ics_splitter.py

"""
A handy script for extracting all events from a particular year
from an ICS file into another ICS file.

@author Derek Ruths (druths@networkdynamics.org)
"""

import argparse
import os
import re

if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('input_file', help='the input ICS file')
    parser.add_argument('year', help='the year of dates to extract')
    parser.add_argument('output_file', help='the output ICS file')

    args = parser.parse_args()

    print(f'Extracting {args.year} events from {args.input_file} into {args.output_file}')

    created_pattern = re.compile('^DTSTART.+%s' % args.year)

    in_fname = args.input_file
    out_fname = args.output_file

    if os.path.exists(out_fname):
        print('ERROR: output file already exists! As a safety check, this script will not overwrite an ICS file')
        exit()

    infh = open(in_fname, 'r')

    # parsing constants
    BEGIN_CALENDAR = 'BEGIN:VCALENDAR'
    END_CALENDAR = 'END:VCALENDAR'
    BEGIN_EVENT = 'BEGIN:VEVENT'
    END_EVENT = 'END:VEVENT'

    CREATED2017_OPENER = 'CREATED:2020'

    in_preamble = True
    in_event = False
    event_content = None
    event_in_2017 = False

    event_count = 0
    out_event_count = 0

    with open(out_fname, 'w') as outfh:
        for line in infh:
            if in_preamble and line.startswith(BEGIN_EVENT):
                in_preamble = False

            if in_preamble:
                outfh.write(line)
            else:
                if line.startswith(BEGIN_EVENT):
                    event_content = []
                    event_count += 1
                    event_in_2017 = False
                    in_event = True

                if in_event:
                    if created_pattern.match(line):
                        event_in_2017 = True
                    event_content.append(line)

                if line.startswith(END_EVENT):
                    in_event = False

                    if event_in_2017:
                        out_event_count += 1
                        outfh.write(''.join(event_content))
        outfh.write(END_CALENDAR)

    print(f'wrote {out_event_count} of {event_count} events')