zulip/zerver/lib/markdown/fenced_code.py

"""
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>

Removes trailing whitespace from code blocks that cause horizontal scrolling
    >>> import markdown
    >>> text = '''
    ... A paragraph before a fenced code block:
    ...
    ... ~~~
    ... Fenced code block    \t\t\t\t\t\t\t
    ... ~~~
    ... '''
    >>> 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>

Language tags:

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

"""
import re
from typing import Any, Dict, Iterable, List, Mapping, MutableSequence, Optional

import markdown
from django.utils.html import escape
from lxml import etree
from markdown.extensions.codehilite import CodeHilite, CodeHiliteExtension
from pygments.lexers import get_lexer_by_name
from pygments.util import ClassNotFound

from zerver.lib.exceptions import MarkdownRenderingException
from zerver.lib.tex import render_tex

# Global vars
FENCE_RE = re.compile("""
    # ~~~ or ```
    (?P<fence>
        ^(?:~{3,}|`{3,})
    )

    [ ]* # spaces

    (
        \\{?\\.?
        (?P<lang>
            [a-zA-Z0-9_+-./#]*
        ) # "py" or "javascript"
        \\}?
    ) # language, like ".py" or "{javascript}"
    [ ]* # spaces
    (
        \\{?\\.?
        (?P<header>
            [^~`]*
        )
        \\}?
    ) # header for features that use fenced block header syntax (like spoilers)
    $
    """, re.VERBOSE)


CODE_WRAP = '<pre><code{}>{}\n</code></pre>'
LANG_TAG = ' class="{}"'

def validate_curl_content(lines: List[str]) -> None:
    error_msg = """
Missing required -X argument in curl command:

{command}
""".strip()

    for line in lines:
        regex = r'curl [-](sS)?X "?(GET|DELETE|PATCH|POST)"?'
        if line.startswith('curl'):
            if re.search(regex, line) is None:
                raise MarkdownRenderingException(error_msg.format(command=line.strip()))


CODE_VALIDATORS = {
    'curl': validate_curl_content,
}

class FencedCodeExtension(markdown.Extension):
    def __init__(self, config: Mapping[str, Any] = {}) -> None:
        self.config = {
            'run_content_validators': [
                config.get('run_content_validators', False),
                'Boolean specifying whether to run content validation code in CodeHandler',
            ],
        }

        for key, value in config.items():
            self.setConfig(key, value)

    def extendMarkdown(self, md: markdown.Markdown, md_globals: Dict[str, Any]) -> None:
        """ Add FencedBlockPreprocessor to the Markdown instance. """
        md.registerExtension(self)
        processor = FencedBlockPreprocessor(
            md, run_content_validators=self.config['run_content_validators'][0])
        md.preprocessors.register(processor, 'fenced_code_block', 25)


class BaseHandler:
    def handle_line(self, line: str) -> None:
        raise NotImplementedError()

    def done(self) -> None:
        raise NotImplementedError()

def generic_handler(processor: Any, output: MutableSequence[str],
                    fence: str, lang: str, header: str,
                    run_content_validators: bool=False,
                    default_language: Optional[str]=None) -> BaseHandler:
    lang = lang.lower()
    if lang in ('quote', 'quoted'):
        return QuoteHandler(processor, output, fence, default_language)
    elif lang == 'math':
        return TexHandler(processor, output, fence)
    elif lang == 'spoiler':
        return SpoilerHandler(processor, output, fence, header)
    else:
        return CodeHandler(processor, output, fence, lang, run_content_validators)

def check_for_new_fence(processor: Any, output: MutableSequence[str], line: str,
                        run_content_validators: bool=False,
                        default_language: Optional[str]=None) -> None:
    m = FENCE_RE.match(line)
    if m:
        fence = m.group('fence')
        lang = m.group('lang')
        header = m.group('header')
        if not lang and default_language:
            lang = default_language
        handler = generic_handler(processor, output, fence, lang, header,
                                  run_content_validators, default_language)
        processor.push(handler)
    else:
        output.append(line)

