[BE] Provide script to run on console for bulk assignment

Purpose of this MR

• The current MR presents the Code Suggestions Bulk User Assignment rake task.
• The script accepts a CSV file path as a parameter and handles user assignments.
• This task is specifically designated for manual use and not automated or running within the GitLab codebase.

Local Setup and Validation Instructions

For details on setting up and validating the script locally, kindly document the file in the MR.

Related to #431619

ee/lib/duo_pro/bulk_user_assignment.rb

@@ -5,6 +5,7 @@
 # add_on_purchase = GitlabSubscriptions::AddOnPurchase.find_by(add_on: GitlabSubscriptions::AddOn.code_suggestions.last)
 # 2. Set the `usernames` variable to point to your usernames array
 # usernames = ["user1", "user2", "user3", "user4", "user5"]
+# If reading from a CSV file usernames =  CSV.read(FILE_PATH, headers: true).map { |row| row['username'] }
 # 3. Execute the bulk assignment:
 #    ```ruby
 #    DuoPro::BulkUserAssignment.new(usernames, add_on_purchase).execute!
@@ -17,7 +18,8 @@
 
 module DuoPro
   class BulkUserAssignment
-    # rubocop: disable CodeReuse/ActiveRecord -- Script does not belong to the codebase
+    include GitlabSubscriptions::SubscriptionHelper
+
     attr_reader :usernames, :add_on_purchase, :success_assignments, :failed_assignments
 
     def initialize(usernames, add_on_purchase)
@@ -28,10 +30,19 @@ def initialize(usernames, add_on_purchase)
     end
 
     def execute!
+      return 'Running on SaaS detected; this class is for self-managed instances only' if gitlab_saas?
       return 'AddOn not purchased' unless add_on_purchase
 
+      process_users(usernames)
+
+      { success_assignments: success_assignments, failed_assignments: failed_assignments }
+    end
+
+    private
+
+    def process_users(usernames)
       usernames.each do |username|
-        user_to_be_assigned = find_user_by_username(username)
+        user_to_be_assigned = User.find_by_username(username)
 
         unless user_to_be_assigned
           log_failed_assignment("User is not found: #{username}")
@@ -40,25 +51,13 @@ def execute!
 
         result = assign!(user_to_be_assigned)
 
-        if result[:errors].empty?
-          log_success_assignment(result[:user])
-        else
-          log_failed_assignment("Failed to assign seat to user: #{username}, Errors: #{result[:errors]}")
-
-          if result[:errors].include?("NO_SEATS_AVAILABLE")
-            failed_assignments << "##No seats are left; users starting from @#{username} onwards were not assigned.##"
-            break
-          end
+        if result[:errors].include?("NO_SEATS_AVAILABLE")
+          log_no_seats_avilable(result, username)
+          break
         end
-      end
-
-      { success_assignments: success_assignments, failed_assignments: failed_assignments }
-    end
 
-    private
-
-    def find_user_by_username(username)
-      User.find_by(username: username)
+        log_result(result, username)
+      end
     end
 
     def assign!(user)
@@ -67,20 +66,28 @@ def assign!(user)
         user: user
       ).execute
 
-      if create_service.success?
-        { user: user, errors: create_service.errors }
-      else
-        { errors: create_service.errors }
-      end
+      { errors: create_service.errors }
     end
 
-    def log_success_assignment(user)
-      success_assignments << "User assigned: #{user.username}"
+    def log_no_seats_avilable(result, username)
+      log_failed_assignment("Failed to assign seat to user: #{username}, Errors: #{result[:errors]}")
+      log_failed_assignment("##No seats are left; users starting from @#{username} onwards were not assigned.##")
+    end
+
+    def log_success_assignment(username)
+      success_assignments << "User assigned: #{username}"
     end
 
     def log_failed_assignment(message)
       failed_assignments << message
     end
-    # rubocop: enable CodeReuse/ActiveRecord
+
+    def log_result(result, username)
+      if result[:errors].empty?
+        log_success_assignment(username)
+      else
+        log_failed_assignment("Failed to assign seat to user: #{username}, Errors: #{result[:errors]}")
+      end
+    end
   end
 end