import re
import types
try:
    from htmlentitydefs import name2codepoint
except ImportError:
    name2codepoint = {}
from bs4.dammit import EntitySubstitution

from util import isList

DEFAULT_OUTPUT_ENCODING = "utf-8"


def _match_css_class(str):
    """Build a RE to match the given CSS class."""
    return re.compile(r"(^|.*\s)%s($|\s)" % str)


def _alias(attr):
    """Alias one attribute name to another for backward compatibility"""
    @property
    def alias(self):
        return getattr(self, attr)

    @alias.setter
    def alias(self):
        return setattr(self, attr)
    return alias


class PageElement(object):
    """Contains the navigational information for some part of the page
    (either a tag or a piece of text)"""

    def setup(self, parent=None, previous=None):
        """Sets up the initial relations between this element and
        other elements."""
        self.parent = parent
        self.previous = previous
        self.next = None
        self.previous_sibling = None
        self.next_sibling = None
        if self.parent and self.parent.contents:
            self.previous_sibling = self.parent.contents[-1]
            self.previous_sibling.next_sibling = self

    nextSibling = _alias("next_sibling") # BS3
    previousSibling = _alias("previous_sibling") # BS3

    def replace_with(self, replace_with):
        if replace_with is self:
            return
        old_parent = self.parent
        my_index = self.parent.index(self)
        if (hasattr(replace_with, 'parent')
            and replace_with.parent is self.parent):
            # We're replacing this element with one of its siblings.
            if self.parent.index(replace_with) < my_index:
                # Furthermore, it comes before this element. That
                # means that when we extract it, the index of this
                # element will change.
                my_index -= 1
        self.extract()
        old_parent.insert(my_index, replace_with)
    replaceWith = replace_with # BS3

    def replace_with_children(self):
        my_parent = self.parent
        my_index = self.parent.index(self)
        self.extract()
        for child in reversed(self.contents[:]):
            my_parent.insert(my_index, child)
    replaceWithChildren = replace_with_children # BS3

    def extract(self):
        """Destructively rips this element out of the tree."""
        if self.parent:
            del self.parent.contents[self.parent.index(self)]

        #Find the two elements that would be next to each other if
        #this element (and any children) hadn't been parsed. Connect
        #the two.
        last_child = self._last_recursive_child()
        next_element = last_child.next

        if self.previous:
            self.previous.next = next_element
        if next_element:
            next_element.previous = self.previous
        self.previous = None
        last_child.next = None

        self.parent = None
        if self.previous_sibling:
            self.previous_sibling.next_sibling = self.next_sibling
        if self.next_sibling:
            self.next_sibling.previous_sibling = self.previous_sibling
        self.previous_sibling = self.next_sibling = None
        return self

    def _last_recursive_child(self):
        "Finds the last element beneath this object to be parsed."
        last_child = self
        while hasattr(last_child, 'contents') and last_child.contents:
            last_child = last_child.contents[-1]
        return last_child
    # BS3: Not part of the API!
    _lastRecursiveChild = _last_recursive_child

    def insert(self, position, new_child):
        if (isinstance(new_child, basestring)
            and not isinstance(new_child, NavigableString)):
            new_child = NavigableString(new_child)

        position =  min(position, len(self.contents))
        if hasattr(new_child, 'parent') and new_child.parent is not None:
            # We're 'inserting' an element that's already one
            # of this object's children.
            if new_child.parent is self:
                if self.index(new_child) > position:
                    # Furthermore we're moving it further down the
                    # list of this object's children. That means that
                    # when we extract this element, our target index
                    # will jump down one.
                    position -= 1
            new_child.extract()

        new_child.parent = self
        previous_child = None
        if position == 0:
            new_child.previous_sibling = None
            new_child.previous = self
        else:
            previous_child = self.contents[position - 1]
            new_child.previous_sibling = previous_child
            new_child.previous_sibling.next_sibling = new_child
            new_child.previous = previous_child._last_recursive_child()
        if new_child.previous:
            new_child.previous.next = new_child

        new_childs_last_element = new_child._last_recursive_child()

        if position >= len(self.contents):
            new_child.next_sibling = None

            parent = self
            parents_next_sibling = None
            while not parents_next_sibling:
                parents_next_sibling = parent.next_sibling
                parent = parent.parent
                if not parent: # This is the last element in the document.
                    break
            if parents_next_sibling:
                new_childs_last_element.next = parents_next_sibling
            else:
                new_childs_last_element.next = None
        else:
            next_child = self.contents[position]
            new_child.next_sibling = next_child
            if new_child.next_sibling:
                new_child.next_sibling.previous_sibling = new_child
            new_childs_last_element.next = next_child

