请教这种计算工作时间结束的具体时间戳 应该如何写

请问这种计算工作时间结束的具体时间戳 应该怎么写
起始时间是随机的日期时间戳是X
总共需要工作6天才能完成
但是上班时间只有5天/周
我想得到下周几才能完成，包括具体的时间戳，星期几

这里要如何判断周六日，把他们再每一次都隔过去呢

麻烦写个完整代码，感谢
------解决思路----------------------

<?php

$start_time =rand(time(), time() + 50 * 24 * 60 * 60);

$needed_time = 23;   //day

$work_day = 5;

$needed_week = floor($needed_time/$work_day);

$end_time = $start_time + $needed_week * 7 * 24 * 60 * 60 + $needed_time%$work_day * 24 * 60 * 60;

$end_date = date("Y-m-d", $end_time);

$start_date = date("Y-m-d", $start_time);

$end_week_day = date("w", $end_time);

$weeks = array("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday");

echo "start date: $start_date, end date: $end_date, " . $weeks[$end_week_day] . " after ". $needed_week . " weeks.";

------解决思路----------------------

引用:

<?php

$start_time =rand(time(), time() + 50 * 24 * 60 * 60);

$needed_time = 23;   //day

$work_day = 5;

$needed_week = floor($needed_time/$work_day);

$end_time = $start_time + $needed_week * 7 * 24 * 60 * 60 + $needed_time%$work_day * 24 * 60 * 60;

$end_date = date("Y-m-d", $end_time);

$start_date = date("Y-m-d", $start_time);

$end_week_day = date("w", $end_time);

$weeks = array("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday");

echo "start date: $start_date, end date: $end_date, " . $weeks[$end_week_day] . " after ". $needed_week . " weeks.";

<?php

$start_time =rand(time(), time() + 50 * 24 * 60 * 60);

$needed_time = 23;   //day

$work_day = 5;

$needed_week = floor($needed_time/$work_day);

$end_time = $start_time + $needed_week * 7 * 24 * 60 * 60 + $needed_time%$work_day * 24 * 60 * 60;


$weeks = array("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday");

$end_week_day = date("w", $end_time);

if($end_week_day == 6 
------解决思路----------------------
 $end_week_day == 0)
{
	$needed_week ++;
	$end_time += 2 * 24 * 60 * 60;
}
$end_date = date("Y-m-d", $end_time);

$start_date = date("Y-m-d", $start_time);

$end_week_day = date("w", $end_time);


echo "start date: $start_date, end date: $end_date, " . $weeks[$end_week_day] . " after ". $needed_week . " weeks.";

------解决思路----------------------
与其费脑筋推演算式，还不如用计算机最擅长简单累加

$x = '2015-07-27';
$d = 6;

$t = strtotime($x);
while($d > 1) { //当天不算就 $d > 0
  $t += 86400;
  if(in_array(date('w', $t), array(6,0))) continue;
  $d--;
}
echo date('Y-m-d w', $t);

2015-08-03 1