// Memento — 에디터 상태 스냅샷
class EditorSnapshot {
  private readonly content: string;
  private readonly cursorPosition: number;
  private readonly selectionStart: number | null;
  private readonly selectionEnd: number | null;
  private readonly timestamp: Date;
 
  constructor(
    content: string,
    cursorPosition: number,
    selectionStart: number | null,
    selectionEnd: number | null,
  ) {
    this.content = content;
    this.cursorPosition = cursorPosition;
    this.selectionStart = selectionStart;
    this.selectionEnd = selectionEnd;
    this.timestamp = new Date();
  }
 
  // Originator만 접근하도록 의도된 메서드들
  getContent(): string {
    return this.content;
  }
 
  getCursorPosition(): number {
    return this.cursorPosition;
  }
 
  getSelectionStart(): number | null {
    return this.selectionStart;
  }
 
  getSelectionEnd(): number | null {
    return this.selectionEnd;
  }
 
  getTimestamp(): Date {
    return this.timestamp;
  }
 
  // Caretaker가 표시용으로만 사용
  getDescription(): string {
    const preview = this.content.slice(0, 30);
    return `[${this.timestamp.toLocaleTimeString()}] "${preview}${this.content.length > 30 ? "..." : ""}"`;
  }
}

// Originator — 텍스트 에디터
class TextEditor {
  private content: string = "";
  private cursorPosition: number = 0;
  private selectionStart: number | null = null;
  private selectionEnd: number | null = null;
 
  // 텍스트 입력
  type(text: string): void {
    const before = this.content.slice(0, this.cursorPosition);
    const after = this.content.slice(this.cursorPosition);
    this.content = before + text + after;
    this.cursorPosition += text.length;
    this.clearSelection();
  }
 
  // 텍스트 삭제
  deleteSelection(): void {
    if (this.selectionStart !== null && this.selectionEnd !== null) {
      const before = this.content.slice(0, this.selectionStart);
      const after = this.content.slice(this.selectionEnd);
      this.content = before + after;
      this.cursorPosition = this.selectionStart;
      this.clearSelection();
    }
  }
 
  // 커서 이동
  moveCursor(position: number): void {
    this.cursorPosition = Math.max(0, Math.min(position, this.content.length));
  }
 
  // 선택 영역 설정
  select(start: number, end: number): void {
    this.selectionStart = start;
    this.selectionEnd = end;
  }
 
  private clearSelection(): void {
    this.selectionStart = null;
    this.selectionEnd = null;
  }
 
  // ⭐ 스냅샷 생성 (save)
  save(): EditorSnapshot {
    return new EditorSnapshot(
      this.content,
      this.cursorPosition,
      this.selectionStart,
      this.selectionEnd,
    );
  }
 
  // ⭐ 스냅샷 복원 (restore)
  restore(snapshot: EditorSnapshot): void {
    this.content = snapshot.getContent();
    this.cursorPosition = snapshot.getCursorPosition();
    this.selectionStart = snapshot.getSelectionStart();
    this.selectionEnd = snapshot.getSelectionEnd();
  }
 
  getContent(): string {
    return this.content;
  }
}

// Caretaker — Undo/Redo 히스토리 관리자
class EditorHistory {
  private undoStack: EditorSnapshot[] = [];
  private redoStack: EditorSnapshot[] = [];
 
  // 현재 상태를 저장
  push(snapshot: EditorSnapshot): void {
    this.undoStack.push(snapshot);
    this.redoStack = []; // 새 액션이 발생하면 redo 스택 초기화
  }
 
  // Undo — 이전 스냅샷 반환
  undo(): EditorSnapshot | null {
    const snapshot = this.undoStack.pop();
    if (snapshot) {
      this.redoStack.push(snapshot);
    }
    return snapshot ?? null;
  }
 
  // Redo — 되돌린 스냅샷 다시 적용
  redo(): EditorSnapshot | null {
    const snapshot = this.redoStack.pop();
    if (snapshot) {
      this.undoStack.push(snapshot);
    }
    return snapshot ?? null;
  }
 
  // 히스토리 목록 표시
  showHistory(): void {
    console.log("📚 히스토리:");
    this.undoStack.forEach((s, i) => {
      console.log(`  ${i + 1}. ${s.getDescription()}`);
    });
  }
}

const editor = new TextEditor();
const history = new EditorHistory();
 
// 편집 시작
history.push(editor.save()); // 빈 상태 저장
editor.type("Hello, World!");
console.log(editor.getContent()); // "Hello, World!"
 
history.push(editor.save()); // "Hello, World!" 저장
editor.type(" Welcome to TypeScript.");
console.log(editor.getContent()); // "Hello, World! Welcome to TypeScript."
 
history.push(editor.save()); // 현재 상태 저장
editor.type(" Let's learn Memento Pattern!");
console.log(editor.getContent());
// "Hello, World! Welcome to TypeScript. Let's learn Memento Pattern!"
 
// ⭐ Ctrl+Z! Undo!
const snapshot = history.undo();
if (snapshot) {
  editor.restore(snapshot);
}
console.log(editor.getContent());
// "Hello, World! Welcome to TypeScript."
 
// 한 번 더 Undo
const snapshot2 = history.undo();
if (snapshot2) {
  editor.restore(snapshot2);
}
console.log(editor.getContent());
// "Hello, World!"
 
// Ctrl+Shift+Z! Redo!
const snapshot3 = history.redo();
if (snapshot3) {
  editor.restore(snapshot3);
}
console.log(editor.getContent());
// "Hello, World! Welcome to TypeScript."

git commit -m "보스전 앞 세이브"
# ... 코드를 마구 수정 ...
git checkout .  # 로드!

// 브라우저의 history API도 Memento 패턴
history.pushState({ page: 1 }, "title", "/page1"); // 상태 저장
history.back(); // 이전 상태로 복원
 
window.addEventListener("popstate", (event) => {
  // event.state가 바로 Memento!
  console.log("복원된 상태:", event.state);
});

class SimpleMemento<T> {
  private readonly state: string;
  private readonly timestamp: Date;
 
  constructor(state: T) {
    this.state = JSON.stringify(state); // 직렬화로 깊은 복사
    this.timestamp = new Date();
  }
 
  getState(): T {
    return JSON.parse(this.state);
  }
 
  getTimestamp(): Date {
    return this.timestamp;
  }
}
 
// 사용
class FormState {
  private history: SimpleMemento<Record<string, any>>[] = [];
 
  save(formData: Record<string, any>): void {
    this.history.push(new SimpleMemento(formData));
  }
 
  undo(): Record<string, any> | null {
    this.history.pop(); // 현재 상태 버리기
    const prev = this.history[this.history.length - 1];
    return prev?.getState() ?? null;
  }
}