally)
        :return: the localized stream
        """
        ignore_tags = self.ignore_tags
        include_attrs = self.include_attrs
        skip = 0
        xml_lang = XML_NAMESPACE['lang']
        if not self.extract_text:
            translate_text = False
            translate_attrs = False

        if type(self.translate) is FunctionType:
            gettext = self.translate
            if ctxt:
                ctxt['_i18n.gettext'] = gettext
        else:
            if IS_PYTHON2:
                gettext = self.translate.ugettext
                ngettext = self.translate.ungettext
            else:
                gettext = self.translate.gettext
                ngettext = self.translate.ngettext
            try:
                if IS_PYTHON2:
                    dgettext = self.translate.dugettext
                    dngettext = self.translate.dungettext
                else:
                    dgettext = self.translate.dgettext
                    dngettext = self.translate.dngettext
            except AttributeError:
                dgettext = lambda _, y: gettext(y)
                dngettext = lambda _, s, p, n: ngettext(s, p, n)
            try:
                if IS_PYTHON2:
                    pgettext = self.translate.upgettext
                    dpgettext = self.translate.dupgettext
                    npgettext = self.translate.unpgettext
                    dnpgettext = self.translate.dunpgettext
                else:
                    pgettext = self.translate.pgettext
                    dpgettext = self.translate.dpgettext
                    npgettext = self.translate.npgettext
                    dnpgettext = self.translate.dnpgettext
            except AttributeError:
                pgettext = lambda _, y: gettext(y)
                dpgettext = lambda d, _, y: dgettext(d, y)
                npgettext = lambda _, s, p, n: ngettext(s, p, n)
                dnpgettext = lambda d, _, s, p, n: dngettext(d, s, p, n)
            if ctxt:
                ctxt['_i18n.gettext'] = gettext
                ctxt['_i18n.ngettext'] = ngettext
                ctxt['_i18n.dgettext'] = dgettext
                ctxt['_i18n.dngettext'] = dngettext
                ctxt['_i18n.pgettext'] = pgettext
                ctxt['_i18n.npgettext'] = npgettext
                ctxt['_i18n.dpgettext'] = dpgettext
                ctxt['_i18n.dnpgettext'] = dnpgettext

        if ctxt and ctxt.get('_i18n.domain'):
            # TODO: This can cause infinite recursion if dgettext is defined
            #       via the AttributeError case above!
            gettext = partial(dgettext, ctxt.get('_i18n.domain'))

        if ctxt and ctxt.get('_i18n.context'):
            if getattr(gettext, 'func', None):
                gettext = partial(dpgettext,
                                  ctxt['_i18n.domain'],
                                  ctxt['_i18n.context'])
            else:
                gettext = partial(pgettext, ctxt['_i18n.context'])

        for kind, data, pos in stream:

            # skip chunks that should not be localized
            if skip:
                if kind is START:
                    skip += 1
                elif kind is END:
                    skip -= 1
                yield kind, data, pos
                continue

            # handle different events that can be localized
            if kind is START:
                tag, attrs = data
                if tag in self.ignore_tags or \
                        isinstance(attrs.get(xml_lang), six.string_types):
                    skip += 1
                    yield kind, data, pos
                    continue

                new_attrs = []
                changed = False

                for name, value in attrs:
                    newval = value
                    if isinstance(value, six.string_types):
                        text = value.strip()
                        if translate_attrs and name in include_attrs and text:
                            newval = gettext(text)
                    else:
                        newval = list(
                            self(_ensure(value), ctxt, translate_text=False)
                        )
                    if newval != value:
                        value = newval
                        changed = True
                    new_attrs.append((name, value))
                if changed:
                    attrs = Attrs(new_attrs)

                yield kind, (tag, attrs), pos

            elif translate_text and kind is TEXT:
                text = data.strip()
                if text:
                    data = data.replace(text, six.text_type(gettext(text)))
                yield kind, data, pos

            elif kind is SUB:
                directives, substream = data
                current_domain = None
                current_context = None
                for idx, directive in enumerate(directives):
                    # Organize directives to make everything work
                    # FIXME: There's got to be a better way to do this!
                    if isinstance(directive, DomainDirective):
                        # Grab current domain and update context
                        current_domain = directive.domain
                        ctxt.push({'_i18n.domain': current_domain})
                        # Put domain directive as the first one in order to
                        # update context before any other directives evaluation
                        directives.insert(0, directives.pop(idx))
                    if isinstance(directive, ContextDirective):
                        # Grab current (msg)context and update context
                        current_context = directive.context
                        ctxt.push({'_i18n.context': current_context})
                        # Put context directive either first in the case of
                        # no domain, or 2nd in the case there is a domain, to
                        # update context before any other directives evaluation
                        directives.insert(1 if current_domain else 0,
                                          directives.pop(idx))

