"""
Fenced Code Extension for Python Markdown
=========================================

This extension adds Fenced Code Blocks to Python-Markdown.

    >>> import markdown
    >>> text = '''
    ... A paragraph before a fenced code block:
    ...
    ... ~~~
    ... Fenced code block
    ... ~~~
    ... '''
    >>> html = markdown.markdown(text, extensions=['fenced_code'])
    >>> print html
    <p>A paragraph before a fenced code block:</p>
    <pre><code>Fenced code block
    </code></pre>

Works with safe_mode also (we check this because we are using the HtmlStash):

    >>> print markdown.markdown(text, extensions=['fenced_code'], safe_mode='replace')
    <p>A paragraph before a fenced code block:</p>
    <pre><code>Fenced code block
    </code></pre>

Include tilde's in a code block and wrap with blank lines:

    >>> text = '''
    ... ~~~~~~~~
    ...
    ... ~~~~
    ... ~~~~~~~~'''
    >>> print markdown.markdown(text, extensions=['fenced_code'])
    <pre><code>
    ~~~~
    </code></pre>

Language tags:

    >>> text = '''
    ... ~~~~{.python}
    ... # Some python code
    ... ~~~~'''
    >>> print markdown.markdown(text, extensions=['fenced_code'])
    <pre><code class="python"># Some python code
    </code></pre>

Optionally backticks instead of tildes as per how github's code block markdown is identified:

    >>> text = '''
    ... `````
    ... # Arbitrary code
    ... ~~~~~ # these tildes will not close the block
    ... `````'''
    >>> print markdown.markdown(text, extensions=['fenced_code'])
    <pre><code># Arbitrary code
    ~~~~~ # these tildes will not close the block
    </code></pre>

Copyright 2007-2008 [Waylan Limberg](http://achinghead.com/).

Project website: <http://packages.python.org/Markdown/extensions/fenced_code_blocks.html>
Contact: markdown@freewisdom.org

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

Dependencies:
* [Python 2.4+](http://python.org)
* [Markdown 2.0+](http://packages.python.org/Markdown/)
* [Pygments (optional)](http://pygments.org)

"""

from __future__ import absolute_import
from __future__ import unicode_literals
from . import Extension
from ..preprocessors import Preprocessor
from .codehilite import CodeHilite, CodeHiliteExtension
import re

# Global vars
FENCED_BLOCK_RE = re.compile( \
    r'(?P<fence>^(?:~{3,}|`{3,}))[ ]*(\{?\.?(?P<lang>[a-zA-Z0-9_+-]*)\}?)?[ ]*\n(?P<code>.*?)(?<=\n)(?P=fence)[ ]*$',
    re.MULTILINE|re.DOTALL
    )
CODE_WRAP = '<pre><code%s>%s</code></pre>'
LANG_TAG = ' class="%s"'

class FencedCodeExtension(Extension):

    def extendMarkdown(self, md, md_globals):
        """ Add FencedBlockPreprocessor to the Markdown instance. """
        md.registerExtension(self)

        md.preprocessors.add('fenced_code_block',
                                 FencedBlockPreprocessor(md),
                                 ">normalize_whitespace")


class FencedBlockPreprocessor(Preprocessor):

    def __init__(self, md):
        super(FencedBlockPreprocessor, self).__init__(md)

        self.checked_for_codehilite = False
        self.codehilite_conf = {}

    def run(self, lines):
        """ Match and store Fenced Code Blocks in the HtmlStash. """

        # Check for code hilite extension
        if not self.checked_for_codehilite:
            for ext in self.markdown.registeredExtensions:
                if isinstance(ext, CodeHiliteExtension):
                    self.codehilite_conf = ext.config
                    break

            self.checked_for_codehilite = True

        text = "\n".join(lines)
        while 1:
            m = FENCED_BLOCK_RE.search(text)
            if m:
                lang = ''
                if m.group('lang'):
                    lang = LANG_TAG % m.group('lang')

                # If config is not empty, then the codehighlite extension
                # is enabled, so we call it to highlite the code
                if self.codehilite_conf:
                    highliter = CodeHilite(m.group('code'),
                            linenums=self.codehilite_conf['linenums'][0],
                            guess_lang=self.codehilite_conf['guess_lang'][0],
                            css_class=self.codehilite_conf['css_class'][0],
                            style=self.codehilite_conf['pygments_style'][0],
                            lang=(m.group('lang') or None),
                            noclasses=self.codehilite_conf['noclasses'][0])

                    code = highliter.hilite()
                else:
                    code = CODE_WRAP % (lang, self._escape(m.group('code')))

                placeholder = self.markdown.htmlStash.store(code, safe=True)
                text = '%s\n%s\n%s'% (text[:m.start()], placeholder, text[m.end():])
            else:
                break
        return text.split("\n")

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


def makeExtension(configs=None):
    return FencedCodeExtension(configs=configs)