Add ProviderCodeGenerator to handle provider code duplicates in tests

Move to a class so we can properly organise the code.

Get the provider code first and then attempt to generate an unique
provider code.

I used #to_set

Why .to_set?

Set uses hash-based lookups, which are O(1) (constant time).

Author: tomas-stefano

spec/factories/providers.rb

@@ -5,10 +5,7 @@
     provider_name { "ACME SCITT#{rand(1_000_000)}" }
 
     sequence(:provider_code) do |n|
-      loop do
-        code = format("#{('A'..'Z').to_a.sample}%02d", n % 100)
-        break code unless Provider.exists?(provider_code: code)
-      end
+      ProviderCodeGenerator.new(n).call
     end
 
     trait :with_anonymised_data do

spec/support/provider_code_generator.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+class ProviderCodeGenerator
+  def initialize(sequence_number)
+    @sequence_number = sequence_number
+    @existing_codes = Provider.pluck(:provider_code).to_set
+  end
+
+  def call
+    attempt_count = 0
+    possible_code = nil
+
+    until possible_code && @existing_codes.exclude?(possible_code)
+      possible_code = format("#{('A'..'Z').to_a.sample}%02d", @sequence_number % 100)
+
+      if @existing_codes.include?(possible_code)
+        attempt_count += 1
+        Rails.logger.warn("ProviderCodeGenerator: Collision detected for #{possible_code}, retrying (attempt ##{attempt_count})")
+      end
+    end
+
+    possible_code
+  end
+end