                # If this is an i18n directive, no need to translate text
                # nodes here
                is_i18n_directive = any([
                    isinstance(d, ExtractableI18NDirective)
                    for d in directives
                ])

                substream = list(self(substream, ctxt,
                                      translate_text=not is_i18n_directive,
                                      translate_attrs=translate_attrs))
                yield kind, (directives, substream), pos

                if current_domain:
                    ctxt.pop()
                if current_context:
                    ctxt.pop()
            else:
                yield kind, data, pos

    def extract(self, stream, gettext_functions=GETTEXT_FUNCTIONS,
                search_text=True, comment_stack=None, context_stack=None):
        """Extract localizable strings from the given template stream.

        For every string found, this function yields a ``(lineno, function,
        message, comments)`` tuple, where:

        * ``lineno`` is the number of the line on which the string was found,
        * ``function`` is the name of the ``gettext`` function used (if the
          string was extracted from embedded Python code), and
        *  ``message`` is the string itself (a ``unicode`` object, or a tuple
           of ``unicode`` objects for functions with multiple string
           arguments).
        *  ``comments`` is a list of comments related to the message, extracted
           from ``i18n:comment`` attributes found in the markup

        >>> tmpl = MarkupTemplate('''<html xmlns:py="http://genshi.edgewall.org/">
        ...   <head>
        ...     <title>Example</title>
        ...   </head>
        ...   <body>
        ...     <h1>Example</h1>
        ...     <p>${_("Hello, %(name)s") % dict(name=username)}</p>
        ...     <p>${ngettext("You have %d item", "You have %d items", num)}</p>
        ...   </body>
        ... </html>''', filename='example.html')
        >>> for line, func, msg, comments in Translator().extract(tmpl.stream):
        ...    print('%d, %r, %r' % (line, func, msg))
        3, None, 'Example'
        6, None, 'Example'
        7, '_', 'Hello, %(name)s'
        8, 'ngettext', ('You have %d item', 'You have %d items', None)
        
        :param stream: the event stream to extract strings from; can be a
                       regular stream or a template stream
        :param gettext_functions: a sequence of function names that should be
                                  treated as gettext-style localization
                                  functions
        :param search_text: whether the content of text nodes should be
                            extracted (used internally)

        :note: Changed in 0.4.1: For a function with multiple string arguments
               (such as ``ngettext``), a single item with a tuple of strings is
               yielded, instead an item for each string argument.
        :note: Changed in 0.6: The returned tuples now include a fourth
               element, which is a list of comments for the translator.
        """
        if not self.extract_text:
            search_text = False
        if comment_stack is None:
            comment_stack = []
        if context_stack is None:
            context_stack = []
        skip = 0

        xml_lang = XML_NAMESPACE['lang']

        for kind, data, pos in stream:
            if skip:
                if kind is START:
                    skip += 1
                if kind is END:
                    skip -= 1

            if kind is START and not skip:
                tag, attrs = data
                if tag in self.ignore_tags or \
                        isinstance(attrs.get(xml_lang), six.string_types):
                    skip += 1
                    continue

                for message in self._extract_attrs((kind, data, pos),
                                                   gettext_functions,
                                                   search_text=search_text):
                    yield message

            elif not skip and search_text and kind is TEXT:
                text = data.strip()
                if text and [ch for ch in text if ch.isalpha()]:
                    yield contextify(pos[1], None, text, comment_stack[-1:],
                                     context_stack[-1:])

            elif kind is EXPR or kind is EXEC:
                for funcname, strings in extract_from_code(data,
                                                           gettext_functions):
                    # XXX: Do we need to grab i18n:comment from comment_stack ???
                    yield pos[1], funcname, strings, []

            elif kind is SUB:
                directives, substream = data
                in_comment = False
                in_context = False

