Fixes #2366 - "Warten auf Erinnerung" - Inconsistent timestamps

app/models/transaction/notification.rb

@@ -125,11 +125,13 @@ class Transaction::Notification
           identifier = user.login
         end
 
+        already_notified_cutoff = Time.use_zone(Setting.get('timezone_default').presence || 'UTC') { Time.current.beginning_of_day }
+
         already_notified = History.where(
           history_type_id:   History.type_lookup('notification').id,
           history_object_id: History.object_lookup('Ticket').id,
           o_id:              ticket.id
-        ).where('created_at > ?', Time.zone.now.beginning_of_day).exists?(['value_to LIKE ?', "%#{identifier}(#{@item[:type]}:%"])
+        ).where('created_at > ?', already_notified_cutoff).exists?(['value_to LIKE ?', "%#{identifier}(#{@item[:type]}:%"])
 
         next if already_notified
       end

spec/models/transaction/notification_spec.rb

@@ -0,0 +1,45 @@
+# Copyright (C) 2012-2021 Zammad Foundation, http://zammad-foundation.org/
+
+require 'rails_helper'
+
+RSpec.describe Transaction::Notification, type: :model do
+  describe 'pending ticket reminder repeats after midnight at selected time zone' do
+    let(:group)  { create(:group) }
+    let(:user)   { create(:agent) }
+    let(:ticket) { create(:ticket, owner: user, state_name: 'open', pending_time: Time.current) }
+
+    before do
+      user.groups << group
+      ticket
+
+      Setting.set('timezone_default', 'America/Santiago')
+      freeze_time
+      run(ticket, user, 'reminder_reached')
+      OnlineNotification.destroy_all
+    end
+
+    it 'notification not sent at UTC midnight' do
+      travel_to Time.current.end_of_day + 1.minute
+
+      expect { run(ticket, user, 'reminder_reached') }.not_to change(OnlineNotification, :count)
+    end
+
+    it 'notification sent at selected time zone midnight' do
+      travel_to Time.use_zone('America/Santiago') { Time.current.end_of_day + 1.minute }
+
+      expect { run(ticket, user, 'reminder_reached') }.to change(OnlineNotification, :count).by(1)
+    end
+  end
+
+  def run(ticket, user, type)
+    described_class.new(
+      object:           ticket.class.name,
+      type:             type,
+      object_id:        ticket.id,
+      interface_handle: 'scheduler',
+      changes:          nil,
+      created_at:       Time.current,
+      user_id:          user.id
+    ).perform
+  end
+end