Pandoc include filter

pandoc-filter-include.py

#!/usr/bin/env python

"""
Include contents from other files, even recursively.

Examples:

- Include first chaper from markdown file

    [](chapter1.md){.include .markdown}

- Include Java class skipping the packages. Furter attributes are preserved.

    [AnyPojo Class Impl.](../src/AnyPojo.java){.include .java .code from=7}

"""

from pandocfilters import toJSONFilter, get_value, stringify
from pandocfilters import CodeBlock

from urllib import parse
from io import open

import pypandoc
import json
import sys
import os

def content_from(path, start, end):
    with open(path, encoding = 'utf-8') as f:
        lines = f.readlines()
        start = int(start) - 1
        end = int(end)
        return ''.join(lines[start:end])

def links(key, value, format, meta):
    if key != 'Para' or not value:
        return None

    firstChild = value[0]
    key = firstChild['t']
    value = firstChild['c']

    if key != 'Link':
        return None

    [ident, classes, attributes], caption, [path, _] = value

    if not 'include' in classes:
        return None

    start, attributes = get_value(attributes, 'from', 1)
    end, attributes = get_value(attributes, 'to', sys.maxsize)

    path = parse.unquote(path)
    content = content_from(path, start, end)
    classes.remove('include')

    if 'code' in classes:
        classes.remove('code')

        if caption:
            attributes += [['caption', stringify(caption)]]

        return CodeBlock((ident, classes, attributes), content)

    else:
        if len(classes) != 1:
            raise Exception('A direct include has the ' +
                'input type as second class')

        input_format = classes[0]
        this_filter = os.path.realpath(__file__)
        json_content = pypandoc.convert_text(content,
            to = 'json',
            format = input_format,
            filters = [ this_filter ])

        content = json.loads(json_content)
        return content['blocks']

if __name__ == "__main__":
    toJSONFilter(links)