Fix parallel Stripe subscriptions and improve subscription sync

app/controllers/admin_controller.rb

@@ -267,6 +267,9 @@ def perform_unsubscribe
     @users = User.where(email: emails)
     @users.each do |user|
       if user.on_premium_plan?
+        # Cancel on Stripe too, or the user stays subscribed there and keeps
+        # getting billed after we've unsubscribed them on our end.
+        SubscriptionService.cancel_stripe_subscriptions!(user)
         SubscriptionService.cancel_all_existing_subscriptions(user)
         UnsubscribedMailer.unsubscribed(user).deliver_now! if Rails.env.production?
       end

app/controllers/subscriptions_controller.rb

@@ -135,6 +135,7 @@ def information
     @selected_plan = BillingPlan.find_by(stripe_plan_id: params['plan'], available: true)
     @stripe_customer = Stripe::Customer.retrieve(current_user.stripe_customer_id)
     @stripe_payment_methods = @stripe_customer.list_payment_methods(type: 'card')
+    @stripe_subscriptions = SubscriptionService.billable_stripe_subscriptions(current_user.stripe_customer_id)
   end
 
   # Save a payment method
@@ -179,10 +180,6 @@ def information_change
 
   def delete_payment_method
     stripe_customer = Stripe::Customer.retrieve current_user.stripe_customer_id
-
-    # Use safe navigation to handle customers without subscriptions
-    subscriptions = stripe_customer.subscriptions&.data || []
-    stripe_subscription = subscriptions.first
 
     payment_methods = stripe_customer.list_payment_methods(type: 'card')
     payment_methods.data.each do |payment_method|
@@ -191,17 +188,18 @@ def delete_payment_method
 
     notice = ['Your payment method has been successfully deleted.']
 
-    # Check if user has a non-starter subscription using modern API
-    if stripe_subscription&.items&.data&.any?
-      current_price_id = stripe_subscription.items.data[0].price.id
-      if current_price_id != 'starter'
-        # Cancel the user's at the end of its effective period on Stripe's end, so they don't get rebilled
-        stripe_subscription.delete(at_period_end: true)
-
-        active_billing_plan = BillingPlan.find_by(stripe_plan_id: current_price_id)
-        if active_billing_plan
-          notice << "Your #{active_billing_plan.name} subscription will end on #{Time.at(stripe_subscription.current_period_end).strftime('%B %d')}."
-        end
+    # With no card on file, make sure every paid subscription stops rebilling
+    # at the end of its current period.
+    SubscriptionService.billable_stripe_subscriptions(current_user.stripe_customer_id).each do |stripe_subscription|
+      current_price_id = SubscriptionService.subscription_price_ids(stripe_subscription).first
+      next if current_price_id.nil? || current_price_id == 'starter'
+
+      Stripe::Subscription.update(stripe_subscription.id, { cancel_at_period_end: true })
+
+      active_billing_plan = BillingPlan.find_by(stripe_plan_id: current_price_id)
+      period_end = SubscriptionService.subscription_period_end(stripe_subscription)
+      if active_billing_plan && period_end
+        notice << "Your #{active_billing_plan.name} subscription will end on #{Time.at(period_end).strftime('%B %d')}."
       end
     end
 
@@ -281,12 +279,26 @@ def move_user_to_plan_requested(plan_id)
   end
 
   def process_plan_change(user, new_plan_id)
-    # General flow we're going to take here:
-    # 1. Cancel all existing plans, reversing their benefits
-    SubscriptionService.cancel_all_existing_subscriptions(user)
-
-    # 2. Add a new plan, adding its benefits
-    SubscriptionService.add_subscription(user, new_plan_id)
+    # Serialize plan changes per user with a row lock, so repeated clicks on a
+    # slow page (or two racing requests) can't both act on stale subscription
+    # state and double-subscribe the user on Stripe.
+    # requires_new gives us our own savepoint, so a declined card rolls back the
+    # local downgrade below even if we're ever called inside another transaction.
+    user.transaction(requires_new: true) do
+      user.lock!
+
+      # General flow we're going to take here:
+      # 1. Cancel all existing plans, reversing their benefits
+      SubscriptionService.cancel_all_existing_subscriptions(user)
+
+      # 2. Add a new plan, adding its benefits
+      SubscriptionService.add_subscription(user, new_plan_id)
+    end
+  rescue Stripe::CardError
+    # with_lock runs in a transaction, so letting the error escape it rolled the
+    # local downgrade back: the user keeps the plan and bandwidth they had
+    # before their card was declined.
+    :failed_card
   end
 
   def set_sidenav_expansion

app/controllers/users_controller.rb

@@ -92,20 +92,9 @@ def delete_my_account # :(
       return
     end
 
-    # Make sure the user is set to Starter on Stripe so we don't keep charging them
-    stripe_customer = Stripe::Customer.retrieve(current_user.stripe_customer_id)
-
-    # Use safe navigation to handle customers without subscriptions
-    subscriptions = stripe_customer.subscriptions&.data || []
-    stripe_subscription = subscriptions.first
-    if stripe_subscription
-      # Update subscription to starter plan using modern API
-      Stripe::Subscription.modify(stripe_subscription.id, {
-        items: [{
-          id: stripe_subscription.items.data[0].id,
-          price: 'starter'
-        }]
-      })
+    # Cancel every billable subscription on Stripe so we don't keep charging them
+    SubscriptionService.billable_stripe_subscriptions(current_user.stripe_customer_id).each do |stripe_subscription|
+      Stripe::Subscription.cancel(stripe_subscription.id)
     end
 
     report_user_deletion_to_slack(current_user)

app/models/users/user.rb

@@ -296,27 +296,11 @@ def initialize_stripe_customer
         self.stripe_customer_id = customer_data.id
         self.save
 
-        # If we're creating this Customer in Stripe for the first time, we should also associate them with the free tier
-        # Get the customer's available payment methods (if any)
-        payment_methods = Stripe::PaymentMethod.list({
-          customer: self.stripe_customer_id,
-          type: 'card'
-        })
-
-        default_payment_method = payment_methods.data.first&.id
-
-        # Create subscription with payment method if available
-        subscription_params = {
-          customer: self.stripe_customer_id,
-          items: [{ price: 'starter' }]
-        }
-
-        # Add default payment method if available (free tier may not have payment methods)
-        if default_payment_method
-          subscription_params[:default_payment_method] = default_payment_method
-        end
-
-        Stripe::Subscription.create(subscription_params)
+        # If we're creating this Customer in Stripe for the first time, we should also associate them with the free tier.
+        # This goes through SubscriptionService so it obeys the same
+        # one-subscription-per-customer invariant as every other code path, and
+        # can't leave a brand new user with a parallel subscription.
+        SubscriptionService.sync_stripe_subscriptions_to_plan(self, 'starter')
       else
         # In test environment, just set a dummy customer ID
         self.stripe_customer_id = 'test_customer_id'