"""
========================= FOOTNOTES =================================

This section adds footnote handling to markdown.  It can be used as
an example for extending python-markdown with relatively complex
functionality.  While in this case the extension is included inside
the module itself, it could just as easily be added from outside the
module.  Not that all markdown classes above are ignorant about
footnotes.  All footnote functionality is provided separately and
then added to the markdown instance at the run time.

Footnote functionality is attached by calling extendMarkdown()
method of FootnoteExtension.  The method also registers the
extension to allow it's state to be reset by a call to reset()
method.

Example:
    Footnotes[^1] have a label[^label] and a definition[^!DEF].

    [^1]: This is a footnote
    [^label]: A footnote on "label"
    [^!DEF]: The footnote for definition

"""

import re, markdown
from markdown import etree

FN_BACKLINK_TEXT = "zz1337820767766393qq"
NBSP_PLACEHOLDER =  "qq3936677670287331zz"
DEF_RE = re.compile(r'(\ ?\ ?\ ?)\[\^([^\]]*)\]:\s*(.*)')


class FootnoteExtension(markdown.Extension):
    """ Footnote Extension. """

    def __init__ (self, configs):

        self.config = {'PLACE_MARKER':
                       ["///Footnotes Go Here///",
                        "The text string that marks where the footnotes go"]}

        self.parser = markdown.MarkdownParser()

        for key, value in configs:
            self.config[key][0] = value
            
        self.reset()

    def extendMarkdown(self, md, md_globals):
        """ Add pieces to Markdown. """
        md.registerExtension(self)
        # Insert a preprocessor before ReferencePreprocessor
        md.preprocessors.add("footnote", FootnotePreprocessor(self),
                             "<reference")
        # Insert an inline pattern before ImageReferencePattern
        FOOTNOTE_RE = r'\[\^([^\]]*)\]' # blah blah [^1] blah
        md.inlinePatterns.add("footnote", FootnotePattern(FOOTNOTE_RE, self),
                              "<reference")
        # Insert a tree-processor that would actually add the footnote div
        # This must be before the inline treeprocessor so inline patterns
        # run on the contents of the div.
        md.treeprocessors.add("footnote", FootnoteTreeprocessor(self),
                                 "<inline")
        # Insert a postprocessor after amp_substitute oricessor
        md.postprocessors.add("footnote", FootnotePostprocessor(self),
                                  ">amp_substitute")

    def reset(self):
        """ Clear the footnotes on reset. """
        self.footnotes = markdown.OrderedDict()

    def findFootnotesPlaceholder(self, root):
        
        def finder(element):
            for child in element:
                if child.text:
                    if child.text.find(self.getConfig("PLACE_MARKER")) > -1:
                        return child, True
                if child.tail:
                    if child.tail.find(self.getConfig("PLACE_MARKER")) > -1:
                        return (child, element), False
                finder(child)
            return None
                
        res = finder(root)
        return res

    def setFootnote(self, id, text):
        self.footnotes[id] = text

    def makeFootnoteId(self, id):
        return 'fn:%s' % id

    def makeFootnoteRefId(self, id):
        return 'fnref:%s' % id

    def makeFootnotesDiv(self, root):
        """Creates the div with class='footnote' and populates it with
           the text of the footnotes.

           @returns: the footnote div as a dom element """

        if not self.footnotes.keys():
            return None

        div = etree.Element("div")
        div.set('class', 'footnote')
        hr = etree.SubElement(div, "hr")
        ol = etree.SubElement(div, "ol")

        for id in self.footnotes.keys():
            li = etree.SubElement(ol, "li")
            li.set("id", self.makeFootnoteId(id))
            self.parser.parseChunk(li, self.footnotes[id].split("\n"), 
                                        looseList=1)

            backlink = etree.Element("a")
            backlink.set("href", "#" + self.makeFootnoteRefId(id))
            backlink.set("rev", "footnote")
            backlink.set("title", "Jump back to footnote %d in the text" % \
                            (self.footnotes.index(id)+1))
            backlink.text = FN_BACKLINK_TEXT

            if li.getchildren():
                node = li[-1]
                if node.tag == "p":
                    node.text = node.text + NBSP_PLACEHOLDER
                    node.append(backlink)
                else:
                    p = etree.SubElement(li, "p")
                    p.append(backlink)
        return div


class FootnotePreprocessor(markdown.Preprocessor):
    """ Find all footnote references and store for later use. """

    def __init__ (self, footnotes):
        self.footnotes = footnotes

    def run(self, lines):
        lines = self._handleFootnoteDefinitions(lines)
        text = "\n".join(lines)
        return text.split("\n")

    def _handleFootnoteDefinitions(self, lines):
        """Recursively finds all footnote definitions in the lines.

            @param lines: a list of lines of text
            @returns: a string representing the text with footnote
                      definitions removed """

        i, id, footnote = self._findFootnoteDefinition(lines)

        if id :
            plain = lines[:i]
            detabbed, theRest = self.footnotes.parser.detectTabbed(lines[i+1:])
            self.footnotes.setFootnote(id,
                                       footnote + "\n"
                                       + "\n".join(detabbed))
            more_plain = self._handleFootnoteDefinitions(theRest)
            return plain + [""] + more_plain
        else :
            return lines

    def _findFootnoteDefinition(self, lines):
        """Finds the first line of a footnote definition.

            @param lines: a list of lines of text
            @returns: the index of the line containing a footnote definition """

        counter = 0
        for line in lines:
            m = DEF_RE.match(line)
            if m:
                return counter, m.group(2), m.group(3)
            counter += 1
        return counter, None, None


class FootnotePattern(markdown.Pattern):
    """ InlinePattern for footnote markers in a document's body text. """

    def __init__(self, pattern, footnotes):
        markdown.Pattern.__init__(self, pattern)
        self.footnotes = footnotes

    def handleMatch(self, m):
        sup = etree.Element("sup")
        a = etree.SubElement(sup, "a")
        id = m.group(2)
        sup.set('id', self.footnotes.makeFootnoteRefId(id))
        a.set('href', '#' + self.footnotes.makeFootnoteId(id))
        a.set('rel', 'footnote')
        a.text = str(self.footnotes.footnotes.index(id) + 1)
        return sup


class FootnoteTreeprocessor(markdown.Treeprocessor):
    """ Build and append footnote div to end of document. """

    def __init__ (self, footnotes):
        self.footnotes = footnotes

    def run(self, root):
        footnotesDiv = self.footnotes.makeFootnotesDiv(root)
        if footnotesDiv:
            result = self.footnotes.findFootnotesPlaceholder(root)
            if result:
                node, isText = result
                if isText:
                    node.text = None
                    node.getchildren().insert(0, footnotesDiv)
                else:
                    child, element = node
                    ind = element.getchildren().find(child)
                    element.getchildren().insert(ind + 1, footnotesDiv)
                    child.tail = None
                fnPlaceholder.parent.replaceChild(fnPlaceholder, footnotesDiv)
            else:
                root.append(footnotesDiv)

class FootnotePostprocessor(markdown.Postprocessor):
    """ Replace FN_BACKLINK_TEXT with html entity ``&#8617;``. """

    def run(self, text):
        text = text.replace(FN_BACKLINK_TEXT, "&#8617;")
        return text.replace(NBSP_PLACEHOLDER, "&#160;")

def makeExtension(configs=[]):
    """ Return an instance of the FootnoteExtension """
    return FootnoteExtension(configs=configs)