pandocfilters.py

# Author: John MacFarlane <jgm@berkeley.edu>
# Copyright: (C) 2013 John MacFarlane
# License: BSD3

"""
Functions to aid writing python scripts that process the pandoc
AST serialized as JSON.
"""

import sys
import json
import io


def walk(x, action, format, 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'], format, meta)
                if res is None:
                    array.append(walk(item, action, format, meta))
                elif isinstance(res, list):
                    for z in res:
                        array.append(walk(z, action, format, meta))
                else:
                    array.append(walk(res, action, format, meta))
            else:
                array.append(walk(item, action, format, meta))
        return array
    elif isinstance(x, dict):
        obj = {}
        for k in x:
            obj[k] = walk(x[k], action, format, meta)
        return obj
    else:
        return x


def toJSONFilter(action):
    """Converts an action into a filter that reads a JSON-formatted
    pandoc document from stdin, transforms it by walking the tree
    with the action, and returns a new JSON-formatted pandoc document
    to stdout.  The argument is a function action(key, value, format, meta),
    where key is the type of the pandoc object (e.g. 'Str', 'Para'),
    value is the contents of the object (e.g. a string for 'Str',
    a list of inline elements for 'Para'), format is the target
    output format (which will be taken for the first command line
    argument if present), and meta is the document's metadata.
    If the function returns None, the object to which it applies
    will remain unchanged.  If it returns an object, the object will
    be replaced.    If it returns a list, the list will be spliced in to
    the list to which the target object belongs.    (So, returning an
    empty list deletes the object.)
    """
    input_stream = io.TextIOWrapper(sys.stdin.buffer, encoding='utf-8')
    doc = json.loads(input_stream.read())
    if len(sys.argv) > 1:
        format = sys.argv[1]
    else:
        format = ""
    altered = walk(doc, action, format, doc[0]['unMeta'])
    json.dump(altered, sys.stdout)


def stringify(x):
    """Walks the tree x and returns concatenated string content,
    leaving out all formatting.
    """
    result = []

    def go(key, val, format, meta):
        if key in ['Str', 'MetaString']:
            result.append(val)
        elif key == 'Code':
            result.append(val[1])
        elif key == 'Math':
            result.append(val[1])
        elif key == 'LineBreak':
            result.append(" ")
        elif key == 'Space':
            result.append(" ")

    walk(x, go, "", {})
    return ''.join(result)


def attributes(attrs):
    """Returns an attribute list, constructed from the
    dictionary attrs.
    """
    attrs = attrs or {}
    ident = attrs.get("id", "")
    classes = attrs.get("classes", [])
    keyvals = [[x, attrs[x]] for x in attrs if (x != "classes" and x != "id")]
    return [ident, classes, keyvals]


def elt(eltType, numargs):
    def fun(*args):
        lenargs = len(args)
        if lenargs != numargs:
            raise ValueError(eltType + ' expects '
                             + str(numargs) + ' arguments, but given '
                             + str(lenargs))
        if numargs == 0:
            xs = []
        elif len(args) == 1:
            xs = args[0]
        else:
            xs = args
        return {'t': eltType, 'c': xs}
    return fun

# Constructors for block elements

Plain = elt('Plain', 1)
Para = elt('Para', 1)
CodeBlock = elt('CodeBlock', 2)
RawBlock = elt('RawBlock', 2)
BlockQuote = elt('BlockQuote', 1)
OrderedList = elt('OrderedList', 2)
BulletList = elt('BulletList', 1)
DefinitionList = elt('DefinitionList', 1)
Header = elt('Header', 3)
HorizontalRule = elt('HorizontalRule', 0)
Table = elt('Table', 5)
Div = elt('Div', 2)
Null = elt('Null', 0)

# Constructors for inline elements

Str = elt('Str', 1)
Emph = elt('Emph', 1)
Strong = elt('Strong', 1)
Strikeout = elt('Strikeout', 1)
Superscript = elt('Superscript', 1)
Subscript = elt('Subscript', 1)
SmallCaps = elt('SmallCaps', 1)
Quoted = elt('Quoted', 2)
Cite = elt('Cite', 2)
Code = elt('Code', 2)
Space = elt('Space', 0)
LineBreak = elt('LineBreak', 0)
Math = elt('Math', 2)
RawInline = elt('RawInline', 2)
Link = elt('Link', 2)
Image = elt('Image', 2)
Note = elt('Note', 1)
Span = elt('Span', 2)