#!/usr/bin/python3
#
# markdown2html.py — simple Markdown-to-HTML converter for use with Mutt
#
# Mutt recently learnt [how to compose `multipart/alternative`
# emails][1]. This script assumes a message has been composed using Markdown
# (with a lot of pandoc extensions enabled), and translates it to `text/html`
# for Mutt to tie into such a `multipart/alternative` message.
#
# [1]: https://gitlab.com/muttmua/mutt/commit/0e566a03725b4ad789aa6ac1d17cdf7bf4e7e354)
#
# Configuration:
# muttrc:
# set send_multipart_alternative=yes
# set send_multipart_alternative_filter=/path/to/markdown2html.py
#
# Optionally, Custom CSS styles will be read from `~/.mutt/markdown2html.css`,
# if present.
#
# Requirements:
# - python3
# - PyPandoc (and pandoc installed, or downloaded)
# - Pynliner
#
# Optional:
# - Pygments, if installed, then syntax highlighting is enabled
#
# Latest version:
# https://git.madduck.net/etc/mutt.git/blob_plain/HEAD:/.mutt/markdown2html
#
# Copyright © 2019 martin f. krafft <madduck@madduck.net>
# Released under the GPL-2+ licence, just like Mutt itself.
#
import pypandoc
import pynliner
import re
import os
import sys
try:
from pygments.formatters import get_formatter_by_name
formatter = get_formatter_by_name('html', style='default')
DEFAULT_CSS = formatter.get_style_defs('.sourceCode')
except ImportError:
DEFAULT_CSS = ""
DEFAULT_CSS += '''
.quote {
padding: 0 0.5em;
margin: 0;
font-style: italic;
border-left: 2px solid #ccc;
color: #999;
font-size: 80%;
}
.quotelead {
font-style: italic;
margin-bottom: -1em;
color: #999;
font-size: 80%;
}
.quotechar { display: none; }
.footnote-ref, .footnote-back { text-decoration: none;}
.signature {
color: #999;
font-family: monospace;
white-space: pre;
margin: 1em 0 0 0;
font-size: 80%;
}
table, th, td {
border-collapse: collapse;
border: 1px solid #999;
}
th, td { padding: 0.5em; }
.header {
background: #eee;
}
.even { background: #eee; }
'''
STYLESHEET = os.path.join(os.path.expanduser('~/.mutt'),
'markdown2html.css')
if os.path.exists(STYLESHEET):
DEFAULT_CSS += open(STYLESHEET).read()
HTML_DOCUMENT = '''<!DOCTYPE html>
<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<meta charset="utf-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes"/>
<title>HTML E-Mail</title>
</head><body class="email">
{htmlbody}
</body></html>'''
SIGNATURE_HTML = \
'<div class="signature"><span class="leader">-- </span>{sig}</div>'
def _preprocess_markdown(mdwn):
'''
Preprocess Markdown for handling by the converter.
'''
# convert hard line breaks within paragraphs to 2 trailing spaces, which
# is the markdown way of representing hard line breaks. Note how the
# regexp will not match between paragraphs.
ret = re.sub(r'(\S)\n(\s*\S)', r'\g<1> \n\g<2>', mdwn, flags=re.MULTILINE)
# Clients like Thunderbird need the leading '>' to be able to properly
# create nested quotes, so we duplicate the symbol, the first instance
# will tell pandoc to create a blockquote, while the second instance will
# be a <span> containing the character, along with a class that causes CSS
# to actually hide it from display. However, this does not work with the
# text-mode HTML2text converters, and so it's left commented for now.
#ret = re.sub(r'\n>', r' \n>[>]{.quotechar}', ret, flags=re.MULTILINE)
return ret
def _identify_quotes_for_later(mdwn):
'''
Email quoting such as:
```
On 1970-01-01, you said:
> The Flat Earth Society has members all around the globe.
```
isn't really properly handled by Markdown, so let's do our best to
identify the individual elements, and mark them, using a syntax similar to
what pandoc uses already in some cases. As pandoc won't actually use these
data (yet?), we call `self._reformat_quotes` later to use these markers
to slap the appropriate classes on the HTML tags.
'''
def generate_lines_with_context(mdwn):
'''
Iterates the input string line-wise, returning a triplet of
previous, current, and next line, the first and last of which
will be None on the first and last line of the input data
respectively.
