web.rb

require 'sinatra'
require 'stripe'
require 'dotenv'
require 'json'
require 'encrypted_cookie'

Dotenv.load
Stripe.api_key = ENV['STRIPE_TEST_SECRET_KEY']

use Rack::Session::EncryptedCookie,
  :secret => 'replace_me_with_a_real_secret_key' # Actually use something secret here!

get '/' do
  status 200
  return "Great, your backend is set up. Now you can configure the Stripe example apps to point here."
end

post '/ephemeral_keys' do
  authenticate!
  begin
    key = Stripe::EphemeralKey.create(
      {customer: @customer.id},
      {stripe_version: params["api_version"]}
    )
  rescue Stripe::StripeError => e
    status 402
    return "Error creating ephemeral key: #{e.message}"
  end

  status 200
  key.to_json
end

post '/charge' do
  authenticate!
  # Get the credit card details submitted
  payload = params
  if request.content_type.include? 'application/json' and params.empty? 
    payload = indifferent_params(JSON.parse(request.body.read))
  end

  source = payload[:source]
  customer = payload[:customer_id] || @customer.id
  # Create the charge on Stripe's servers - this will charge the user's card
  begin
    charge = Stripe::Charge.create(
      :amount => payload[:amount], # this number should be in cents
      :currency => "usd",
      :customer => customer,
      :source => source,
      :description => "Example Charge",
      :shipping => payload[:shipping],
    )
  rescue Stripe::StripeError => e
    status 402
    return "Error creating charge: #{e.message}"
  end

  status 200
  return "Charge successfully created"
end

def authenticate!
  # This code simulates "loading the Stripe customer for your current session".
  # Your own logic will likely look very different.
  return @customer if @customer
  if session.has_key?(:customer_id)
    customer_id = session[:customer_id]
    begin
      @customer = Stripe::Customer.retrieve(customer_id)
    rescue Stripe::InvalidRequestError
    end
  else
    begin
      @customer = Stripe::Customer.create(:description => "mobile SDK example customer")
    rescue Stripe::InvalidRequestError
    end
    session[:customer_id] = @customer.id
  end
  @customer
end

# This endpoint is used by the Obj-C and Android example apps to create a charge.
post '/create_charge' do
  # Create the charge on Stripe's servers
  begin
    charge = Stripe::Charge.create(
      :amount => params[:amount], # this number should be in cents
      :currency => "usd",
      :source => params[:source],
      :description => "Example Charge"
    )
  rescue Stripe::StripeError => e
    status 402
    return "Error creating charge: #{e.message}"
  end

  status 200
  return "Charge successfully created"
end

# This endpoint responds to webhooks sent by Stripe. To use it, you'll need
# to add its URL (https://{your-app-name}.herokuapp.com/stripe-webhook)
# in the webhook settings section of the Dashboard.
# https://dashboard.stripe.com/account/webhooks
post '/stripe-webhook' do
  json = JSON.parse(request.body.read)

  # Retrieving the event from Stripe guarantees its authenticity
  event = Stripe::Event.retrieve(json["id"])
  source = event.data.object

  # For sources that require additional user action from your customer
  # (e.g. authorizing the payment with their bank), you should use webhooks
  # to create a charge after the source becomes chargeable.
  # For more information, see https://stripe.com/docs/sources#best-practices
  WEBHOOK_CHARGE_CREATION_TYPES = ['bancontact', 'giropay', 'ideal', 'sofort', 'three_d_secure']
  if event.type == 'source.chargeable' && WEBHOOK_CHARGE_CREATION_TYPES.include?(source.type)
    begin
      charge = Stripe::Charge.create(
        :amount => source.amount,
        :currency => source.currency,
        :source => source.id,
        :customer => source.metadata["customer"],
        :description => "Example Charge"
      )
    rescue Stripe::StripeError => e
      p "Error creating charge: #{e.message}"
      return
    end
    # After successfully creating a charge, you should complete your customer's
    # order and notify them that their order has been fulfilled (e.g. by sending
    # an email). When creating the source in your app, consider storing any order
    # information (e.g. order number) as metadata so that you can retrieve it
    # here and use it to complete your customer's purchase.
  end
  status 200
end