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

app = Flask(__name__)

PORT = int(os.environ.get('PORT', 5000))

BASE_URL = os.environ.get('BASE_URL', None)

EXCLUDED_COURSES = os.environ.get('COURSES', '').split(',')
EXCLUDED_TYPES = os.environ.get('TYPES', '').split(',')

YEAR = os.environ.get('YEAR', '4')
GROUP = os.environ.get('GROUP', '1')
ALLOWED_YEARS = os.environ.get('ALLOWED_YEARS', '3,4,5').split(',')
ALLOWED_GROUPS = os.environ.get('ALLOWED_GROUPS', '1,2,3').split(',')


@app.route("/")
def hello():
    url = BASE_URL
    if url is None:
        return ""

    year = request.args.get('year', '')
    group = request.args.get('group', '')

    try:
        int(year)
        if year not in ALLOWED_YEARS:
            raise ValueError('year not allowed')
    except ValueError:
        year = YEAR

    try:
        int(group)
        if group not in ALLOWED_GROUPS:
            raise ValueError('group not allowed')
    except ValueError:
        group = GROUP

    url += "&promo={year}&groupe={group}".format(year=year, group=group)
    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):
    """
    Determines whether an event should be added to the returned calendar or not.

    :param event: The event to determine if should be added or not.
    :type event: Component
    :return: True if the event should be added, False otherwise.
    :rtype: bool
    """
    course_code = event['SUMMARY'].split('-')[1].split('/')[0]
    course_type = event['SUMMARY'].split('/')[1].split('_')[1]

    # Get user specified excluded courses/types if exist
    excluded_courses = request.args.get('excluded_courses', '')
    excluded_types = request.args.get('excluded_types', '')

    if excluded_courses == '':
        excluded_courses = EXCLUDED_COURSES
    else:
        excluded_courses = excluded_courses.split(',')

    if excluded_types == '':
        excluded_types = EXCLUDED_TYPES
    else:
        excluded_types = excluded_types.split(',')

    # Filter against courses and types
    return \
        course_code not in excluded_courses \
        and course_type not in excluded_types

if __name__ == "__main__":
    app.run('0.0.0.0', PORT)