calendar-booking/calendar_booking_api.py

import bisect
from datetime import datetime, timedelta
from flask import Flask, jsonify, make_response, redirect, request
from google.auth.transport.requests import Request
from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build
import pytz


# Monday to Friday
WEEK_DAYS = {1, 2, 3, 4, 5}

# 9 to 5
FROM = 9
TO = 17

TIMEZONE_NAME = 'America/New_York'
TIMEZONE = pytz.timezone(TIMEZONE_NAME)

AVAILABILITY_LIFETIME = timedelta(minutes=2)

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

UTC = pytz.timezone('UTC')

creds = Credentials.from_authorized_user_file('creds.json', SCOPES)


def read_datetime(dct):
    dt = datetime.fromisoformat(dct['dateTime']).replace(tzinfo=None)
    dt = pytz.timezone(dct['timeZone']).localize(dt)
    return dt


def asiso(dt):
    return dt.isoformat()[:19]


def asutciso(dt):
    return asiso(dt.astimezone(UTC)) + 'Z'


def aslocal(dt):
    return dt.astimezone(TIMEZONE).strftime('%Y-%m-%d %H:%M:%S')


def get_availability():
    if not creds.valid:
        creds.refresh(Request())
    service = build('calendar', 'v3', credentials=creds)

    # Get events for the next 2 weeks
    now = datetime.utcnow()
    start = datetime(now.year, now.month, now.day)
    end = start + timedelta(days=14)
    events_result = service.events().list(
        calendarId='primary',
        timeMin=asutciso(now),
        timeMax=asutciso(end),
        maxResults=200,
        singleEvents=True,
        orderBy='startTime',
    ).execute()

    # Build a list of possible time slots for the next 2 weeks
    availability = []
    for day in range(14):
        day = start + timedelta(days=day)
        if day.weekday() not in WEEK_DAYS:
            continue
        for hour in range(FROM, TO):
            for minute in (0, 30):
                availability.append(TIMEZONE.localize(
                    day.replace(hour=hour, minute=minute),
                ))

    for event in events_result.get('items', []):
        event_start = read_datetime(event['start'])
        event_end = read_datetime(event['end'])

        # Find the first slot that starts less than 30min before this event
        first_idx = bisect.bisect_right(
            availability,
            event_start - timedelta(minutes=30),
        )

        # Find the first slot that starts after this event ends
        last_idx = bisect.bisect_left(
            availability,
            event_end,
        )

        # Remove the slots from the availability
        del availability[first_idx:last_idx]

    return availability


availability = get_availability()
availability_as_of_date = datetime.utcnow()


app = Flask('calendar_booking_api')


@app.route('/availability')
def api_availability():
    global availability, availability_as_of_date
    if (
        availability_as_of_date is None
        or availability_as_of_date + AVAILABILITY_LIFETIME < datetime.utcnow()
    ):
        availability = get_availability()
        availability_as_of_date = datetime.utcnow()

    return jsonify({'availability': [asutciso(time) for time in availability]})


@app.route('/book', methods=['POST', 'OPTIONS'])
def api_book():
    # Allow cross-origin
    if request.method == 'OPTIONS':
        response = make_response()
        response.headers.add(
            'Access-Control-Allow-Origin',
            'https://vicky.rampin.org',
        )
        response.headers.add(
            'Access-Control-Allow-Headers',
            'Content-Type',
        )
        response.headers.add(
            'Access-Control-Allow-Methods',
            'POST',
        )
        return response

    if not creds.valid:
        creds.refresh(Request())
    service = build('calendar', 'v3', credentials=creds)

    full_name = request.form['name']
    email = request.form['email']
    topic = request.form['topic']
    date = request.form['date']

    end = start + timedelta(minutes=30)

    service.events().insert(
        calendarId='primary',
        body=dict(
            start={'dateTime': asiso(start), 'timeZone': TIMEZONE_NAME},
            end={'dateTime': asiso(end), 'timeZone': TIMEZONE_NAME},
            summary="Meeting with Vicky",
            description="Meeting scheduled from the web",
        ),
    )

    response = redirect('https://vicky.rampin.org/book-successful', 303)
    response.headers.add(
        'Access-Control-Allow-Origin',
        'https://vicky.rampin.org',
    )
    return response