export interface EditHistory<T> { past: T[]; present: T; future: T[] }
const LIMIT = 40;

export function createEditHistory<T>(present: T): EditHistory<T> {
  return { past: [], present, future: [] };
}

export function commitEdit<T>(history: EditHistory<T>, present: T): EditHistory<T> {
  if (present === history.present) return history;
  return { past: [...history.past, history.present].slice(-LIMIT), present, future: [] };
}

export function undoEdit<T>(history: EditHistory<T>): EditHistory<T> {
  if (!history.past.length) return history;
  return { past: history.past.slice(0, -1), present: history.past.at(-1)!, future: [history.present, ...history.future] };
}

export function redoEdit<T>(history: EditHistory<T>): EditHistory<T> {
  if (!history.future.length) return history;
  return { past: [...history.past, history.present].slice(-LIMIT), present: history.future[0], future: history.future.slice(1) };
}