Getting non overlapping between two dates with Carbon - laravel

Question

UseCase: Admin assigns tasks to People. Before we assign them we can see their tasks in a gantt chart. According to the task assign date and deadline, conflict days (overlap days) are generated between tasks.
I wrote this function to get overlapping dates between two dates. But now I need to get non overlapping days between two dates, below is the function I wrote.
$tasks = Assign_review_tasks::where('assigned_to', $employee)
->where('is_active', \Constants::$REVIEW_ACTIVE)
->whereNotNull('permit_id')->get();
$obj['task'] = count($tasks);
// count($tasks));
if (count($tasks) > 0) {
if (count($tasks) > 1) {
$start_one = $tasks[count($tasks) - 1]->start_date;
$end_one = $tasks[count($tasks) - 1]->end_date;
$end_two = $tasks[count($tasks) - 2]->end_date;
$start_two = $tasks[count($tasks) - 2]->start_date;
if ($start_one <= $end_two && $end_one >= $start_two) { //If the dates overlap
$obj['day'] = Carbon::parse(min($end_one, $end_two))->diff(Carbon::parse(max($start_two, $start_one)))->days + 1; //return how many days overlap
} else {
$obj['day'] = 0;
}
// $arr[] = $obj;
} else {
$obj['day'] = 0;
}
} else {
$obj['day'] = 0;
}
$arr[] = $obj;
start_date and end_date are taken from database,
I tried modifying it to,
(Carbon::parse((min($end_one, $end_two))->add(Carbon::parse(max($start_two, $start_one))))->days)->diff(Carbon::parse(min($end_one, $end_two))->diff(Carbon::parse(max($start_two, $start_one)))->days + 1);
But it didn't work, in simple terms this is what I want,
Non conflicting days = (end1-start1 + end2-start2)- Current overlapping days
I'm having trouble translate this expression . Could you help me? Thanks in advance

Answer 1

before trying to reimplement complex stuff I recommend you take a look at enhanced-period for Carbon
composer require cmixin/enhanced-period
CarbonPeriod::diff macro method is what I think you're looking for:
use Carbon\CarbonPeriod;
use Cmixin\EnhancedPeriod;
CarbonPeriod::mixin(EnhancedPeriod::class);
$a = CarbonPeriod::create('2018-01-01', '2018-01-31');
$b = CarbonPeriod::create('2018-02-10', '2018-02-20');
$c = CarbonPeriod::create('2018-02-11', '2018-03-31');
$current = CarbonPeriod::create('2018-01-20', '2018-03-15');
foreach ($current->diff($a, $b, $c) as $period) {
foreach ($period as $day) {
echo $day . "\n";
}
}
This will output all the days that are in $current but not in any of the other periods. (E.g. non-conflicting days)