Fat Enums: Using the state machine - transitions and validation

StateMachineUsage.php

<?php

$status = OrderStatus::Pending;

// Check if transition is valid
$status->canTransitionTo(OrderStatus::Processing); // true
$status->canTransitionTo(OrderStatus::Delivered);  // false

// Perform the transition
$newStatus = $status->transitionTo(OrderStatus::Processing);
// Returns OrderStatus::Processing

// Invalid transitions throw
$status->transitionTo(OrderStatus::Delivered);
// InvalidStateTransition: "Cannot transition from Pending to Delivered.
//   Valid transitions from Pending: Processing, Cancelled"

// Check from the other direction
OrderStatus::Shipped->canTransitionFrom(OrderStatus::Processing); // true
OrderStatus::Shipped->canTransitionFrom(OrderStatus::Pending);    // false

// Final states cannot transition anywhere
OrderStatus::Delivered->canTransitionTo(OrderStatus::Pending); // false
OrderStatus::Delivered->transitionTo(OrderStatus::Pending);
// InvalidStateTransition: "Delivered is a final state and cannot transition"