Defining delivery dates

Generate a shipping rate code for a standard shipping with $10 flat rate and express shipping with $20 flat rate.
The standard shipping is delivered between 4 to 8 business days; the express shipping between 2 to 3 business days. 
Business days do not include weekends. Include the delivery dates in the rates.
Modify the description to show the maximum delivery date in the format "Estimated delivery before Tue, Nov1, 2023"

export async function calculateShippingRates(DATA, env) {
    try {
        // Helper function to add business days, excluding weekends
        function addBusinessDays(startDate, numberOfDays) {
            let currentDate = new Date(startDate);
            while (numberOfDays > 0) {
                currentDate = new Date(currentDate.setDate(currentDate.getDate() + 1));
                // Exclude weekends
                if (currentDate.getDay() !== 0 && currentDate.getDay() !== 6) {
                    numberOfDays--;
                }
            }
            return currentDate;
        }

        // Function to format date
        function formatDate(date) {
            const options = { weekday: 'short', year: 'numeric', month: 'short', day: 'numeric' };
            return date.toLocaleDateString("en-US", options);
        }

        // Calculate delivery dates for standard and express shipping
        const standardMinDeliveryDate = addBusinessDays(new Date(), 4);
        const standardMaxDeliveryDate = addBusinessDays(new Date(), 8);
        const expressMinDeliveryDate = addBusinessDays(new Date(), 2);
        const expressMaxDeliveryDate = addBusinessDays(new Date(), 3);

        // Prepare shipping rates
        const rates = [
            {
                service_name: "Standard Shipping",
                service_code: "STD_FLAT_RATE",
                total_price: "1000", // $10 flat rate in cents
                description: `Estimated delivery before ${formatDate(standardMaxDeliveryDate)}`,
                currency: DATA.currency,
                min_delivery_date: standardMinDeliveryDate.toISOString().split('T')[0],
                max_delivery_date: standardMaxDeliveryDate.toISOString().split('T')[0]
            },
            {
                service_name: "Express Shipping",
                service_code: "EXP_FLAT_RATE",
                total_price: "2000", // $20 flat rate in cents
                description: `Estimated delivery before ${formatDate(expressMaxDeliveryDate)}`,
                currency: DATA.currency,
                min_delivery_date: expressMinDeliveryDate.toISOString().split('T')[0],
                max_delivery_date: expressMaxDeliveryDate.toISOString().split('T')[0]
            }
        ];

        return { rates };
    } catch (error) {
        // Return error message in case of exceptions
        return { 
            rates: [{
                service_name: "Error",
                service_code: "ERR",
                total_price: null,
                description: error.message,
                currency: DATA.currency,
                min_delivery_date: "",
                max_delivery_date: ""
            }]
        };
    }
}