InvoiceShelf/app/Services/Document/InvoiceBalanceService.php

<?php

namespace App\Services\Document;

use App\Models\Invoice;

class InvoiceBalanceService
{
    public function allocatedTotal(Invoice $invoice): int
    {
        return (int) $invoice->allocations()->sum('amount');
    }

    public function creditedTotal(Invoice $invoice): int
    {
        return -(int) $invoice->creditNotes()->sum('total');
    }

    /**
     * Recalculate an invoice exclusively from durable credits and payment
     * allocations. Callers that change allocations must hold the invoice lock.
     */
    public function recalculate(Invoice $invoice): void
    {
        $allocated = $this->allocatedTotal($invoice);
        $credited = $this->creditedTotal($invoice);
        $due = max(0, (int) $invoice->total - $allocated - $credited);

        $invoice->due_amount = $due;
        $invoice->base_due_amount = (int) round($due * $invoice->exchange_rate);

        if ($due === 0) {
            $invoice->status = Invoice::STATUS_COMPLETED;
            $invoice->paid_status = Invoice::STATUS_PAID;
            $invoice->overdue = false;
        } else {
            $invoice->status = $invoice->getPreviousStatus();
            $invoice->paid_status = $allocated > 0
                ? Invoice::STATUS_PARTIALLY_PAID
                : Invoice::STATUS_UNPAID;
        }

        $invoice->save();
    }
}