class OuterHandler(BaseHandler):
    def __init__(self, processor: Any, output: MutableSequence[str],
                 run_content_validators: bool=False,
                 default_language: Optional[str]=None) -> None:
        self.output = output
        self.processor = processor
        self.run_content_validators = run_content_validators
        self.default_language = default_language

    def handle_line(self, line: str) -> None:
        check_for_new_fence(self.processor, self.output, line,
                            self.run_content_validators, self.default_language)

    def done(self) -> None:
        self.processor.pop()

class CodeHandler(BaseHandler):
    def __init__(self, processor: Any, output: MutableSequence[str],
                 fence: str, lang: str, run_content_validators: bool=False) -> None:
        self.processor = processor
        self.output = output
        self.fence = fence
        self.lang = lang
        self.lines: List[str] = []
        self.run_content_validators = run_content_validators

    def handle_line(self, line: str) -> None:
        if line.rstrip() == self.fence:
            self.done()
        else:
            self.lines.append(line.rstrip())

    def done(self) -> None:
        text = '\n'.join(self.lines)

        # run content validators (if any)
        if self.run_content_validators:
            validator = CODE_VALIDATORS.get(self.lang, lambda text: None)
            validator(self.lines)

        text = self.processor.format_code(self.lang, text)
        text = self.processor.placeholder(text)
        processed_lines = text.split('\n')
        self.output.append('')
        self.output.extend(processed_lines)
        self.output.append('')
        self.processor.pop()

class QuoteHandler(BaseHandler):
    def __init__(self, processor: Any, output: MutableSequence[str],
                 fence: str, default_language: Optional[str]=None) -> None:
        self.processor = processor
        self.output = output
        self.fence = fence
        self.lines: List[str] = []
        self.default_language = default_language

    def handle_line(self, line: str) -> None:
        if line.rstrip() == self.fence:
            self.done()
        else:
            check_for_new_fence(self.processor, self.lines, line, default_language=self.default_language)

    def done(self) -> None:
        text = '\n'.join(self.lines)
        text = self.processor.format_quote(text)
        processed_lines = text.split('\n')
        self.output.append('')
        self.output.extend(processed_lines)
        self.output.append('')
        self.processor.pop()


class SpoilerHandler(BaseHandler):
    def __init__(self, processor: Any, output: MutableSequence[str],
                 fence: str, spoiler_header: str) -> None:
        self.processor = processor
        self.output = output
        self.fence = fence
        self.spoiler_header = spoiler_header
        self.lines: List[str] = []

    def handle_line(self, line: str) -> None:
        if line.rstrip() == self.fence:
            self.done()
        else:
            check_for_new_fence(self.processor, self.lines, line)

    def done(self) -> None:
        if len(self.lines) == 0:
            # No content, do nothing
            return
        else:
            header = self.spoiler_header
            text = '\n'.join(self.lines)

        text = self.processor.format_spoiler(header, text)
        processed_lines = text.split('\n')
        self.output.append('')
        self.output.extend(processed_lines)
        self.output.append('')
        self.processor.pop()

class TexHandler(BaseHandler):
    def __init__(self, processor: Any, output: MutableSequence[str], fence: str) -> None:
        self.processor = processor
        self.output = output
        self.fence = fence
        self.lines: List[str] = []

    def handle_line(self, line: str) -> None:
        if line.rstrip() == self.fence:
            self.done()
        else:
            self.lines.append(line)

    def done(self) -> None:
        text = '\n'.join(self.lines)
        text = self.processor.format_tex(text)
        text = self.processor.placeholder(text)
        processed_lines = text.split('\n')
        self.output.append('')
        self.output.extend(processed_lines)
        self.output.append('')
        self.processor.pop()


class FencedBlockPreprocessor(markdown.preprocessors.Preprocessor):
    def __init__(self, md: markdown.Markdown, run_content_validators: bool=False) -> None:
        markdown.preprocessors.Preprocessor.__init__(self, md)

        self.checked_for_codehilite = False
        self.run_content_validators = run_content_validators
        self.codehilite_conf: Dict[str, List[Any]] = {}

    def push(self, handler: BaseHandler) -> None:
        self.handlers.append(handler)

    def pop(self) -> None:
        self.handlers.pop()

    def run(self, lines: Iterable[str]) -> List[str]:
        """ Match and store Fenced Code Blocks in the HtmlStash. """

        output: List[str] = []

        processor = self
        self.handlers: List[BaseHandler] = []

        default_language = None
        try:
            default_language = self.md.zulip_realm.default_code_block_language
        except AttributeError:
            pass
        handler = OuterHandler(processor, output, self.run_content_validators, default_language)
        self.push(handler)

        for line in lines:
            self.handlers[-1].handle_line(line)

        while self.handlers:
            self.handlers[-1].done()

