formats a datetime (yyyy-mm-dd hh:mm:ss) into a human readable elapsed format

gistfile1.php

/**
 * formats a datetime (yyyy-mm-dd hh:mm:ss) into a human readable elapsed format
 *
 * @return string
 * @param string datetime
 * @param string word that will end the string
 * @param int maximum value before returning the datetime in the datetime_format
 * @param string max unit to use
 * @param string datetime format
 */
function format_time_elapsed($datetime, $end_word = 'ago', $max_value = '', $max_unit = 'years', $datetime_format = 'm/d/Y')
{
    $time = strtotime($datetime);
    $diff = time() - $time;
    $units = array();
    $units[] = array('unit' => 'seconds', 'value' => 1);
    $units[] = array('unit' => 'minutes', 'value' => 60);
    $units[] = array('unit' => 'hours',   'value' => 60 * 60);
    $units[] = array('unit' => 'days',    'value' => 60 * 60 * 24);
    $units[] = array('unit' => 'weeks',   'value' => 60 * 60 * 24 * 7);
    $units[] = array('unit' => 'months',  'value' => 60 * 60 * 24 * 30);
    $units[] = array('unit' => 'years',   'value' => 60 * 60 * 24 * 365);
    
    $return_unit = '';
    $return_value = '';
    foreach ($units as $key => $value)
    {
        if ($diff > $value['value'] and isset($units[$key + 1]) and $diff > $units[$key + 1]['value'] and $value['unit'] != $max_unit)
        {
            continue;
        }
        else
        {
            $return_value = round($diff / $value['value']);
            $return_unit = $value['unit'];
            if ($return_value == 1)
            {
                $return_unit = rtrim($return_unit, 's');
            }
            break;
        }
    }
    
    if ($max_value and $return_value > $max_value)
    {
        return format_datetime($datetime, $datetime_format);
    }
    else
    {
        return $return_value . ' ' . $return_unit . ' ' . $end_word;
    }
}