memento.php

<?php

class Memento
{
    private State $state;

    public function __construct(State $stateToSave)
    {
        $this->state = $stateToSave;
    }

    public function getState(): State
    {
        return $this->state;
    }
}


class State
{
    const STATE_CREATED = 'created';
    const STATE_OPENED = 'opened';
    const STATE_ASSIGNED = 'assigned';
    const STATE_CLOSED = 'closed';

    private string $state;

    /**
     * @var string[]
     */
    private static array $validStates = [
        self::STATE_CREATED,
        self::STATE_OPENED,
        self::STATE_ASSIGNED,
        self::STATE_CLOSED,
    ];

    public function __construct(string $state)
    {
        self::ensureIsValidState($state);

        $this->state = $state;
    }

    private static function ensureIsValidState(string $state)
    {
        if (!in_array($state, self::$validStates)) {
            throw new InvalidArgumentException('Invalid state given');
        }
    }

    public function __toString(): string
    {
        return $this->state;
    }
}


class Ticket
{
    private State $currentState;

    public function __construct()
    {
        $this->currentState = new State(State::STATE_CREATED);
    }

    public function open()
    {
        $this->currentState = new State(State::STATE_OPENED);
    }

    public function assign()
    {
        $this->currentState = new State(State::STATE_ASSIGNED);
    }

    public function close()
    {
        $this->currentState = new State(State::STATE_CLOSED);
    }

    public function saveToMemento(): Memento
    {
        return new Memento(clone $this->currentState);
    }

    public function restoreFromMemento(Memento $memento)
    {
        $this->currentState = $memento->getState();
    }

    public function getState(): State
    {
        return $this->currentState;
    }
    
}

// USAGE
  $ticket = new Ticket();

// open the ticket
$ticket->open();
$openedState = $ticket->getState();

$memento = $ticket->saveToMemento();

$ticket->assign();

$ticket->restoreFromMemento($memento);

$ticket->getState()

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