Ruby service for Microsoft Outlook calendar API

outlook_calendar_service.rb

class OutlookCalendarService
  APP_ID = your_app_id
  APP_SECRET = your_app_secret

  LOGIN_API_DOMAIN = 'https://login.microsoftonline.com'
  AUTHORIZE_PATH = '/common/oauth2/v2.0/authorize'
  TOKEN_PATH = '/common/oauth2/v2.0/token'

  CALENDAR_API_DOMAIN = 'https://outlook.office365.com'
  VERSION_PATH = '/api/v2.0'

  SCOPES = ['openid', 'https://outlook.office.com/Calendars.ReadWrite']

  attr_reader :callback_url

  def initialize(callback_url)
    @callback_url = callback_url
  end

  def login_url
    auth_code.authorize_url(redirect_uri: callback_url, scope: scopes)
  end

  def auth(code)
    auth_code.get_token(code, redirect_uri: callback_url, scope: scopes)
  end

  def email(auth)
    decoded_token(auth)['preferred_username']
  end

  def create_event(token, attributes = {})
    url = "#{ CALENDAR_API_DOMAIN }#{ VERSION_PATH }/me/events"
    headers = create_event_headers(token)
    body = create_event_attributes(attributes)
    do_post_request(url, headers, body)
  end

  private

  def oauth_client
    @oauth_client ||= OAuth2::Client.new(APP_ID,
                                         APP_SECRET,
                                         site: LOGIN_API_DOMAIN,
                                         authorize_url: AUTHORIZE_PATH,
                                         token_url: TOKEN_PATH)
  end

  def auth_code
    oauth_client.auth_code
  end

  def scopes
    SCOPES.join(' ')
  end

  def encoded_token(auth)
    id_token = auth.params['id_token']
    token_parts = id_token.split('.')
    encoded_token = token_parts[1]
    leftovers = token_parts[1].length.modulo(4)

    if leftovers == 2
      encoded_token += '=='
    elsif leftovers == 3
      encoded_token += '='
    end

    encoded_token
  end

  def decoded_token(auth)
    decoded_token = Base64.urlsafe_decode64(encoded_token(auth))
    JSON.parse(decoded_token)
  end

  def create_event_headers(token)
    { 'Authorization' => "Bearer #{ token }",
      'Accept' => 'application/json',
      'Content-Type' => 'application/json',
      'User-Agent' => 'Vesper',
      'client-request-id' => rand(100000..999999),
      'return-client-request-id' => 'true' }
  end

  def create_event_attributes(attributes)
    { 'Subject' => attributes[:summary],
      'Body' => { 'ContentType' => 'HTML', 'Content' => attributes[:description] },
      'Start' => { 'DateTime' => attributes[:start_at], 'TimeZone' => attributes[:time_zone] },
      'End' => { 'DateTime' => attributes[:end_at], 'TimeZone' => attributes[:time_zone] },
      'Attendees' => attributes[:attendees_emails].map { |email| { 'EmailAddress' => { 'Address' => email }, 'Type' => 'Required' } } }
  end
end