html.py

'''
Comparing two html documents.
'''
import re
from HTMLParser import HTMLParseError
from django.utils.htmlparser import HTMLParser


WHITESPACE = re.compile('\s+')


def normalize_whitespace(string):
    return WHITESPACE.sub(' ', string)


class Element(object):
    def __init__(self, name, attributes):
        self.name = name
        self.attributes = sorted(attributes)
        self.children = []

    def append(self, element):
        if isinstance(element, basestring):
            element = normalize_whitespace(element)
            if self.children:
                if isinstance(self.children[-1], basestring):
                    self.children[-1] += element
                    self.children[-1] = normalize_whitespace(self.children[-1])
                    return
        elif self.children:
            # removing last children if it is only whitespace
            # this can result in incorrect dom representations since
            # whitespace between inline tags like <span> is significant
            if isinstance(self.children[-1], basestring):
                if self.children[-1].isspace():
                    self.children.pop()
        if element:
            self.children.append(element)

    def finalize(self):
        def rstrip_last_element(children):
            if children:
                if isinstance(children[-1], basestring):
                    children[-1] = children[-1].rstrip()
                    if not children[-1]:
                        children.pop()
                        children = rstrip_last_element(children)
            return children

        rstrip_last_element(self.children)
        for i, child in enumerate(self.children):
            if isinstance(child, basestring):
                self.children[i] = child.strip()
            elif hasattr(child, 'finalize'):
                child.finalize()

    def __eq__(self, element):
        if self.name != element.name:
            return False
        if len(self.attributes) != len(element.attributes):
            return False
        if self.attributes != element.attributes:
            # attributes without a value is same as attribute with value that
            # equals the attributes name:
            # <input checked> == <input checked="checked">
            for i in range(len(self.attributes)):
                attr, value = self.attributes[i]
                other_attr, other_value = element.attributes[i]
                if value is None:
                    value = attr
                if other_value is None:
                    other_value = other_attr
                if attr != other_attr or value != other_value:
                    return False
        if self.children != element.children:
            return False
        return True

    def __ne__(self, element):
        return not self.__eq__(element)

    def _count(self, element, count=True):
        if not isinstance(element, basestring):
            if self == element:
                return 1
        i = 0
        for child in self.children:
            # child is text content and element is also text content, then
            # make a simple "text" in "text"
            if isinstance(child, basestring):
                if isinstance(element, basestring):
                    if count:
                        i += child.count(element)
                    elif element in child:
                        return 1
            else:
                i += child._count(element, count=count)
                if not count and i:
                    return i
        return i

    def __contains__(self, element):
        return self._count(element, count=False) > 0

    def count(self, element):
        return self._count(element, count=True)

    def __getitem__(self, key):
        return self.children[key]

    def __unicode__(self):
        output = u'<%s' % self.name
        for key, value in self.attributes:
            if value:
                output += u' %s="%s"' % (key, value)
            else:
                output += u' %s' % key
        if self.children:
            output += u'>\n'
            output += u''.join(unicode(c) for c in self.children)
            output += u'\n</%s>' % self.name
        else:
            output += u' />'
        return output

    def __str__(self):
        return str(unicode(self))

    def __repr__(self):
        return unicode(self)


class RootElement(Element):
    def __init__(self):
        super(RootElement, self).__init__(None, ())

    def __unicode__(self):
        return u''.join(unicode(c) for c in self.children)


class Parser(HTMLParser):
    SELF_CLOSING_TAGS = ('br' , 'hr', 'input', 'img', 'meta', 'spacer',
        'link', 'frame', 'base', 'col')

    def __init__(self):
        HTMLParser.__init__(self)
        self.root = RootElement()
        self.open_tags = []
        self.element_positions = {}

    def error(self, msg):
        raise HTMLParseError(msg, self.getpos())

    def format_position(self, position=None, element=None):
        if not position and element:
            position = self.element_positions[element]
        if position is None:
            position = self.getpos()
        if hasattr(position, 'lineno'):
            position = position.lineno, position.offset
        return 'Line %d, Column %d' % position

    @property
    def current(self):
        if self.open_tags:
            return self.open_tags[-1]
        else:
            return self.root

    def handle_startendtag(self, tag, attrs):
        self.handle_starttag(tag, attrs)
        if tag not in self.SELF_CLOSING_TAGS:
            self.handle_endtag(tag)

    def handle_starttag(self, tag, attrs):
        element = Element(tag, attrs)
        self.current.append(element)
        if tag not in self.SELF_CLOSING_TAGS:
            self.open_tags.append(element)
        self.element_positions[element] = self.getpos()

    def handle_endtag(self, tag):
        if not self.open_tags:
            self.error("Unexpected end tag `%s` (%s)" % (
                tag, self.format_position()))
        element = self.open_tags.pop()
        while element.name != tag:
            if not self.open_tags:
                self.error("Unexpected end tag `%s` (%s)" % (
                    tag, self.format_position()))
            element = self.open_tags.pop()

    def handle_data(self, data):
        self.current.append(data)

    def handle_charref(self, name):
        self.current.append('&%s;' % name)

    def handle_entityref(self, name):
        self.current.append('&%s;' % name)


def parse_html(html):
    '''
    Takes a string that contains *valid* HTML and turns it into an python
    object structure that can be easily compared against other HTML on
    semantical equivilance. Syntactical differences like which quotation is
    used on arguments will be ignored.
    '''
    parser = Parser()
    parser.feed(html)
    parser.close()
    document = parser.root
    document.finalize()
    # Removing ROOT element if it's not necessary
    if len(document.children) == 1:
        if not isinstance(document.children[0], basestring):
            document = document.children[0]
    return document