/**
 * 获得几天前，几小时前，几月前
 * @param int $time 时间戳
 * @param array $unit 时间单位
 * @return bool|string
 */
function date_before($time, $unit = null) {
	$time = intval($time);
	$unit = is_null($unit) ? array("年", "月", "星期", "天", "小时", "分钟", "秒") : $unit;
	switch (true) {
		case $time < (NOW - 31536000) :
			return floor((NOW - $time) / 31536000) . $unit[0] . '前';
		case $time < (NOW - 2592000) :
			return floor((NOW - $time) / 2592000) . $unit[1] . '前';
		case $time < (NOW - 604800) :
			return floor((NOW - $time) / 604800) . $unit[2] . '前';
		case $time < (NOW - 86400) :
			return floor((NOW - $time) / 86400) . $unit[3] . '前';
		case $time < (NOW - 3600) :
			return floor((NOW - $time) / 3600) . $unit[4] . '前';
		case $time < (NOW - 60) :
			return floor((NOW - $time) / 60) . $unit[5] . '前';
		default :
			return floor(NOW - $time) . $unit[6] . '前';
	}
}