topnotch_website/app/Models/Payment.php

<?php

namespace App\Models;

use App\Enums\InvoiceStatus;
use App\Observers\PaymentObserver;
use Illuminate\Database\Eloquent\Attributes\ObservedBy;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;
use Illuminate\Database\Eloquent\SoftDeletes;
use Illuminate\Support\Collection;

#[ObservedBy(PaymentObserver::class)]

class Payment extends Model
{
    use SoftDeletes;

    protected $fillable = [
        'customer_id',
        'check_number',
        'date',
        'amount',
        'unapplied_amount',
        'notes',
    ];

    public function applyToInvoices(Collection $invoices): void
    {
        $remaining = $this->unapplied_amount ?? $this->amount;

        $filteredInvoices = $invoices->whereIn('status', [
            InvoiceStatus::UNPAID,
            InvoiceStatus::PARTIALLY_PAID,
        ]);

        foreach ($filteredInvoices as $invoice) {
            $balance = $invoice->remainingBalance();

            if ($remaining <= 0) {
                break;
            }

            $applied = min($remaining, $balance);
            $invoice->payments()->attach($this->id, ['applied_amount' => $applied]);

            $remaining -= $applied;

            if ($invoice->remainingBalance() == 0) {
                $invoice->setStatus(InvoiceStatus::PAID);
            } elseif ($applied > 0) {
                $invoice->setStatus(InvoiceStatus::PARTIALLY_PAID);
            }
        }

        $this->unapplied_amount = $remaining;
        $this->saveQuietly();
    }

    public function customer(): BelongsTo
    {
        return $this->belongsTo(Customer::class);
    }

    public function invoices(): BelongsToMany
    {
        return $this->belongsToMany(Invoice::class)
            ->withPivot('applied_amount')
            ->withTimestamps();
    }
}