cal-proxy/app.py

from flask import Flask
import os
import urllib.request
from icalendar.cal import Calendar, Component

app = Flask(__name__)


@app.route("/")
def hello():
    url = os.environ.get('URL', None)
    if url is None:
        return ""

    cal_str = urllib.request.urlopen(url).read()

    FILTERED_EVENTS = os.environ.get('COURSES', '').split(',')

    cal = Component.from_ical(cal_str)
    other = Calendar()

    # Copy all properties of calendar
    for k, v in cal.items():
        other.add(k, v)

    # Copy the VTIMEZONE component
    other.add_component(cal.walk('VTIMEZONE')[0])

    # Filter and copy VEVENTs
    for ev in cal.walk('VEVENT'):
        course_code = ev['SUMMARY'].split('-')[1].split('/')[0]
        if course_code not in FILTERED_EVENTS:
            other.add_component(ev)

    return other.to_ical().replace(b'\r\n', b'\n').strip()

if __name__ == "__main__":
    port = int(os.environ.get('PORT', 5000))
    app.run('0.0.0.0', port)