This gem uses the Facebook Messenger API to send and receive Facebook messages. Note that you will need to configure a webhook URL in your web app to which facebook messages will be posted. Please go through the getting started guide for setting up Facebook Messenger API, which is a pre-requisite step for using this gem.

The following steps uses a rails setup, but the gem can be used in any ruby web framework that is capable of creating an API endpoint for the configured webhook.

1. Add the following to an initializer config/initializers/<name>.rb to setup your fb access token and fb verify token

   require 'fb/messenger'
   
   Fb::Messenger.configure do |config|
     config.access_token = 'FB_MESSENGER_ACCESS_TOKEN'
     config.verify_token = 'FB_MESSENGER_VERIFY_TOKEN'
   end

2. Ensure that you have subscribers for each of the messenger webhook events, namely 'message', 'postback', and 'deliver', e.g., add the following to the same config/initializers/<name>.rb file:

   Fb::Messenger::Receiver.configure do |receiver|
     receiver.subscribe 'message', MsgSubscriber.new
     receiver.subscribe 'postback', PostBackSubscriber.new
     receiver.subscribe 'delivery', DeliverySubscriber.new
   end

   Where the classes MsgSubscriber, PostBackSubscriber, and DeliverSubscriber (arbitary class names) implements a call method seen in Fb::Messenger::Subscriber::Base

   Usually in the call method, you would use the Fb::Messenger::Client to create reply message back to the sender.

3. In routes.rb specify two endpoints, one for verifying the webhook and one for handling webhook POST requests, e.g.,

   Rails.application.routes.draw do
     get 'facebook/webhook' => 'facebook#verify'
     post 'facebook/webhook' => 'facebook#webhook'
   end

4. In the corresponding controller that implements the webhook add the following:

   def webhook
     Fb::Messenger::Receiver.receive(params[:entry])
     head 200
   end

   Note that you need to return 2XX to indicate that you have received the message. To implement the verify controller action method for this example, please see the fb messenger getting started guide.

The Fb::Messenger::Client is used for sending fb messages. In the following examples, id can represent different types of facebook id's, such as page id's or user id's (see: https://developers.facebook.com/docs/messenger-platform/send-api-reference). Note that the Fb::Messenger::Client can be used in your subscriber call methods to reply back to messages.

Send Text Messages:

Fb::Messenger::Client.send_message_text(id, "your message here")

Send Generic Template Messages:

item = Fb::Messenger::Template::GenericItem.new
# assign values to each attribute
item.title = 'title'
item.subtitle = '...'
item.image_url = '...'

button = Fb::Messenger::Template::Button.new
# see: https://developers.facebook.com/docs/messenger-platform/send-api-reference/button-template
button.type = 'postback'
button.title = '...'
# this can be a json string that your Subscriber for postback must handle
button.payload = '...'

# you can add multiple buttons
item.buttons << button

generic = Fb::Messenger::Template::Generic
# you can add multiple generic items
generic.generic_items << item

template_msg = generic.template
Fb::Messenger::Client.send_message_template(id, template_msg)

Send Receipt Template Messages:

item = Fb::Messenger::Template::ReceiptItem.new
item.title = 'title'
item.subtitle = '...'
item.quantity = '...'
item.price = '...'
item.currency = '...'
item.image_url = '...'

receipt = Fb::Messenger::Template::Receipt.new

# Please see https://developers.facebook.com/docs/messenger-platform/send-api-reference/receipt-template for example values
receipt.recipient_name = '...'
receipt.order_number = '...'
receipt.currency = '...'
# payment_method cannot be nil
receipt.payment_method = '...'
receipt.order_url = '...'
receipt.timestamp = '...'
receipt.total_cost = '...'
# can add multiple items
receipt.receipt_items << item

template_msg = receipt.template
Fb::Messenger::Client.send_message_template(id, template_msg)

The gem is available as open source under the terms of the MIT License.