Add Envelope Addon Option to Woocommerce Product

functions.php

<?php

/** 
 * Adding Checkbox and Price Field in Product Admin Panel 
 */
function custom_add_envelope_checkbox_and_price() {
    echo '<div class="custom-envelop-checkbox">';
    
    // Envelope activation checkbox
    woocommerce_wp_checkbox( array(
        'id' => 'custom_envelope_active',
        'label' => __('Activate Envelope', 'woocommerce'),
        'description' => __('Check to activate envelope.', 'woocommerce'),
    ));

    // Custom price input field for Envelope Price
    woocommerce_wp_text_input( array(
        'id' => 'custom_envelope_price',
        'label' => __('Envelope Price', 'woocommerce'),
        'description' => __('Set the price for the envelope (leave empty for default €50).', 'woocommerce'),
        'type' => 'number',
        'desc_tip' => true,
        'custom_attributes' => array( 'step' => '0.01', 'min' => '0' )
    ));

    echo '</div>';
}
add_action( 'woocommerce_product_options_general_product_data', 'custom_add_envelope_checkbox_and_price' );

/** 
 * Saving Envelope Checkbox and Price to Product Meta
 */
function custom_save_envelope_checkbox_and_price( $post_id ) {
    $product = wc_get_product( $post_id );

    // Save the envelope activation
    $checkbox_value = isset( $_POST['custom_envelope_active'] ) ? 'yes' : 'no';
    $product->update_meta_data( 'custom_envelope_active', $checkbox_value );

    // Save the custom envelope price
    $envelope_price = isset( $_POST['custom_envelope_price'] ) ? $_POST['custom_envelope_price'] : '50'; // Default to €50 if no price set
    $product->update_meta_data( 'custom_envelope_price', sanitize_text_field( $envelope_price ) );

    $product->save();
}
add_action( 'woocommerce_process_product_meta', 'custom_save_envelope_checkbox_and_price' );

/** 
 * Displaying the Envelope Checkbox on Product Page
 */
add_action( 'woocommerce_before_add_to_cart_button', 'add_custom_checkbox_to_product', 10 );
function add_custom_checkbox_to_product() {
    global $product;
    
    // Check if the product has the 'custom_envelope_active' meta
    $custom_envelope_active = get_post_meta( $product->get_id(), 'custom_envelope_active', true );

    // If 'custom_envelope_active' is set to 'yes', display the checkbox
    if ( $custom_envelope_active === 'yes' ) {
        $custom_envelope_price = get_post_meta( $product->get_id(), 'custom_envelope_price', true );
        $custom_envelope_price = !empty( $custom_envelope_price ) ? $custom_envelope_price : '50'; // Default to 50 if no price set

        echo '<div class="custom-checkbox">
                <input type="checkbox" id="add_custom_option" name="add_custom_option" value="1" />
                <label for="add_custom_option">Add Envelope Price for €' . esc_html( $custom_envelope_price ) . '</label>
              </div>';
        // Store the price in a hidden input for use in the cart
        echo '<input type="hidden" id="custom_envelope_price" name="custom_envelope_price" value="' . esc_attr( $custom_envelope_price ) . '" />';
    }
}

/** 
 * Adding Envelope Price to Cart Item Data
 */
add_filter( 'woocommerce_add_cart_item_data', 'add_envelope_price_to_cart', 10, 2 );
function add_envelope_price_to_cart( $cart_item_data, $product_id ) {
    if ( isset( $_POST['add_custom_option'] ) && $_POST['add_custom_option'] == '1' ) {
        $envelope_price = isset( $_POST['custom_envelope_price'] ) ? $_POST['custom_envelope_price'] : 50; // Default €50 if not set
        $cart_item_data['custom_envelope_price'] = $envelope_price;
    }
    return $cart_item_data;
}

/** 
 * Add Envelope Price to Cart Total (Subtotal)
 */
add_action( 'woocommerce_cart_calculate_fees', 'add_envelope_price_to_cart_total', 20, 1 );
function add_envelope_price_to_cart_total( $cart ) {
    $envelope_total = 0;

    // Loop through each cart item to check for the envelope option
    foreach ( $cart->get_cart() as $cart_item ) {
        if ( isset( $cart_item['custom_envelope_price'] ) ) {
            $envelope_total += $cart_item['custom_envelope_price'];  // Add the envelope price to total
        }
    }

    // If there's an envelope price, add it as a fee
    if ( $envelope_total > 0 ) {
        $cart->add_fee( 'Envelope Price', $envelope_total, true, '' );  // true indicates taxable
    }
}

/** 
 * Display Envelope Price in the Cart Item
 */
add_filter( 'woocommerce_get_item_data', 'display_envelope_price_in_cart_item', 10, 2 );
function display_envelope_price_in_cart_item( $item_data, $cart_item ) {
    if ( isset( $cart_item['custom_envelope_price'] ) ) {
        $item_data[] = array(
            'name'  => 'Envelope Price',
            'value' => '€' . esc_html( $cart_item['custom_envelope_price'] )
        );
    }
    return $item_data;
}

/** 
 * Update Elementor Mini Cart Subtotal Dynamically Using AJAX
 */
add_filter( 'woocommerce_add_to_cart_fragments', 'update_elementor_mini_cart_after_add_to_cart' );
function update_elementor_mini_cart_after_add_to_cart( $fragments ) {
    ob_start();
    
    // Get the total envelope price
    $envelope_total = 0;
    foreach ( WC()->cart->get_cart() as $cart_item ) {
        if ( isset( $cart_item['custom_envelope_price'] ) ) {
            $envelope_total += $cart_item['custom_envelope_price'];  // Add the envelope price
        }
    }

    // Get the cart subtotal
    $cart_subtotal = WC()->cart->get_subtotal();

    // Add the envelope price to the subtotal
    $updated_subtotal = $cart_subtotal + $envelope_total;

    ?>
    <div class="elementor-menu-cart__subtotal">
        <strong>Subtotal:</strong>
        <span class="woocommerce-Price-amount amount">
            <bdi>
                <span class="woocommerce-Price-currencySymbol">€</span>&nbsp;
                <?php echo number_format( $updated_subtotal, 2 ); ?>
            </bdi>
        </span>
    </div>
    <?php
    
    // Return the updated fragment
    $fragments['div.elementor-menu-cart__subtotal'] = ob_get_clean();
    return $fragments;
}