        # This fiddly handling of new lines at the end of our output was done to make
        # existing tests pass. Markdown is just kind of funny when it comes to new lines,
        # but we could probably remove this hack.
        if len(output) > 2 and output[-2] != '':
            output.append('')
        return output

    def format_code(self, lang: str, text: str) -> str:
        if lang:
            langclass = LANG_TAG.format(lang)
        else:
            langclass = ''

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

            self.checked_for_codehilite = True

        # 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(text,
                                   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=(lang or None),
                                   noclasses=self.codehilite_conf['noclasses'][0])

            code = highliter.hilite()
        else:
            code = CODE_WRAP.format(langclass, self._escape(text))

        # To support our "view in playground" feature, the frontend
        # needs to know what Pygments language was used for
        # highlighting this code block.  We record this in a data
        # attribute attached to the outer `pre` element.
        # Unfortunately, the pygments API doesn't offer a way to add
        # this, so we need to do it in a post-processing step.
        if lang:
            parsed_code = etree.HTML(code)
            div_tag = parsed_code[0][0]

            # For the value of our data element, we get the lexer
            # subclass name instead of directly using the language,
            # since that canonicalizes aliases (Eg: `js` and
            # `javascript` will be mapped to `JavaScript`).
            try:
                code_language = get_lexer_by_name(lang).name
            except ClassNotFound:
                # If there isn't a Pygments lexer by this name, we
                # still tag it with the user's data-code-language
                # value, since this allows hooking up a "playground"
                # for custom "languages" that aren't known to Pygments.
                #
                # The escaping isn't strictly necessary, in that the
                # characters allowed for language values should all be
                # safe, but doing escaping here makes it easy to
                # reason about.
                code_language = self._escape(lang)

            div_tag.attrib['data-code-language'] = code_language
            # lxml implicitly converts tags like <span></span> into <span/>.
            # Specifying method="c14n" when converting to string prevents that.
            code = etree.tostring(div_tag, method="c14n").decode()
        return code

    def format_quote(self, text: str) -> str:
        paragraphs = text.split("\n\n")
        quoted_paragraphs = []
        for paragraph in paragraphs:
            lines = paragraph.split("\n")
            quoted_paragraphs.append("\n".join("> " + line for line in lines if line != ''))
        return "\n\n".join(quoted_paragraphs)

    def format_spoiler(self, header: str, text: str) -> str:
        output = []
        header_div_open_html = '<div class="spoiler-block"><div class="spoiler-header">'
        end_header_start_content_html = '</div><div class="spoiler-content" aria-hidden="true">'
        footer_html = '</div></div>'

        output.append(self.placeholder(header_div_open_html))
        output.append(header)
        output.append(self.placeholder(end_header_start_content_html))
        output.append(text)
        output.append(self.placeholder(footer_html))
        return "\n\n".join(output)

    def format_tex(self, text: str) -> str:
        paragraphs = text.split("\n\n")
        tex_paragraphs = []
        for paragraph in paragraphs:
            html = render_tex(paragraph, is_inline=False)
            if html is not None:
                tex_paragraphs.append(html)
            else:
                tex_paragraphs.append('<span class="tex-error">' +
                                      escape(paragraph) + '</span>')
        return "\n\n".join(tex_paragraphs)

    def placeholder(self, code: str) -> str:
        return self.md.htmlStash.store(code)

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


def makeExtension(*args: Any, **kwargs: None) -> FencedCodeExtension:
    return FencedCodeExtension(kwargs)

if __name__ == "__main__":
    import doctest
    doctest.testmod()