                for idx, directive in enumerate(directives):
                    # Do a first loop to see if there's a comment directive
                    # If there is update context and pop it from directives
                    if isinstance(directive, CommentDirective):
                        in_comment = True
                        comment_stack.append(directive.comment)
                        if len(directives) == 1:
                            # in case we're in the presence of something like:
                            # <p i18n:comment="foo">Foo</p>
                            for message in self.extract(
                                    substream, gettext_functions,
                                    search_text=search_text and not skip,
                                    comment_stack=comment_stack,
                                    context_stack=context_stack):
                                yield message
                        directives.pop(idx)
                    elif isinstance(directive, ContextDirective):
                        in_context = True
                        context_stack.append(directive.context)
                        if len(directives) == 1:
                            for message in self.extract(
                                    substream, gettext_functions,
                                    search_text=search_text and not skip,
                                    comment_stack=comment_stack,
                                    context_stack=context_stack):
                                yield message
                        directives.pop(idx)
                    elif not isinstance(directive, I18NDirective):
                        # Remove all other non i18n directives from the process
                        directives.pop(idx)

                if not directives and not in_comment and not in_context:
                    # Extract content if there's no directives because
                    # strip was pop'ed and not because comment was pop'ed.
                    # Extraction in this case has been taken care of.
                    for message in self.extract(
                            substream, gettext_functions,
                            search_text=search_text and not skip):
                        yield message

                for directive in directives:
                    if isinstance(directive, ExtractableI18NDirective):
                        for message in directive.extract(self,
                                substream, gettext_functions,
                                search_text=search_text and not skip,
                                comment_stack=comment_stack,
                                context_stack=context_stack):
                            yield message
                    else:
                        for message in self.extract(
                                substream, gettext_functions,
                                search_text=search_text and not skip,
                                comment_stack=comment_stack,
                                context_stack=context_stack):
                            yield message

                if in_comment:
                    comment_stack.pop()

                if in_context:
                    context_stack.pop()

    def get_directive_index(self, dir_cls):
        total = len(self._dir_order)
        if dir_cls in self._dir_order:
            return self._dir_order.index(dir_cls) - total
        return total

    def setup(self, template):
        """Convenience function to register the `Translator` filter and the
        related directives with the given template.

        :param template: a `Template` instance
        """
        template.filters.insert(0, self)
        if hasattr(template, 'add_directives'):
            template.add_directives(Translator.NAMESPACE, self)

    def _extract_attrs(self, event, gettext_functions, search_text):
        for name, value in event[1][1]:
            if search_text and isinstance(value, six.string_types):
                if name in self.include_attrs:
                    text = value.strip()
                    if text:
                        yield event[2][1], None, text, []
            else:
                for message in self.extract(_ensure(value), gettext_functions,
                                            search_text=False):
                    yield message


class MessageBuffer(object):
    """Helper class for managing internationalized mixed content.

    :since: version 0.5
    """

    def __init__(self, directive=None):
        """Initialize the message buffer.

        :param directive: the directive owning the buffer
        :type directive: I18NDirective
        """
        # params list needs to be copied so that directives can be evaluated
        # more than once
        self.orig_params = self.params = directive.params[:]
        self.directive = directive
        self.string = []
        self.events = {}
        self.values = {}
        self.depth = 1
        self.order = 1
        self._prev_order = None
        self.stack = [0]
        self.subdirectives = {}

    def _add_event(self, order, event):
        if order == self._prev_order:
            self.events[order][-1].append(event)
        else:
            self._prev_order = order
            self.events.setdefault(order, [])
            self.events[order].append([event])

    def append(self, kind, data, pos):
        """Append a stream event to the buffer.

