path: root/markdown.py

#!/usr/bin/env python
"""
Python Markdown
===============

Python Markdown converts Markdown to HTML and can be used as a library or
called from the command line.

## Basic usage as a module:

    import markdown
    md = Markdown()
    html = md.convert(your_text_string)

## Basic use from the command line:

    python markdown.py source.txt > destination.html

Run "python markdown.py --help" to see more options.

## Extensions

See <http://www.freewisdom.org/projects/python-markdown/> for more
information and instructions on how to extend the functionality of
Python Markdown.  Read that before you try modifying this file.

## Authors and License

Started by [Manfred Stienstra](http://www.dwerg.net/).  Continued and
maintained  by [Yuri Takhteyev](http://www.freewisdom.org), [Waylan
Limberg](http://achinghead.com/) and [Artem Yunusov](http://blog.splyer.com).

Contact: markdown@freewisdom.org

Copyright 2007, 2008 The Python Markdown Project (v. 1.7 and later)
Copyright 2007 Benjamin C. Wilson (Treap implementation)
Copyright 2004, 2005, 2006 Yuri Takhteyev (v. 0.2-1.6b)
Copyright 2004 Manfred Stienstra (the original version)

License: BSD (see docs/LICENSE for details).
"""

version = "2.0-alpha"
version_info = (2,0,0, "beta")

import re
import sys
import codecs
import htmlentitydefs
import logging
from logging import DEBUG, INFO, WARN, ERROR, CRITICAL
from urlparse import urlparse, urlunparse


"""
CONSTANTS
=============================================================================
"""

"""
Constants you might want to modify
-----------------------------------------------------------------------------
"""

# default logging level for command-line use
COMMAND_LINE_LOGGING_LEVEL = CRITICAL
TAB_LENGTH = 4               # expand tabs to this many spaces
ENABLE_ATTRIBUTES = True     # @id = xyz -> <... id="xyz">
SMART_EMPHASIS = True        # this_or_that does not become this<i>or</i>that
HTML_REMOVED_TEXT = "[HTML_REMOVED]" # text used instead of HTML in safe mode
BLOCK_LEVEL_ELEMENTS = re.compile("p|div|h[1-6]|blockquote|pre|table|dl|ol|ul"
                                  +"|script|noscript|form|fieldset|iframe|math"
                                  +"|ins|del|hr|hr/|style|li|tr")

"""
Constants you probably do not need to change
-----------------------------------------------------------------------------
"""

RTL_BIDI_RANGES = ( (u'\u0590', u'\u07FF'),
                     # Hebrew (0590-05FF), Arabic (0600-06FF),
                     # Syriac (0700-074F), Arabic supplement (0750-077F),
                     # Thaana (0780-07BF), Nko (07C0-07FF).
                    (u'\u2D30', u'\u2D7F'), # Tifinagh
                    )

EXECUTABLE_NAME_FOR_USAGE = "python markdown.py"
""" The name used in the usage statement displayed for python versions < 2.3.
(With python 2.3 and higher the usage statement is generated by optparse
and uses the actual name of the executable called.) """

# Placeholders
STX = u'\u0002'  # Use STX ("Start of text") for start-of-placeholder
ETX = u'\u0003'  # Use ETX ("End of text") for end-of-placeholder
HTML_PLACEHOLDER_PREFIX = STX+"wzxhzdk:"
HTML_PLACEHOLDER = HTML_PLACEHOLDER_PREFIX + "%d" + ETX
INLINE_PLACEHOLDER_PREFIX = STX+"klzzwxh:"
INLINE_PLACEHOLDER = INLINE_PLACEHOLDER_PREFIX + "%s" + ETX
AMP_SUBSTITUTE = STX+"amp"+ETX

def wrapRe(raw_re) : return re.compile("^%s$" % raw_re, re.DOTALL)
CORE_RE = {
    'header':          wrapRe(r'(#{1,6})[ \t]*(.*?)[ \t]*(#*)'), # # A title
    'reference-def':   wrapRe(r'(\ ?\ ?\ ?)\[([^\]]*)\]:\s*([^ ]*)(.*)'),
                               # [Google]: http://www.google.com/
    'containsline':    wrapRe(r'([-]*)$|^([=]*)'), # -----, =====, etc.
    'ol':              wrapRe(r'[ ]{0,3}[\d]*\.\s+(.*)'), # 1. text
    'ul':              wrapRe(r'[ ]{0,3}[*+-]\s+(.*)'), # "* text"
    'isline1':         wrapRe(r'(\**)'), # ***
    'isline2':         wrapRe(r'(\-*)'), # ---
    'isline3':         wrapRe(r'(\_*)'), # ___
    'tabbed':          wrapRe(r'((\t)|(    ))(.*)'), # an indented line
    'quoted':          wrapRe(r'[ ]{0,2}> ?(.*)'), # a quoted block ("> ...")
    'containsline':    re.compile(r'^([-]*)$|^([=]*)$', re.M),
    'attr':            re.compile("\{@([^\}]*)=([^\}]*)}") # {@id=123}
}
"""Basic and reusable regular expressions."""


"""
AUXILIARY GLOBAL FUNCTIONS
=============================================================================
"""

def message(level, text):
    """ A wrapper method for logging debug messages. """
    logging.getLogger('MARKDOWN').log(level, text)

def isString(s):
    """ Check if it's string """
    return isinstance(s, unicode) or isinstance(s, str)

## Import
def importETree():
    """Import the best implementation of ElementTree, return a module object."""
    etree_in_c = None
    try: # Is it Python 2.5+ with C implemenation of ElementTree installed?
        import xml.etree.cElementTree as etree_in_c
    except ImportError:
        try: # Is it Python 2.5+ with Python implementation of ElementTree?
            import xml.etree.ElementTree as etree
        except ImportError:
            try: # An earlier version of Python with cElementTree installed?
                import cElementTree as etree_in_c
            except ImportError:
                try: # An earlier version of Python with Python ElementTree?
                    import elementtree.ElementTree as etree
                except ImportError:
                    message(CRITICAL, "Failed to import ElementTree")
                    sys.exit(1)
    if etree_in_c and etree_in_c.VERSION < "1.0":
        message(CRITICAL, "For cElementTree version 1.0 or higher is required.")
        sys.exit(1)
    elif etree_in_c :
        return etree_in_c
    elif etree.VERSION < "1.1":
        message(CRITICAL, "For ElementTree version 1.1 or higher is required")
        sys.exit(1)
    else :
        return etree

def isBlockLevel(tag):
    """Check if the tag is a block level HTML tag."""
    return BLOCK_LEVEL_ELEMENTS.match(tag)

def handleAttributes(text, parent):
    """Set values of an element based on attribute definitions ({@id=123})."""
    def attributeCallback(match):
        parent.set(match.group(1), match.group(2))
    return CORE_RE['attr'].sub(attributeCallback, text)

def dequote(string):
    """Remove quotes from around a string."""
    if ( ( string.startswith('"') and string.endswith('"'))
         or (string.startswith("'") and string.endswith("'")) ):
        return string[1:-1]
    else:
        return string


"""
OVERALL DESIGN
=============================================================================

Markdown processing takes place in three steps:

1. A bunch of "preprocessors" munge the input text.
2. MarkdownParser() parses the high-level structural elements of the
   pre-processed text into an ElementTree.
3. A bunch of Patterns are run against the ElementTree, detecting inline
   markup.
4. Some extra use-defined post-processors are run.
5. The output is written to a string.

Those steps are put together by the Markdown() class.

The code below is organized as follows:

1. MarkdownParser class - does basic parsing.
2. All the post-processors, patterns, etc.
3. Markdown class - does the high-level wrapping.
"""


"""
CORE MARKDOWN PARSER
=============================================================================

This class handles basic Markdown parsing.  It doesn't concern itself with
inline elements such as **bold** or *italics*, but rather just catches blocks,
lists, quotes, etc.
"""

class MarkdownParser:
    """Parser Markdown into a ElementTree."""

    def __init__(self):
        pass

    def parseDocument(self, lines):
        """Parse a markdown string into an ElementTree."""
        # Create a ElementTree from the lines
        root = etree.Element("div")
        buffer = []
        for line in lines:
            if line.startswith("#"):
                self.parseChunk(root, buffer)
                buffer = [line]
            else:
                buffer.append(line)

        self.parseChunk(root, buffer)

        return etree.ElementTree(root)

    def parseChunk(self, parent_elem, lines, inList=0, looseList=0):
        """Process a chunk of markdown-formatted text and attach the parse to
        an ElementTree node.

