Allow post-close cancellations with frozen waitlist progression

app/controllers/admin/invitations_controller.rb

@@ -1,5 +1,6 @@
 class Admin::InvitationsController < Admin::ApplicationController
   include Admin::WorkshopConcerns
+  include WaitlistPromotionConcerns
 
   def update
     set_and_decorate_workshop
@@ -80,10 +81,12 @@ def attending_failed
   end
 
   def update_to_not_attending
-    @invitation.update!(attending: false, last_overridden_by_id: current_user.id)
+    freed_seat = release_seat(last_overridden_by_id: current_user.id)
     MemberActivityRecorder.record(actor: current_user, key: 'invitation.rsvp_override',
                                   trackable: @invitation, recipient: @invitation.member)
 
+    promote_next_waitlist_member if freed_seat && @workshop.future?
+
     {
       message: "You have removed #{@invitation.member.full_name} from the workshop.",
       error: false

app/controllers/concerns/waitlist_promotion_concerns.rb

@@ -0,0 +1,30 @@
+# Shared by controllers that cancel a workshop invitation and fill the freed
+# seat from the waiting list. Requires @invitation and the decorated
+# @workshop presenter to be set by the including controller.
+module WaitlistPromotionConcerns
+  extend ActiveSupport::Concern
+
+  included do
+    include InstanceMethods
+  end
+
+  module InstanceMethods
+    private
+
+    # Releases the invitation's seat under a row lock so two concurrent
+    # cancellation requests cannot each believe they freed a seat. Returns true
+    # only when this request moved a seat-holder to not attending.
+    def release_seat(additional_attributes = {})
+      @invitation.with_lock do
+        was_attending = @invitation.attending.eql?(true)
+        @invitation.update!(additional_attributes.merge(attending: false))
+        was_attending
+      end
+    end
+
+    def promote_next_waitlist_member
+      promoted = WaitingList.promote_next(@invitation.workshop, @invitation.role)
+      @workshop.send_attending_email(promoted, true) if promoted
+    end
+  end
+end

app/controllers/waiting_lists_controller.rb

@@ -8,6 +8,10 @@ class WaitingListsController < ApplicationController
   skip_forgery_protection only: %i[create destroy]
 
   def create # rubocop:disable Metrics/MethodLength
+    # Joins and leaves stop at the earlier of the RSVP close time and the
+    # 3.5-hour freeze, so the waitlist handed to security stays stable.
+    return back_with_message(t('messages.waiting_list.closed')) if waitlist_closed?
+
     @invitation.assign_attributes(invitation_params)
 
     return back_with_message(@invitation.errors.full_messages) unless @invitation.valid?(:waitinglist)
@@ -26,6 +30,8 @@ def create # rubocop:disable Metrics/MethodLength
   end
 
   def destroy
+    return back_with_message(t('messages.waiting_list.closed')) if waitlist_closed?
+
     WaitingList.find_by(invitation_id: @invitation.id).destroy
     MemberActivityRecorder.record(actor: @invitation.member, key: 'waiting_list.left',
                                   trackable: @invitation)
@@ -35,6 +41,10 @@ def destroy
 
   private
 
+  def waitlist_closed?
+    !@invitation.workshop.waitlist_open?
+  end
+
   def token
     params.permit(:invitation_id)[:invitation_id]
   end

app/controllers/workshop_invitation_controller.rb

@@ -1,5 +1,6 @@
 class WorkshopInvitationController < ApplicationController
   include WorkshopInvitationConcerns
+  include WaitlistPromotionConcerns
 
   # NOTE: This controller handles workshop invitations (WorkshopInvitation model).
   # It provides accept/reject RSVP actions for workshop attendees via token-based links.
@@ -57,25 +58,16 @@ def accept
   # Inline reject from InvitationControllerConcerns
   def reject
     @workshop = WorkshopPresenter.decorate(@invitation.workshop)
-    closes_at = @invitation.workshop.rsvp_closes_at
-    rsvp_deadline = [@invitation.workshop.date_and_time - 3.5.hours, closes_at].compact.min
-    if rsvp_deadline >= Time.zone.now
+    if @invitation.workshop.cancellations_open?
       if @invitation.attending.eql? false
         redirect_back(fallback_location: invitation_path(@invitation),
                       notice: t('messages.not_attending_already'))
       else
-        @invitation.update!(attending: false)
+        freed_seat = release_seat
         MemberActivityRecorder.record(actor: @invitation.member, key: 'workshop_invitation.rejected',
                                       trackable: @invitation)
 
