How to show personalized 'Welcome Message' in facebook messenger?

Question

I would like to show 'welcome message' like 'Hi Robert, welcome to my application'. So I need to send:

1. "https://graph.facebook.com/v2.6/USER_ID?fields=first_name,last_name,profile_pic,locale,timezone,gender&access_token=PAGE_ACCESS_TOKEN"

2. using 'first_name' from 1st request, send "https://graph.facebook.com/v2.6/PAGE_ID/thread_settings?access_token=PAGE_ACCESS_TOKEN" request to set 'welcome message'.

However, I need to know user_id before first request.

My questions:

1. What are steps to create 'Welcome message'?
2. How to show 'Welcome message', when user opened facebook messenger window?

I reviewed https://developers.facebook.com/docs/messenger-platform document, and I have still questions.

Answer 1

So you can make this with a "get started" Button. This button is only there if the User Messages the bot for the first time.

With this command you can set the button:

curl -X POST -H "Content-Type: application/json" -d '{
  "setting_type":"call_to_actions",
  "thread_state":"new_thread",
  "call_to_actions":[
    {
      "payload":"USER_DEFINED_PAYLOAD"
    }
  ]
}' "https://graph.facebook.com/v2.6/me/thread_settings?access_token=PAGE_ACCESS_TOKEN"      

As you can see if the Button is pressed your Webhook recieves a "postback"

this is the callback you get:

{
  "sender":{
    "id":"USER_ID"
  },
  "recipient":{
    "id":"PAGE_ID"
  },
  "timestamp":1458692752478,
  "postback":{
    "payload":"USER_DEFINED_PAYLOAD"
  }
}  

So this is from where you can get User id

Now you can code a Function for this. My looks like this:

function receivedPostback(event) {
  var senderID = event.sender.id;
  var recipientID = event.recipient.id;
  var timeOfPostback = event.timestamp;

  // The 'payload' param is a developer-defined field which is set in a postback 
  // button for Structured Messages. 
  var payload = event.postback.payload;

  console.log("Received postback for user %d and page %d with payload '%s' " + 
    "at %d", senderID, recipientID, payload, timeOfPostback);


  if (payload) {

    // When a postback is called, we'll send a message back to the sender to 
    // let them know it was successful
      switch (payload) {
        case 'USER_DEFINED_PAYLOAD':
          startedConv(senderID);
          break;

       default:
         sendTextMessage(senderID, "Postback called");
       }

My startedConv() looks like this

function startedConv(recipientId){
var name;

request({
          url: 'https://graph.facebook.com/v2.6/'+ recipientId +'?fields=first_name',
          qs: {access_token: PAGE_ACCESS_TOKEN},
          method: 'GET'
      }, function(error, response, body) {
          if (error) {
              console.log('Error sending message: ', error);
          } else if (response.body.error) {
              console.log('Error: ', response.body.error);
          }else{
              name = JSON.parse(body);
              sendTextMessage(recipientId, "Hello "+ name.first_name+", how can i help you ? ")
          }
      });
}