        Process a section of a source document, looking for high
        level structural elements like lists, block quotes, code
        segments, html blocks, etc.  Some those then get stripped
        of their high level markup (e.g. get unindented) and the
        lower-level markup is processed recursively.

        Keyword arguments:

        * parent_elem: The ElementTree element to which the content will be
                       added.
        * lines: a list of lines
        * inList: a level

        Returns: None

        """
        # Loop through lines until none left.
        while lines:
            # Skipping empty line
            if not lines[0]:
                lines = lines[1:]
                continue

            # Check if this section starts with a list, a blockquote or
            # a code block.  If so, process them.
            processFn = { 'ul':     self.__processUList,
                          'ol':     self.__processOList,
                          'quoted': self.__processQuote,
                          'tabbed': self.__processCodeBlock}
            for regexp in ['ul', 'ol', 'quoted', 'tabbed']:
                m = CORE_RE[regexp].match(lines[0])
                if m:
                    processFn[regexp](parent_elem, lines, inList)
                    return

            # We are NOT looking at one of the high-level structures like
            # lists or blockquotes.  So, it's just a regular paragraph
            # (though perhaps nested inside a list or something else).  If
            # we are NOT inside a list, we just need to look for a blank
            # line to find the end of the block.  If we ARE inside a
            # list, however, we need to consider that a sublist does not
            # need to be separated by a blank line.  Rather, the following
            # markup is legal:
            #
            # * The top level list item
            #
            #     Another paragraph of the list.  This is where we are now.
            #     * Underneath we might have a sublist.
            #

            if inList:
                start, lines  = self.__linesUntil(lines, (lambda line:
                                 CORE_RE['ul'].match(line)
                                 or CORE_RE['ol'].match(line)
                                                  or not line.strip()))
                self.parseChunk(parent_elem, start, inList-1,
                                looseList=looseList)
                inList = inList-1

            else: # Ok, so it's just a simple block
                test = lambda line: not line.strip() or line[0] == '>'
                paragraph, lines = self.__linesUntil(lines, test)
                if len(paragraph) and paragraph[0].startswith('#'):
                    self.__processHeader(parent_elem, paragraph)
                elif len(paragraph) and CORE_RE["isline3"].match(paragraph[0]):
                    self.__processHR(parent_elem)
                    lines = paragraph[1:] + lines
                elif paragraph:
                    self.__processParagraph(parent_elem, paragraph,
                                          inList, looseList)

            if lines and not lines[0].strip():
                lines = lines[1:]  # skip the first (blank) line

    def __processHR(self, parentElem):
        hr = etree.SubElement(parentElem, "hr")

    def __processHeader(self, parentElem, paragraph):
        m = CORE_RE['header'].match(paragraph[0])
        if m:
            level = len(m.group(1))
            h = etree.SubElement(parentElem, "h%d" % level)
            h.text = m.group(2).strip()
        else:
            message(CRITICAL, "We've got a problem header!")

    def __processParagraph(self, parentElem, paragraph, inList, looseList):

        if ( parentElem.tag == 'li'
                and not (looseList or parentElem.getchildren())):

            # If this is the first paragraph inside "li", don't
            # put <p> around it - append the paragraph bits directly
            # onto parentElem
            el = parentElem
        else:
            # Otherwise make a "p" element
            el = etree.SubElement(parentElem, "p")

        dump = []

        # Searching for hr or header
        for line in paragraph:
            # it's hr
            if CORE_RE["isline3"].match(line):
                el.text = "\n".join(dump)
                self.__processHR(el)
                dump = []
            # it's header
            elif line.startswith("#"):
                el.text = "\n".join(dump)
                self.__processHeader(parentElem, [line])
                dump = []
            else:
                dump.append(line)
        if dump:
            text = "\n".join(dump)
            el.text = text

    def __processUList(self, parentElem, lines, inList):
        self.__processList(parentElem, lines, inList, listexpr='ul', tag='ul')

    def __processOList(self, parentElem, lines, inList):
        self.__processList(parentElem, lines, inList, listexpr='ol', tag='ol')

    def __processList(self, parentElem, lines, inList, listexpr, tag):
        """
        Given a list of document lines starting with a list item,
        finds the end of the list, breaks it up, and recursively
        processes each list item and the remainder of the text file.

        Keyword arguments:

        * parentElem: A ElementTree element to which the content will be added
        * lines: a list of lines
        * inList: a level

        Returns: None

        """
        ul = etree.SubElement(parentElem, tag) # ul might actually be '<ol>'

        looseList = 0

        # Make a list of list items
        items = []
        item = -1

        i = 0  # a counter to keep track of where we are
        for line in lines:
            loose = 0
            if not line.strip():
                # If we see a blank line, this _might_ be the end of the list
                i += 1
                loose = 1

                # Find the next non-blank line
                for j in range(i, len(lines)):
                    if lines[j].strip():
                        next = lines[j]
                        break
                else:
                    # There is no more text => end of the list
                    break

                # Check if the next non-blank line is still a part of the list

                if ( CORE_RE[listexpr].match(next) or
                     CORE_RE['tabbed'].match(next) ):
                    # get rid of any white space in the line
                    items[item].append(line.strip())
                    looseList = loose or looseList
                    continue
                else:
                    break # found end of the list

            # Now we need to detect list items (at the current level)
            # while also detabing child elements if necessary

            for expr in ['ul', 'ol', 'tabbed']:
                m = CORE_RE[expr].match(line)
                if m:
                    if expr in ['ul', 'ol']:  # We are looking at a new item
                        #if m.group(1) :
                        # Removed the check to allow for a blank line
                        # at the beginning of the list item
                        items.append([m.group(1)])
                        item += 1
                    elif expr == 'tabbed':  # This line needs to be detabbed
                        items[item].append(m.group(4)) #after the 'tab'
                    i += 1
                    break
            else:
                items[item].append(line)  # Just regular continuation
                i += 1 # added on 2006.02.25
        else:
            i += 1

        # Add the ElementTree elements
        for item in items:
            li = etree.SubElement(ul, "li")
            self.parseChunk(li, item, inList + 1, looseList = looseList)

        # Process the remaining part of the section
        self.parseChunk(parentElem, lines[i:], inList)

    def __linesUntil(self, lines, condition):
        """
        A utility function to break a list of lines upon the
        first line that satisfied a condition.  The condition
        argument should be a predicate function.

        """
        i = -1
        for line in lines:
            i += 1
            if condition(line):
                break
        else:
            i += 1
        return lines[:i], lines[i:]

    def __processQuote(self, parentElem, lines, inList):
        """
        Given a list of document lines starting with a quote finds
        the end of the quote, unindents it and recursively
        processes the body of the quote and the remainder of the
        text file.

        Keyword arguments:

        * parentElem: ElementTree element to which the content will be added
        * lines: a list of lines
        * inList: a level

        Returns: None

        """
        dequoted = []
        i = 0
        blank_line = False # allow one blank line between paragraphs
        for line in lines:
            m = CORE_RE['quoted'].match(line)
            if m:
                dequoted.append(m.group(1))
                i += 1
                blank_line = False
            elif not blank_line and line.strip() != '':
                dequoted.append(line)
                i += 1
            elif not blank_line and line.strip() == '':
                dequoted.append(line)
                i += 1
                blank_line = True
            else:
                break

        blockquote = etree.SubElement(parentElem, "blockquote")

        self.parseChunk(blockquote, dequoted, inList)
        self.parseChunk(parentElem, lines[i:], inList)

    def __processCodeBlock(self, parentElem, lines, inList):
        """
        Given a list of document lines starting with a code block
        finds the end of the block, puts it into the ElementTree verbatim
        wrapped in ("<pre><code>") and recursively processes the
        the remainder of the text file.

        Keyword arguments:

        * parentElem: ElementTree element to which the content will be added
        * lines: a list of lines
        * inList: a level

        Returns: None

        """
        detabbed, theRest = self.detectTabbed(lines)
        pre = etree.SubElement(parentElem, "pre")
        code = etree.SubElement(pre, "code")
        text = "\n".join(detabbed).rstrip()+"\n"
        code.text = AtomicString(text)
        self.parseChunk(parentElem, theRest, inList)

    def detectTabbed(self, lines):
        """ Find indented text and remove indent before further proccesing.

