from __future__ import print_function

import datetime
import os.path

from google.auth.transport.requests import Request
from google.oauth2.credentials import Credentials
from google_auth_oauthlib.flow import InstalledAppFlow
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError
from pprint import pprint

SCOPES = ['https://www.googleapis.comd/auth/calendar.readonly']

def authorize():
    creds = None

    if os.path.exists('token.json'):
        creds = Credentials.from_authorized_user_file('token.json', SCOPES)

    if not creds or not creds.valid:
        if creds and creds.expired and creds.refresh_token:
            creds.refresh(Request())
        else:
            flow = InstalledAppFlow.from_client_secrets_file('credentials.json', SCOPES)
            creds = flow.run_local_server(port=7384)

        with open('token.json', 'w') as token:
            token.write(creds.to_json())

    return creds

def construct_calendar_service(creds):
    return build('calendar', 'v3', credentials=creds)

def list_all_calendars(calendar_service):
    page_token = None
    list_of_entries = []

    while True:
        calendar_list = calendar_service.calendarList().list(pageToken=page_token).execute()
        
        list_of_entries.extend(calendar_list['items'])

        page_token = calendar_list.get('nextPageToken')

        if not page_token:
            break

    return list_of_entries

def main():
    creds = authorize()

    service = construct_calendar_service(creds)

    all_calendars = list_all_calendars(service)

    pprint(all_calendars)

if __name__ == '__main__':
    main()