// todo: take a dependency on some relative time library.

const thresholds = [

1000, 'second',

1000 * 60, 'minute',

1000 * 60 * 60, 'hour',

1000 * 60 * 60 * 24, 'day',

1000 * 60 * 60 * 24 * 7, 'week',

1000 * 60 * 60 * 24 * 27, 'month'

];

const formatOptions: Intl.DateTimeFormatOptions = { month: 'short', day: 'numeric', year: 'numeric' };

export function timeAgo(current: number, value: Date) {

const elapsed = current - value.getTime();

if (elapsed < 5000) {

return 'just now';

}

let i = 0;

while (i + 2 < thresholds.length && elapsed * 1.1 > thresholds[i + 2]) {

i += 2;

}

const divisor = thresholds[i] as number;

const text = thresholds[i + 1] as string;

const units = Math.round(elapsed / divisor);

if (units > 3 && i === thresholds.length - 2) {

return `on ${value.toLocaleDateString(undefined, formatOptions)}`;

}

return units === 1 ? `${text === 'hour' ? 'an' : 'a'} ${text} ago` : `${units} ${text}s ago`;

}