/* =============================================================================
 * spreadsheet_history.ts  (주인 A)
 * 되돌리기 · 다시 — 명령과 되돌림 짝을 쌓음(메모리만 · 캐시에 안 넣음).
 * undo() 는 되돌림 짝을 · redo() 는 원래 명령을 돌려줌 — 적용은 부른 쪽(`applyCommand`).
 * ========================================================================== */

import type { Command, History } from "./spreadsheet_types";

/** `limit` = 쌓을 수(넘으면 오래된 것부터 버림) */
export function createHistory(limit = 100): History {
  let done: [Command, Command][] = [];
  let undone: [Command, Command][] = [];
  return {
    push(command, undo) {
      done.push([command, undo]);
      if (done.length > limit) done.shift();
      undone = [];
    },
    undo() {
      const pair = done.pop();
      if (!pair) return null;
      undone.push(pair);
      return pair[1];
    },
    redo() {
      const pair = undone.pop();
      if (!pair) return null;
      done.push(pair);
      return pair[0];
    },
    canUndo: () => done.length > 0,
    canRedo: () => undone.length > 0,
    clear() {
      done = [];
      undone = [];
    },
  };
}