import optparse
import sys

from docutils.core import publish_parts
from docutils.frontend import OptionParser
from docutils.parsers.rst import Parser


def transform(writer=None, part=None):
    p = optparse.OptionParser(add_help_option=False)

    # Collect all the command line options
    docutils_parser = OptionParser(components=(writer, Parser()))

    for group in docutils_parser.option_groups:
        p.add_option_group(group.title, None).add_options(group.option_list)

    p.add_option('--part', default=part)

    opts, args = p.parse_args()

    settings = dict({'file_insertion_enabled': False,
                     'raw_enabled': False}, **opts.__dict__)

    if len(args) == 1:
        try:
            content = open(args[0], 'r').read()
        except IOError:
            content = args[0]
    else:
        content = sys.stdin.read()

    parts = publish_parts(source=content, settings_overrides=settings,
                          writer=writer)

    if opts.part in parts:
        return parts[opts.part]
    return ''