ruby 49 lines · 8 steps

A state machine for order transitions in Ruby

A frozen transition table drives valid order state changes, records history, and fires side effects on each move.

Explained by highlit

Intermediate state-machine data-driven error-handling callbacks immutability

1class Order
class InvalidTransition < StandardError; end
3 
TRANSITIONS = {
  pending:   %i[paid cancelled],
  paid:      %i[shipped refunded],
  shipped:   %i[delivered],
  delivered: %i[],
  cancelled: %i[],
  refunded:  %i[]
}.freeze
12 
attr_reader :state, :history
14 
def initialize(state: :pending)
  @state = state.to_sym
  @history = []
end
19 
def transition_to!(target)
  target = target.to_sym
  unless can_transition_to?(target)
    raise InvalidTransition, "cannot move order from #{state} to #{target}"
  end
25 
  @history << { from: state, to: target, at: Time.now }
  @state = target
  run_callback(target)
  self
end
31 
def can_transition_to?(target)
  TRANSITIONS.fetch(state, []).include?(target.to_sym)
end
35 
def final?
  TRANSITIONS.fetch(state, []).empty?
end
39 
private
41 
def run_callback(target)
  case target
  when :paid      then PaymentMailer.confirmation(self).deliver_later
  when :shipped   then ShipmentJob.perform_later(id: object_id)
  when :refunded  then RefundService.new(self).process!
  end
end
49end

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Encoding legal transitions as data keeps validation logic small and easy to audit.
2Raising a domain-specific error makes illegal transitions loud and self-documenting.
3Separating the guard, the state mutation, and the side effect keeps each concern testable.

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