Extract plaintext TODOs from Remember the Milk (RTM) iCalendar export

icalendar_todos.py

#!/usr/bin/env python3

import argparse
import functools
import icalendar
import operator
import re

TAGS_PATTERN = re.compile(r'Tags: ([\w\d]+(?:, [\w\d]+)*)')

# The RTM iCalendar export doesn't include information about which list
# VTODO items came from, so we have to use a heuristic to separate fiction
# books from fiction movies.
BOOK_PATTERN = re.compile(r'.+\, ".*"')

def main():
    parser = argparse.ArgumentParser(
        description='Extract TODOs from an RTM iCalendar export')
    parser.add_argument('input')
    parser.add_argument('--tag', default=None,
                        help='Only include items with the given tag')
    parser.add_argument('--book', default=False, action='store_true',
                        help='Only include items that look like books')
    parser.add_argument('--no-book', default=False, action='store_true',
                        help='Only include items that don\'t look like books')
    args = parser.parse_args()

    predicates = []

    if args.book:
        predicates.append(lambda item: todo_is_book(item))
    if args.no_book:
        predicates.append(lambda item: not todo_is_book(item))
    if args.tag is not None:
        predicates.append(lambda item: todo_has_tag(item, args.tag))

    def predicate(item):
        return functools.reduce(operator.and_,
                                map(lambda p: p(item), predicates), True)

    for item in get_todos(get_ical_object(args.input), predicate):
        print(get_scalar_property(item, 'SUMMARY'))

def get_ical_object(path):
    with open(path, 'rb') as f:
        cal = icalendar.Calendar.from_ical(f.read())
    return cal

def get_todos(cal, predicate=None):
    if predicate is None:
        predicate = lambda _: True

    for item in cal.walk(name='VTODO'):
        if predicate(item):
            yield item

def get_scalar_property(item, name):
    return item.decoded(name).decode()

def todo_has_tag(item, tag):
    m = re.search(TAGS_PATTERN, get_scalar_property(item, 'DESCRIPTION'))
    if m is None:
        return False

    item_tags = m.group(1).split(', ')
    return tag in item_tags

def todo_is_book(item):
    return re.match(BOOK_PATTERN, get_scalar_property(item, 'SUMMARY')) is not None

if __name__ == '__main__':
    main()