        Keyword arguments:

        * lines: an array of strings
        * fn: a function that returns a substring of a string
           if the string matches the necessary criteria

        Returns: a list of post processes items and the unused
        remainder of the original list

        """
        items = []
        item = -1
        i = 0 # to keep track of where we are

        def detab(line):
            match = CORE_RE['tabbed'].match(line)
            if match:
               return match.group(4)

        for line in lines:
            if line.strip(): # Non-blank line
                line = detab(line)
                if line:
                    items.append(line)
                    i += 1
                    continue
                else:
                    return items, lines[i:]

            else: # Blank line: _maybe_ we are done.
                i += 1 # advance

                # Find the next non-blank line
                for j in range(i, len(lines)):
                    if lines[j].strip():
                        next_line = lines[j]; break
                else:
                    break # There is no more text; we are done.

                # Check if the next non-blank line is tabbed
                if detab(next_line): # Yes, more work to do.
                    items.append("")
                    continue
                else:
                    break # No, we are done.
        else:
            i += 1

        return items, lines[i:]


"""
INLINE PROCESSOR
=============================================================================

This class handles basic Markdown parsing.  It doesn't concern itself with
inline elements such as **bold** or *italics*, but rather just catches blocks,
lists, quotes, etc.
"""

class InlineProcessor:
    """
    An auxiliary class to traverse a Markdown tree, applying inline patterns.
    """

    def __init__ (self, patterns):
        self.__inlinePatterns = patterns
        self.__placeholder_prefix = INLINE_PLACEHOLDER_PREFIX
        self.__placeholder_suffix = ETX
        self.__placeholder_length = 4 + len(self.__placeholder_prefix) \
                                      + len(self.__placeholder_suffix)
        self.__placeholder_re = re.compile(INLINE_PLACEHOLDER % r'([0-9]{4})')

    def __makePlaceholder(self, type):
        """ Generate a placeholder """
        id = "%04d" % len(self.stashed_nodes)
        hash = INLINE_PLACEHOLDER % id
        return hash, id

    def __findPlaceholder(self, data, index):
        """
        Extract id from data string, start from index

        Keyword arguments:

        * data: string
        * index: index, from which we start search

        Returns: placeholder id and string index, after the found placeholder.
        """

        m = self.__placeholder_re.search(data, index)
        if m:
            return m.group(1), m.end()
        else:
            return None, index + 1

    def __stashNode(self, node, type):
        """ Add node to stash """
        placeholder, id = self.__makePlaceholder(type)
        self.stashed_nodes[id] = node
        return placeholder

    def __handleInline(self, data, patternIndex=0):
        """
        Process string with inline patterns and replace it
        with placeholders

        Keyword arguments:

        * data: A line of Markdown text
        * patternIndex: The index of the inlinePattern to start with

        Returns: String with placeholders.

        """
        if not isinstance(data, AtomicString):
            startIndex = 0
            while patternIndex < len(self.__inlinePatterns):
                data, matched, startIndex = self.__applyPattern(
                                                 self.__inlinePatterns[patternIndex],
                                                 data, patternIndex, startIndex)
                if not matched:
                    patternIndex += 1
        return data

    def __processElementText(self, node, subnode, isText=True):
        """
        Process placeholders in Element.text or Element.tail
        of Elements popped from self.stashed_nodes.

        Keywords arguments:

        * node: parent node
        * subnode: processing node
        * isText: bool variable, True - it's text, False - it's tail

        Returns: None

        """
        if isText:
            text = subnode.text
            subnode.text = None
        else:
            text = subnode.tail
            subnode.tail = None

        childResult = self.__processPlaceholders(text, subnode)

        if not isText and node is not subnode:
            pos = node.getchildren().index(subnode)
            node.remove(subnode)
        else:
            pos = 0

        childResult.reverse()
        for newChild in childResult:
            node.insert(pos, newChild)

    def __processPlaceholders(self, data, parent):
        """
        Process string with placeholders and generate ElementTree tree.

        Keyword arguments:

        * data: string with placeholders instead of ElementTree elements.
        * parent: Element, which contains processing inline data

        Returns: list with ElementTree elements with applied inline patterns.
        """
        def linkText(text):
            if text:
                if result:
                    if result[-1].tail:
                        result[-1].tail += text
                    else:
                        result[-1].tail = text
                else:
                    if parent.text:
                        parent.text += text
                    else:
                        parent.text = text

        result = []
        strartIndex = 0
        while data:
            index = data.find(self.__placeholder_prefix, strartIndex)
            if index != -1:
                id, phEndIndex = self.__findPlaceholder(data, index)

                if self.stashed_nodes.has_key(id):
                    node = self.stashed_nodes.get(id)

                    if index > 0:
                        text = data[strartIndex:index]
                        linkText(text)

                    if not isString(node): # it's Element
                        for child in [node] + node.getchildren():
                            if child.tail:
                                if child.tail.strip():
                                    self.__processElementText(node, child, False)
                            if child.text:
                                if child.text.strip():
                                    self.__processElementText(child, child)
                    else: # it's just a string
                        linkText(node)
                        strartIndex = phEndIndex
                        continue

                    strartIndex = phEndIndex
                    result.append(node)

                else: # wrong placeholder
                    end = index + len(prefix)
                    linkText(data[strartIndex:end])
                    strartIndex = end
            else:
                text = data[strartIndex:]
                linkText(text)
                data = ""

        return result

    def __applyPattern(self, pattern, data, patternIndex, startIndex=0):
        """
        Check if the line fits the pattern, create the necessary
        elements, add it to stashed_nodes.

        Keyword arguments:

        * data: the text to be processed
        * pattern: the pattern to be checked
        * patternIndex: index of current pattern
        * startIndex: string index, from which we starting search

        Returns: String with placeholders instead of ElementTree elements.

        """
        match = pattern.getCompiledRegExp().match(data[startIndex:])
        leftData = data[:startIndex]

        if not match:
            return data, False, 0

        node = pattern.handleMatch(match)

        if node is None:
            return data, True, len(leftData) + match.span(len(match.groups()))[0]

        if not isString(node):
            if not isinstance(node.text, AtomicString):
                # We need to process current node too
                for child in [node] + node.getchildren():
                    if not isString(node):
                        if child.text:
                            child.text = self.__handleInline(child.text,
                                                            patternIndex + 1)
                        if child.tail:
                            child.tail = self.__handleInline(child.tail,
                                                            patternIndex)

        placeholder = self.__stashNode(node, pattern.type())

        return "%s%s%s%s" % (leftData,
                             match.group(1),
                             placeholder, match.groups()[-1]), True, 0

    def applyInlinePatterns(self, markdownTree):
        """Apply inline patterns to a parsed Markdown tree.

        Iterate over ElementTree, find elements with inline tag, apply inline
        patterns and append newly created Elements to tree.  If you don't
        want process your data with inline paterns, instead of normal string,
        use subclass AtomicString:

            node.text = AtomicString("data won't be processed with inline patterns")

        Arguments:

        * markdownTree: ElementTree object, representing Markdown tree.

        Returns: ElementTree object with applied inline patterns.

        """
        self.stashed_nodes = {}

        stack = [markdownTree.getroot()]

        while stack:
            currElement = stack.pop()
            insertQueue = []
            for child in currElement.getchildren():
                if child.text and not isinstance(child.text, AtomicString):
                    text = child.text
                    child.text = None
                    lst = self.__processPlaceholders(self.__handleInline(
                                                    text), child)
                    stack += lst
                    insertQueue.append((child, lst))

                if child.getchildren():
                    stack.append(child)

            for element, lst in insertQueue:
                if element.text:
                    element.text = handleAttributes(element.text, element)
                i = 0
                for newChild in lst:
                    # Processing attributes
                    if newChild.tail:
                        newChild.tail = handleAttributes(newChild.tail,
                                                         element)
                    if newChild.text:
                        newChild.text = handleAttributes(newChild.text,
                                                         newChild)
                    element.insert(i, newChild)
                    i += 1

        return markdownTree


"""
PRE-PROCESSORS
=============================================================================

Preprocessors work on source text before we start doing anything too
complicated.  There are two types of preprocessors: TextPreprocessor and
Preprocessor.
"""

class Processor:
    def __init__(self, markdown_instance=None):
        if markdown_instance:
            self.markdown = markdown_instance

class TextPreprocessor (Processor):
    """
    TextPreprocessors are run before the text is broken into lines.

