Plan 05: Import Step Handler Registry

Objective

Replace the repetitive string-matching dispatch in ImportSessionsController#update with a handler registry pattern (C5), improving maintainability without changing behavior.

Context

• app/controllers/source_monitor/import_sessions_controller.rb:42-47 dispatches via 5 sequential if/return branches
• Same pattern appears in show (lines 34-37) with prepare_*_context methods
• This is a pure refactoring -- no behavior change, no new files, no route changes
• The controller already includes 4 concerns that provide the step handler methods

Tasks

Task 1: Add step handler registry constant

Add to ImportSessionsController (near the top, after includes):

STEP_HANDLERS = {
  "upload" => :handle_upload_step,
  "preview" => :handle_preview_step,
  "health_check" => :handle_health_check_step,
  "configure" => :handle_configure_step,
  "confirm" => :handle_confirm_step
}.freeze

Task 2: Refactor update action

Replace the 5 if/return branches in update with:

def update
  handler = STEP_HANDLERS[@current_step]
  return send(handler) if handler

  # fallback for unknown steps (existing behavior)
  @import_session.update!(session_attributes)
  @current_step = target_step
  @import_session.update_column(:current_step, @current_step) if @import_session.current_step != @current_step
  redirect_to source_monitor.step_import_session_path(@import_session, step: @current_step), allow_other_host: false
end

Task 3: Refactor show action context preparation

Similarly, add a context preparation registry or simplify the show method:

STEP_CONTEXTS = {
  "preview" => :prepare_preview_context,
  "health_check" => :prepare_health_check_context,
  "configure" => :prepare_configure_context,
  "confirm" => :prepare_confirm_context
}.freeze

Then in show:

def show
  context_method = STEP_CONTEXTS[@current_step]
  send(context_method) if context_method
  persist_step!
  render :show
end

Task 4: Verify

• bin/rails test -- all pass (especially import_sessions_controller_test.rb)
• bin/rubocop -- zero offenses
• Verify each step still works by tracing the handler dispatch