templates/cart_discount.html

<div class="apply-coupon">
    <label for="coupon-code">Coupon Code:</label>
    <input type="text" id="coupon-code" name="coupon_code" placeholder="Enter your coupon code">
    <button type="button" onclick="applyCoupon()">Apply Coupon</button>
    <p id="coupon-message"></p>  <!-- To display coupon status -->
</div>
<div>
    <p>Subtotal: $<span id="subtotal">{{ subtotal }}</span></p>
    <p>Discount: $<span id="discount">0</span></p>
    <p>Total: $<span id="total-price">{{ subtotal }}</span></p>
</div>

<script>
function applyCoupon() {
    const couponCode = document.getElementById('coupon-code').value;
    const subtotal = parseFloat(document.getElementById('subtotal').innerText);
    const couponMessage = document.getElementById('coupon-message');

    if (couponCode) {
        fetch('/apply_coupon', {
            method: 'POST',
            headers: {
                'Content-Type': 'application/json'
            },
            body: JSON.stringify({ coupon_code: couponCode, subtotal: subtotal })
        })
        .then(response => response.json())
        .then(data => {
            if (data.success) {
                const discount = data.discount;
                const totalPrice = subtotal - discount;
                document.getElementById('discount').innerText = discount;
                document.getElementById('total-price').innerText = totalPrice;
                couponMessage.innerText = `Coupon applied! You saved $${discount}`;
                couponMessage.style.color = 'green';
            } else {
                couponMessage.innerText = data.message;
                couponMessage.style.color = 'red';
            }
        })
        .catch(error => {
            console.error('Error applying coupon:', error);
            couponMessage.innerText = 'Error applying coupon.';
            couponMessage.style.color = 'red';
        });
    } else {
        couponMessage.innerText = 'Please enter a coupon code.';
        couponMessage.style.color = 'red';
    }
}
</script>