# -*- coding: utf-8 -*-
#
# Copyright (C) 2006-2009 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/.

"""Implementation of a number of stream filters."""

try:
    any
except NameError:
    from genshi.util import any
import re

from genshi.core import Attrs, QName, stripentities
from genshi.core import END, START, TEXT, COMMENT

__all__ = ['HTMLFormFiller', 'HTMLSanitizer']
__docformat__ = 'restructuredtext en'


class HTMLFormFiller(object):
    """A stream filter that can populate HTML forms from a dictionary of values.
    
    >>> from genshi.input import HTML
    >>> html = HTML('''<form>
    ...   <p><input type="text" name="foo" /></p>
    ... </form>''')
    >>> filler = HTMLFormFiller(data={'foo': 'bar'})
    >>> print(html | filler)
    <form>
      <p><input type="text" name="foo" value="bar"/></p>
    </form>
    """
    # TODO: only select the first radio button, and the first select option
    #       (if not in a multiple-select)
    # TODO: only apply to elements in the XHTML namespace (or no namespace)?

    def __init__(self, name=None, id=None, data=None, passwords=False):
        """Create the filter.
        
        :param name: The name of the form that should be populated. If this
                     parameter is given, only forms where the ``name`` attribute
                     value matches the parameter are processed.
        :param id: The ID of the form that should be populated. If this
                   parameter is given, only forms where the ``id`` attribute
                   value matches the parameter are processed.
        :param data: The dictionary of form values, where the keys are the names
                     of the form fields, and the values are the values to fill
                     in.
        :param passwords: Whether password input fields should be populated.
                          This is off by default for security reasons (for
                          example, a password may end up in the browser cache)
        :note: Changed in 0.5.2: added the `passwords` option
        """
        self.name = name
        self.id = id
        if data is None:
            data = {}
        self.data = data
        self.passwords = passwords

    def __call__(self, stream):
        """Apply the filter to the given stream.
        
        :param stream: the markup event stream to filter
        """
        in_form = in_select = in_option = in_textarea = False
        select_value = option_value = textarea_value = None
        option_start = None
        option_text = []
        no_option_value = False

        for kind, data, pos in stream:

            if kind is START:
                tag, attrs = data
                tagname = tag.localname

                if tagname == 'form' and (
                        self.name and attrs.get('name') == self.name or
                        self.id and attrs.get('id') == self.id or
                        not (self.id or self.name)):
                    in_form = True

                elif in_form:
                    if tagname == 'input':
                        type = attrs.get('type', '').lower()
                        if type in ('checkbox', 'radio'):
                            name = attrs.get('name')
                            if name and name in self.data:
                                value = self.data[name]
                                declval = attrs.get('value')
                                checked = False
                                if isinstance(value, (list, tuple)):
                                    if declval:
                                        checked = declval in [unicode(v) for v
                                                              in value]
                                    else:
                                        checked = any(value)
                                else:
                                    if declval:
                                        checked = declval == unicode(value)
                                    elif type == 'checkbox':
                                        checked = bool(value)
                                if checked:
                                    attrs |= [(QName('checked'), 'checked')]
                                elif 'checked' in attrs:
                                    attrs -= 'checked'
                        elif type in ('', 'hidden', 'text') \
                                or type == 'password' and self.passwords:
                            name = attrs.get('name')
                            if name and name in self.data:
                                value = self.data[name]
                                if isinstance(value, (list, tuple)):
                                    value = value[0]
                                if value is not None:
                                    attrs |= [
                                        (QName('value'), unicode(value))
                                    ]
                    elif tagname == 'select':
                        name = attrs.get('name')
                        if name in self.data:
                            select_value = self.data[name]
                            in_select = True
                    elif tagname == 'textarea':
                        name = attrs.get('name')
                        if name in self.data:
                            textarea_value = self.data.get(name)
                            if isinstance(textarea_value, (list, tuple)):
                                textarea_value = textarea_value[0]
                            in_textarea = True
                    elif in_select and tagname == 'option':
                        option_start = kind, data, pos
                        option_value = attrs.get('value')
                        if option_value is None:
                            no_option_value = True
                            option_value = ''
                        in_option = True
                        continue
                yield kind, (tag, attrs), pos

            elif in_form and kind is TEXT:
                if in_select and in_option:
                    if no_option_value:
                        option_value += data
                    option_text.append((kind, data, pos))
                    continue
                elif in_textarea:
                    continue
                yield kind, data, pos

            elif in_form and kind is END:
                tagname = data.localname
                if tagname == 'form':
                    in_form = False
                elif tagname == 'select':
                    in_select = False
                    select_value = None
                elif in_select and tagname == 'option':
                    if isinstance(select_value, (tuple, list)):
                        selected = option_value in [unicode(v) for v
                                                    in select_value]
                    else:
                        selected = option_value == unicode(select_value)
                    okind, (tag, attrs), opos = option_start
                    if selected:
                        attrs |= [(QName('selected'), 'selected')]
                    elif 'selected' in attrs:
                        attrs -= 'selected'
                    yield okind, (tag, attrs), opos
                    if option_text:
                        for event in option_text:
                            yield event
                    in_option = False
                    no_option_value = False
                    option_start = option_value = None
                    option_text = []
                elif tagname == 'textarea':
                    if textarea_value:
                        yield TEXT, unicode(textarea_value), pos
                    in_textarea = False
                yield kind, data, pos

            else:
                yield kind, data, pos


class HTMLSanitizer(object):
    """A filter that removes potentially dangerous HTML tags and attributes
    from the stream.
    