    Each TextPreprocessor implements a "run" method that takes a pointer to a
    text string of the document, modifies it as necessary and returns
    either the same pointer or a pointer to a new string.

    TextPreprocessors must extend markdown.TextPreprocessor.

    """

    def run(self, text):
        """
        Each subclass of TextPreprocessor should override the `run` method,
        which takes the document text as a single string and returns the
        (possibly modified) document as a single string.

        """
        pass


class Preprocessor (Processor):
    """
    Preprocessors are run after the text is broken into lines.

    Each preprocessor implements a "run" method that takes a pointer to a
    list of lines of the document, modifies it as necessary and returns
    either the same pointer or a pointer to a new list.

    Preprocessors must extend markdown.Preprocessor.

    """
    def run(self, lines):
        """
        Each subclass of Preprocessor should override the `run` method, which
        takes the document as a list of strings split by newlines and returns
        the (possibly modified) list of lines.

        """
        pass


class HtmlBlockPreprocessor(TextPreprocessor):
    """Remove html blocks from the text and store them for later retrieval."""

    right_tag_patterns = ["</%s>", "%s>"]

    def _get_left_tag(self, block):
        return block[1:].replace(">", " ", 1).split()[0].lower()

    def _get_right_tag(self, left_tag, block):
        for p in self.right_tag_patterns:
            tag = p % left_tag
            i = block.rfind(tag)
            if i > 2:
                return tag.lstrip("<").rstrip(">"), i + len(p)-2 + len(left_tag)
        return block.rstrip()[-len(left_tag)-2:-1].lower(), len(block)

    def _equal_tags(self, left_tag, right_tag):
        if left_tag == 'div' or left_tag[0] in ['?', '@', '%']: # handle PHP, etc.
            return True
        if ("/" + left_tag) == right_tag:
            return True
        if (right_tag == "--" and left_tag == "--"):
            return True
        elif left_tag == right_tag[1:] \
            and right_tag[0] != "<":
            return True
        else:
            return False

    def _is_oneliner(self, tag):
        return (tag in ['hr', 'hr/'])

    def run(self, text):
        new_blocks = []
        text = text.split("\n\n")
        items = []
        left_tag = ''
        right_tag = ''
        in_tag = False # flag

        while text:
            block = text[0]
            if block.startswith("\n"):
                block = block[1:]
            text = text[1:]

            if block.startswith("\n"):
                block = block[1:]

            if not in_tag:
                if block.startswith("<"):
                    left_tag = self._get_left_tag(block)
                    right_tag, data_index = self._get_right_tag(left_tag, block)

                    if data_index < len(block):
                        text.insert(0, block[data_index:])
                        block = block[:data_index]

                    if not (isBlockLevel(left_tag) \
                        or block[1] in ["!", "?", "@", "%"]):
                        new_blocks.append(block)
                        continue

                    if self._is_oneliner(left_tag):
                        new_blocks.append(block.strip())
                        continue

                    if block[1] == "!":
                        # is a comment block
                        left_tag = "--"
                        right_tag, data_index = self._get_right_tag(left_tag, block)
                        # keep checking conditions below and maybe just append

                    if block.rstrip().endswith(">") \
                        and self._equal_tags(left_tag, right_tag):
                        new_blocks.append(
                            self.markdown.htmlStash.store(block.strip()))
                        continue
                    else: #if not block[1] == "!":
                        # if is block level tag and is not complete

                        if isBlockLevel(left_tag) or left_tag == "--" \
                        and not block.rstrip().endswith(">"):
                            items.append(block.strip())
                            in_tag = True
                        else:
                            new_blocks.append(
                            self.markdown.htmlStash.store(block.strip()))

                        continue

                new_blocks.append(block)

            else:
                items.append(block.strip())

                right_tag, data_index = self._get_right_tag(left_tag, block)

                if self._equal_tags(left_tag, right_tag):
                    # if find closing tag
                    in_tag = False
                    new_blocks.append(
                        self.markdown.htmlStash.store('\n\n'.join(items)))
                    items = []

        if items:
            new_blocks.append(self.markdown.htmlStash.store('\n\n'.join(items)))
            new_blocks.append('\n')

        return "\n\n".join(new_blocks)


class HeaderPreprocessor(Preprocessor):

    """Replace underlined headers with hashed headers.

    (To avoid the need for lookahead later.)

    """

    def run (self, lines):
        i = -1
        while i+1 < len(lines):
            i = i+1
            if not lines[i].strip():
                continue

            if lines[i].startswith("#"):
                lines.insert(i+1, "\n")

            if (i+1 <= len(lines)
                  and lines[i+1]
                  and lines[i+1][0] in ['-', '=']):

                underline = lines[i+1].strip()

                if underline == "="*len(underline):
                    lines[i] = "# " + lines[i].strip()
                    lines[i+1] = ""
                elif underline == "-"*len(underline):
                    lines[i] = "## " + lines[i].strip()
                    lines[i+1] = ""

        return lines


class LinePreprocessor(Preprocessor):
    """Convert HR lines to "___" format."""
    blockquote_re = re.compile(r'^(> )+')

    def run (self, lines):
        for i in range(len(lines)):
            prefix = ''
            m = self.blockquote_re.search(lines[i])
            if m:
                prefix = m.group(0)
            if self._isLine(lines[i][len(prefix):]):
                lines[i] = prefix + "___"
        return lines

    def _isLine(self, block):
        """Determine if a block should be replaced with an <HR>"""
        if block.startswith("    "):
            return False  # a code block
        text = "".join([x for x in block if not x.isspace()])
        if len(text) <= 2:
            return False
        for pattern in ['isline1', 'isline2', 'isline3']:
            m = CORE_RE[pattern].match(text)
            if (m and m.group(1)):
                return True
        else:
            return False


class ReferencePreprocessor(Preprocessor):
    """Remove reference definitions from the text and store them for later use."""
    def run (self, lines):
        new_text = [];
        for line in lines:
            m = CORE_RE['reference-def'].match(line)
            if m:
                id = m.group(2).strip().lower()
                t = m.group(4).strip()  # potential title
                if not t:
                    self.markdown.references[id] = (m.group(3), t)
                elif (len(t) >= 2
                      and (t[0] == t[-1] == "\""
                           or t[0] == t[-1] == "\'"
                           or (t[0] == "(" and t[-1] == ")") ) ):
                    self.markdown.references[id] = (m.group(3), t[1:-1])
                else:
                    new_text.append(line)
            else:
                new_text.append(line)

        return new_text #+ "\n"


"""
INLINE PATTERNS
=============================================================================

Inline patterns such as *emphasis* are handled by means of auxiliary
objects, one per pattern.  Pattern objects must be instances of classes
that extend markdown.Pattern.  Each pattern object uses a single regular
expression and needs support the following methods:

    pattern.getCompiledRegExp() # returns a regular expression

    pattern.handleMatch(m) # takes a match object and returns
                           # an ElementTree element or just plain text

All of python markdown's built-in patterns subclass from Pattern,
but you can add additional patterns that don't.

Also note that all the regular expressions used by inline must
capture the whole block.  For this reason, they all start with
'^(.*)' and end with '(.*)!'.  In case with built-in expression
Pattern takes care of adding the "^(.*)" and "(.*)!".

Finally, the order in which regular expressions are applied is very
important - e.g. if we first replace http://.../ links with <a> tags
and _then_ try to replace inline html, we would end up with a mess.
So, we apply the expressions in the following order:

* escape and backticks have to go before everything else, so
  that we can preempt any markdown patterns by escaping them.

* then we handle auto-links (must be done before inline html)

* then we handle inline HTML.  At this point we will simply
  replace all inline HTML strings with a placeholder and add
  the actual HTML to a hash.

* then inline images (must be done before links)

* then bracketed links, first regular then reference-style

* finally we apply strong and emphasis
"""


"""
The actual regular expressions for patterns
-----------------------------------------------------------------------------
"""

NOBRACKET = r'[^\]\[]*'
BRK = ( r'\[('
        + (NOBRACKET + r'(\[')*6
        + (NOBRACKET+ r'\])*')*6
        + NOBRACKET + r')\]' )
NOIMG = r'(?<!\!)'

