src/hebrew/lib/addMonths.ts

import { toGregorianDate, toHebrewDate } from "../utils/dateConversion.js";
import {
  clampHebrewDay,
  monthIndexToHebrewDate,
  monthsSinceEpoch,
} from "../utils/serial.js";

export function addMonths(date: Date, amount: number): Date {
  if (amount === 0) {
    return new Date(date.getTime());
  }
  const hebrew = toHebrewDate(date);
  const targetIndex = monthsSinceEpoch(hebrew) + amount;
  const target = monthIndexToHebrewDate(targetIndex, hebrew.day);
  const day = clampHebrewDay(target.year, target.monthIndex, target.day);
  return toGregorianDate({ ...target, day });
}