-        next_spot = WaitingList.next_spot(@invitation.workshop, @invitation.role)
-
-        if next_spot.present?
-          invitation = next_spot.invitation
-          next_spot.destroy
-          invitation.update(attending: true, rsvp_time: Time.zone.now, automated_rsvp: true)
-          @workshop.send_attending_email(invitation, true)
-        end
+        promote_next_waitlist_member if freed_seat
 
         redirect_back(
           fallback_location: invitation_path(@invitation),

app/models/concerns/rsvp_closable.rb

@@ -11,11 +11,18 @@ module InstanceMethods
     # The time after which new RSVPs are no longer accepted. Models with an
     # explicit close time override this to prefer the stored value.
     def effective_rsvp_closes_at
-      date_and_time - DEFAULT_RSVPS_CLOSE_OFFSET
+      rsvp_freezes_at
     end
 
     def rsvp_available?
       effective_rsvp_closes_at.future?
     end
+
+    # The instant when member RSVP changes freeze, regardless of a custom
+    # close time. This method alone owns the default offset; actions are
+    # blocked at exactly this moment, not after it.
+    def rsvp_freezes_at
+      date_and_time - DEFAULT_RSVPS_CLOSE_OFFSET
+    end
   end
 end

app/models/waiting_list.rb

@@ -22,8 +22,21 @@ def self.coaches(workshop)
     by_workshop(workshop).where_role('Coach').where(auto_rsvp: true).map(&:member)
   end
 
-  def self.next_spot(workshop, role)
-    by_workshop(workshop).where_role(role).where(auto_rsvp: true).first
+  # Pops the next auto-RSVP waitlist entry and confirms its invitation. The
+  # caller sends the attendance email for the promoted invitation.
+  def self.promote_next(workshop, role)
+    transaction do
+      # SKIP LOCKED lets a concurrent promoter that holds another freed seat
+      # take the next entry instead of racing on this one.
+      next_spot = by_workshop(workshop).where_role(role).where(auto_rsvp: true)
+                                       .order(:created_at).lock('FOR UPDATE SKIP LOCKED').first
+      return unless next_spot
+
+      invitation = next_spot.invitation
+      next_spot.destroy!
+      invitation.update!(attending: true, rsvp_time: Time.zone.now, automated_rsvp: true)
+      invitation
+    end
   end
 
   def self.coaches_for(workshop)

app/models/workshop.rb

@@ -136,6 +136,21 @@ def effective_rsvp_closes_at
     rsvp_closes_at || super
   end
 
+  # The last moment a member may join or leave the waiting list. The waitlist
+  # goes to security at the RSVP close time, so both lists must be stable
+  # after that point, and member actions freeze 3.5 hours before the start.
+  def waitlist_closes_at
+    [rsvp_closes_at, rsvp_freezes_at].compact.min
+  end
+
+  def waitlist_open?
+    waitlist_closes_at > Time.zone.now
+  end
+
+  def cancellations_open?
+    rsvp_freezes_at > Time.zone.now
+  end
+
   private
 
