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

app = Flask(__name__)

FILTERED_COURSES = os.environ.get('COURSES', '').split(',')
FILTERED_TYPES = os.environ.get('TYPES', '').split(',')
YEAR = int(os.environ.get('YEAR', '4'))
GROUP = int(os.environ.get('GROUP', '1'))
GENERAL_GROUP = int(os.environ.get('GENERAL_GROUP', '0'))
GROUPS = [GROUP, GENERAL_GROUP]


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

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

    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'):
        if should_add(ev):
            other.add_component(ev)

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


def should_add(event):
    course_code = event['SUMMARY'].split('-')[1].split('/')[0]
    course_type = event['SUMMARY'].split('/')[1].split('_')[1]
    year = event['SUMMARY'][0]
    group = event['SUMMARY'][-1]

    return \
        course_code not in FILTERED_COURSES \
        and course_type not in FILTERED_TYPES \
        and year == YEAR \
        and group in GROUPS


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