strprfcrm/app/Services/ProductionCalendarService.php

<?php

declare(strict_types=1);

namespace App\Services;

use App\Models\ProductionCalendarDay;
use Carbon\CarbonImmutable;
use DateTimeInterface;
use InvalidArgumentException;

class ProductionCalendarService
{
    public function addWorkingDays(DateTimeInterface|string $startDate, int $workingDays): CarbonImmutable
    {
        if ($workingDays < 0) {
            throw new InvalidArgumentException('Количество рабочих дней не может быть отрицательным.');
        }

        $date = CarbonImmutable::parse($startDate)->startOfDay();
        if ($workingDays === 0) {
            return $date;
        }

        $overrides = ProductionCalendarDay::query()
            ->pluck('is_working_day', 'date')
            ->map(static fn (mixed $value): bool => (bool) $value);

        $remaining = $workingDays;
        while ($remaining > 0) {
            $date = $date->addDay();
            $key = $date->toDateString();
            $isWorkingDay = $overrides->has($key)
                ? $overrides->get($key)
                : ! $date->isWeekend();

            if ($isWorkingDay) {
                $remaining--;
            }
        }

        return $date;
    }
}