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

This extension adds Fenced Code Blocks to Python-Markdown.

See <https://Python-Markdown.github.io/extensions/fenced_code_blocks>
for documentation.

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


All changes Copyright 2008-2014 The Python Markdown Project

License: [BSD](http://www.opensource.org/licenses/bsd-license.php)
"""

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


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):
    FENCED_BLOCK_RE = re.compile(r'''
(?P<fence>^(?:~{3,}|`{3,}))[ ]*         # Opening ``` or ~~~
(```(?P<lang>[\w#.+-]*)\n)?[ ]*        # Optional {, and lang
# Optional highlight lines, single- or double-quote-delimited
(hl_lines=(?P<quot>"|')(?P<hl_lines>.*?)(?P=quot))?[ ]*
}?[ ]*\n                                # Optional closing }
(?P<code>.*?)(?<=\n)
(?P=fence)[ ]*$''', re.MULTILINE | re.DOTALL | re.VERBOSE)
    CODE_WRAP = '<pre><code%s>%s</code></pre>'
    LANG_TAG = ' class=language-"%s"'

    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 = self.FENCED_BLOCK_RE.search(text)
            if m:
                lang = ''
                if m.group('lang'):
                    lang = self.LANG_TAG % m.group('lang')

                # If config is not empty, then the codehighlite extension
                # is enabled, so we call it to highlight 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],
                        use_pygments=self.codehilite_conf['use_pygments'][0],
                        lang=(m.group('lang') or None),
                        noclasses=self.codehilite_conf['noclasses'][0],
                        hl_lines=parse_hl_lines(m.group('hl_lines'))
                    )

                    code = highliter.hilite()
                else:
                    code = self.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(*args, **kwargs):
    return FencedCodeExtension(*args, **kwargs)
