@technobuddha/library/relativeTime/relativeTime.ts

A large library of useful functions

import { space, ticksPerSecond, secondsPerMinute, secondsPerHour, secondsPerDay } from '../constants';
import floor       from '../floor';
import isSameDay   from '../isSameDay';
import formatDate  from '../formatDate';
import addTime     from '../addTime';
import plural      from '../plural';

export type Options = {
    /** Describe the time difference as a time on a nearby day  */
    todayTomorrowYesterday?: boolean;
    /** Passed to {@link formatDate} to display a time */
    timeFormat?: string;
    /** Passed to {@link formatSate} to display a year, month and day */
    ymdFormat?: string;
    /** Passed to {@link formatDate} to dislay a month and day */
    mdFormat?: string;
};

/**
 * Describe the difference between two dates in a simple format
 *
 * @param input The date
 * @param relativeTo The date to compare to
 * @param __namedParameters see {@link Options}
 * @returns string describing the time difference between the two dates
 */
export function relativeTime(
    input: Date,
    relativeTo: Date,
    {
        todayTomorrowYesterday = false,
        timeFormat = 'H:mm TT',
        ymdFormat = 'MMMM D YYYY',
        mdFormat = 'MMMM D',
    }:  Options = {}
) {
    const text  = [] as string[];

    if(todayTomorrowYesterday) {
        if(isSameDay(input, relativeTo))
            text.push(`today ${formatDate(input, timeFormat)} -`);
        else
        if(isSameDay(input, addTime(relativeTo, { days: 1 })))
            text.push(`tomorrow ${formatDate(input, timeFormat)} -`);
        else
        if(isSameDay(input, addTime(relativeTo, { days: -1 })))
            text.push(`yesterday ${formatDate(input, timeFormat)} -`);
    }

    let   diff  = (input.getTime() - relativeTo.getTime()) / ticksPerSecond;
    let   sign  = 1;

    if(diff < 0) { sign = -1; diff = Math.abs(diff); }

    const d = floor((diff) / secondsPerDay, { tolerance: 0.05 });
    const h = floor((diff - d * secondsPerDay) / secondsPerHour, { tolerance: 0.05 });
    const m = floor((diff - d * secondsPerDay - h * secondsPerHour) / secondsPerMinute, { tolerance: 0.05 });
    const s = floor((diff - d * secondsPerDay - h * secondsPerHour - m * secondsPerMinute), { tolerance: 0.05 });
    if(d > 90) {
        text.push(formatDate(input, ymdFormat));
        sign = 0;
    } else if(d > 30) {
        text.push(formatDate(input, mdFormat));
        sign = 0;
    } else if(d > 0) {
        text.push(plural('day', d));
        if(d < 4 && h > 1)
            text.push(plural('hour', h));
    } else if(h > 0) {
        text.push(plural('hour', h));
        if(h < 4 && m > 0)
            text.push(plural('minute', m));
    } else if(m > 0) {
        text.push(plural('minute', m));
        if(m < 4 && s > 0)
            text.push(plural('second', s));
    } else if(s > 0) {
        text.push(plural('second', s));
    }

    if(sign === -1)   text.push('ago');
    if(sign === 1)    text.push(d || h || m || s ? 'from now' : 'now');

    return text.join(space);
}

export default relativeTime;