        if new_childs_last_element.next:
            new_childs_last_element.next.previous = new_childs_last_element
        self.contents.insert(position, new_child)

    def append(self, tag):
        """Appends the given tag to the contents of this tag."""
        self.insert(len(self.contents), tag)

    def find_next(self, name=None, attrs={}, text=None, **kwargs):
        """Returns the first item that matches the given criteria and
        appears after this Tag in the document."""
        return self._find_one(self.find_all_next, name, attrs, text, **kwargs)
    findNext = find_next # BS3

    def find_all_next(self, name=None, attrs={}, text=None, limit=None,
                    **kwargs):
        """Returns all items that match the given criteria and appear
        after this Tag in the document."""
        return self._find_all(name, attrs, text, limit, self.next_elements,
                             **kwargs)
    findAllNext = find_all_next # BS3

    def find_next_sibling(self, name=None, attrs={}, text=None, **kwargs):
        """Returns the closest sibling to this Tag that matches the
        given criteria and appears after this Tag in the document."""
        return self._find_one(self.find_next_siblings, name, attrs, text,
                             **kwargs)
    findNextSibling = find_next_sibling # BS3

    def find_next_siblings(self, name=None, attrs={}, text=None, limit=None,
                           **kwargs):
        """Returns the siblings of this Tag that match the given
        criteria and appear after this Tag in the document."""
        return self._find_all(name, attrs, text, limit,
                              self.next_siblings, **kwargs)
    findNextSiblings = find_next_siblings  # BS3
    fetchNextSiblings = find_next_siblings # BS2

    def find_previous(self, name=None, attrs={}, text=None, **kwargs):
        """Returns the first item that matches the given criteria and
        appears before this Tag in the document."""
        return self._find_one(
            self.find_all_previous, name, attrs, text, **kwargs)
    findPrevious = find_previous # BS3

    def find_all_previous(self, name=None, attrs={}, text=None, limit=None,
                        **kwargs):
        """Returns all items that match the given criteria and appear
        before this Tag in the document."""
        return self._find_all(name, attrs, text, limit, self.previous_elements,
                           **kwargs)
    findAllPrevious = find_all_previous # BS3
    fetchPrevious = find_all_previous   # BS2

    def find_previous_sibling(self, name=None, attrs={}, text=None, **kwargs):
        """Returns the closest sibling to this Tag that matches the
        given criteria and appears before this Tag in the document."""
        return self._find_one(self.find_previous_siblings, name, attrs, text,
                             **kwargs)
    findPreviousSibling = find_previous_sibling # BS3

    def find_previous_siblings(self, name=None, attrs={}, text=None,
                               limit=None, **kwargs):
        """Returns the siblings of this Tag that match the given
        criteria and appear before this Tag in the document."""
        return self._find_all(name, attrs, text, limit,
                              self.previous_siblings, **kwargs)
    findPreviousSiblings = find_previous_siblings  # BS3
    fetchPreviousSiblings = find_previous_siblings # BS2

    def find_parent(self, name=None, attrs={}, **kwargs):
        """Returns the closest parent of this Tag that matches the given
        criteria."""
        # NOTE: We can't use _find_one because findParents takes a different
        # set of arguments.
        r = None
        l = self.find_parents(name, attrs, 1)
        if l:
            r = l[0]
        return r
    findParent = find_parent # BS3

    def find_parents(self, name=None, attrs={}, limit=None, **kwargs):
        """Returns the parents of this Tag that match the given
        criteria."""

        return self._find_all(name, attrs, None, limit, self.parents,
                             **kwargs)
    findParents = find_parents  # BS3
    fetchParents = find_parents # BS2

    #These methods do the real heavy lifting.

    def _find_one(self, method, name, attrs, text, **kwargs):
        r = None
        l = method(name, attrs, text, 1, **kwargs)
        if l:
            r = l[0]
        return r

    def _find_all(self, name, attrs, text, limit, generator, **kwargs):
        "Iterates over a generator looking for things that match."

