customer_decorator.rb

class CustomerDecorator < Draper::Decorator
  delegate_all
  # [ other decorator logic here ... ]
  def state_completition_in_percent
    customer_state_index = Customer.state.values.index(state).to_f + 1
    return 100 if state == :terminated
    total_states_count_without_terminated_state = Customer.state.values.length - 1
    completion = customer_state_index / total_states_count_without_terminated_state
    (completion * 100).round(0)
  end
end