Add markdown2html contrib script.

This was contributed by martin f. kraft, to give an example script for the new $send_multipart_alternative_filter funtionality.
author: Kevin McCarthy <kevin@8t8.us> 2019-11-09 13:43:11 -0800
committer: Kevin McCarthy <kevin@8t8.us> 2019-11-09 13:43:11 -0800
commit: 183c468721b3d404e2505d4b27394f41ad6dfdaa (patch)
tree: 3aaafb9dbbe422a8de786aa9bde0a4f0c72954a6 /contrib
parent: 202ec2c8a4bc8ddc7a3ecafbe82af6b167fc6ae2 (diff)
2 files changed, 310 insertions, 1 deletions
diff --git a/contrib/Makefile.am b/contrib/Makefile.am
index 4d25f42e..973aed23 100644
--- a/contrib/Makefile.am
+++ b/contrib/Makefile.am
@@ -6,7 +6,7 @@ SAMPLES = Mush.rc Pine.rc gpg.rc pgp2.rc pgp5.rc pgp6.rc Tin.rc \
 	sample.mailcap sample.muttrc sample.muttrc-sidebar sample.muttrc-tlr \
 	sample.muttrc-compress sample.muttrc-starter \
 	sample.vimrc-sidebar colors.default colors.linux smime.rc \
-	ca-bundle.crt smime_keys_test.pl mutt_xtitle
+	ca-bundle.crt smime_keys_test.pl mutt_xtitle markdown2html
 
 EXTRA_DIST = language.txt language50.txt  \
 	patch.slang-1.2.2.keypad.1	\
diff --git a/contrib/markdown2html b/contrib/markdown2html
new file mode 100644
index 00000000..be705d65
--- /dev/null
+++ b/contrib/markdown2html
@@ -0,0 +1,309 @@
+#!/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 re.match(r'^.+:\s*$', cur) and nxt.startswith('>'):
+            ret.append(f'{{.quotelead}}{cur.strip()}')
+            # pandoc needs an empty line before the blockquote, so
+            # we enter one for the purpose of HTML rendition:
+            ret.append('')
+            continue
+
+        # The first blockquote after such a lead-in gets marked as the
+        # "initial" quote:
+        elif prev and re.match(r'^.+:\s*$', 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 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('<p>{.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()
author	Kevin McCarthy <kevin@8t8.us>	2019-11-09 13:43:11 -0800
committer	Kevin McCarthy <kevin@8t8.us>	2019-11-09 13:43:11 -0800
commit	183c468721b3d404e2505d4b27394f41ad6dfdaa (patch)
tree	3aaafb9dbbe422a8de786aa9bde0a4f0c72954a6 /contrib
parent	202ec2c8a4bc8ddc7a3ecafbe82af6b167fc6ae2 (diff)