    >>> from genshi import HTML
    >>> html = HTML('<div><script>alert(document.cookie)</script></div>')
    >>> print(html | HTMLSanitizer())
    <div/>
    
    The default set of safe tags and attributes can be modified when the filter
    is instantiated. For example, to allow inline ``style`` attributes, the
    following instantation would work:
    
    >>> html = HTML('<div style="background: #000"></div>')
    >>> sanitizer = HTMLSanitizer(safe_attrs=HTMLSanitizer.SAFE_ATTRS | set(['style']))
    >>> print(html | sanitizer)
    <div style="background: #000"/>
    
    Note that even in this case, the filter *does* attempt to remove dangerous
    constructs from style attributes:

    >>> html = HTML('<div style="background: url(javascript:void); color: #000"></div>')
    >>> print(html | sanitizer)
    <div style="color: #000"/>
    
    This handles HTML entities, unicode escapes in CSS and Javascript text, as
    well as a lot of other things. However, the style tag is still excluded by
    default because it is very hard for such sanitizing to be completely safe,
    especially considering how much error recovery current web browsers perform.
    
    It also does some basic filtering of CSS properties that may be used for
    typical phishing attacks. For more sophisticated filtering, this class
    provides a couple of hooks that can be overridden in sub-classes.
    
    :warn: Note that this special processing of CSS is currently only applied to
           style attributes, **not** style elements.
    """

    SAFE_TAGS = frozenset(['a', 'abbr', 'acronym', 'address', 'area', 'b',
        'big', 'blockquote', 'br', 'button', 'caption', 'center', 'cite',
        'code', 'col', 'colgroup', 'dd', 'del', 'dfn', 'dir', 'div', 'dl', 'dt',
        'em', 'fieldset', 'font', 'form', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6',
        'hr', 'i', 'img', 'input', 'ins', 'kbd', 'label', 'legend', 'li', 'map',
        'menu', 'ol', 'optgroup', 'option', 'p', 'pre', 'q', 's', 'samp',
        'select', 'small', 'span', 'strike', 'strong', 'sub', 'sup', 'table',
        'tbody', 'td', 'textarea', 'tfoot', 'th', 'thead', 'tr', 'tt', 'u',
        'ul', 'var'])

    SAFE_ATTRS = frozenset(['abbr', 'accept', 'accept-charset', 'accesskey',
        'action', 'align', 'alt', 'axis', 'bgcolor', 'border', 'cellpadding',
        'cellspacing', 'char', 'charoff', 'charset', 'checked', 'cite', 'class',
        'clear', 'cols', 'colspan', 'color', 'compact', 'coords', 'datetime',
        'dir', 'disabled', 'enctype', 'for', 'frame', 'headers', 'height',
        'href', 'hreflang', 'hspace', 'id', 'ismap', 'label', 'lang',
        'longdesc', 'maxlength', 'media', 'method', 'multiple', 'name',
        'nohref', 'noshade', 'nowrap', 'prompt', 'readonly', 'rel', 'rev',
        'rows', 'rowspan', 'rules', 'scope', 'selected', 'shape', 'size',
        'span', 'src', 'start', 'summary', 'tabindex', 'target', 'title',
        'type', 'usemap', 'valign', 'value', 'vspace', 'width'])

    SAFE_SCHEMES = frozenset(['file', 'ftp', 'http', 'https', 'mailto', None])

    URI_ATTRS = frozenset(['action', 'background', 'dynsrc', 'href', 'lowsrc',
        'src'])

    def __init__(self, safe_tags=SAFE_TAGS, safe_attrs=SAFE_ATTRS,
                 safe_schemes=SAFE_SCHEMES, uri_attrs=URI_ATTRS):
        """Create the sanitizer.
        
        The exact set of allowed elements and attributes can be configured.
        
        :param safe_tags: a set of tag names that are considered safe
        :param safe_attrs: a set of attribute names that are considered safe
        :param safe_schemes: a set of URI schemes that are considered safe
        :param uri_attrs: a set of names of attributes that contain URIs
        """
        self.safe_tags = safe_tags
        "The set of tag names that are considered safe."
        self.safe_attrs = safe_attrs
        "The set of attribute names that are considered safe."
        self.uri_attrs = uri_attrs
        "The set of names of attributes that may contain URIs."
        self.safe_schemes = safe_schemes
        "The set of URI schemes that are considered safe."

    def __call__(self, stream):
        """Apply the filter to the given stream.
        
