invoiceninja/app/Helpers/Invoice/Refund.php

<?php
/**
 * Invoice Ninja (https://invoiceninja.com).
 *
 * @link https://github.com/invoiceninja/invoiceninja source repository
 *
 * @copyright Copyright (c) 2021. Invoice Ninja LLC (https://invoiceninja.com)
 *
 * @license https://www.elastic.co/licensing/elastic-license
 */

namespace App\Helpers\Invoice;

use App\Models\RecurringInvoice;
use Illuminate\Support\Carbon;

class Refund
{

    public function proRata(float $amount, Carbon $from_date, Carbon $to_date, int $frequency) :float
    {
        $days = $from_date->diffInDays($to_date);
        $days_in_frequency = $this->getDaysInFrequency($frequency);

        return round( (($days/$days_in_frequency) * $amount),2);
    }

    private function getDaysInFrequency($frequency)
    {

        switch ($frequency) {
            case RecurringInvoice::FREQUENCY_DAILY:
                return 1;
            case RecurringInvoice::FREQUENCY_WEEKLY:
                return 7;
            case RecurringInvoice::FREQUENCY_TWO_WEEKS:
                return 14;
            case RecurringInvoice::FREQUENCY_FOUR_WEEKS:
                return now()->diffInDays(now()->addWeeks(4));
            case RecurringInvoice::FREQUENCY_MONTHLY:
                return now()->diffInDays(now()->addMonthNoOverflow());
            case RecurringInvoice::FREQUENCY_TWO_MONTHS:
                return now()->diffInDays(now()->addMonthNoOverflow(2));
            case RecurringInvoice::FREQUENCY_THREE_MONTHS:
                return now()->diffInDays(now()->addMonthNoOverflow(3));
            case RecurringInvoice::FREQUENCY_FOUR_MONTHS:
                return now()->diffInDays(now()->addMonthNoOverflow(4));
            case RecurringInvoice::FREQUENCY_SIX_MONTHS:
                return now()->diffInDays(now()->addMonthNoOverflow(6));
            case RecurringInvoice::FREQUENCY_ANNUALLY:
                return now()->diffInDays(now()->addYear());
            case RecurringInvoice::FREQUENCY_TWO_YEARS:
                return now()->diffInDays(now()->addYears(2));
            case RecurringInvoice::FREQUENCY_THREE_YEARS:
                return now()->diffInDays(now()->addYears(3));
            default:
                return 0;
        }

    }

}