working messsenger bot

.gitignore

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+.idea
+config/default.json
+ngrok

config/default.json.example

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+{
+  "facebook": {
+    "page": {
+      "access_token": "YOUR_PAGE_ACCESS_TOKEN"
+    }
+  }
+}

index.js

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+'use strict';
+let express = require('express'),
+    bodyParser = require('body-parser'),
+    app = express(),
+    request = require('request'),
+    config = require('config'),
+    images = require('./pics');
+
+app.use(bodyParser.urlencoded({ extended: false }));
+app.use(bodyParser.json());
+
+let users = {};
+
+app.listen(8989, () => console.log('Example app listening on port 8989!'));
+
+app.get('/', (req, res) => res.send('Hello World!'));
+
+
+// Creates the endpoint for our webhook
+app.post('/webhook', (req, res) => {
+
+    let body = req.body;
+
+    // Checks this is an event from a page subscription
+    if (body.object === 'page') {
+
+        // Iterates over each entry - there may be multiple if batched
+        body.entry.forEach(function(entry) {
+
+            // Gets the message. entry.messaging is an array, but
+            // will only ever contain one message, so we get index 0
+            let webhook_event = entry.messaging[0];
+            console.log(webhook_event);
+
+            // Get the sender PSID
+            let sender_psid = webhook_event.sender.id;
+            console.log('Sender PSID: ' + sender_psid);
+
+            // Check if the event is a message or postback and
+            // pass the event to the appropriate handler function
+            if (webhook_event.message) {
+                handleMessage(sender_psid, webhook_event.message);
+            } else if (webhook_event.postback) {
+                handlePostback(sender_psid, webhook_event.postback);
+            }
+        });
+
+        // Returns a '200 OK' response to all requests
+        res.status(200).send('EVENT_RECEIVED');
+    } else {
+        // Returns a '404 Not Found' if event is not from a page subscription
+        res.sendStatus(404);
+    }
+
+});
+
+// Adds support for GET requests to our webhook
+app.get('/webhook', (req, res) => {
+
+    // Your verify token. Should be a random string.
+    let VERIFY_TOKEN = "1476955067";
+
+    // Parse the query params
+    let mode = req.query['hub.mode'];
+    let token = req.query['hub.verify_token'];
+    let challenge = req.query['hub.challenge'];
+
+    // Checks if a token and mode is in the query string of the request
+    if (mode && token) {
+
+        // Checks the mode and token sent is correct
+        if (mode === 'subscribe' && token === VERIFY_TOKEN) {
+
+            // Responds with the challenge token from the request
+            console.log('WEBHOOK_VERIFIED');
+            res.status(200).send(challenge);
+
+        } else {
+            // Responds with '403 Forbidden' if verify tokens do not match
+            res.sendStatus(403);
+        }
+    }
+});
+
+function getImage(type, sender_id){
+    // create user if doesn't exist
+    if(users[sender_id] === undefined){
+        users = Object.assign({
+            [sender_id] : {
+                'cats_count' : 0,
+                'dogs_count' : 0
+            }
+        }, users);
+    }
+
+    let count = images[type].length, // total available images by type
+        user = users[sender_id], // // user requesting image
+        user_type_count = user[type+'_count'];
+
+
+    // update user before returning image
+    let updated_user = {
+        [sender_id] : Object.assign(user, {
+            [type+'_count'] : count === user_type_count + 1 ? 0 : user_type_count + 1
+        })
+    };
+    // update users
+    users = Object.assign(users, updated_user);
+
+    console.log(users);
+    return images[type][user_type_count];
+}
+
+function askTemplate(text){
+    return {
+        "attachment":{
+            "type":"template",
+            "payload":{
+                "template_type":"button",
+                "text": text,
+                "buttons":[
+                    {
+                        "type":"postback",
+                        "title":"Cats",
+                        "payload":"CAT_PICS"
+                    },
+                    {
+                        "type":"postback",
+                        "title":"Dogs",
+                        "payload":"DOG_PICS"
+                    }
+                ]
+            }
+        }
+    }
+}
+
+function imageTemplate(type, sender_id){
+    return {
+        "attachment":{
+            "type":"image",
+            "payload":{
+                "url": getImage(type, sender_id),
+                "is_reusable":true
+            }
+        }
+    }
+}
+
+// Handles messages events
+function handleMessage(sender_psid, received_message) {
+    let response;
+
+    // Check if the message contains text
+    if (received_message.text) {
+
+        // Create the payload for a basic text message
+        response = askTemplate();
+    }
+
+    // Sends the response message
+    callSendAPI(sender_psid, response);
+}
+
+function handlePostback(sender_psid, received_postback) {
+    let response;
+
+    // Get the payload for the postback
+    let payload = received_postback.payload;
+
+    // Set the response based on the postback payload
+    if (payload === 'CAT_PICS') {
+        response = imageTemplate('cats', sender_psid);
+        callSendAPI(sender_psid, response, function(){
+            callSendAPI(sender_psid, askTemplate('Show me more'));
+        });
+    } else if (payload === 'DOG_PICS') {
+        response = imageTemplate('dogs', sender_psid);
+        callSendAPI(sender_psid, response, function(){
+            callSendAPI(sender_psid, askTemplate('Show me more'));
+        });
+    } else if(payload === 'GET_STARTED'){
+        response = askTemplate('Are you a Cat or Dog Person?');
+        callSendAPI(sender_psid, response);
+    }
+    // Send the message to acknowledge the postback
+}
+
+// Sends response messages via the Send API
+function callSendAPI(sender_psid, response, cb = null) {
+    // Construct the message body
+    let request_body = {
+        "recipient": {
+            "id": sender_psid
+        },
+        "message": response
+    };
+
+    // Send the HTTP request to the Messenger Platform
+    request({
+        "uri": "https://graph.facebook.com/v2.6/me/messages",
+        "qs": { "access_token": config.get('facebook.page.access_token') },
+        "method": "POST",
+        "json": request_body
+    }, (err, res, body) => {
+        if (!err) {
+            if(cb){
+                cb();
+            }
+        } else {
+            console.error("Unable to send message:" + err);
+        }
+    });
+}