How to replace an existing state machine

We'll see how you can flat-out replace state machines with your custom implementation. Not something you'll need every day, as it comes with its drawbacks, but it can bring you a lot of flexibility if needed.

A custom state machine can be specified through the state_machines option in config/initializers/spree.rb.

For instance, if you wanted to replace the payment state machine, you could create your own one like this:

lib/my_store/state_machines/payment.rb

# frozen_string_literal: true

module MyStore
  class StateMachines
    module Payment
      extend ActiveSupport::Concern

      included do
        state_machine initial: :custom_state do
          # Event, transition & hook definitions
        end
      end
    end
  end
end

And then you'd need to tell Solidus to use it:

config/initializers/spree.rb

# ...
Spree.config do |config|
  config.state_machines.payment = 'MyStore::StateMachines::Payment'
  # ...
end