function pad(n: number) {
  return n >= 10 ? n.toString() : '0' + n;
}

function lc(w: string) {
  const c = w.charCodeAt(0);
  return c >= 100 ? c - 32 : c;
}

export function isEqual(dateA: Date, dateB: Date) {
  if (!dateA || !dateB) return dateA === dateB;
  return dateA.getTime() === dateB.getTime();
}

export function getDaysInMonth(year: number, monthIndex: number) {
  return new Date(monthIndex === 11 ? year + 1 : year, monthIndex === 11 ? 0 : monthIndex + 1, 0).getDate();
}

export function isValid(date: unknown): date is Date {
  return date instanceof Date && !Number.isNaN(date.getTime());
}

/**
 * Simple date parse function. Only support simple format like yyyy-mm-dd or dd/mm/yyyy
 * @param {String} inputStr input string to parse
 * @param {String} format simple date format
 */
export function parse(inputStr: string, format: string) {
  const fm = format.match(/y+|m+|d+/gi);
  const im = inputStr.match(/\d+/g);
  if (!fm || !im || fm.length !== 3 || im.length !== 3) return null;
  const ds = [0, 0, 0]; // [year, month, day]
  fm.forEach((s, i) => {
    const c = lc(s);
    ds[c === 89 ? 0 : c === 77 ? 1 : 2] = Number(im[i]);
  });
  if (ds[0] <= 0 || ds[1] <= 0 || ds[2] < 0) {
    return null;
  }
  return new Date(ds[0], ds[1] - 1, ds[2]);
}

/**
 * Simple date format function. Only support simple format like yyyy-mm-dd.
 * @param {Date} date date to format
 * @param {String} formatStr simple date format
 */
export function format(date: Date, formatStr: string) {
  return formatStr.replace(/y+|m+|d+/gi, (match) => {
    const c = lc(match);
    return pad(c === 89 ? date.getFullYear() : c === 77 ? date.getMonth() + 1 : date.getDate());
  });
}

/**
 * parse simple date format to regexp string.
 * @param {String} formatStr format string
 * @returns {String}
 */
export function formatToReStr(formatStr: string) {
  return formatStr.replace(/y+|m+|d+|\\/gi, (match) => {
    const c = lc(match);
    return c === 92 ? '\\\\' : `[0-9]{${c === 89 ? 4 : 2}}`;
  });
}