BACKTICK_RE = r'(?<!\\)(`+)(.+?)(?<!`)\2(?!`)' # `e=f()` or ``e=f("`")``
ESCAPE_RE = r'\\(.)'                             # \<
EMPHASIS_RE = r'(\*)([^\*]*)\2'                    # *emphasis*
STRONG_RE = r'(\*{2}|_{2})(.*?)\2'                      # **strong**
STRONG_EM_RE = r'(\*{3}|_{3})(.*?)\2'            # ***strong***

if SMART_EMPHASIS:
    EMPHASIS_2_RE = r'(?<!\S)(_)(\S.*?)\2'        # _emphasis_
else:
    EMPHASIS_2_RE = r'(_)(.*?)\2'                 # _emphasis_

LINK_RE = NOIMG + BRK + \
r'''\(\s*(<.*?>|((?:(?:\(.*?\))|[^\(\)]))*?)\s*((['"])(.*)\12)?\)'''
# [text](url) or [text](<url>)

IMAGE_LINK_RE = r'\!' + BRK + r'\s*\((<.*?>|([^\)]*))\)'
# ![alttxt](http://x.com/) or ![alttxt](<http://x.com/>)
REFERENCE_RE = NOIMG + BRK+ r'\s*\[([^\]]*)\]'           # [Google][3]
IMAGE_REFERENCE_RE = r'\!' + BRK + '\s*\[([^\]]*)\]' # ![alt text][2]
NOT_STRONG_RE = r'( \* )'                        # stand-alone * or _
AUTOLINK_RE = r'<((?:f|ht)tps?://[^>]*)>'        # <http://www.123.com>
AUTOMAIL_RE = r'<([^> \!]*@[^> ]*)>'               # <me@example.com>

HTML_RE = r'(\<([a-zA-Z/][^\>]*?|\!--.*?--)\>)'               # <...>
ENTITY_RE = r'(&[\#a-zA-Z0-9]*;)'               # &amp;
LINE_BREAK_RE = r'  \n'                     # two spaces at end of line
LINE_BREAK_2_RE = r'  $'                    # two spaces at end of text


"""
The pattern classes
-----------------------------------------------------------------------------
"""

class Pattern:
    """Base class that inline patterns subclass. """

    def __init__ (self, pattern, markdown_instance=None):
        """
        Create an instant of an inline pattern.

        Keyword arguments:

        * pattern: A regular expression that matches a pattern

        """
        self.pattern = pattern
        self.compiled_re = re.compile("^(.*?)%s(.*?)$" % pattern, re.DOTALL)

        # Api for Markdown to pass safe_mode into instance
        self.safe_mode = False
        if markdown_instance:
            self.markdown = markdown_instance

    def getCompiledRegExp (self):
        """ Return a compiled regular expression. """
        return self.compiled_re

    def handleMatch(self, m):
        """Return a ElementTree element from the given match.

        Subclasses should override this method.

        Keyword arguments:

        * m: A re match object containing a match of the pattern.

        """
        pass

    def type(self):
        """ Return class name, to define pattern type """
        return self.__class__.__name__

BasePattern = Pattern # for backward compatibility

class SimpleTextPattern (Pattern):
    """ Return a simple text of group(2) of a Pattern. """
    def handleMatch(self, m):
        text = m.group(2)
        if text == INLINE_PLACEHOLDER_PREFIX:
            return None
        return text

class SimpleTagPattern (Pattern):
    """
    Return element of type `tag` with a text attribute of group(3)
    of a Pattern.

    """
    def __init__ (self, pattern, tag):
        Pattern.__init__(self, pattern)
        self.tag = tag

    def handleMatch(self, m):
        el = etree.Element(self.tag)
        el.text = m.group(3)
        return el


class SubstituteTagPattern (SimpleTagPattern):
    """ Return a eLement of type `tag` with no children. """
    def handleMatch (self, m):
        return etree.Element(self.tag)


class BacktickPattern (Pattern):
    """ Return a `<code>` element containing the matching text. """
    def __init__ (self, pattern):
        Pattern.__init__(self, pattern)
        self.tag = "code"

    def handleMatch(self, m):
        el = etree.Element(self.tag)
        el.text = AtomicString(m.group(3).strip())
        return el


class DoubleTagPattern (SimpleTagPattern):
    """Return a ElementTree element nested in tag2 nested in tag1.

    Useful for strong emphasis etc.

    """
    def handleMatch(self, m):
        tag1, tag2 = self.tag.split(",")
        el1 = etree.Element(tag1)
        el2 = etree.SubElement(el1, tag2)
        el2.text = m.group(3)
        return el1


class HtmlPattern (Pattern):
    """ Store raw inline html and return a placeholder. """
    def handleMatch (self, m):
        rawhtml = m.group(2)
        inline = True
        place_holder = self.markdown.htmlStash.store(rawhtml)
        return place_holder


class LinkPattern (Pattern):
    """ Return a link element from the given match. """
    def handleMatch(self, m):
        el = etree.Element("a")
        el.text = m.group(2)
        title = m.group(11)
        href = m.group(9)

        if href:
            if href[0] == "<":
                href = href[1:-1]
            el.set("href", self.sanitize_url(href.strip()))
        else:
            el.set("href", "")

        if title:
            title = dequote(title) #.replace('"', "&quot;")
            el.set("title", title)
        return el

    def sanitize_url(self, url):
        """
        Sanitize a url against xss attacks in "safe_mode".

        Rather than specifically blacklisting `javascript:alert("XSS")` and all
        its aliases (see <http://ha.ckers.org/xss.html>), we whitelist known
        safe url formats. Most urls contain a network location, however some
        are known not to (i.e.: mailto links). Script urls do not contain a
        location. Additionally, for `javascript:...`, the scheme would be
        "javascript" but some aliases will appear to `urlparse()` to have no
        scheme. On top of that relative links (i.e.: "foo/bar.html") have no
        scheme. Therefore we must check "path", "parameters", "query" and
        "fragment" for any literal colons. We don't check "scheme" for colons
        because it *should* never have any and "netloc" must allow the form:
        `username:password@host:port`.

        """
        locless_schemes = ['', 'mailto', 'news']
        scheme, netloc, path, params, query, fragment = url = urlparse(url)
        safe_url = False
        if netloc != '' or scheme in locless_schemes:
            safe_url = True

        for part in url[2:]:
            if ":" in part:
                safe_url = False

        if self.markdown.safeMode and not safe_url:
            return ''
        else:
            return urlunparse(url)

class ImagePattern(LinkPattern):
    """ Return a img element from the given match. """
    def handleMatch(self, m):
        el = etree.Element("img")
        src_parts = m.group(9).split()
        if src_parts:
            src = src_parts[0]
            if src[0] == "<" and src[-1] == ">":
                src = src[1:-1]
            el.set('src', self.sanitize_url(src))
        else:
            el.set('src', "")
        if len(src_parts) > 1:
            el.set('title', dequote(" ".join(src_parts[1:])))

        if ENABLE_ATTRIBUTES:
            truealt = handleAttributes(m.group(2), el)
        else:
            truealt = m.group(2)

        el.set('alt', truealt)
        return el

class ReferencePattern(LinkPattern):
    """ Match to a stored reference and return link element. """
    def handleMatch(self, m):
        if m.group(9):
            id = m.group(9).lower()
        else:
            # if we got something like "[Google][]"
            # we'll use "google" as the id
            id = m.group(2).lower()

        if not self.markdown.references.has_key(id): # ignore undefined refs
            return None
        href, title = self.markdown.references[id]

        text = m.group(2)
        return self.makeTag(href, title, text)

    def makeTag(self, href, title, text):
        el = etree.Element('a')

        el.set('href', self.sanitize_url(href))
        if title:
            el.set('title', title)

        el.text = text
        return el


class ImageReferencePattern (ReferencePattern):
    """ Match to a stored reference and return img element. """
    def makeTag(self, href, title, text):
        el = etree.Element("img")
        el.set("src", self.sanitize_url(href))
        if title:
            el.set("title", title)
        el.set("alt", text)
        return el


class AutolinkPattern (Pattern):
    """ Return a link Element given an autolink (`<http://example/com>`). """
    def handleMatch(self, m):
        el = etree.Element("a")
        el.set('href', m.group(2))
        el.text = AtomicString(m.group(2))
        return el

class AutomailPattern (Pattern):
    """
    Return a mailto link Element given an automail link (`<foo@example.com>`).
    """
    def handleMatch(self, m):
        el = etree.Element('a')
        email = m.group(2)
        if email.startswith("mailto:"):
            email = email[len("mailto:"):]

        def codepoint2name(code):
            """Return entity definition by code, or the code if not defined."""
            entity = htmlentitydefs.codepoint2name.get(code)
            if entity:
                return "%s%s;" % (AMP_SUBSTITUTE, entity)
            else:
                return "%s#%d;" % (AMP_SUBSTITUTE, code)

        letters = [codepoint2name(ord(letter)) for letter in email]
        el.text = AtomicString(''.join(letters))

        mailto = "mailto:" + email
        mailto = "".join([AMP_SUBSTITUTE + '#%d;' %
                          ord(letter) for letter in mailto])
        el.set('href', mailto)
        return el