        if isinstance(name, SoupStrainer):
            strainer = name
        elif text is None and not limit and not attrs and not kwargs:
            # findAll*(True)
            if name is True or name is None:
                return [element for element in generator
                        if isinstance(element, Tag)]
            # findAll*('tag-name')
            elif isinstance(name, basestring):
                return [element for element in generator
                        if isinstance(element, Tag) and element.name == name]
            else:
                strainer = SoupStrainer(name, attrs, text, **kwargs)
        else:
            # Build a SoupStrainer
            strainer = SoupStrainer(name, attrs, text, **kwargs)
        results = ResultSet(strainer)
        while True:
            try:
                i = generator.next()
            except StopIteration:
                break
            if i:
                found = strainer.search(i)
                if found:
                    results.append(found)
                    if limit and len(results) >= limit:
                        break
        return results

    #These generators can be used to navigate starting from both
    #NavigableStrings and Tags.
    @property
    def next_elements(self):
        i = self
        while i is not None:
            i = i.next
            yield i

    @property
    def next_siblings(self):
        i = self
        while i is not None:
            i = i.next_sibling
            yield i

    @property
    def previous_elements(self):
        i = self
        while i is not None:
            i = i.previous
            yield i

    @property
    def previous_siblings(self):
        i = self
        while i is not None:
            i = i.previous_sibling
            yield i

    @property
    def parents(self):
        i = self
        while i is not None:
            i = i.parent
            yield i

    # Old non-property versions of the generators, for backwards
    # compatibility with BS3.
    def nextGenerator(self):
        return self.next_elements

    def nextSiblingGenerator(self):
        return self.next_siblings

    def previousGenerator(self):
        return self.previous_elements

    def previousSiblingGenerator(self):
        return self.previous_siblings

    def parentGenerator(self):
        return self.parents

    # Utility methods
    def substitute_encoding(self, str, encoding=None):
        encoding = encoding or "utf-8"
        return str.replace("%SOUP-ENCODING%", encoding)


class NavigableString(unicode, PageElement):

    PREFIX = ''
    SUFFIX = ''

    def __new__(cls, value):
        """Create a new NavigableString.

        When unpickling a NavigableString, this method is called with
        the string in DEFAULT_OUTPUT_ENCODING. That encoding needs to be
        passed in to the superclass's __new__ or the superclass won't know
        how to handle non-ASCII characters.
        """
        if isinstance(value, unicode):
            return unicode.__new__(cls, value)
        return unicode.__new__(cls, value, DEFAULT_OUTPUT_ENCODING)

    def __getnewargs__(self):
        return (unicode(self),)

    def __getattr__(self, attr):
        """text.string gives you text. This is for backwards
        compatibility for Navigable*String, but for CData* it lets you
        get the string without the CData wrapper."""
        if attr == 'string':
            return self
        else:
            raise AttributeError, "'%s' object has no attribute '%s'" % (self.__class__.__name__, attr)

    def output_ready(self, substitute_html_entities=False):
        if substitute_html_entities:
            output = EntitySubstitution.substitute_html(self)
        else:
            output = self
        return self.PREFIX + output + self.SUFFIX


class CData(NavigableString):

    PREFIX = u'<![CDATA['
    SUFFIX = u']]>'


class ProcessingInstruction(NavigableString):

    PREFIX = u'<?'
    SUFFIX = u'?>'


class Comment(NavigableString):

    PREFIX = u'<!--'
    SUFFIX = u'-->'


class Declaration(NavigableString):
    PREFIX = u'<!'
    SUFFIX = u'!>'


class Doctype(NavigableString):

    @classmethod
    def for_name_and_ids(cls, name, pub_id, system_id):
        value = name
        if pub_id is not None:
            value += ' PUBLIC "%s"' % pub_id
        if system_id is not None:
            value += ' SYSTEM "%s"' % system_id

        return Doctype(value)

    PREFIX = u'<!DOCTYPE '
    SUFFIX = u'>'


class Tag(PageElement):

    """Represents a found HTML tag with its attributes and contents."""

    def __init__(self, parser, builder, name, attrs=None, parent=None,
                 previous=None):
        "Basic constructor."

        # We don't actually store the parser object: that lets extracted
        # chunks be garbage-collected.
        self.parser_class = parser.__class__
        self.name = name
        if attrs is None:
            attrs = {}
        else:
            attrs = dict(attrs)
        self.attrs = attrs
        self.contents = []
        self.setup(parent, previous)
        self.hidden = False

        # Set up any substitutions, such as the charset in a META tag.
        self.contains_substitutions = builder.set_up_substitutions(self)

        self.can_be_empty_element = builder.can_be_empty_element(name)

    parserClass = _alias("parser_class") # BS3

    @property
    def is_empty_element(self):
        """Is this tag an empty-element tag? (aka a self-closing tag)

        A tag that has contents is never an empty-element tag.

