document.addEventListener('DOMContentLoaded', () => {
    const newProjectForm = document.getElementById('new-project-form');
    const tableBody = document.querySelector('.table tbody');

    newProjectForm.addEventListener('submit', (event) => {
        event.preventDefault();

        const roomNumber = document.getElementById('room-number').value;
        const roomType = document.getElementById('room-type').value;
        const rate = parseFloat(document.getElementById('rate').value);
        const guestName = document.getElementById('guest-name').value;
        const guestPhone = document.getElementById('guest-phone').value;
        const checkInDate = document.getElementById('check-in-date').value;
        const checkOutDate = document.getElementById('check-out-date').value;

        try {
            // Input Validation (Crucial for robust code)
            if (!roomNumber || !roomType || isNaN(rate) || !guestName || !guestPhone || !checkInDate || !checkOutDate) {
                throw new Error("Пожалуйста, заполните все поля корректно.");
            }

            const newRow = document.createElement('tr');

            const roomNumberCell = document.createElement('td');
            roomNumberCell.textContent = roomNumber;

            const roomTypeCell = document.createElement('td');
            roomTypeCell.textContent = roomType;

            const rateCell = document.createElement('td');
            rateCell.textContent = rate.toFixed(2);

            const availabilityCell = document.createElement('td');
            availabilityCell.textContent = 'Доступен';

            const guestNameCell = document.createElement('td');
            guestNameCell.textContent = guestName;

            const guestPhoneCell = document.createElement('td');
            guestPhoneCell.textContent = guestPhone;

            const datesCell = document.createElement('td');
            datesCell.textContent = `${checkInDate} - ${checkOutDate}`; // Correct template literal

            const costCell = document.createElement('td');
            const checkInDateObj = new Date(checkInDate);
            const checkOutDateObj = new Date(checkOutDate);
            const timeDiff = checkOutDateObj.getTime() - checkInDateObj.getTime();
            const numNights = Math.ceil(timeDiff / (1000 * 3600 * 24));

            if (isNaN(numNights) || numNights < 0) {
                throw new Error("Неверные даты. Убедитесь, что дата выезда позже даты заезда.");
            }

            const cost = numNights * rate;
            costCell.textContent = cost.toFixed(2);

            newRow.appendChild(roomNumberCell);
            newRow.appendChild(roomTypeCell);
            newRow.appendChild(rateCell);
            newRow.appendChild(availabilityCell);
            newRow.appendChild(guestNameCell);
            newRow.appendChild(guestPhoneCell);
            newRow.appendChild(datesCell);
            newRow.appendChild(costCell);

            tableBody.appendChild(newRow);

            newProjectForm.reset();

        } catch (error) {
            console.error("Произошла ошибка:", error);
            alert("Произошла ошибка при обработке данных: " + error.message + ". Пожалуйста, проверьте введенные данные.");  // Show error message to user
        }
    });
});