Memento Pattern Generator

Creates Memento pattern infrastructure for capturing and restoring object state without violating encapsulation.

When to Use

Scenario	Example
Undo/Redo functionality	Document editor, form drafts, game state
State snapshots	Transaction rollback, checkpoint systems
State history tracking	Audit trail, version history
Transactional operations	Multi-step processes with rollback

Component Characteristics

Originator

• Creates memento from current state
• Restores state from memento
• Owns the state being saved
• Knows what to save/restore

Memento

• Stores originator's internal state
• Immutable snapshot (readonly)
• Protects against external access
• Returns state only to originator

Caretaker

• Manages memento history
• Requests state saves
• Triggers state restoration
• Never examines memento contents

---

Generation Process

Step 1: Generate Memento

Path: src/Domain/{BoundedContext}/Memento/

1. {Name}Memento.php — Immutable state snapshot

Step 2: Generate Originator

Path: src/Domain/{BoundedContext}/

1. {Name}.php — Object with createMemento() and restore() methods

Step 3: Generate Caretaker

Path: src/Application/{BoundedContext}/

1. {Name}History.php — Manages memento stack for undo/redo

Step 4: Generate Value Objects (Optional)

Path: src/Domain/{BoundedContext}/ValueObject/

1. {State}.php — State representation value object

Step 5: Generate Tests

1. {Name}MementoTest.php — Memento creation tests
2. {Name}HistoryTest.php — Caretaker undo/redo tests

---

File Placement

Component	Path
Memento	src/Domain/{BoundedContext}/Memento/
Originator	src/Domain/{BoundedContext}/
Caretaker	src/Application/{BoundedContext}/
Value Objects	src/Domain/{BoundedContext}/ValueObject/
Unit Tests	tests/Unit/Domain/{BoundedContext}/

---

Naming Conventions

Component	Pattern	Example
Memento	{Name}Memento	DocumentMemento
Originator	{Name}	Document
Caretaker	{Name}History	DocumentHistory
Create Method	createMemento()	createMemento()
Restore Method	restore() or restoreFromMemento()	restore()
Test	{ClassName}Test	DocumentMementoTest

---

Quick Template Reference

Memento

final readonly class {Name}Memento
{
    public function __construct(
        private {StateType} $state,
        private \DateTimeImmutable $createdAt
    ) {}

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

    public function createdAt(): \DateTimeImmutable
    {
        return $this->createdAt;
    }
}

Originator

final class {Name}
{
    private {StateType} $state;

    public function createMemento(): {Name}Memento
    {
        return new {Name}Memento(
            state: $this->state,
            createdAt: new \DateTimeImmutable()
        );
    }

    public function restore({Name}Memento $memento): void
    {
        $this->state = $memento->state();
    }
}

Caretaker

final class {Name}History
{
    private array $mementos = [];
    private int $currentIndex = -1;

    public function save({Name}Memento $memento): void
    {
        $this->mementos = array_slice($this->mementos, 0, $this->currentIndex + 1);
        $this->mementos[] = $memento;
        ++$this->currentIndex;
    }

    public function undo(): ?{Name}Memento
    {
        if ($this->currentIndex > 0) {
            --$this->currentIndex;
            return $this->mementos[$this->currentIndex];
        }
        return null;
    }

    public function redo(): ?{Name}Memento
    {
        if ($this->currentIndex < count($this->mementos) - 1) {
            ++$this->currentIndex;
            return $this->mementos[$this->currentIndex];
        }
        return null;
    }
}

---

Usage Example

// Create originator
$document = new Document(content: 'Initial text');

// Create caretaker
$history = new DocumentHistory();

// Save initial state
$history->save($document->createMemento());

// Make changes
$document->setContent('Modified text');
$history->save($document->createMemento());

$document->setContent('Final text');
$history->save($document->createMemento());

// Undo changes
$memento = $history->undo();
if ($memento) {
    $document->restore($memento); // Back to 'Modified text'
}

// Redo changes
$memento = $history->redo();
if ($memento) {
    $document->restore($memento); // Forward to 'Final text'
}

---

Common Memento Examples

Domain	Use Cases
Document Editor	Text content, formatting, cursor position
Form Management	Draft state, field values, validation state
Game Development	Player state, level progress, inventory
Order Processing	Order draft, item changes, pricing snapshots
Configuration	Settings snapshots, rollback points

---

Anti-patterns to Avoid

Anti-pattern	Problem	Solution
Mutable memento	State corruption	Use readonly classes
Public state access	Breaks encapsulation	Expose only via getters
Large state copies	Memory overhead	Store only changed fields
Missing timestamp	No audit trail	Include createdAt
Unbounded history	Memory leak	Implement history limit

---

References

For complete PHP templates and examples, see:

• references/templates.md — Memento, Originator, Caretaker templates
• references/examples.md — Document, Order, Form state management with tests