server.js

// server.js
// where your node app starts

// init project
var express = require('express');
var app = express();
var bodyParser = require('body-parser');
var request = require('request');
var moment = require('moment');
// we've started you off with Express,
// but feel free to use whatever libs or frameworks you'd like through `package.json`.

// http://expressjs.com/en/starter/static-files.html
app.use(express.static('public'));
app.use(bodyParser.urlencoded({extended: true}));

app.get("/", function (request, response) {
  response.sendFile(__dirname + '/views/index.html');
});

app.post('/meetupbot', function (req, res) {
  /* /meetupbot calls the meetupbot and response is list of commands */
  var userName = req.body.user_name;
  var reply = {
    "text": "Hello, " +userName+ " I am a MeetupBot. I show list of meetups going on near your location.\n Try following commands :",
    "attachments": [
       {
         title: "1) /meetupbot-find <location> (& <group>)",
         text: `use this to find local meetup-groups based on your location \nfor ex: /meetupbot-find New-York
         \noptional: add parameter for your interests: '/meetupbot-find New-York & <interest>'`,
         color: "#764FA5"
       },
       {
         title: "2) /meetupbot-show <location> & <interest>",
         text: "use this to find meetup-events based on your location and interests \nfor ex: /meetupbot-show Mumbai & Javascript (Don't forget to use ampersand (&).)",
         color: "#764FA5"
       }
    ]
  };
  res.json(reply);
});

app.post('/meetupbot-show', function(req, res) {
  /* /meetupbot-show <Location> <Category/Interest> */
  var userName = req.body.user_name;
  var commandText = req.body.text;
  var area = commandText.split('&')[0];
  var interest = commandText.split('&')[1];
  var reply = {};
  var location={};
  var attachment=[];

  if(!commandText || commandText == undefined){
    reply.text = 'Please provide a location along with the command @'+userName+'\nFor ex: /meetupbot-show Mumbai & Javascript.';
    return res.json({text: reply.text});
  } else if(interest =='' || interest == undefined){
    reply.text = 'Please provide a location & search term along with the command @'+userName+'\nFor ex: /meetupbot-show Mumbai & Javascript.\nIt helps in filtering the list of meetups according to your interest :blush:.'+'\nActually it will be difficult to show a long list of meetups for me right now :stuck_out_tongue_winking_eye:.';
    res.json(reply);
  } else {
     reply.text = 'Hey '+userName+',\nThis is the list of meetups near '+area+'.';
     getGeoCode(area)
       .then((data) => {
         location.lat = data.lat;
         location.lon = data.lng;
         getMeetupEvents(location, interest)
           .then((events) =>{
             if(events.length == 0){
               reply.text = 'No Meetups found in '+area+' :sleuth_or_spy: .\nMake sure the location you entered is correct and try again.:slightly_smiling_face:';
               return res.json(reply);
             }
             events.forEach((event) => {
               var status = (event.status != undefined) ? ('Status - '+event.status) : 'Status - visible only to Members';
               var date = new Date(event.time + event.utc_offset);
               date = moment(date).format('lll');
               var venue = (event.venue != undefined) ? event.venue.address_1 : 'Only visible to members';
               attachment.push({
                 title: 'Group - '+event.group.name,
                 text: '<'+event.link+'| Event - '+event.name+'>',
                 author_name: status,
                 title_link: 'https://www.meetup.com/'+event.group.urlname,
                 color: "#764FA5",
                 fields: [
                   { "title": "Date", "value": date, "short": true },
                   { "title": "Venue", "value": venue, "short": true },
                   { "title": "RSVP Count", "value": event.yes_rsvp_count, "short": true }
                 ]
               });
             });
             reply.attachments = attachment;
             return res.json(reply);
           }) // catch for getMeetupEvents
           .catch((e) => {
             console.log("error occured in getMeetupEvents promise as "+e);
             return res.json({text: 'Ops something went wrong. Please try again :blush:'});
           });
       }) // catch for getGeoCode
      .catch((e) => {
         console.log("error in geocode as "+e);
         return res.json({text: 'Ops something went wrong. Please try again :blush:'});
       });
  }
});

app.post('/meetupbot-find', function(req, res) {
    var location = {};
    var commandText = req.body.text.replace(" ", "");
    var userName = req.body.user_name;
    var reply = {};
    var area,interest;

    if(commandText.includes("&")) {
      area = commandText.split("&")[0];
      interest = commandText.split("&")[1];
    } else {
      area = commandText;
      interest = "";
    }

    if(!commandText || commandText == undefined){
      reply.text = '@' + userName + ` Please provide a location along with the command \nFor ex: /meetupbot-find London
       (& <category>)`;
      return res.json(reply);
    } else if(interest === undefined) {
      reply.text = '@' + userName + ' Please use the correct syntax: /meetupbot-find <location> & <interest>';
      return res.json(reply);
    } else {
      reply.text = "Hey @" + userName +"\nThose are the groups near " + area;
      if(interest) reply.text += " for" + interest;

      getGeoCode(area)
        .then(function(data) {
          location.lat = data.lat;
          location.lon = data.lng;