        :param stream: the markup event stream to filter
        """
        waiting_for = None

        for kind, data, pos in stream:
            if kind is START:
                if waiting_for:
                    continue
                tag, attrs = data
                if not self.is_safe_elem(tag, attrs):
                    waiting_for = tag
                    continue

                new_attrs = []
                for attr, value in attrs:
                    value = stripentities(value)
                    if attr not in self.safe_attrs:
                        continue
                    elif attr in self.uri_attrs:
                        # Don't allow URI schemes such as "javascript:"
                        if not self.is_safe_uri(value):
                            continue
                    elif attr == 'style':
                        # Remove dangerous CSS declarations from inline styles
                        decls = self.sanitize_css(value)
                        if not decls:
                            continue
                        value = '; '.join(decls)
                    new_attrs.append((attr, value))

                yield kind, (tag, Attrs(new_attrs)), pos

            elif kind is END:
                tag = data
                if waiting_for:
                    if waiting_for == tag:
                        waiting_for = None
                else:
                    yield kind, data, pos

            elif kind is not COMMENT:
                if not waiting_for:
                    yield kind, data, pos

    def is_safe_css(self, propname, value):
        """Determine whether the given css property declaration is to be
        considered safe for inclusion in the output.
        
        :param propname: the CSS property name
        :param value: the value of the property
        :return: whether the property value should be considered safe
        :rtype: bool
        :since: version 0.6
        """
        if propname == 'position':
            return False
        if propname.startswith('margin') and '-' in value:
            # Negative margins can be used for phishing
            return False
        return True

    def is_safe_elem(self, tag, attrs):
        """Determine whether the given element should be considered safe for
        inclusion in the output.
        
        :param tag: the tag name of the element
        :type tag: QName
        :param attrs: the element attributes
        :type attrs: Attrs
        :return: whether the element should be considered safe
        :rtype: bool
        :since: version 0.6
        """
        if tag not in self.safe_tags:
            return False
        if tag.localname == 'input':
            input_type = attrs.get('type', '').lower()
            if input_type == 'password':
                return False
        return True

    def is_safe_uri(self, uri):
        """Determine whether the given URI is to be considered safe for
        inclusion in the output.
        
        The default implementation checks whether the scheme of the URI is in
        the set of allowed URIs (`safe_schemes`).
        
        >>> sanitizer = HTMLSanitizer()
        >>> sanitizer.is_safe_uri('http://example.org/')
        True
        >>> sanitizer.is_safe_uri('javascript:alert(document.cookie)')
        False
        
        :param uri: the URI to check
        :return: `True` if the URI can be considered safe, `False` otherwise
        :rtype: `bool`
        :since: version 0.4.3
        """
        if '#' in uri:
            uri = uri.split('#', 1)[0] # Strip out the fragment identifier
        if ':' not in uri:
            return True # This is a relative URI
        chars = [char for char in uri.split(':', 1)[0] if char.isalnum()]
        return ''.join(chars).lower() in self.safe_schemes

    def sanitize_css(self, text):
        """Remove potentially dangerous property declarations from CSS code.
        
        In particular, properties using the CSS ``url()`` function with a scheme
        that is not considered safe are removed:
        
        >>> sanitizer = HTMLSanitizer()
        >>> sanitizer.sanitize_css(u'''
        ...   background: url(javascript:alert("foo"));
        ...   color: #000;
        ... ''')
        [u'color: #000']
        
        Also, the proprietary Internet Explorer function ``expression()`` is
        always stripped:
        
        >>> sanitizer.sanitize_css(u'''
        ...   background: #fff;
        ...   color: #000;
        ...   width: e/**/xpression(alert("foo"));
        ... ''')
        [u'background: #fff', u'color: #000']
        
        :param text: the CSS text; this is expected to be `unicode` and to not
                     contain any character or numeric references
        :return: a list of declarations that are considered safe
        :rtype: `list`
        :since: version 0.4.3
        """
        decls = []
        text = self._strip_css_comments(self._replace_unicode_escapes(text))
        for decl in text.split(';'):
            decl = decl.strip()
            if not decl:
                continue
            try:
                propname, value = decl.split(':', 1)
            except ValueError:
                continue
            if not self.is_safe_css(propname.strip().lower(), value.strip()):
                continue
            is_evil = False
            if 'expression' in value:
                is_evil = True
            for match in re.finditer(r'url\s*\(([^)]+)', value):
                if not self.is_safe_uri(match.group(1)):
                    is_evil = True
                    break
            if not is_evil:
                decls.append(decl.strip())
        return decls

    _NORMALIZE_NEWLINES = re.compile(r'\r\n').sub
    _UNICODE_ESCAPE = re.compile(r'\\([0-9a-fA-F]{1,6})\s?').sub

    def _replace_unicode_escapes(self, text):
        def _repl(match):
            return unichr(int(match.group(1), 16))
        return self._UNICODE_ESCAPE(_repl, self._NORMALIZE_NEWLINES('\n', text))

    _CSS_COMMENTS = re.compile(r'/\*.*?\*/').sub

    def _strip_css_comments(self, text):
        return self._CSS_COMMENTS('', text)