"""
POST-PROCESSORS
=============================================================================

Markdown also allows post-processors, which are similar to preprocessors in
that they need to implement a "run" method. However, they are run after core
processing.

There are two types of post-processors: Postprocessor and TextPostprocessor
"""

class Postprocessor (Processor):
    """
    Postprocessors are run before the ElementTree serialization.

    Each Postprocessor implements a "run" method that takes a pointer to a
    ElementTree, modifies it as necessary and returns a ElementTree
    document.

    Postprocessors must extend markdown.Postprocessor.

    """
    def run(self, root):
        """
        Subclasses of Postprocessor should implement a `run` method, which
        takes a root Element. Method can return another Element, and global
        root Element will be replaced, or just modify current and return None.
        """
        pass


class TextPostprocessor (Processor):
    """
    TextPostprocessors are run after the ElementTree it converted back into text.

    Each TextPostprocessor implements a "run" method that takes a pointer to a
    text string, modifies it as necessary and returns a text string.

    TextPostprocessors must extend markdown.TextPostprocessor.

    """

    def run(self, text):
        """
        Subclasses of TextPostprocessor should implement a `run` method, which
        takes the html document as a single text string and returns a
        (possibly modified) string.

        """
        pass


class PrettifyPostprocessor(Postprocessor):
    """Add linebreaks to the html document."""
    def _prettifyETree(self, elem):
        """Recursively add linebreaks to ElementTree children."""
        i = "\n"
        if isBlockLevel(elem.tag) and elem.tag not in ['code', 'pre']:
            if (not elem.text or not elem.text.strip()) \
                    and len(elem) and isBlockLevel(elem[0].tag):
                elem.text = i
            for e in elem:
                if isBlockLevel(e.tag):
                    self._prettifyETree(e)
            if not elem.tail or not elem.tail.strip():
                elem.tail = i
        if not elem.tail or not elem.tail.strip():
            elem.tail = i

    def run(self, root):
        """.Add linebreaks to ElementTree root object."""
        self._prettifyETree(root)
        # Do <br />'s seperately as they are often in the middle of
        # inline content and missed by _prettifyETree.
        brs = root.getiterator('br')
        for br in brs:
            if not br.tail or not br.tail.strip():
                br.tail = '\n'
            else:
                br.tail = '\n%s' % br.tail


class RawHtmlTextPostprocessor(TextPostprocessor):
    """ Restore raw html to the document. """

    def run(self, text):
        """ Iterate over html stash and restore "safe" html. """
        for i in range(self.markdown.htmlStash.html_counter):
            html, safe  = self.markdown.htmlStash.rawHtmlBlocks[i]
            if self.markdown.safeMode and not safe:
                if str(self.markdown.safeMode).lower() == 'escape':
                    html = self.escape(html)
                elif str(self.markdown.safeMode).lower() == 'remove':
                    html = ''
                else:
                    html = HTML_REMOVED_TEXT
            if safe or not self.markdown.safeMode:
                text = text.replace("<p>%s</p>" % (HTML_PLACEHOLDER % i),
                                    html + "\n")
            text =  text.replace(HTML_PLACEHOLDER % i, html)
        return text

    def escape(self, html):
        """ Basic html escaping """
        html = html.replace('&', '&amp;')
        html = html.replace('<', '&lt;')
        html = html.replace('>', '&gt;')
        return html.replace('"', '&quot;')


class AndSubstitutePostprocessor(TextPostprocessor):
    """ Restore valid entities """
    def __init__(self):
        pass

    def run(self, text):
        text =  text.replace(AMP_SUBSTITUTE, "&")
        return text


"""
MISC AUXILIARY CLASSES
=============================================================================
"""

class AtomicString(unicode):
    """A string which should not be further processed."""
    pass


class HtmlStash:
    """
    This class is used for stashing HTML objects that we extract
    in the beginning and replace with place-holders.
    """

    def __init__ (self):
        """ Create a HtmlStash. """
        self.html_counter = 0 # for counting inline html segments
        self.rawHtmlBlocks=[]

    def store(self, html, safe=False):
        """
        Saves an HTML segment for later reinsertion.  Returns a
        placeholder string that needs to be inserted into the
        document.

        Keyword arguments:

        * html: an html segment
        * safe: label an html segment as safe for safemode

        Returns : a placeholder string

        """
        self.rawHtmlBlocks.append((html, safe))
        placeholder = HTML_PLACEHOLDER % self.html_counter
        self.html_counter += 1
        return placeholder

    def reset(self):
        self.html_counter = 0
        self.rawHtmlBlocks = []


from operator import itemgetter

class Treap(dict):
    """Extends dict to allow assignment of priority. 

    A treap is a binary search tree that orders the nodes by adding a priority
    attribute to a node, as well as a key. The nodes are ordered so that the
    keys form a binary search tree and the priorities obey the min heap order
    property. The name treap is a composition of tree and heap.

    The priority determines the node's location in the heap, which allows
    extracting the dictionary's nodes in a prioritized order. Each new node
    entry causes the heap to re-balance.

    Keyword Argument:
      default -- begin/end, determines where unprioritized dict entry is ordered. (Default: begin.)

    """
    _r_BRACE = re.compile(r'^([<>])?(.+)')
    def __init__(self, default='end'):
        self.default = '_'+('begin',default)[default in ('begin','end')]
        self.priority = None
        self._lastItem = "_begin"
        self._tree  = { 
            '_begin' : {'heap':('_begin','B'),'kids' : {},'prio' : 'B'}
            ,'_end' : {'heap':('_end','E'),'kids' : {},'prio' : 'E'}
        }
        self._reset()
        dict.__setitem__(self, '_begin', None)
        dict.__setitem__(self, '_end', None)

    def __delitem__(self, key):
        # Remove item from hash-tree and linking its kids to its parent
        parn, brace = self._prior(self._tree[key]['prio'])
        self._tree[parn]['kids'].pop(key, None)
        for k, b in self._tree[key]['kids'].items(): 
            self.link(k, b + parn)
        del self._tree[key]
        dict.__delitem__(self, key)

    def __setitem__(self, key, val, *args):
        if key not in self._tree:
            if len(args): 
                prio = args[0]
            else:
                prio = (self.default, self.priority)[self.priority != None]

            self._tree.setdefault(key, {'kids' : {},'prio' : prio})
            self.link(key, prio)
        self._reset()
        dict.__setitem__(self, key, val)

    def add(self, k, v, p=None): 
        """Adds key/value to dict and sets priority."""
        if p is None:
            p = self._lastItem
        self.__setitem__(k, v, p)
        self._lastItem = ">%s" % k

    def _reset(self): self._heap=[];self._keys=[];self._vals=[];self._items=[];

    def _prior(self, p):
        m = self._r_BRACE.match(p)
        if m.group(1) is None: b = '='
        else: b = m.group(1)
        return m.group(2), b

    def link(self, key, priority):
        """Sets priority for already-existing key/value pair."""
        self._reset()
        parn, brace = self._prior(priority)
        #if parn in self._tree:
        try:
            self._tree[parn]['kids'][key] = brace
            if 'heap' in self._tree[parn]:
                self._tree[key]['heap']=(
                    key,
                    self._tree[parn]['heap'][1]+brace
                )
                for k,v in self._tree[key]['kids'].iteritems(): 
                    self.link(k, v+key)
            self._tree[key]['prio'] = priority

        except: 
            message(CRITICAL, 
                    "Key (%s)'s parent (%s) missing." % (key, priority))

    def items(self):
        """Returns list of unsorted key/value tuples."""
        if not len(self._items):
            dic = dict.copy(self)
            del dic['_begin']
            del dic['_end']
            self._items = dic.items()
        return self._items
    
    def values(self): 
        """Returns list of unsorted values."""
        if not len(self._vals):
            dic = dict.copy(self)
            del dic['_begin']
            del dic['_end']
            self._vals = dic.values()
        return self._vals

    def keys(self):
        """Returns list of unsorted keys."""
        if not len(self._keys):
            self._keys = dict.keys(self)
            self._keys.remove('_begin')
            self._keys.remove('_end')
            
        return self._keys

    def heapsorted(self, keys=0, items=0):
        """Do heap sort and return list. (Default returns values.)