'''
prev = cur = nxt = None
lines = iter(mdwn.splitlines())
cur = next(lines)
for nxt in lines:
yield prev, cur, nxt
prev = cur
cur = nxt
yield prev, cur, None
ret = []
for prev, cur, nxt in generate_lines_with_context(mdwn):
# The lead-in to a quote is a single line immediately preceding the
# quote, and ending with ':'. Note that there could be multiple of
# these:
if nxt is not None and re.match(r'^\s*[^>].+:\s*$', cur) and nxt.startswith('>'):
ret.append(f'{{.quotelead}}{cur.strip()}')
# pandoc needs an empty line before the blockquote, so
# we enter one for the purpose of HTML rendition:
ret.append('')
continue
# The first blockquote after such a lead-in gets marked as the
# "initial" quote:
elif prev is not None and re.match(r'^\s*[^>].+:\s*$', prev) and cur.startswith('>'):
ret.append(re.sub(r'^(\s*>\s*)+(.+)',
r'\g<1>{.quoteinitial}\g<2>',
cur, flags=re.MULTILINE))
# All other occurrences of blockquotes get the "subsequent" marker:
elif cur.startswith('>') and prev is not None and not prev.startswith('>'):
ret.append(re.sub(r'^((?:\s*>\s*)+)(.+)',
r'\g<1>{.quotesubsequent}\g<2>',
cur, flags=re.MULTILINE))
else: # pass through everything else.
ret.append(cur)
return '\n'.join(ret)
def _reformat_quotes(html):
'''
Earlier in the pipeline, we marked email quoting, using markers, which we
now need to turn into HTML classes, so that we can use CSS to style them.
'''
ret = html.replace('{.quotelead}', '<p class="quotelead">')
ret = re.sub(r'<blockquote>\n((?:<blockquote>\n)*)<p>(?:\{\.quote(\w+)\})',
r'<blockquote class="quote \g<2>">\n\g<1><p>', ret, flags=re.MULTILINE)
return ret
def _convert_with_pandoc(mdwn, inputfmt='markdown', outputfmt='html5',
ext_enabled=None, ext_disabled=None,
standalone=True, title="HTML E-Mail"):
'''
Invoke pandoc to do the actual conversion of Markdown to HTML5.
'''
if not ext_enabled:
ext_enabled = [ 'backtick_code_blocks',
'line_blocks',
'fancy_lists',
'startnum',
'definition_lists',
'example_lists',
'table_captions',
'simple_tables',
'multiline_tables',
'grid_tables',
'pipe_tables',
'all_symbols_escapable',
'intraword_underscores',
'strikeout',
'superscript',
'subscript',
'fenced_divs',
'bracketed_spans',
'footnotes',
'inline_notes',
'emoji',
'tex_math_double_backslash',
'autolink_bare_uris'
]
if not ext_disabled:
ext_disabled = [ 'tex_math_single_backslash',
'tex_math_dollars',
'smart',
'raw_html'
]
enabled = '+'.join(ext_enabled)
disabled = '-'.join(ext_disabled)
inputfmt = f'{inputfmt}+{enabled}-{disabled}'
args = []
if standalone:
args.append('--standalone')
if title:
args.append(f'--metadata=pagetitle:"{title}"')
return pypandoc.convert_text(mdwn, format=inputfmt, to=outputfmt,
extra_args=args)
def _apply_styling(html):
'''
Inline all styles defined and used into the individual HTML tags.
'''
return pynliner.Pynliner().from_string(html).with_cssString(DEFAULT_CSS).run()
def _postprocess_html(html):
'''
Postprocess the generated and styled HTML.
'''
return html
def convert_markdown_to_html(mdwn):
'''
Converts the input Markdown to HTML, handling separately the body, as well
as an optional signature.
'''
parts = re.split(r'^-- $', mdwn, 1, flags=re.MULTILINE)
body = parts[0]
if len(parts) == 2:
sig = parts[1]
else:
sig = None
html=''
if body:
body = _preprocess_markdown(body)
body = _identify_quotes_for_later(body)
html = _convert_with_pandoc(body, standalone=False)
html = _reformat_quotes(html)
if sig:
sig = _preprocess_markdown(sig)
html += SIGNATURE_HTML.format(sig='<br/>'.join(sig.splitlines()))
html = HTML_DOCUMENT.format(htmlbody=html)
html = _apply_styling(html)
html = _postprocess_html(html)
return html
def main():
'''
Convert text on stdin to HTML, and print it to stdout, like mutt would
expect.
'''
html = convert_markdown_to_html(sys.stdin.read())
if html:
# mutt expects the content type in the first line, so:
print(f'text/html\n\n{html}')
if __name__ == '__main__':
main()
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