human-friendly-dates.ts

// Some configrable constants we need to do our work: 

/**
 * Past this number of days we'll no longer display the 
 * day of the week and instead we'll display the date
 * with the month
 */
const DATE_WITH_MONTH_THRESHOLD_IN_DAYS: number = 6;

/**
 * Past this number of seconds it's now longer "now" when
 * we're displaying dates
 */
const NOW_THRESHOLD_IN_SECONDS: number = 10;

/**
 * Past this number of hours we'll no longer display "hours
 * ago" and instead we'll display "today"
 */
const TODAY_AT_THRESHOLD_IN_HOURS: number = 12;

// The actual work starts here:

/**
 * Retrieve a human-friendly date string relative to now and in the
 * current locale e.g. "two minutes ago"
 */
function humanFriendlyDate(date: Date): string {
  const unixTimestamp: number = millisecondsToSeconds(date.valueOf());
  
  const now: number = millisecondsToSeconds(Date.now());
  
  const diffComponents: DateTimeComponents =
    getDateTimeComponents(now - unixTimestamp);
  
  const { years, months, days, hours, minutes, seconds } = diffComponents;
  
  if (years > 0) {
    return formatLocalizedDateWithOrdinal(currentLocale,
                                          date,
                                          { includeYear: true });
  }
  
  if (months > 0 || days > DATE_WITH_MONTH_THRESHOLD_IN_DAYS) {
    return formatLocalizedDateWithOrdinal(currentLocale,
                                          date,
                                          { includeYear: false });
  }
  
  if (days > 1) {
    return date.toLocaleDateString(currentLocale, { weekday: "long" }); 
  }
  
  if (days === 1) {
    return __("yesterday");
  }
  
  if (hours > TODAY_AT_THRESHOLD_IN_HOURS) {
    return __("today at") + " " + 
      date.toLocaleTimeString(currentLocale,
                              { hour: "numeric", minute: "2-digit" }); 
  }
  
  if (hours > 0) {
    return _p("hours ago", hours);
  }
  
  if (minutes > 0) {
    return _p("minutes ago", minutes);
  }
  
  if (seconds > NOW_THRESHOLD_IN_SECONDS) {
    return _p("seconds ago", seconds);
  }
  
  return __("just now");
}