<?php

namespace App\Support;

use App\Models\Invoice;

class VatCalculator
{
    public static function refresh(Invoice $invoice): Invoice
    {
        if ($invoice->vat_number) {
            return $invoice;
        }

        $tax = self::taxFor($invoice);

        if ((int) $invoice->tax !== $tax) {
            $invoice->forceFill(['tax' => $tax])->saveQuietly();
        }

        return $invoice;
    }

    public static function taxFor(Invoice $invoice): int
    {
        $items = $invoice->invoiceItems()->with('product:id,product_type')->get();
        $gross = (int) $items->sum('total_price');

        if ($gross <= 0) {
            return 0;
        }

        $payable = min((int) $invoice->total, $gross);
        $tax = 0.0;

        foreach ($items as $item) {
            $rate = VatSettings::rateFor($item->product?->product_type);
            $share = $payable * ((int) $item->total_price / $gross);
            $tax += $share * $rate / (100 + $rate);
        }

        return (int) round($tax);
    }
}