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 codecs
import hashlib
import io
import json
import os
import sys
import atexit
import shutil
import tempfile


# some utility-functions: make it easier to create your own filters


def get_filename4code(module, content, ext=None):
    """Generate filename based on content

    The function ensures that the (temporary) directory exists, so that the
    file can be written.

    By default, the directory won't be cleaned up,
    so a filter can use the directory as a cache and
    decide not to regenerate if there's no change.

    In case the user preferres the files to be temporary files,
    an environment variable `PANDOCFILTER_CLEANUP` can be set to
    any non-empty value such as `1` to
    make sure the directory is created in a temporary location and removed
    after finishing the filter. In this case there's no caching and files
    will be regenerated each time the filter is run.

    Example:
        filename = get_filename4code("myfilter", code)
    """
    if os.getenv('PANDOCFILTER_CLEANUP'):
        imagedir = tempfile.mkdtemp(prefix=module)
        atexit.register(lambda: shutil.rmtree(imagedir))
    else:
        imagedir = module + "-images"
    fn = hashlib.sha1(content.encode(sys.getfilesystemencoding())).hexdigest()
    if not os.path.isdir(imagedir):
        try:
            os.makedirs(imagedir)
            sys.stderr.write('Created directory ' + imagedir + '\n')
        except OSError:
            sys.stderr.write('Could not create directory "' + imagedir + '"\n')
    if ext:
        fn += "." + ext
    return os.path.join(imagedir, fn)

def get_value(kv, key, value = None):
    """get value from the keyvalues (options)"""
    res = []
    for k, v in kv:
        if k == key:
            value = v
        else:
            res.append([k, v])
    return value, res

def get_caption(kv):
    """get caption from the keyvalues (options)

    Example:
      if key == 'CodeBlock':
        [[ident, classes, keyvals], code] = value
        caption, typef, keyvals = get_caption(keyvals)
        ...
        return Para([Image([ident, [], keyvals], caption, [filename, typef])])
    """
    caption = []
    typef = ""
    value, res = get_value(kv, u"caption")
    if value is not None:
        caption = [Str(value)]
        typef = "fig:"

    return caption, typef, res


def get_extension(format, default, **alternates):
    """get the extension for the result, needs a default and some specialisations

    Example:
      filetype = get_extension(format, "png", html="svg", latex="eps")
    """
    try:
        return alternates[format]
    except KeyError:
        return default

# end of utilities


def walk(x, action, format, meta):
    """Walk a tree, applying an action to every object.
    Returns a modified tree.  An action is a function of the form
    `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 (as supplied by the
      `format` argument of `walk`)
    * `meta` is the document's metadata

    The return of an action is either:

    * `None`: this means that the object should remain unchanged
    * a pandoc object: this will replace the original object
    * a list of pandoc objects: these will replace the original object; the
      list is merged with the neighbors of the orignal objects (spliced into
      the list the original object belongs to); returning an empty list deletes
      the object
    """
    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, 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):
        return {k: walk(v, action, format, meta) for k, v in x.items()}
    else:
        return x

def toJSONFilter(action):
    """Like `toJSONFilters`, but takes a single action as argument.
    """
    toJSONFilters([action])


def toJSONFilters(actions):
    """Generate a JSON-to-JSON filter from stdin to stdout

    The filter:

    * reads a JSON-formatted pandoc document from stdin
    * transforms it by walking the tree and performing the actions
    * returns a new JSON-formatted pandoc document to stdout

    The argument `actions` is a list of functions of the form
    `action(key, value, format, meta)`, as described in more
    detail under `walk`.

    This function calls `applyJSONFilters`, with the `format`
    argument provided by the first command-line argument,
    if present.  (Pandoc sets this by default when calling
    filters.)
    """
    try:
        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)

    source = input_stream.read()
    if len(sys.argv) > 1:
        format = sys.argv[1]
    else:
        format = ""

    sys.stdout.write(applyJSONFilters(actions, source, format))

def applyJSONFilters(actions, source, format=""):
    """Walk through JSON structure and apply filters

    This:

    * reads a JSON-formatted pandoc document from a source string
    * transforms it by walking the tree and performing the actions
    * returns a new JSON-formatted pandoc document as a string

    The `actions` argument is a list of functions (see `walk`
    for a full description).

    The argument `source` is a string encoded JSON object.

    The argument `format` is a string describing the output format.

    Returns a the new JSON-formatted pandoc document.
    """

    doc = json.loads(source)

    if 'meta' in doc:
        meta = doc['meta']
    elif doc[0]:  # old API
        meta = doc[0]['unMeta']
    else:
        meta = {}
    altered = doc
    for action in actions:
        altered = walk(altered, action, format, meta)

    return json.dumps(altered)


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 == 'SoftBreak':
            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 = list(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', 3)
Image = elt('Image', 3)
Note = elt('Note', 1)
SoftBreak = elt('SoftBreak', 0)
Span = elt('Span', 2)