Pay subscription changes

.Pay subscription notifications.md

Goal: send a notification when a customer subscribes, churns, pauses, etc.

This is the barebones working version. Is there something I'm missing in Pay that could help with this?

If not, happy to clean it up and submit a PR if it will be valuable for others.

Note: This first-pass implementation is ugly, but the tests pass. There is obviously a lot to improve in terms of code quality, but my bigger focus is on the direction and idea.

concerns_pay_subscription_extensions.rb

module Pay
  module SubscriptionExtensions
    extend ActiveSupport::Concern

    included do
      after_commit :send_admin_notification
    end

    def send_admin_notification
      case SubscriptionChanges.new(self)
      when :subscribed
        # subscribed
      when :churned
        # churned
      when :resubscribed
        # resubscribed
      when :plan_changed
        # plan_changes
      when :paused
        # paused
      when :unpaused
        # unpaused
      end
    end
  end
end

initializers_pay.rb

Pay.setup do |config|
  # ...
end

Rails.application.config.to_prepare do
  Pay::Subscription.include Pay::SubscriptionExtensions
end

models_pay_subscription_changes.rb

module Pay
  class SubscriptionChanges
    private attr_reader :subscription

    def initialize(subscription)
      @subscription = subscription
    end

    def status
      ends_at_changes = subscription.previous_changes[:ends_at]
      proccessor_plan_changes = subscription.previous_changes[:processor_plan]
      data_changes = subscription.previous_changes[:data]

      if ends_at_changes&.first.present? && ends_at_changes&.last.nil?
        :resubscribed
      elsif ends_at_changes&.first.nil? && ends_at_changes&.last.present?
        :churned
      elsif proccessor_plan_changes&.first.nil? && proccessor_plan_changes&.last.present?
        :subscribed
      elsif subscription.previous_changes.key?(:processor_plan)
        :plan_changed
      elsif data_changes.first[:pause_behavior].present? && data_changes.last[:pause_behavior].nil?
        :unpaused
      elsif data_changes.first[:pause_behavior].nil? && data_changes.last[:pause_behavior].present?
        :paused
      end
    end
  end
end

pay_subscription_changes_test.rb

require "test_helper"

class Pay::SubscriptionChangesTest < ActiveSupport::TestCase
  test "subscribed: processor_plan nil -> present" do
    subscription = create_subscription!
    status = Pay::SubscriptionChanges.new(subscription).status
    assert_equal :subscribed, status
  end

  test "churned: ends_at nil -> present" do
    subscription = create_subscription!
    subscription.update!(ends_at: Date.tomorrow)

    status = Pay::SubscriptionChanges.new(subscription).status

    assert_equal :churned, status
  end

  test "resubscribed: ends_at present -> nil" do
    subscription = create_subscription!(ends_at: Date.tomorrow)
    subscription.update!(ends_at: nil)

    status = Pay::SubscriptionChanges.new(subscription).status

    assert_equal :resubscribed, status
  end

  test "plan_changed: processor_plan present -> present" do
    subscription = create_subscription!
    subscription.update!(processor_plan: :new_plan)

    status = Pay::SubscriptionChanges.new(subscription).status

    assert_equal :plan_changed, status
  end

  test "paused: pause_behavior nil -> present" do
    subscription = create_subscription!
    subscription.update!(data: {
      pause_behavior: :void
    })

    status = Pay::SubscriptionChanges.new(subscription).status

    assert_equal :paused, status
  end

  test "unpaused: pause_behavior present -> nil" do
    subscription = create_subscription!(pause_behavior: :void)
    subscription.update!(data: {
      pause_behavior: nil
    })

    status = Pay::SubscriptionChanges.new(subscription).status

    assert_equal :unpaused, status
  end

  def create_subscription!(ends_at: nil, pause_behavior: nil)
    Pay::Subscription.create!(
      customer: pay_customers(:one),
      name: "sub_name",
      processor_id: :sub_id,
      processor_plan: :processor_plan,
      status: :active,
      ends_at: ends_at,
      data: {
        pause_behavior: pause_behavior
      }
    )
  end
end