/**
 * Copyright 2017 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

'use strict';

const functions = require('firebase-functions');
const {google} = require('googleapis');
const {WebhookClient} = require('dialogflow-fulfillment');

// 需輸入Google Calander API裡的 calendar ID and service account JSON
const calendarId = '此處換成CALENDAR ID'; // Example: 6ujc6j6rgfk02cp02vg6h38cs0@group.calendar.google.com
const serviceAccount = {}; // 貼上JSON物件，The JSON object looks like: { "type": "service_account", ... }

// 設定 Google Calendar service account credentials
const serviceAccountAuth = new google.auth.JWT({
  email: serviceAccount.client_email,
  key: serviceAccount.private_key,
  scopes: 'https://www.googleapis.com/auth/calendar'
});

const calendar = google.calendar('v3');
process.env.DEBUG = 'dialogflow:*'; // It enables lib debugging statements

const timeZone = 'America/Los_Angeles';  // Change it to your time zone
const timeZoneOffset = '-07:00';         // Change it to your time zone offset

exports.dialogflowFirebaseFulfillment = functions.https.onRequest((request, response) => {
  const agent = new WebhookClient({ request, response });

  function makeAppointment (agent) {
    // Use the Dialogflow's date and time parameters to create Javascript Date instances, 'dateTimeStart' and 'dateTimeEnd',
    // which are used to specify the appointment's time.
    const appointmentDuration = 1;// Define the length of the appointment to be one hour.
    const dateTimeStart = convertParametersDate(agent.parameters.date, agent.parameters.time);
    const dateTimeEnd = addHours(dateTimeStart, appointmentDuration);
    const appointmentTimeString = getLocaleTimeString(dateTimeStart);
    const appointmentDateString = getLocaleDateString(dateTimeStart);
    // Check the availability of the time slot and set up an appointment if the time slot is available on the calendar
    return createCalendarEvent(dateTimeStart, dateTimeEnd).then(() => {
      agent.add(`Got it. I have your appointment scheduled on ${appointmentDateString} at ${appointmentTimeString}. See you soon. Good-bye.`);
    }).catch(() => {
      agent.add(`Sorry, we're booked on ${appointmentDateString} at ${appointmentTimeString}. Is there anything else I can do for you?`);
    });
  }
  let intentMap = new Map();
  intentMap.set('Make Appointment', makeAppointment);  // It maps the intent 'Make Appointment' to the function 'makeAppointment()'
  agent.handleRequest(intentMap);
});

function createCalendarEvent (dateTimeStart, dateTimeEnd) {
  return new Promise((resolve, reject) => {
    calendar.events.list({  // List all events in the specified time period
      auth: serviceAccountAuth,
      calendarId: calendarId,
      timeMin: dateTimeStart.toISOString(),
      timeMax: dateTimeEnd.toISOString()
    }, (err, calendarResponse) => {
      // Check if there exists any event on the calendar given the specified the time period
      if (err || calendarResponse.data.items.length > 0) {
        reject(err || new Error('Requested time conflicts with another appointment'));
      } else {
        // Create an event for the requested time period
        calendar.events.insert({ auth: serviceAccountAuth,
          calendarId: calendarId,
          resource: {summary: 'Bike Appointment',
            start: {dateTime: dateTimeStart},
            end: {dateTime: dateTimeEnd}}
        }, (err, event) => {
          err ? reject(err) : resolve(event);
        }
        );
      }
    });
  });
}

// A helper function that receives Dialogflow's 'date' and 'time' parameters and creates a Date instance.
function convertParametersDate(date, time){
  return new Date(Date.parse(date.split('T')[0] + 'T' + time.split('T')[1].split('-')[0] + timeZoneOffset));
}

// A helper function that adds the integer value of 'hoursToAdd' to the Date instance 'dateObj' and returns a new Data instance.
function addHours(dateObj, hoursToAdd){
  return new Date(new Date(dateObj).setHours(dateObj.getHours() + hoursToAdd));
}

// A helper function that converts the Date instance 'dateObj' into a string that represents this time in English.
function getLocaleTimeString(dateObj){
  return dateObj.toLocaleTimeString('en-US', { hour: 'numeric', hour12: true, timeZone: timeZone });
}

// A helper function that converts the Date instance 'dateObj' into a string that represents this date in English. 
function getLocaleDateString(dateObj){
  return dateObj.toLocaleDateString('en-US', { weekday: 'long', month: 'long', day: 'numeric', timeZone: timeZone });
}