PHP: format relative date

relative_format.php

<?php

function formatDate($date, $point = 'now') {
    $point = date_create($point);
    $date = date_create_from_format('Y-m-d H:i:s', $date);
    $interval = date_diff($point, $date);
    $delta = $point->getTimestamp() - $date->getTimestamp();

    $SECOND = 1;
    $MINUTE = 60 * $SECOND;
    $HOUR = 60 * $MINUTE;
    $DAY = 24 * $HOUR;
    $MONTH = 30 * $DAY;
    $YEAR = 12 * $MONTH;

    if ($delta < 0) {
        return "not yet";
    }
    if ($delta == 0) {
        return 'just now';
    }
    if ($delta == 1) {
        return "one second ago";
    }

    if ($delta < 1 * $MINUTE) {
        return sprintf("%d seconds ago", $interval->format('%s'));
    }
    if ($delta < 2 * $MINUTE) {
        return "a minute ago";
    }
    if ($delta < 1 * $HOUR) {
        return sprintf("%d minutes ago", $interval->format('%i'));
    }
    if ($delta < 2 * $HOUR) {
        return "an hour ago";
    }
    if ($delta < 1 * $DAY) {
        return sprintf("%d hours ago", $interval->format('%h'));
    }
    if ($delta < 2 * $DAY) {
        return "yesterday";
    }
    if ($delta < 1 * $MONTH) {
        return sprintf("%d days ago", $interval->format('%d'));
    }
    if ($delta < 2 * $MONTH) {
        return "one month ago";
    }
    if ($delta < 1 * $YEAR) {
        return sprintf("%d months ago", $interval->format('%m'));
    }
    if ($delta < 2 * $YEAR) {
        return "one year ago";
    }

    return sprintf("%d years ago", $interval->format('%y'));
}