i18n-js/src/helpers/strftime.ts

A small library to provide I18n on JavaScript.

import { StrftimeOptions } from "../typing";

const DEFAULT_OPTIONS: StrftimeOptions = {
  meridian: { am: "AM", pm: "PM" },
  dayNames: [
    "Sunday",
    "Monday",
    "Tuesday",
    "Wednesday",
    "Thursday",
    "Friday",
    "Saturday",
  ],
  abbrDayNames: ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"],
  monthNames: [
    null,
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December",
  ],
  abbrMonthNames: [
    null,
    "Jan",
    "Feb",
    "Mar",
    "Apr",
    "May",
    "Jun",
    "Jul",
    "Aug",
    "Sep",
    "Oct",
    "Nov",
    "Dec",
  ],
};

/**
 * Formats time according to the directives in the given format string.
 * The directives begins with a percent (`%`) character. Any text not listed
 * as a directive will be passed through to the output string.
 *
 * The accepted formats are:
 *
 * ```
 * %a  - The abbreviated weekday name (Sun)
 * %A  - The full weekday name (Sunday)
 * %b  - The abbreviated month name (Jan)
 * %B  - The full month name (January)
 * %c  - The preferred local date and time representation
 * %d  - Day of the month (01..31)
 * %-d - Day of the month (1..31)
 * %H  - Hour of the day, 24-hour clock (00..23)
 * %-H - Hour of the day, 24-hour clock (0..23)
 * %k  - Hour of the day, 24-hour clock (0..23)
 * %I  - Hour of the day, 12-hour clock (01..12)
 * %-I - Hour of the day, 12-hour clock (1..12)
 * %l  - Hour of the day, 12-hour clock (1..12)
 * %m  - Month of the year (01..12)
 * %-m - Month of the year (1..12)
 * %M  - Minute of the hour (00..59)
 * %-M - Minute of the hour (0..59)
 * %p  - Meridian indicator (AM  or  PM)
 * %P  - Meridian indicator (am  or  pm)
 * %S  - Second of the minute (00..60)
 * %-S - Second of the minute (0..60)
 * %w  - Day of the week (Sunday is 0, 0..6)
 * %y  - Year without a century (00..99)
 * %-y - Year without a century (0..99)
 * %Y  - Year with century
 * %z  - Timezone offset (+0545)
 * %Z  - Timezone offset (+0545)
 * ```
 *
 * @private
 *
 * @param {date} date  The date that must be formatted.
 *
 * @param {string} format The formatting string.
 *
 * @param {StrftimeOptions} options The options that will be used to generate a
 * formatted date string.
 *
 * @returns {string} The formatted date string.
 */
export function strftime(
  date: Date,
  format: string,
  options: Partial<StrftimeOptions> = {},
): string {
  const {
    abbrDayNames,
    dayNames,
    abbrMonthNames,
    monthNames,
    meridian: AM_PM,
    utc,
  } = { ...DEFAULT_OPTIONS, ...options };

  if (isNaN(date.getTime())) {
    throw new Error(
      "strftime() requires a valid date object, but received an invalid date.",
    );
  }

  const weekDay = utc ? date.getUTCDay() : date.getDay();
  const day = utc ? date.getUTCDate() : date.getDate();
  const year = utc ? date.getUTCFullYear() : date.getFullYear();
  const month = (utc ? date.getUTCMonth() : date.getMonth()) + 1;
  const hour = utc ? date.getUTCHours() : date.getHours();
  let hour12 = hour;
  const meridian = hour > 11 ? "pm" : "am";
  const secs = utc ? date.getUTCSeconds() : date.getSeconds();
  const mins = utc ? date.getUTCMinutes() : date.getMinutes();
  const offset = utc ? 0 : date.getTimezoneOffset();
  const absOffsetHours = Math.floor(Math.abs(offset / 60));
  const absOffsetMinutes = Math.abs(offset) - absOffsetHours * 60;
  const timezoneoffset =
    (offset > 0 ? "-" : "+") +
    (absOffsetHours.toString().length < 2
      ? "0" + absOffsetHours
      : absOffsetHours) +
    (absOffsetMinutes.toString().length < 2
      ? "0" + absOffsetMinutes
      : absOffsetMinutes);

  if (hour12 > 12) {
    hour12 = hour12 - 12;
  } else if (hour12 === 0) {
    hour12 = 12;
  }

  format = format.replace("%a", abbrDayNames[weekDay]);
  format = format.replace("%A", dayNames[weekDay]);
  format = format.replace("%b", abbrMonthNames[month] as string);
  format = format.replace("%B", monthNames[month] as string);
  format = format.replace("%d", day.toString().padStart(2, "0"));
  format = format.replace("%e", day.toString());
  format = format.replace("%-d", day.toString());
  format = format.replace("%H", hour.toString().padStart(2, "0"));
  format = format.replace("%-H", hour.toString());
  format = format.replace("%k", hour.toString());
  format = format.replace("%I", hour12.toString().padStart(2, "0"));
  format = format.replace("%-I", hour12.toString());
  format = format.replace("%l", hour12.toString());
  format = format.replace("%m", month.toString().padStart(2, "0"));
  format = format.replace("%-m", month.toString());
  format = format.replace("%M", mins.toString().padStart(2, "0"));
  format = format.replace("%-M", mins.toString());
  format = format.replace("%p", AM_PM[meridian]);
  format = format.replace("%P", AM_PM[meridian].toLowerCase());
  format = format.replace("%S", secs.toString().padStart(2, "0"));
  format = format.replace("%-S", secs.toString());
  format = format.replace("%w", weekDay.toString());
  format = format.replace("%y", year.toString().padStart(2, "0").substr(-2));
  format = format.replace(
    "%-y",
    year.toString().padStart(2, "0").substr(-2).replace(/^0+/, ""),
  );
  format = format.replace("%Y", year.toString());
  format = format.replace(/%z/i, timezoneoffset);

  return format;
}