Generic Stripe receipt webhook with Sinatra and Mailgun

email_receipt.rb

# A simple text-based email receipt webhook, written for Sinatra. Sends email receipts for one-off charges.
# See https://github.com/adamjstevenson/stripe-ruby-webhook-receipts for more specifics

require 'sinatra'
require 'stripe'
require 'mailgun-ruby'

# Set your Stripe secret key as an environment variable: https://dashboard.stripe.com/account/apikeys
Stripe.api_key = ENV['STRIPE_KEY']

# Set mailgun API key and domain: https://mailgun.com/app/domains
mg_client = Mailgun::Client.new ENV['MAILGUN_KEY']
mg_domain = ENV['MAILGUN_DOMAIN']

# Listen for a POST to the /webhook endpoint
post "/webhook" do
  # Retrieve the request's body and parse it as JSON
  event_json = JSON.parse(request.body.read)

  # Retrieve the event from Stripe
  event = Stripe::Event.retrieve(event_json['id'])

  # Only respond to `charge.succeeded` events with an email address available
  if event.type.eql?('charge.succeeded') && event.data.object.metadata.email
    
    # Send an email receipt
    message_params = {
      from: "postmaster@#{mg_domain}", # Your domain or Mailgun Sandbox domain
      to: event.data.object.metadata.email, # Email address for the charge, storing in metadata here
      subject: 'Your SITE-NAME.COM email receipt',
      text: text_email(event)
    }
    
    result = mg_client.send_message(mg_domain, message_params).to_h!
    puts result
  else 
    # Nothing to see here, return a 200
    status 200
  end
end

# Text email
def text_email(event)
  <<-EOF
  Hi there, 

  Thank you for your purchase: here's your payment receipt!

  Questions? Please contact [email protected].

  =================================================================
  SITE-NAME RECEIPT - Payment for #{event.data.object.description}

  Total: #{format_amount(event.data.object.amount)} #{event.data.object.currency}

  Charged to: #{event.data.object.source.brand} ending in #{event.data.object.source.last4}
  Payment ID: #{event.data.object.id}
  Date: #{Time.now.strftime("%m/%d/%Y")}

  SITE-NAME.COM
  3180 18th Street
  San Francisco, CA 94110
  =================================================================

  EOF
end

def format_amount(amount)
  sprintf('$%0.2f', amount.to_f / 100.0).gsub(/(\d)(?=(\d\d\d)+(?!\d))/, "\\1,")
end