Example of using Stripe Subscriptions to handle usage based billing for recurring payments

stripe_usage_based_billing_with_subscriptions.rb

# Mike Bianco <mike@suitesync.io>
# Description: Example of using Stripe's subscription billing to add usage based billing
#              information to the customer's recurring invoice

require 'stripe'
require 'sinatra'

Stripe.api_key = ENV['STRIPE_KEY']

# This example uses sinatra to listen for webhooks. You can easily use rails, or any other framework/language.
# Listen to Stripe events using webhooks
#
#   - https://stripe.com/docs/webhooks
#   - https://dashboard.stripe.com/account/webhooks
#
# In order to test this example out, you'll need to bind Stripe's webhooks to this local server:
#
#   1. Create a server to forward requests locally: `ngrok http 8081`
#   2. Setup the resulting ngrok domain in Stripe: https://dashboard.stripe.com/account/webhooks
#   3. Set your Stripe key: `export STRIPE_KEY=sk_test`
#   4. Run `ruby stripe_usage_based_billing_with_subscriptions.rb` to start the local server
#   5. Visit http://localhost:8081/example to trigger an example

# set port & host explicitly to match ngrok so Stripe can send us webhooks
set :port, 8081
set :bind, 'localhost'

def generate_example_plan
  plan = (Stripe::Plan.retrieve('example-usage-plan') rescue nil)
  return plan if plan

  Stripe::Plan.create(
    id: 'example-usage-plan',
    name: 'Example Usage Based Billing Plan',
    amount: 10_00,
    interval: 'month',
    currency: 'usd',
  )
end

post "/" do
  event_json = JSON.parse(request.body.read)

  # https://stripe.com/docs/api#list_events
  # invoice.created is fired an hour or so before the invoice is paid

  if event_json['type'] == 'invoice.created'
    invoice_id = event_json['data']['object']['id']
    customer_id = event_json['data']['object']['customer']

    # initial invoices are always paid immediately; we only want to run usage based billing
    # after the initial billing period

    is_invoice_paid = event_json['data']['object']['paid']

    if is_invoice_paid
      status 200
      return
    end

    puts "adding invoice item to invoice: #{invoice_id}"

    # the line item can be mapped to a NetSuite item based on the name, or a direct
    # reference to a NetSuite item: https://dashboard.suitesync.io/docs/invoices#standalone-invoice-items

    invoice_item = Stripe::InvoiceItem.create(
      customer: customer_id,
      invoice: invoice_id,
      amount: (rand * 100).round,
      currency: 'usd',
      description: 'Usage Based Billing',

      # add custom information about the charge
      # metadata: { }
    )
  end

  status 200
end

get '/example' do
  plan = generate_example_plan

  customer = Stripe::Customer.create
  customer.sources.create(source: 'tok_visa')

  customer.subscriptions.create(
    plan: plan.id,
    trial_end: Time.now.to_i + 5
  )

  puts customer.id
end