implements a service to handle subscription extension after reservation, comes with tests

app/services/subscription_extension_after_reservation.rb

@@ -0,0 +1,26 @@
+class SubscriptionExtensionAfterReservation
+  attr_accessor :user, :reservation
+
+  def initialize(reservation)
+    @user, @reservation = reservation.user, reservation
+  end
+
+  def extend_subscription_if_eligible
+    extend_subscription if eligible_to_extension?
+  end
+
+  def eligible_to_extension?
+    return false unless reservation.reservable_type == 'Training'
+    return false if user.reservations.where(reservable_type: 'Training').count != 1
+    return false unless user.subscription
+    return false if user.subscription.is_expired?
+    return false unless user.subscribed_plan.is_rolling
+    return true
+  end
+
+  def extend_subscription
+    user.subscription.update_columns(
+      expired_at: reservation.slots.first.start_at + user.subscribed_plan.duration
+    )
+  end
+end

test/services/subscription_extension_after_reservation_test.rb

@@ -0,0 +1,50 @@
+require 'test_helper'
+
+class SubscriptionExtensionAfterReservationTest < ActiveSupport::TestCase
+  setup do
+    @machine = Machine.find(6)
+    @training = Training.find(2)
+
+    @plan = Plan.find(3)
+    @plan.update!(is_rolling: true)
+
+    @user = User.joins(:subscriptions).find_by(subscriptions: { plan: @plan })
+
+    @user.reservations.destroy_all # ensure no reservations
+
+    @availability = @machine.availabilities.first
+    slot = Slot.new(start_at: @availability.start_at, end_at: @availability.end_at, availability_id: @availability.id)
+    @reservation_machine = Reservation.new(user: @user, reservable: @machine, slots: [slot])
+    @reservation_training = Reservation.new(user: @user, reservable: @training, slots: [slot])
+    @reservation_training.save!
+  end
+
+  test "is eligible for extension because all conditions are met by default (test setup)" do
+    assert SubscriptionExtensionAfterReservation.new(@reservation_training).eligible_to_extension?
+  end
+
+  test "not eligible if reservable is a machine" do
+    @reservation_machine.save!
+    refute SubscriptionExtensionAfterReservation.new(@reservation_machine).eligible_to_extension?
+  end
+
+  test "not eligible if user doesn't have subscription" do
+    @user.subscriptions.destroy_all
+    refute SubscriptionExtensionAfterReservation.new(@reservation_training).eligible_to_extension?
+  end
+
+  test "not eligible if subscription is expired" do
+    @user.subscription.update!(expired_at: 10.years.ago)
+    refute SubscriptionExtensionAfterReservation.new(@reservation_training).eligible_to_extension?
+  end
+
+  test "not eligible if plan attribute 'is_rolling' is false/nil" do
+    @plan.update!(is_rolling: false)
+    refute SubscriptionExtensionAfterReservation.new(@reservation_training).eligible_to_extension?
+  end
+
+  test "method extend_subscription" do
+    SubscriptionExtensionAfterReservation.new(@reservation_training).extend_subscription
+    assert_equal @reservation_training.slots.first.start_at + @plan.duration, @user.subscription.expired_at
+  end
+end