        :param kind: the stream event kind
        :param data: the event data
        :param pos: the position of the event in the source
        """
        if kind is SUB:
            # The order needs to be +1 because a new START kind event will
            # happen and we we need to wrap those events into our custom kind(s)
            order = self.stack[-1] + 1
            subdirectives, substream = data
            # Store the directives that should be applied after translation
            self.subdirectives.setdefault(order, []).extend(subdirectives)
            self._add_event(order, (SUB_START, None, pos))
            for skind, sdata, spos in substream:
                self.append(skind, sdata, spos)
            self._add_event(order, (SUB_END, None, pos))
        elif kind is TEXT:
            if '[' in data or ']' in data:
                # Quote [ and ] if it ain't us adding it, ie, if the user is
                # using those chars in their templates, escape them
                data = data.replace('[', r'\[').replace(']', r'\]')
            self.string.append(data)
            self._add_event(self.stack[-1], (kind, data, pos))
        elif kind is EXPR:
            if self.params:
                param = self.params.pop(0)
            else:
                params = ', '.join(['"%s"' % p for p in self.orig_params if p])
                if params:
                    params = "(%s)" % params
                raise IndexError("%d parameters%s given to 'i18n:%s' but "
                                 "%d or more expressions used in '%s', line %s"
                                 % (len(self.orig_params), params,
                                    self.directive.tagname,
                                    len(self.orig_params) + 1,
                                    os.path.basename(pos[0] or
                                                     'In-memory Template'),
                                    pos[1]))
            self.string.append('%%(%s)s' % param)
            self._add_event(self.stack[-1], (kind, data, pos))
            self.values[param] = (kind, data, pos)
        else:
            if kind is START:
                self.string.append('[%d:' % self.order)
                self.stack.append(self.order)
                self._add_event(self.stack[-1], (kind, data, pos))
                self.depth += 1
                self.order += 1
            elif kind is END:
                self.depth -= 1
                if self.depth:
                    self._add_event(self.stack[-1], (kind, data, pos))
                    self.string.append(']')
                    self.stack.pop()

    def format(self):
        """Return a message identifier representing the content in the
        buffer.
        """
        return ''.join(self.string).strip()

    def translate(self, string, regex=re.compile(r'%\((\w+)\)s')):
        """Interpolate the given message translation with the events in the
        buffer and return the translated stream.

        :param string: the translated message string
        """
        substream = None

        def yield_parts(string):
            for idx, part in enumerate(regex.split(string)):
                if idx % 2:
                    yield self.values[part]
                elif part:
                    yield (TEXT,
                           part.replace(r'\[', '[').replace(r'\]', ']'),
                           (None, -1, -1)
                    )

        parts = parse_msg(string)
        parts_counter = {}
        for order, string in parts:
            parts_counter.setdefault(order, []).append(None)

        while parts:
            order, string = parts.pop(0)
            events = self.events[order]
            if events:
                events = events.pop(0)
            else:
                # create a dummy empty text event so any remaining
                # part of the translation can be processed.
                events = [(TEXT, "", (None, -1, -1))]
            parts_counter[order].pop()

            for event in events:
                if event[0] is SUB_START:
                    substream = []
                elif event[0] is SUB_END:
                    # Yield a substream which might have directives to be
                    # applied to it (after translation events)
                    yield SUB, (self.subdirectives[order], substream), event[2]
                    substream = None
                elif event[0] is TEXT:
                    if string:
                        for part in yield_parts(string):
                            if substream is not None:
                                substream.append(part)
                            else:
                                yield part
                        # String handled, reset it
                        string = None
                elif event[0] is START:
                    if substream is not None:
                        substream.append(event)
                    else:
                        yield event
                    if string:
                        for part in yield_parts(string):
                            if substream is not None:
                                substream.append(part)
                            else:
                                yield part
                        # String handled, reset it
                        string = None
                elif event[0] is END:
                    if string:
                        for part in yield_parts(string):
                            if substream is not None:
                                substream.append(part)
                            else:
                                yield part
                        # String handled, reset it
                        string = None
                    if substream is not None:
                        substream.append(event)
                    else:
                        yield event
                elif event[0] is EXPR:
                    # These are handled on the strings itself
                    continue
                else:
                    if string:
                        for part in yield_parts(string):
                            if substream is not None:
                                substream.append(part)
                            else:
                                yield part
                        # String handled, reset it
                        string = None
                    if substream is not None:
                        substream.append(event)
                    else:
                        yield event


def parse_msg(string, regex=re.compile(r'(?:\[(\d+)\:)|(?<!\\)\]')):
    """Parse a translated message using Genshi mixed content message
    formatting.

    >>> parse_msg("See [1:Help].")
    [(0, 'See '), (1, 'Help'), (0, '.')]

    >>> parse_msg("See [1:our [2:Help] page] for details.")
    [(0, 'See '), (1, 'our '), (2, 'Help'), (1, ' page'), (0, ' for details.')]

    >>> parse_msg("[2:Details] finden Sie in [1:Hilfe].")
    [(2, 'Details'), (0, ' finden Sie in '), (1, 'Hilfe'), (0, '.')]

    >>> parse_msg("[1:] Bilder pro Seite anzeigen.")
    [(1, ''), (0, ' Bilder pro Seite anzeigen.')]

