overlay_filter

#!/usr/bin/env python

"""overlay_filter

Simplistic pandoc filter to include beamer overlay specifications on
inline tex in markdown

Whereas in normal beamer LaTeX you'd write

    \cmd<overlay>{...}

in markdown write

    \cmd{<overlay>}{...}

then process with

    pandoc --filter overlay_filter

Environments are passed through to LaTeX, so there's no need to filter
them; write onlyenv as normal, for example.

The code for walking the tree in 'walk' and the main block is taken from
the pandocfilters python module, https://github.com/jgm/pandocfilters,
(C) 2013 John MacFarlane. This way we do not require the user's system's
python to have pandocfilters installed, though, of course, I have to
remember to keep up with changes in pandoc's JSON API. The present
script should be compatible with pandoc versions on both sides of the
pandoc 1.18 JSON format change (AG scripsit, December 2016).

This file incorporates work covered by the following copyright and
permission notice:

    Copyright (c) 2013, John MacFarlane
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

     - Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.

     - Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer
     in the documentation and/or other materials provided with the
     distribution.

     - Neither the name of John Macfarlane nor the names of its
     contributors may be used to endorse or promote products derived
     from this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.

"""

import re
import sys
import json
import codecs

ov_pat = re.compile(r'^(\\\w+)(\{<[^>]+>})(.*)$',flags=re.DOTALL)

def overlay_filter(key, value, fmt, meta):
    if key == 'RawInline' and value[0] == 'tex':
        m = ov_pat.match(value[1])
        if m:
            c = m.group(1)
            c += re.sub(r'^\{|}$', "", m.group(2))
            c += m.group(3)
            return { "t": "RawInline", "c": ["tex", c] }

def walk(x, action, fmt, meta):
    """Walk a tree, applying an action to every object.
    Returns a modified tree.
    """
    if isinstance(x, list):
        array = []
        for item in x:
            if isinstance(item, dict) and 't' in item:
                res = action(item['t'],
                        item['c'] if 'c' in item else None, fmt, meta)
                if res is None:
                    array.append(walk(item, action, fmt, meta))
                elif isinstance(res, list):
                    for z in res:
                        array.append(walk(z, action, fmt, meta))
                else:
                    array.append(walk(res, action, fmt, meta))
            else:
                array.append(walk(item, action, fmt, meta))
        return array
    elif isinstance(x, dict):
        obj = {}
        for k in x:
            obj[k] = walk(x[k], action, fmt, meta)
        return obj
    else:
        return x

if __name__ == "__main__":
    # 2vs3: python is teh best
    try:
        import io
        input_stream = io.TextIOWrapper(sys.stdin.buffer, encoding='utf-8')
    except AttributeError:
        # Python 2 does not have sys.stdin.buffer.
        # REF: https://stackoverflow.com/questions/2467928/python-unicodeencode
        input_stream = codecs.getreader("utf-8")(sys.stdin)

    doc = json.loads(input_stream.read())
    # pandoc 1.18 changed the format
    if 'meta' in doc:
        meta = doc['meta']
    elif doc[0]:  # old API
        meta = doc[0]['unMeta']
    else:
        meta = {}

    if len(sys.argv) > 1:
        fmt = sys.argv[1]
    else:
        fmt = ""

    altered = walk(doc, overlay_filter, fmt, meta)
    json.dump(altered, sys.stdout)