   def set_opens_at

app/views/workshop_invitation/_waiting_list.html.haml

@@ -1,15 +1,18 @@
 - if invitation.waiting_list.blank?
   %span.badge.bg-danger The workshop is full.
   %hr
-  - if @invitation.for_student?
-    = simple_form_for @invitation, url: invitation_waiting_list_path(@invitation), method: :post do |f|
-      = f.input :tutorial, collection: @tutorial_titles, include_blank: true
-      = f.input :note, required: false, input_html: { rows: 3, maxlength: 100 }, hint: 'Anything else we should know?', placeholder: 'e.g. I need help understanding selectors'
-      = f.button :button, 'Join the waiting list', class: 'btn btn-primary w-100 mb-0'
+  - if @workshop.waitlist_open?
+    - if @invitation.for_student?
+      = simple_form_for @invitation, url: invitation_waiting_list_path(@invitation), method: :post do |f|
+        = f.input :tutorial, collection: @tutorial_titles, include_blank: true
+        = f.input :note, required: false, input_html: { rows: 3, maxlength: 100 }, hint: 'Anything else we should know?', placeholder: 'e.g. I need help understanding selectors'
+        = f.button :button, 'Join the waiting list', class: 'btn btn-primary w-100 mb-0'
+    - else
+      = simple_form_for @invitation, url: invitation_waiting_list_path(@invitation), method: :post do |f|
+        = f.input :note, required: false, input_html: { rows: 3, maxlength: 100 }
+        = f.button :button, 'Join the waiting list', class: 'btn btn-primary w-100 mb-0'
   - else
-    = simple_form_for @invitation, url: invitation_waiting_list_path(@invitation), method: :post do |f|
-      = f.input :note, required: false, input_html: { rows: 3, maxlength: 100 }
-      = f.button :button, 'Join the waiting list', class: 'btn btn-primary w-100 mb-0'
+    %p= t('messages.waiting_list.closed')
 - else
   %p Waiting List position: <strong>#{invitation.waiting_list_position}</strong>/#{@workshop.waiting_list_count_for(invitation.role)}
   - if @invitation.for_student?
@@ -19,5 +22,5 @@
       #{@invitation.tutorial}
   %p
     #{@invitation.note}
-  = link_to 'Remove from the waiting list', invitation_waiting_list_path(invitation), method: :delete, class: 'btn btn-danger w-100', 'data-confirm' => 'Are you sure you want to let go of your spot? You cannot undo this.'
-
+  - if @workshop.waitlist_open?
+    = link_to 'Remove from the waiting list', invitation_waiting_list_path(invitation), method: :delete, class: 'btn btn-danger w-100', 'data-confirm' => 'Are you sure you want to let go of your spot? You cannot undo this.'

app/views/workshop_invitation/show.html.haml

@@ -65,7 +65,7 @@
                 = simple_form_for @invitation, url: :invitation, method: :put do |f|
                   = f.input :note, required: false, input_html: { rows: 3, maxlength: 100 }
                   = f.button :button, 'Update note', class: 'btn btn-primary w-100 mb-2'
-              - if @workshop.rsvp_available?
+              - if @workshop.cancellations_open?
                 = link_to 'I can no longer attend', reject_invitation_url(@invitation), class: 'btn btn-danger w-100', role: 'button'
               - else
                 %p= t('workshop.invitation.cant_make_it_note', email: @workshop.chapter.email)

config/locales/en.yml

@@ -198,6 +198,8 @@ en:
       updated_details: "Invitation details successfully updated."
       closed: "RSVPs for this workshop are now closed."
       rsvps_closed: "RSVPs have now closed."
+    waiting_list:
+      closed: "You can no longer join or leave the waiting list. RSVPs have now closed for this workshop."
     invalid_format: "The requested format is invalid: %{invalid_format}"
   notifications:
     provider_already_connected: "You are already signed in!"

spec/controllers/admin/invitations_controller_spec.rb

@@ -101,6 +101,51 @@
       expect(response).to redirect_to(admin_workshop_rsvp_url(workshop))
     end
 
+    it 'promotes the next waitlisted member when the workshop is in the future' do
+      invitation.update!(attending: true)
+      waitlisted_invitation = Fabricate(:workshop_invitation, workshop:, tutorial: nil)
+      WaitingList.add(waitlisted_invitation, true)
+      request.env['HTTP_REFERER'] = admin_workshop_rsvp_url(workshop)
+
+      put :update, params: { workshop_id: workshop.id, id: invitation.token, attending: 'false' }
+
+      expect(waitlisted_invitation.reload.attending).to be(true)
+    end
+
+    it 'does not promote when the removed invitation never held a seat' do
+      invitation.update!(attending: nil)
+      waitlisted_invitation = Fabricate(:workshop_invitation, workshop:, tutorial: nil)
+      WaitingList.add(waitlisted_invitation, true)
+      request.env['HTTP_REFERER'] = admin_workshop_rsvp_url(workshop)
+
+      put :update, params: { workshop_id: workshop.id, id: invitation.token, attending: 'false' }
+
+      expect(waitlisted_invitation.reload.attending).to be_nil
+    end
+
+    it 'does not promote when the removed invitation already declined' do
+      invitation.update!(attending: false)
+      waitlisted_invitation = Fabricate(:workshop_invitation, workshop:, tutorial: nil)
+      WaitingList.add(waitlisted_invitation, true)
+      request.env['HTTP_REFERER'] = admin_workshop_rsvp_url(workshop)
+
+      put :update, params: { workshop_id: workshop.id, id: invitation.token, attending: 'false' }
+
+      expect(waitlisted_invitation.reload.attending).to be_nil
+    end
+
+    it 'does not promote from the waiting list when the workshop has started' do
+      workshop.update!(date_and_time: 1.hour.ago, ends_at: 1.hour.ago + 2.hours)
+      invitation.update!(attending: true)
+      waitlisted_invitation = Fabricate(:workshop_invitation, workshop:, tutorial: nil)
+      WaitingList.add(waitlisted_invitation, true)
+      request.env['HTTP_REFERER'] = admin_workshop_rsvp_url(workshop)
+
+      put :update, params: { workshop_id: workshop.id, id: invitation.token, attending: 'false' }
+
+      expect(waitlisted_invitation.reload.attending).to be_nil
+    end
+
     it 'redirects back preserving the search term and page' do
       request.env['HTTP_REFERER'] = admin_workshop_rsvp_url(workshop, q: 'Zoe', page: 2)
 

