Facebook like human readable time stamp using php function

Want to share php function which results in grammatically correct facebook like human reable time format.
   
    example:
    echo get_time_ago(strtotime('now'));
   
    Result:
    less than 1 minute ago

function get_time_ago($time_stamp)
    {
        $time_difference = strtotime('now') - $time_stamp;

        if ($time_difference >= 60 * 60 * 24 * 365.242199)
        {
            /*
             * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 365.242199 days/year
             * This means that the time difference is 1 year or more
             */
            return get_time_ago_string($time_stamp, 60 * 60 * 24 * 365.242199, 'year');
        }
        elseif ($time_difference >= 60 * 60 * 24 * 30.4368499)
        {
            /*
             * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 30.4368499 days/month
             * This means that the time difference is 1 month or more
             */
            return get_time_ago_string($time_stamp, 60 * 60 * 24 * 30.4368499, 'month');
        }
        elseif ($time_difference >= 60 * 60 * 24 * 7)
        {
            /*
             * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 7 days/week
             * This means that the time difference is 1 week or more
             */
            return get_time_ago_string($time_stamp, 60 * 60 * 24 * 7, 'week');
        }
        elseif ($time_difference >= 60 * 60 * 24)
        {
            /*
             * 60 seconds/minute * 60 minutes/hour * 24 hours/day
             * This means that the time difference is 1 day or more
             */
            return get_time_ago_string($time_stamp, 60 * 60 * 24, 'day');
        }
        elseif ($time_difference >= 60 * 60)
        {
            /*
             * 60 seconds/minute * 60 minutes/hour
             * This means that the time difference is 1 hour or more
             */
            return get_time_ago_string($time_stamp, 60 * 60, 'hour');
        }
        else
        {
            /*
             * 60 seconds/minute
             * This means that the time difference is a matter of minutes
             */
            return get_time_ago_string($time_stamp, 60, 'minute');
        }
    }

    function get_time_ago_string($time_stamp, $divisor, $time_unit)
    {
        $time_difference = strtotime("now") - $time_stamp;
        $time_units      = floor($time_difference / $divisor);

        settype($time_units, 'string');

        if ($time_units === '0')
        {
            return 'less than 1 ' . $time_unit . ' ago';
        }
        elseif ($time_units === '1')
        {
            return '1 ' . $time_unit . ' ago';
        }
        else
        {
            /*
             * More than "1" $time_unit. This is the "plural" message.
             */
            // TODO: This pluralizes the time unit, which is done by adding "s" at the end; this will not work for i18n!
            return $time_units . ' ' . $time_unit . 's ago';
        }
    }