          findMeetupGroups(location, interest)
            .then(function(groups) {
              if (groups.length === 0) {
                reply.text = 'No groups found near '+area+` :sleuth_or_spy: .\nMake sure the location you entered is correct
                and you didn\'t forget the "&". \nPlease  try again.:slightly_smiling_face:`;
                return res.json(reply);
              } else if (groups.length > 20) {
                reply.attachments = [];
                for (var i = 0; i <21; i++) {
                  var current = groups[i];
                  composeAttachments(reply.attachments, current);
                }
                return res.json(reply);
              } else {
                reply.attachments = [];
                groups.forEach(function(group) {
                    composeAttachments(reply.attachments, group);
                });
                return res.json(reply);
              }
            })
            .catch(function() { //catch for findMeetupGroups
              return res.json({text: 'Ops something went wrong. Please try again :blush:'});
            });
      })
      .catch(function() { // catch for getGeoCode
          return res.json({text: 'Ops something went wrong. Please try again :blush:'});
      });
    }
});

/*
*function to get the Geocode from google geocode API.
*/
function getGeoCode(location){
  return new Promise(function(resolve, reject) {
    var options = {
      method: 'GET',
      url: 'http://maps.googleapis.com/maps/api/geocode/json',
      qs: { address: location }
    };

    request(options, function (error, res, body) {
      if (error) {
        console.log("Error occured in getGeoCode as "+error);
        reject();
      } else {
        body = JSON.parse(body);
        var loc = body.results[0].geometry.location;
        resolve(loc);
      }
    });
  });
}
/*
*function to get meetups near your city/town/location using meetup API
*/
function getMeetupEvents(location, interest) {
  var key = process.env.SECRET;

  return new Promise((resolve, reject) => {
    var options = { method: 'GET',
      url: 'https://api.meetup.com/find/events',
      qs: {
        key: key,
        lat: location.lat,
        lon: location.lon,
        text: interest,
        radius: 10
      }
    };

    console.log(options);
    request(options, function (error, response, body) {
      if (error) {
        console.log("error occured in getMeetupEvents as "+error);
        reject();
      } else {
        body = JSON.parse(body);
        console.log(body.length);
        resolve(body);
      }
    });
  });
}

/*
*function to get meetup-groups near your city/town/location using meetup API
*/
function findMeetupGroups (location, interest){
    var key = process.env.SECRET;

    return new Promise(function(resolve, reject){
      var options = {
        method: "GET",
        url: "https://api.meetup.com/find/groups",
        qs: {
          key: key,
          lat: location.lat,
          lon: location.lon,
          radius: 10
        }
      };
      if(!(interest === undefined || interest === "")) options.qs.text = interest;

      //api-request
      request(options, function(error, response, body) {
        if(error) {
          console.log("error occured in findMeetupGroups: " + error);
          reject();
         } else {
           body = JSON.parse(body);
           resolve(body);
         }
      });
    });
}

//function to help compose reply
function composeAttachments(arr, obj){
  arr.push({
    title: obj.name,
    text: /*obj.description,*/removeHtml(obj.description),
    color: "#764FA5",
    mrkdwn_in: ["text", "attachments"],
    fields: [
      {"title": "Link","value": obj.link,"short": true},
      {"title": "Members","value": obj.members,"short": true},
    ]
  });
}

function removeHtml(str) {
  var tags = /<\/?\w+>/g, bold = /<\/?b>/g, entities = /&\w+;/g, italics = /<\/?i>/g;
  var linebreak = /<\/?br>/g, imgAndA = /<(?:a\s|img\s).+>/g;
  var descr;
  // cut str to 300 characters
  if (str.length>300) descr=str.substr(0, 300);
  else descr = str;
  var description = descr.replace(bold, "*").replace(italics, "_").replace(entities, "").replace(linebreak, "\n");
  var result = description.replace(tags, "").replace(imgAndA, "").replace(/<\w*$/, "");
  return result + "...";
}

app.get('/redirected', function(req,res){
  //route for redirection for the add to slack button
  doOauth(req.query)
    .then((data)=>{
      //got the tooken i.e successfully installed the MeetupBot on slack channel.
      console.log('doOauth then block with data as '+JSON.stringify(data));
      res.redirect('/');
    })
    .catch((err)=>{
     res.json({'error': 'Ops Something went wrong! Please try again.'});
     console.log('error as '+err);
    });
});

function doOauth(data){
  return new Promise((resolve, reject) => {
    var options = {
      method: 'POST',
      headers:{
        'content-type': 'application/x-www-form-urlencoded',
        charset: 'utf-8',
      },
      url: 'https://slack.com/api/oauth.access',
      form: {
        'client_id': process.env.slackClientId,
        'client_secret': process.env.slackSecret,
        'code': data.code
      },
      json: true,
      'redirect_uri':'https://meetupbot.glitch.me/redirected'
    };

    console.log(options);
    request(options, function (error, response, body) {
      if (error) {
        console.log("error occured in doOauth as "+error);
        reject();
      } else{
        resolve(body);
      }
    });
  });
}

// listen for requests :)
var listener = app.listen(process.env.PORT, function () {
  console.log('Your app is listening on port ' + listener.address().port);
});