spec/controllers/waiting_lists_controller_spec.rb

@@ -45,6 +45,54 @@
         end.to change(WaitingList, :count).by(1)
       end
     end
+
+    context 'when the custom close time has passed' do
+      let(:workshop) { Fabricate(:workshop, rsvp_closes_at: 1.hour.ago, date_and_time: 4.hours.from_now) }
+
+      it 'does not create a waiting list entry' do
+        expect do
+          post :create, params: { invitation_id: invitation.token }
+        end.not_to change(WaitingList, :count)
+      end
+
+      it 'redirects with a closed message' do
+        post :create, params: { invitation_id: invitation.token }
+
+        expect(flash[:notice]).to include('RSVPs have now closed for this workshop')
+      end
+    end
+
+    context 'when the 3.5 hour freeze has been reached' do
+      let(:workshop) { Fabricate(:workshop, date_and_time: 3.hours.from_now) }
+
+      it 'does not create a waiting list entry' do
+        expect do
+          post :create, params: { invitation_id: invitation.token }
+        end.not_to change(WaitingList, :count)
+      end
+    end
+
+    context 'when the custom close time is later than the freeze' do
+      let(:workshop) { Fabricate(:workshop, rsvp_closes_at: 2.hours.from_now, date_and_time: 4.hours.from_now) }
+
+      # The earlier of the two instants is the gate: joins still work until
+      # the freeze, even though the custom close time has not passed yet.
+      it 'creates a waiting list entry' do
+        expect do
+          post :create, params: { invitation_id: invitation.token }
+        end.to change(WaitingList, :count).by(1)
+      end
+    end
+
+    context 'when the freeze passed but the custom close time is still in the future' do
+      let(:workshop) { Fabricate(:workshop, rsvp_closes_at: 2.hours.from_now, date_and_time: 3.hours.from_now) }
+
+      it 'does not create a waiting list entry' do
+        expect do
+          post :create, params: { invitation_id: invitation.token }
+        end.not_to change(WaitingList, :count)
+      end
+    end
   end
 
   describe 'DELETE #destroy' do
@@ -60,5 +108,40 @@
         end.to change(WaitingList, :count).by(-1)
       end
     end
+
+    context 'when the waitlist is closed' do
+      let(:waiting_list) { Fabricate(:waiting_list) }
+      let(:invitation) { waiting_list.invitation }
+
+      before do
+        invitation.workshop.update!(date_and_time: 3.hours.from_now)
+        invitation # materialize the fabricated waiting list entry outside the change block
+      end
+
+      it 'keeps the entry on the waiting list' do
+        expect do
+          delete :destroy, params: { invitation_id: invitation.token }
+        end.not_to change(WaitingList, :count)
+      end
+
+      it 'redirects with a closed message' do
+        delete :destroy, params: { invitation_id: invitation.token }
+
+        expect(flash[:notice]).to include('RSVPs have now closed for this workshop')
+      end
+    end
+
+    context 'when the waitlist is open' do
+      let(:waiting_list) { Fabricate(:waiting_list) }
+      let(:invitation) { waiting_list.invitation }
+
+      before { invitation } # materialize the fabricated waiting list entry outside the change block
+
+      it 'removes the entry' do
+        expect do
+          delete :destroy, params: { invitation_id: invitation.token }
+        end.to change(WaitingList, :count).by(-1)
+      end
+    end
   end
 end