    :param string: the translated message string
    :return: a list of ``(order, string)`` tuples
    :rtype: `list`
    """
    parts = []
    stack = [0]
    while True:
        mo = regex.search(string)
        if not mo:
            break

        if mo.start() or stack[-1]:
            parts.append((stack[-1], string[:mo.start()]))
        string = string[mo.end():]

        orderno = mo.group(1)
        if orderno is not None:
            stack.append(int(orderno))
        else:
            stack.pop()
        if not stack:
            break

    if string:
        parts.append((stack[-1], string))

    return parts


def extract_from_code(code, gettext_functions):
    """Extract strings from Python bytecode.

    >>> from genshi.template.eval import Expression
    >>> expr = Expression('_("Hello")')
    >>> list(extract_from_code(expr, GETTEXT_FUNCTIONS))
    [('_', 'Hello')]
    
    >>> expr = Expression('ngettext("You have %(num)s item", '
    ...                            '"You have %(num)s items", num)')
    >>> list(extract_from_code(expr, GETTEXT_FUNCTIONS))
    [('ngettext', ('You have %(num)s item', 'You have %(num)s items', None))]
    
    :param code: the `Code` object
    :type code: `genshi.template.eval.Code`
    :param gettext_functions: a sequence of function names
    :since: version 0.5
    """
    def _walk(node):
        if isinstance(node, ast.Call) and isinstance(node.func, ast.Name) \
                and node.func.id in gettext_functions:
            strings = []
            def _add(arg):
                if isinstance(arg, _ast_Str) \
                        and isinstance(_ast_Str_value(arg), six.text_type):
                    strings.append(_ast_Str_value(arg))
                elif isinstance(arg, _ast_Str):
                    strings.append(six.text_type(_ast_Str_value(arg), 'utf-8'))
                elif arg:
                    strings.append(None)
            [_add(arg) for arg in node.args]
            if hasattr(node, 'starargs'):
                _add(node.starargs)
            if hasattr(node, 'kwargs'):
                _add(node.kwargs)
            if len(strings) == 1:
                strings = strings[0]
            else:
                strings = tuple(strings)
            yield node.func.id, strings
        elif node._fields:
            children = []
            for field in node._fields:
                child = getattr(node, field, None)
                if isinstance(child, list):
                    for elem in child:
                        children.append(elem)
                elif isinstance(child, ast.AST):
                    children.append(child)
            for child in children:
                for funcname, strings in _walk(child):
                    yield funcname, strings
    return _walk(code.ast)


def extract(fileobj, keywords, comment_tags, options):
    """Babel extraction method for Genshi templates.

    :param fileobj: the file-like object the messages should be extracted from
    :param keywords: a list of keywords (i.e. function names) that should be
                     recognized as translation functions
    :param comment_tags: a list of translator tags to search for and include
                         in the results
    :param options: a dictionary of additional options (optional)
    :return: an iterator over ``(lineno, funcname, message, comments)`` tuples
    :rtype: ``iterator``
    """
    template_class = options.get('template_class', MarkupTemplate)
    if isinstance(template_class, six.string_types):
        module, clsname = template_class.split(':', 1)
        template_class = getattr(__import__(module, {}, {}, [clsname]), clsname)
    encoding = options.get('encoding', None)

    extract_text = options.get('extract_text', True)
    if isinstance(extract_text, six.string_types):
        extract_text = extract_text.lower() in ('1', 'on', 'yes', 'true')

    ignore_tags = options.get('ignore_tags', Translator.IGNORE_TAGS)
    if isinstance(ignore_tags, six.string_types):
        ignore_tags = ignore_tags.split()
    ignore_tags = [QName(tag) for tag in ignore_tags]

    include_attrs = options.get('include_attrs', Translator.INCLUDE_ATTRS)
    if isinstance(include_attrs, six.string_types):
        include_attrs = include_attrs.split()
    include_attrs = [QName(attr) for attr in include_attrs]

    tmpl = template_class(fileobj, filename=getattr(fileobj, 'name', None),
                          encoding=encoding)
    tmpl.loader = None

    translator = Translator(None, ignore_tags, include_attrs, extract_text)
    if hasattr(tmpl, 'add_directives'):
        tmpl.add_directives(Translator.NAMESPACE, translator)
    for message in translator.extract(tmpl.stream, gettext_functions=keywords):
        yield message
