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', '')

    year = validate(year, ALLOWED_YEARS, YEAR)
    group = validate(group, ALLOWED_GROUPS, 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 VTIMEZONE components
    for ev in cal.walk('VTIMEZONE'):
        other.add_component(ev)

    # 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


def validate(item, validation_list, default):
    """
    Validates an item from user input against a list of possible values.

    :param item: The item to validate.
    :type item: object
    :param validation_list: The list of possible values.
    :type item: list(object)
    :param default: The default value to fallback on if item is not in list.
    :type default: object
    :return: The item if it is valid (in the list), or default
    :rtype: object
    """
    try:
        int(item)
        if item not in validation_list:
            raise ValueError(item.__name__ + ' not allowed')
    except ValueError:
        return default
    return item

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