        Keyword Arguments:
          keys -- when true, returns heap-sorted list of keys. (default: false)
          items -- when true, returns heap-sorted list of key/value tuples. (default: false)
          (if both set, items have precedent.)

        """
        if not len(self._heap):
            self._heap = [
                (k, dict.__getitem__(self,k)) for k in [
                    s[0] for s in sorted( 
                        [v['heap'] for v in self._tree.values()]
                        ,key=itemgetter(1)
                    )
                ]
            ]
            for h in self._heap:
                if h[0] in ('_begin','_end'):
                    self._heap.remove(h)

        if items:
            return self._heap
        elif keys:
            return [ h[0] for h in self._heap ]

        return [ h[1] for h in self._heap ]

"""
Markdown
=============================================================================
"""

class Markdown:
    """Convert Markdown to HTML."""

    def __init__(self,
                 extensions=[],
                 extension_configs={},
                 safe_mode = False):
        """
        Creates a new Markdown instance.

        Keyword arguments:

        * extensions: A list of extensions.
           If they are of type string, the module mdx_name.py will be loaded.
           If they are a subclass of markdown.Extension, they will be used
           as-is.
        * extension-configs: Configuration setting for extensions.
        * safe_mode: Disallow raw html. One of "remove", "replace" or "escape".

        """
        self.parser = MarkdownParser()
        self.safeMode = safe_mode
        self.registeredExtensions = []
        self.docType = ""
        self.stripTopLevelTags = True

        self.textPreprocessors = Treap()
        self.textPreprocessors.add("html_block",
                                   HtmlBlockPreprocessor(self))
        self.preprocessors = Treap()
        self.preprocessors.add("header", HeaderPreprocessor(self))
        
        self.preprocessors.add("line", LinePreprocessor(self))
        self.preprocessors.add("reference", ReferencePreprocessor(self))
        # footnote preprocessor will be inserted with "<reference"

        self.postprocessors = Treap()
        self.postprocessors.add("prettify", PrettifyPostprocessor(self))

        self.textPostprocessors = Treap()
        self.textPostprocessors.add("raw_html", RawHtmlTextPostprocessor(self))
        self.textPostprocessors.add("amp_substitute", AndSubstitutePostprocessor())
        # footnote postprocessor will be inserted with ">amp_substitute"

        self.prePatterns = []

        self.inlinePatterns = Treap()
        self.inlinePatterns.add("backtick", BacktickPattern(BACKTICK_RE))
        self.inlinePatterns.add("escape", SimpleTextPattern(ESCAPE_RE))
        self.inlinePatterns.add("reference", ReferencePattern(REFERENCE_RE, self))
        self.inlinePatterns.add("link", LinkPattern(LINK_RE, self))
        self.inlinePatterns.add("image_link", ImagePattern(IMAGE_LINK_RE, self))
        self.inlinePatterns.add("image_reference",
                                ImageReferencePattern(IMAGE_REFERENCE_RE, self))
        self.inlinePatterns.add("autolink", AutolinkPattern(AUTOLINK_RE, self))
        self.inlinePatterns.add("automail", AutomailPattern(AUTOMAIL_RE, self))
        self.inlinePatterns.add("linebreak2",
                                SubstituteTagPattern(LINE_BREAK_2_RE, 'br'))
        self.inlinePatterns.add("linebreak",
                                SubstituteTagPattern(LINE_BREAK_RE, 'br'))
        self.inlinePatterns.add("html", HtmlPattern(HTML_RE, self))
        self.inlinePatterns.add("entity", HtmlPattern(ENTITY_RE, self))
        self.inlinePatterns.add("not_strong", SimpleTextPattern(NOT_STRONG_RE))
        self.inlinePatterns.add("strong_em",
                                DoubleTagPattern(STRONG_EM_RE, 'strong,em'))
        self.inlinePatterns.add("strong", SimpleTagPattern(STRONG_RE, 'strong'))
        self.inlinePatterns.add("emphasis", SimpleTagPattern(EMPHASIS_RE, 'em'))
        self.inlinePatterns.add("emphasis2",
                                SimpleTagPattern(EMPHASIS_2_RE, 'em'))
        # The order of the handlers matters!!!

        self.references = {}
        self.htmlStash = HtmlStash()
        self.registerExtensions(extensions = extensions,
                                configs = extension_configs)
        self.reset()

    def registerExtensions(self, extensions, configs):
        """
        Register extensions with this instance of Markdown.

        Keyword aurguments:

        * extensions: A list of extensions, which can either
           be strings or objects.  See the docstring on Markdown.
        * configs: A dictionary mapping module names to config options.

        """
        for ext in extensions:
            if isinstance(ext, basestring):
                ext = load_extension(ext, configs.get(ext, []))
            elif hasattr(ext, 'extendMarkdown'):
                # Looks like an Extension.
                # Nothing to do here.
                pass
            else:
                message(ERROR, "Incorrect type! Extension '%s' is "
                               "neither a string or an Extension." %(repr(ext)))
                continue
            ext.extendMarkdown(self, globals())

    def registerExtension(self, extension):
        """ This gets called by the extension """
        self.registeredExtensions.append(extension)

    def reset(self):
        """
        Resets all state variables so that we can start with a new text.
        """
        self.htmlStash.reset()
        self.references.clear()

        #HTML_BLOCK_PREPROCESSOR.stash = self.htmlStash
        #LINE_PREPROCESSOR.stash = self.htmlStash
        #REFERENCE_PREPROCESSOR.references = self.references
        #HTML_PATTERN.stash = self.htmlStash
        #ENTITY_PATTERN.stash = self.htmlStash
        #REFERENCE_PATTERN.references = self.references
        #IMAGE_REFERENCE_PATTERN.references = self.references
        #RAWHTMLTEXTPOSTPROCESSOR.stash = self.htmlStash
        #RAWHTMLTEXTPOSTPROCESSOR.safeMode = self.safeMode

        for extension in self.registeredExtensions:
            extension.reset()

    def convert (self, source):
        """Convert markdown to serialized XHTML."""

        # Fixup the source text
        if not source:
            return u""  # a blank unicode string
        try:
            source = unicode(source)
        except UnicodeDecodeError:
            message(CRITICAL, 'UnicodeDecodeError: Markdown only accepts unicode or ascii input.')
            return u""

        source = source.replace(STX, "").replace(ETX, "")
        source = source.replace("\r\n", "\n").replace("\r", "\n") + "\n\n"
        source = source.expandtabs(TAB_LENGTH)

        # Run the text preprocessors
        for pp in self.textPreprocessors.heapsorted():
            source = pp.run(source)

        # Split into lines and run the line preprocessors.
        self.lines = source.split("\n")
        for prep in self.preprocessors.heapsorted():
            self.lines = prep.run(self.lines)

        # Parse the high-level elements.
        tree = self.parser.parseDocument(self.lines)

        # Apply inline patterns
        inlineProcessor = InlineProcessor(self.inlinePatterns.heapsorted())
        root = inlineProcessor.applyInlinePatterns(tree).getroot()

        # Run the post-processors
        for postprocessor in self.postprocessors.heapsorted():
            newRoot = postprocessor.run(root)
            if newRoot:
                root = newRoot

        # Serialize _properly_.  Strip top-level tags.
        xml, length = codecs.utf_8_decode(etree.tostring(root, encoding="utf8"))
        if self.stripTopLevelTags:
            xml = xml.strip()[44:-7] + "\n"

        # Run the text post-processors
        for pp in self.textPostprocessors.heapsorted():
            xml = pp.run(xml)

        return xml.strip()

    def convertFile(self, input = None, output = None, encoding = None):
        """Converts a markdown file and returns the HTML as a unicode string.

