<?php
function long_datetime($datetime, $level = 7) {
    $now = new DateTime;
    $datetime = new DateTime($datetime);
    $suffix = $now > $datetime ? ' ago' : ' ahead';
    $diff = $now->diff($dt);
    $diff->w = floor($diff->d / 7);
    $diff->d -= $diff->w * 7;
    $formats = [
        'y' => ' year',
        'm' => ' month',
        'w' => ' week',
        'd' => ' day',
        'h' => ' hour',
        'i' => ' minute',
        's' => ' second',
    ];
    $array = [];
    foreach ($formats as $key => $value) {
        if ($diff->$key) {
            $array[$key] = $diff->$key . $value . ($diff->$key > 1 ? 's' : '');
        }
    }
    $array = array_slice($array, 0, $level);
    return $array ? join(', ', $array) . $suffix : 'now';
}