        A tag that has no contents may or may not be an empty-element
        tag. It depends on the builder used to create the tag. If the
        builder has a designated list of empty-element tags, then only
        a tag whose name shows up in that list is considered an
        empty-element tag.

        If the builder has no designated list of empty-element tags,
        then any tag with no contents is an empty-element tag.
        """
        return len(self.contents) == 0 and self.can_be_empty_element
    isSelfClosing = is_empty_element # BS3


    @property
    def string(self):
        """Convenience property to get the single string within this tag.

        :Return: If this tag has a single string child, return value
         is that string. If this tag has no children, or more than one
         child, return value is None. If this tag has one child tag,
         return value is the 'string' attribute of the child tag,
         recursively.
        """
        if len(self.contents) != 1:
            return None
        child = self.contents[0]
        if isinstance(child, NavigableString):
            return child
        return child.string

    @string.setter
    def string(self, string):
        self.clear()
        self.append(string)

    def get_text(self, separator=u"", strip=False):
        """
        Get all child strings, concatenated using the given separator
        """
        if strip:
            return separator.join(string.strip()
                for string in self.recursive_children
                if isinstance(string, NavigableString) and string.strip())
        else:
            return separator.join(string
                for string in self.recursive_children
                if isinstance(string, NavigableString))
    getText = get_text

    text = property(get_text)

    def decompose(self):
        """Recursively destroys the contents of this tree."""
        self.extract()
        i = self
        while i is not None:
            next = i.next
            i.__dict__.clear()
            i = next

    def clear(self, decompose=False):
        """
        Extract all children. If decompose is True, decompose instead.
        """
        if decompose:
            for element in self.contents[:]:
                if isinstance(element, Tag):
                    element.decompose()
                else:
                    element.extract()
        else:
            for element in self.contents[:]:
                element.extract()

    def index(self, element):
        """
        Find the index of a child by identity, not value. Avoids issues with
        tag.contents.index(element) getting the index of equal elements.
        """
        for i, child in enumerate(self.contents):
            if child is element:
                return i
        raise ValueError("Tag.index: element not in tag")

    def get(self, key, default=None):
        """Returns the value of the 'key' attribute for the tag, or
        the value given for 'default' if it doesn't have that
        attribute."""
        return self.attrs.get(key, default)

    def has_key(self, key):
        return self.attrs.has_key(key)

    def __getitem__(self, key):
        """tag[key] returns the value of the 'key' attribute for the tag,
        and throws an exception if it's not there."""
        return self.attrs[key]

    def __iter__(self):
        "Iterating over a tag iterates over its contents."
        return iter(self.contents)

    def __len__(self):
        "The length of a tag is the length of its list of contents."
        return len(self.contents)

    def __contains__(self, x):
        return x in self.contents

    def __nonzero__(self):
        "A tag is non-None even if it has no contents."
        return True

    def __setitem__(self, key, value):
        """Setting tag[key] sets the value of the 'key' attribute for the
        tag."""
        self.attrs[key] = value

    def __delitem__(self, key):
        "Deleting tag[key] deletes all 'key' attributes for the tag."
        if self.attrs.has_key(key):
            del self.attrs[key]

    def __call__(self, *args, **kwargs):
        """Calling a tag like a function is the same as calling its
        find_all() method. Eg. tag('a') returns a list of all the A tags
        found within this tag."""
        return apply(self.find_all, args, kwargs)

    def __getattr__(self, tag):
        #print "Getattr %s.%s" % (self.__class__, tag)
        if len(tag) > 3 and tag.rfind('Tag') == len(tag)-3: # TODO: Can this be endswith?
            return self.find(tag[:-3])
        elif tag.find('__') != 0: # TODO: Can this be not startswith?
            return self.find(tag)
        raise AttributeError, "'%s' object has no attribute '%s'" % (self.__class__, tag)

    def __eq__(self, other):
        """Returns true iff this tag has the same name, the same attributes,
        and the same contents (recursively) as the given tag."""
        if self is other:
            return True
        if not hasattr(other, 'name') or not hasattr(other, 'attrs') or not hasattr(other, 'contents') or self.name != other.name or self.attrs != other.attrs or len(self) != len(other):
            return False
        for i, my_child in enumerate(self.contents):
            if my_child != other.contents[i]:
                return False
        return True

    def __ne__(self, other):
        """Returns true iff this tag is not identical to the other tag,
        as defined in __eq__."""
        return not self == other

