Bottelet/DaybydayCRM

// Service is any PHP class with methods related to some topic or model, like Invoice, in this case
// Notice: there's no Artisan command like "php artisan make:service".
// You need to create it manually as a simple PHP class in whatever folder you want.
// Usually it's app/Services, which may be further divided into subfolders

class InvoiceCalculator
{
    private $tax;

    public function __construct($invoice)
    {
        if(!$invoice instanceof Invoice && !$invoice instanceof Offer ) {
            throw new \Exception("Not correct type for Invoice Calculator");
        }
        $this->tax = new Tax();
        $this->invoice = $invoice;
    }

    public function getVatTotal()
    {
        $price = $this->getSubTotal()->getAmount();
        return new Money($price * $this->tax->vatRate());
    }

    public function getTotalPrice(): Money
    {
        $price = 0;
        $invoiceLines = $this->invoice->invoiceLines;

        foreach ($invoiceLines as $invoiceLine) {
            $price += $invoiceLine->quantity * $invoiceLine->price;
        }

        return new Money($price);
    }

    public function getSubTotal(): Money
    {
        $price = 0;
        $invoiceLines = $this->invoice->invoiceLines;

        foreach ($invoiceLines as $invoiceLine) {
            $price += $invoiceLine->quantity * $invoiceLine->price;
        }
        return new Money($price / $this->tax->multipleVatRate());
    }

    public function getAmountDue()
    {
        return new Money($this->getTotalPrice()->getAmount() - $this->invoice->payments()->sum('amount'));
    }
}

// There are multiple ways to use and initiate the Service class. 
// In this case, it's just creating the object, passing the parameter of $invoice

// ... other use statements
use App\Services\Invoice\InvoiceCalculator;

class InvoicesController extends Controller
{
    // ... other methods 

    public function show(Invoice $invoice)
    {
        // ...

        $invoiceCalculator = new InvoiceCalculator($invoice);
        $totalPrice = $invoiceCalculator->getTotalPrice();
        $subPrice = $invoiceCalculator->getSubTotal();
        $vatPrice = $invoiceCalculator->getVatTotal();
        $amountDue = $invoiceCalculator->getAmountDue();

        // ...        
    }
}