Revert PR #276

In favour of a pseudo random urn generator that is not reliant of the
database.
This change will simplies the codebase

app/models/urn.rb

@@ -1,41 +1,38 @@
-# == Schema Information
+# frozen_string_literal: true
+
+# Urn represents a Uniform Resource Name (URN) generator.
+# It generates a URN with a fixed prefix and a random alphanumeric suffix.
 #
-# Table name: urns
 #
-#  id         :bigint           not null, primary key
-#  code       :string
-#  prefix     :string
-#  suffix     :integer
-#  created_at :datetime         not null
-#  updated_at :datetime         not null
+# Example:
 #
-class Urn < ApplicationRecord
-  class NoUrnAvailableError < StandardError; end
-
-  PREFIX = "IRP".freeze
-  MAX_SUFFIX = 99_999
-  PADDING_SIZE = MAX_SUFFIX.to_s.size
-  VALID_CODES = {
-    "teacher" => "TE",
-    "salaried_trainee" => "ST",
-  }.freeze
+#   Urn.generate('teacher')          # => "IRPTE12345"
+#   Urn.generate('teacher')          # => "IRPTE12345"
+#   Urn.generate('salaried_trainee') # => "IRPST12345"
+#
+class Urn
+  attr_reader :value
+  attr_writer :suffix
 
-  def self.next(route)
-    code = VALID_CODES.fetch(route)
-    Urn.transaction do
-      urn = find_by!(code:)
-      urn.destroy!
-      urn.to_s
-    end
-  rescue KeyError => e
-    Sentry.capture_exception(e)
-    raise(ArgumentError, "Unknown route #{route}")
-  rescue ActiveRecord::RecordNotFound => e
-    Sentry.capture_exception(e)
-    raise(NoUrnAvailableError, "There no more unique URN available for #{route}")
+  def self.generate(applicant_type)
+    code = applicant_type_code(applicant_type)
+    PREFIX + code + Array.new(LENGTH) { CHARSET.sample }.join
   end
 
-  def to_s
-    [prefix, code, sprintf("%0#{PADDING_SIZE}d", suffix)].join
+  CHARSET = %w[0 1 2 3 4 5 6 7 8 9].freeze
+  PREFIX = "IRP"
+  LENGTH = 5
+  private_constant :CHARSET, :PREFIX, :LENGTH
+
+  def self.applicant_type_code(applicant_type)
+    case applicant_type
+    when "teacher"
+      "TE"
+    when "salaried_trainee"
+      "ST"
+    else
+      raise(ArgumentError, "Invalid applicant type: #{applicant_type}")
+    end
   end
+  private_methods :applicant_type_code
 end

app/services/submit_form.rb

@@ -88,7 +88,7 @@ def create_application
       date_of_entry: form.date_of_entry,
       start_date: form.start_date,
       subject: SubjectStep.new(form).answer.formatted_value,
-      urn: Urn.next(form.application_route),
+      urn: Urn.generate(form.application_route),
       visa_type: form.visa_type,
     )
   end

bin/app-startup.sh

@@ -7,8 +7,6 @@ set -e
 
 # run migrations
 bundle exec rails db:migrate
-# Front load urn generation
-bundle exec rake urn:generate
 
 # add seed data in review environment
 if [[ "$RAILS_ENV" = "review" || "$RAILS_ENV" = "development" ]]; then

db/migrate/20231009110217_add_application_indexes.rb

@@ -0,0 +1,7 @@
+class AddApplicationIndexes < ActiveRecord::Migration[7.0]
+  def change
+    drop_table :urns
+    add_index :applications, :urn, unique: true
+    add_index :applications, :application_route
+  end
+end

spec/factories/applications.rb

@@ -31,7 +31,7 @@
     visa_type { VisaStep::VALID_ANSWERS_OPTIONS.reject { _1 == "Other" }.sample }
     date_of_entry { Time.zone.today }
     start_date { 1.month.from_now.to_date }
-    urn { Urn.next(application_route) }
+    urn { Urn.generate(application_route) }
 
     factory :teacher_application do
       application_route { "teacher" }

spec/features/admin_console/applications_list_spec.rb

@@ -59,8 +59,6 @@
 
   def given_there_are_few_applications
     # Create 2 specific applications for search tests
-    create_list(:urn, 5, code: "TE")
-    create_list(:urn, 5, code: "ST")
     unique_applicant = create(:applicant, given_name: "Unique Given Name", middle_name: "Unique Middle Name", family_name: "Unique Family Name", email_address: "[email protected]")
     create(:application, applicant: unique_applicant, urn: "Unique Urn 1")
 
@@ -72,16 +70,12 @@ def given_there_are_few_applications
   end
 
   def given_there_is_an_application_that_breached_sla
-    create_list(:urn, 5, code: "TE")
-    create_list(:urn, 5, code: "ST")
     applicant = create(:applicant)
     application = create(:application, applicant:)
     application.application_progress.update(initial_checks_completed_at: 4.days.ago)
   end
 
   def given_there_are_applications_with_different_dates
-    create_list(:urn, 5, code: "TE")
-    create_list(:urn, 5, code: "ST")
     create(:application, application_progress: build(:application_progress, :initial_checks_completed, status: :initial_checks))
     create(:application, application_progress: build(:application_progress, :home_office_checks_completed, status: :home_office_checks))
   end