    def __repr__(self, encoding=DEFAULT_OUTPUT_ENCODING):
        """Renders this tag as a string."""
        return self.encode(encoding)

    def __unicode__(self):
        return self.decode()

    def __str__(self):
        return self.encode()

    def encode(self, encoding=DEFAULT_OUTPUT_ENCODING,
               indent_level=None, substitute_html_entities=False):
        return self.decode(indent_level, encoding,
                           substitute_html_entities).encode(encoding)

    def decode(self, indent_level=None,
               eventual_encoding=DEFAULT_OUTPUT_ENCODING,
               substitute_html_entities=False):
        """Returns a Unicode representation of this tag and its contents.

        :param eventual_encoding: The tag is destined to be
           encoded into this encoding. This method is _not_
           responsible for performing that encoding. This information
           is passed in so that it can be substituted in if the
           document contains a <META> tag that mentions the document's
           encoding.
        """
        attrs = []
        if self.attrs:
            for key, val in sorted(self.attrs.items()):
                if val is None:
                    decoded = key
                else:
                    if not isinstance(val, basestring):
                        val = str(val)
                    if (self.contains_substitutions
                        and eventual_encoding is not None
                        and '%SOUP-ENCODING%' in val):
                        val = self.substitute_encoding(val, eventual_encoding)

                    decoded = (key + '='
                               + EntitySubstitution.substitute_xml(val, True))
                attrs.append(decoded)
        close = ''
        closeTag = ''
        if self.is_empty_element:
            close = ' /'
        else:
            closeTag = '</%s>' % self.name

        pretty_print = (indent_level is not None)
        if pretty_print:
            space = (' ' * (indent_level-1))
            indent_contents = indent_level + 1
        else:
            space = ''
            indent_contents = None
        contents = self.decode_contents(
            indent_contents, eventual_encoding, substitute_html_entities)

        if self.hidden:
            # This is the 'document root' object.
            s = contents
        else:
            s = []
            attribute_string = ''
            if attrs:
                attribute_string = ' ' + ' '.join(attrs)
            if pretty_print:
                s.append(space)
            s.append('<%s%s%s>' % (self.name, attribute_string, close))
            if pretty_print:
                s.append("\n")
            s.append(contents)
            if pretty_print and contents and contents[-1] != "\n":
                s.append("\n")
            if pretty_print and closeTag:
                s.append(space)
            s.append(closeTag)
            if pretty_print and closeTag and self.next_sibling:
                s.append("\n")
            s = ''.join(s)
        return s

    def prettify(self, encoding=DEFAULT_OUTPUT_ENCODING):
        return self.encode(encoding, True)

    def decode_contents(self, indent_level=None,
                       eventual_encoding=DEFAULT_OUTPUT_ENCODING,
                       substitute_html_entities=False):
        """Renders the contents of this tag as a Unicode string.

        :param eventual_encoding: The tag is destined to be
           encoded into this encoding. This method is _not_
           responsible for performing that encoding. This information
           is passed in so that it can be substituted in if the
           document contains a <META> tag that mentions the document's
           encoding.
        """
        pretty_print = (indent_level is not None)
        s=[]
        for c in self:
            text = None
            if isinstance(c, NavigableString):
                text = c.output_ready(substitute_html_entities)
            elif isinstance(c, Tag):
                s.append(c.decode(indent_level, eventual_encoding,
                                  substitute_html_entities))
            if text and indent_level:
                text = text.strip()
            if text:
                if pretty_print:
                    s.append(" " * (indent_level-1))
                s.append(text)
                if pretty_print:
                    s.append("\n")
        return ''.join(s)

    #Soup methods

    def find(self, name=None, attrs={}, recursive=True, text=None,
             **kwargs):
        """Return only the first child of this Tag matching the given
        criteria."""
        r = None
        l = self.find_all(name, attrs, recursive, text, 1, **kwargs)
        if l:
            r = l[0]
        return r
    findChild = find

    def find_all(self, name=None, attrs={}, recursive=True, text=None,
                 limit=None, **kwargs):
        """Extracts a list of Tag objects that match the given
        criteria.  You can specify the name of the Tag and any
        attributes you want the Tag to have.

