i18n-js/src/helpers/timeAgoInWords.ts

A small library to provide I18n on JavaScript.

import range from "lodash/range";

import { I18n } from "../I18n";
import { DateTime, TimeAgoInWordsOptions } from "../typing";
import { parseDate } from "./parseDate";

const within = (start: number, end: number, actual: number): boolean =>
  actual >= start && actual <= end;

/**
 * Reports the approximate distance in time between two dates.
 *
 * @private
 *
 * @param {I18n} i18n The `I18n` instance.
 *
 * @param {DateTime} fromTime The initial date.
 *
 * @param {DateTime} toTime The end date.

 * @param {TimeAgoInWordsOptions} options Options.

 * @return {string} The approximate distance between the dates.
 */
export function timeAgoInWords(
  i18n: I18n,
  fromTime: DateTime,
  toTime: DateTime,
  options: TimeAgoInWordsOptions = {},
): string {
  const scope = options.scope || "datetime.distance_in_words";
  const t = (name: string, count = 0): string => i18n.t(name, { count, scope });

  fromTime = parseDate(fromTime);
  toTime = parseDate(toTime);

  let fromInSeconds = fromTime.getTime() / 1000;
  let toInSeconds = toTime.getTime() / 1000;

  if (fromInSeconds > toInSeconds) {
    [fromTime, toTime, fromInSeconds, toInSeconds] = [
      toTime,
      fromTime,
      toInSeconds,
      fromInSeconds,
    ];
  }

  const distanceInSeconds = Math.round(toInSeconds - fromInSeconds);
  const distanceInMinutes = Math.round((toInSeconds - fromInSeconds) / 60);
  const distanceInHours = distanceInMinutes / 60;
  const distanceInDays = distanceInHours / 24;

  const distanceInHoursRounded = Math.round(distanceInMinutes / 60);
  const distanceInDaysRounded = Math.round(distanceInDays);
  const distanceInMonthsRounded = Math.round(distanceInDaysRounded / 30);

  if (within(0, 1, distanceInMinutes)) {
    if (!options.includeSeconds) {
      return distanceInMinutes === 0
        ? t("less_than_x_minutes", 1)
        : t("x_minutes", distanceInMinutes);
    }

    if (within(0, 4, distanceInSeconds)) {
      return t("less_than_x_seconds", 5);
    }

    if (within(5, 9, distanceInSeconds)) {
      return t("less_than_x_seconds", 10);
    }

    if (within(10, 19, distanceInSeconds)) {
      return t("less_than_x_seconds", 20);
    }

    if (within(20, 39, distanceInSeconds)) {
      return t("half_a_minute");
    }

    if (within(40, 59, distanceInSeconds)) {
      return t("less_than_x_minutes", 1);
    }

    return t("x_minutes", 1);
  }

  if (within(2, 44, distanceInMinutes)) {
    return t("x_minutes", distanceInMinutes);
  }

  if (within(45, 89, distanceInMinutes)) {
    return t("about_x_hours", 1);
  }

  if (within(90, 1439, distanceInMinutes)) {
    return t("about_x_hours", distanceInHoursRounded);
  }

  if (within(1440, 2519, distanceInMinutes)) {
    return t("x_days", 1);
  }

  if (within(2520, 43_199, distanceInMinutes)) {
    return t("x_days", distanceInDaysRounded);
  }

  if (within(43_200, 86_399, distanceInMinutes)) {
    return t("about_x_months", Math.round(distanceInMinutes / 43200));
  }

  if (within(86_400, 525_599, distanceInMinutes)) {
    return t("x_months", distanceInMonthsRounded);
  }

  let fromYear = fromTime.getFullYear();

  if (fromTime.getMonth() + 1 >= 3) {
    fromYear += 1;
  }

  let toYear = toTime.getFullYear();

  if (toTime.getMonth() + 1 < 3) {
    toYear -= 1;
  }

  const leapYears =
    fromYear > toYear
      ? 0
      : range(fromYear, toYear).filter(
          (year) => new Date(year, 1, 29).getMonth() == 1,
        ).length;

  const minutesInYear = 525_600;
  const minuteOffsetForLeapYear = leapYears * 1440;
  const minutesWithOffset = distanceInMinutes - minuteOffsetForLeapYear;
  const distanceInYears = Math.trunc(minutesWithOffset / minutesInYear);

  const diff = parseFloat(
    (minutesWithOffset / minutesInYear - distanceInYears).toPrecision(3),
  );

  if (diff < 0.25) {
    return t("about_x_years", distanceInYears);
  }

  if (diff < 0.75) {
    return t("over_x_years", distanceInYears);
  }

  return t("almost_x_years", distanceInYears + 1);
}