PHP Calculating with time with a negative start value - php

Question

I'm trying to convert a certain excel sheet to a php app.
Within the excel sheet you could do time calculations as eg:
A starting time A1 (could be negative), and for every day you add or substract a certain amount of hours and minutes.
- A1= -10:59
- A2= -7:36
- A3= -18:35 (A1 + A2)
- B2= 4:24
- B3= -14:11 (A3 + B2)
And so on ...
Here is some code i've tested with without succes ofcourse...
$startTime = new \DateTime('00:00:00');
$startVal = new \DateInterval('PT10H59M');
$startTime->sub($startVal); // -10:59:00
$timeSpan = new \DateInterval('PT7H36M'); // 7:36:00
$addTime = $startTime->add($timeSpan);
What is the best way to solve this in PHP? I've been testing around with DateTime but this won't allow me te start with a negative time value.
Hope someone can give me a hand.
Kind regards,
Jochem

Answer 1

I have written a simple class to handle this. It works for your given example but I was unable to test further as I cannot get negative times in my version of Excel. Let me know if it fails at some point.
class MyTime
{
private $positive = true;
private $hour=0;
private $minute=0;
/**
* MyTime constructor.
* Split the given time string into hours and minutes and whether it is positive or negative
*
* #param string $timeString In the format '-10:59', '4:35', or optionally just minutes '24'
*/
public function __construct($timeString)
{
if(!empty($timeString))
{
if(strpos($timeString,'-')===0)
{
$this->positive = false;
$timeString = substr($timeString,1);
}
$timeParts = explode(':',$timeString);
if(!empty($timeParts))
{
if(count($timeParts) == 1)
{
$this->hour = 0;
$this->minute = intval($timeParts[0]);
}
else
{
$this->hour = intval($timeParts[0]);
$this->minute = intval($timeParts[1]);
}
}
}
}
public function getHour()
{
return $this->hour;
}
public function getMinute()
{
return $this->minute;
}
/**
* Convert into minutes either negative or positive
* #return int
*/
public function inMinutes()
{
$minutes = ($this->hour*60)+$this->minute;
if(!$this->positive)
{
$minutes *= -1;
}
return $minutes;
}
/**
* Convert back to a string for output
* #return string
*/
public function __toString()
{
return ($this->positive?'':'-').$this->getHour().':'.str_pad($this->getMinute(),2,'0',STR_PAD_LEFT);
}
/**
* Add on the given time which could be negative
* #param MyTime $time
*
* #return $this
*/
public function add(MyTime $time)
{
$newMinutes = $this->inMinutes() + $time->inMinutes();
if($newMinutes<0)
{
$this->hour = (int) ceil($newMinutes/60);
}
else
{
$this->hour = (int) floor($newMinutes/60);
}
$this->minute = abs($newMinutes-($this->hour*60));
if($newMinutes<0)
{
$this->positive = false;
$this->hour *= -1;
}
else
{
$this->positive = true;
}
return $this;
}
}
$time = new MyTime('-10:59');
echo $time."\n";
echo $time->add(new MyTime('-7:36'))."\n";
echo $time->add(new MyTime('4:24'))."\n";
echo $time->add(new MyTime('18:32'))."\n";
$time = new MyTime('10:59');
echo $time."\n";
echo $time->add(new MyTime('-59'))."\n";