        Decodes the file using the provided encoding (defaults to utf-8),
        passes the file content to markdown, and outputs the html to either
        the provided stream or the file with provided name, using the same
        encoding as the source file.

        **Note:** This is the only place that decoding and encoding of unicode
        takes place in Python-Markdown.  (All other code is unicode-in /
        unicode-out.)

        Keyword arguments:

        * input: Name of source text file.
        * output: Name of output file. Writes to stdout if `None`.
        * extensions: A list of extension names (may contain config args).
        * encoding: Encoding of input and output files. Defaults to utf-8.
        * safe_mode: Disallow raw html. One of "remove", "replace" or "escape".

        """

        encoding = encoding or "utf-8"

        # Read the source
        input_file = codecs.open(input, mode="r", encoding=encoding)
        text = input_file.read()
        input_file.close()
        text = text.lstrip(u'\ufeff') # remove the byte-order mark

        # Convert
        html = self.convert(text)

        # Write to file or stdout
        if type(output) == type("string"):
            output_file = codecs.open(output, "w", encoding=encoding)
            output_file.write(html)
            output_file.close()
        else:
            output.write(html.encode(encoding))


"""
Extensions
-----------------------------------------------------------------------------
"""

class Extension:
    """ Base class for extensions to subclass. """
    def __init__(self, configs = {}):
        """Create an instance of an Extention.

        Keyword arguments:

        * configs: A dict of configuration setting used by an Extension.
        """
        self.config = configs

    def getConfig(self, key):
        """ Return a setting for the given key or an empty string. """
        if self.config.has_key(key):
            return self.config[key][0]
        else:
            return ""

    def getConfigInfo(self):
        """ Return all config settings as a list of tuples. """
        return [(key, self.config[key][1]) for key in self.config.keys()]

    def setConfig(self, key, value):
        """ Set a config setting for `key` with the given `value`. """
        self.config[key][0] = value

    def extendMarkdown(self, md, md_globals):
        """
        Add the various proccesors and patterns to the Markdown Instance.

        This method must be overriden by every extension.

        Keyword arguments:

        * md: The Markdown instance.

        * md_globals: Global variables in the markdown module namespace.

        """
        pass

def load_extension(ext_name, configs = []):
    """Load extension by name, then return the module.

    The extension name may contain arguments as part of the string in the
    following format: "extname(key1=value1,key2=value2)"

    """

    # Parse extensions config params (ignore the order)
    configs = dict(configs)
    pos = ext_name.find("(") # find the first "("
    if pos > 0:
        ext_args = ext_name[pos+1:-1]
        ext_name = ext_name[:pos]
        pairs = [x.split("=") for x in ext_args.split(",")]
        configs.update([(x.strip(), y.strip()) for (x, y) in pairs])

    # Setup the module names
    ext_module = 'markdown_extensions'
    module_name_new_style = '.'.join([ext_module, ext_name])
    module_name_old_style = '_'.join(['mdx', ext_name])

    # Try loading the extention first from one place, then another
    try: # New style (markdown_extensons.<extension>)
        module = __import__(module_name_new_style, {}, {}, [ext_module])
    except ImportError:
        try: # Old style (mdx.<extension>)
            module = __import__(module_name_old_style)
        except ImportError:
            pass

    if module :
        # If the module is loaded successfully, we expect it to define a
        # function called makeExtension()
        try:
            return module.makeExtension(configs.items())
        except:
            message(CRITICAL, "Failed to instantiate extension '%s'" % ext_name)
    else:
       message(CRITICAL, "Failed loading extension '%s' from '%s' or '%s'"
               % (ext_name, module_name_new_style, module_name_old_style))

def load_extensions(ext_names):
    """Loads multiple extensions"""
    extensions = []
    for ext_name in ext_names:
        extension = load_extension(ext_name)
        if extension:
            extensions.append(extension)
    return extensions

# Extensions should use "markdown.etree" instead of "etree" (or do `from
# markdown import etree`).  Do not import it by yourself.

etree = importETree()

"""
EXPORTED FUNCTIONS
=============================================================================

Those are the two functions we really mean to export: markdown() and
markdownFromFile().
"""

def markdown(text,
             extensions = [],
             safe_mode = False):
    """Convert a markdown string to HTML and return HTML as a unicode string.

    This is a shortcut function for `Markdown` class to cover the most
    basic use case.  It initializes an instance of Markdown, loads the
    necessary extensions and runs the parser on the given text.

    Keyword arguments:

    * text: Markdown formatted text as Unicode or ASCII string.
    * extensions: A list of extensions or extension names (may contain config args).
    * safe_mode: Disallow raw html.  One of "remove", "replace" or "escape".

    Returns: An HTML document as a string.

    """
    md = Markdown(extensions=load_extensions(extensions),
                  safe_mode = safe_mode)
    return md.convert(text)


def markdownFromFile(input = None,
                     output = None,
                     extensions = [],
                     encoding = None,
                     safe = False):
    """Read markdown code from a file and write it to a file or a stream."""
    md = Markdown(extensions=load_extensions(extensions), safe_mode = safe)
    md.convertFile(input, output, encoding)


"""
COMMAND-LINE SPECIFIC STUFF
=============================================================================

The rest of the code is specifically for handling the case where Python
Markdown is called from the command line.
"""

OPTPARSE_WARNING = """
Python 2.3 or higher required for advanced command line options.
For lower versions of Python use:

      %s INPUT_FILE > OUTPUT_FILE

""" % EXECUTABLE_NAME_FOR_USAGE

def parse_options():
    """
    Define and parse `optparse` options for command-line usage.
    """

    try:
        optparse = __import__("optparse")
    except:
        if len(sys.argv) == 2:
            return {'input': sys.argv[1],
                    'output': None,
                    'safe': False,
                    'extensions': [],
                    'encoding': None }, CRITICAL
        else:
            print OPTPARSE_WARNING
            return None, None

    parser = optparse.OptionParser(usage="%prog INPUTFILE [options]")
    parser.add_option("-f", "--file", dest="filename", default=sys.stdout,
                      help="write output to OUTPUT_FILE",
                      metavar="OUTPUT_FILE")
    parser.add_option("-e", "--encoding", dest="encoding",
                      help="encoding for input and output files",)
    parser.add_option("-q", "--quiet", default = CRITICAL,
                      action="store_const", const=CRITICAL+10, dest="verbose",
                      help="suppress all messages")
    parser.add_option("-v", "--verbose",
                      action="store_const", const=INFO, dest="verbose",
                      help="print info messages")
    parser.add_option("-s", "--safe", dest="safe", default=False,
                      metavar="SAFE_MODE",
                      help="safe mode ('replace', 'remove' or 'escape'  user's HTML tag)")
    parser.add_option("--noisy",
                      action="store_const", const=DEBUG, dest="verbose",
                      help="print debug messages")
    parser.add_option("-x", "--extension", action="append", dest="extensions",
                      help = "load extension EXTENSION", metavar="EXTENSION")

    (options, args) = parser.parse_args()

    if not len(args) == 1:
        parser.print_help()
        return None, None
    else:
        input_file = args[0]

    if not options.extensions:
        options.extensions = []

    return {'input': input_file,
            'output': options.filename,
            'safe': options.safe,
            'extensions': options.extensions,
            'encoding': options.encoding }, options.verbose

def command_line_run():
    """Run Markdown from the command line."""

    # Setup a logger manually for compatibility with Python 2.3
    logger = logging.getLogger('MARKDOWN')
    logger.setLevel(COMMAND_LINE_LOGGING_LEVEL)
    logger.addHandler(logging.StreamHandler())

    # Parse options and adjust logging level if necessary
    options, logging_level = parse_options()
    if not options: sys.exit(0)
    if logging_level: logging.getLogger('MARKDOWN').setLevel(logging_level)

    # Run
    markdownFromFile(**options)

if __name__ == '__main__':
    command_line_run()