        The value of a key-value pair in the 'attrs' map can be a
        string, a list of strings, a regular expression object, or a
        callable that takes a string and returns whether or not the
        string matches for some custom definition of 'matches'. The
        same is true of the tag name."""
        generator = self.recursive_children
        if not recursive:
            generator = self.children
        return self._find_all(name, attrs, text, limit, generator, **kwargs)
    findAll = find_all      # BS3
    findChildren = find_all # BS2

    #Generator methods
    @property
    def children(self):
        # return iter() to make the purpose of the method clear
        return iter(self.contents) # XXX This seems to be untested.

    @property
    def recursive_children(self):
        if not len(self.contents):
            return
        stopNode = self._last_recursive_child().next
        current = self.contents[0]
        while current is not stopNode:
            yield current
            current = current.next

    # Old names for backwards compatibility
    def childGenerator(self):
        return self.children

    def recursiveChildGenerator(self):
        return self.recursive_children


# Next, a couple classes to represent queries and their results.
class SoupStrainer(object):
    """Encapsulates a number of ways of matching a markup element (tag or
    text)."""

    def __init__(self, name=None, attrs={}, text=None, **kwargs):
        self.name = name
        if isinstance(attrs, basestring):
            kwargs['class'] = _match_css_class(attrs)
            attrs = None
        if kwargs:
            if attrs:
                attrs = attrs.copy()
                attrs.update(kwargs)
            else:
                attrs = kwargs
        self.attrs = attrs
        self.text = text

    def __str__(self):
        if self.text:
            return self.text
        else:
            return "%s|%s" % (self.name, self.attrs)

    def search_tag(self, markup_name=None, markup_attrs={}):
        found = None
        markup = None
        if isinstance(markup_name, Tag):
            markup = markup_name
            markup_attrs = markup
        call_function_with_tag_data = callable(self.name) \
                                and not isinstance(markup_name, Tag)

        if (not self.name) \
               or call_function_with_tag_data \
               or (markup and self._matches(markup, self.name)) \
               or (not markup and self._matches(markup_name, self.name)):
            if call_function_with_tag_data:
                match = self.name(markup_name, markup_attrs)
            else:
                match = True
                markup_attr_map = None
                for attr, match_against in self.attrs.items():
                    if not markup_attr_map:
                         if hasattr(markup_attrs, 'get'):
                            markup_attr_map = markup_attrs
                         else:
                            markup_attr_map = {}
                            for k,v in markup_attrs:
                                markup_attr_map[k] = v
                    attr_value = markup_attr_map.get(attr)
                    if not self._matches(attr_value, match_against):
                        match = False
                        break
            if match:
                if markup:
                    found = markup
                else:
                    found = markup_name
        return found
    searchTag = search_tag

    def search(self, markup):
        #print 'looking for %s in %s' % (self, markup)
        found = None
        # If given a list of items, scan it for a text element that
        # matches.
        if isList(markup) and not isinstance(markup, Tag):
            for element in markup:
                if isinstance(element, NavigableString) \
                       and self.search(element):
                    found = element
                    break
        # If it's a Tag, make sure its name or attributes match.
        # Don't bother with Tags if we're searching for text.
        elif isinstance(markup, Tag):
            if not self.text:
                found = self.search_tag(markup)
        # If it's text, make sure the text matches.
        elif isinstance(markup, NavigableString) or \
                 isinstance(markup, basestring):
            if self._matches(markup, self.text):
                found = markup
        else:
            raise Exception, "I don't know how to match against a %s" \
                  % markup.__class__
        return found

    def _matches(self, markup, match_against):
        #print "Matching %s against %s" % (markup, match_against)
        result = False
        if match_against is True:
            result = markup is not None
        elif callable(match_against):
            result = match_against(markup)
        else:
            #Custom match methods take the tag as an argument, but all
            #other ways of matching match the tag name as a string.
            if isinstance(markup, Tag):
                markup = markup.name
            if markup is not None and not isinstance(markup, basestring):
                markup = unicode(markup)
            #Now we know that chunk is either a string, or None.
            if hasattr(match_against, 'match'):
                # It's a regexp object.
                result = markup and match_against.search(markup)
            elif (isList(match_against)
                  and (markup is not None
                       or not isinstance(match_against, basestring))):
                result = markup in match_against
            elif hasattr(match_against, 'items'):
                result = match_against in markup
            elif match_against and isinstance(markup, basestring):
                if isinstance(markup, unicode):
                    match_against = unicode(match_against)
                else:
                    match_against = str(match_against)

            if not result:
                result = match_against == markup
        return result


class ResultSet(list):
    """A ResultSet is just a list that keeps track of the SoupStrainer
    that created it."""
    def __init__(self, source):
        list.__init__([])
        self.source = source