function register_pending_order_summary_page() {
    add_submenu_page( 'woocommerce', 'Warehouse Picking List', 'Warehouse Picking List', 'read', 'pending_order_summary_page', 'pending_order_summary_page_callback' );
}

function pending_order_summary_page_callback() {  ?>

    <div class="wrap">

        <h1>Pending Order Summary</h1>
        <p id="pendingordersubtitle">This is a list of all the products needed to complete all 'Processing' orders.<br /><hr /></p>

        <?php

        // Create an array to store order line items
        $output_stack = array();

        // Create an array to store order line item ids
        $output_stack_ids = array();

        // Array to display the results in numerical order
        $output_diplay_array = array();

        // SQL code
        global $wpdb;
        $order_line_items;

        // Get the order ID of processing orders
        $order_ids = $wpdb->get_results( $wpdb->prepare("SELECT ID FROM {$wpdb->prefix}posts WHERE post_type = %s AND post_status = %s;", 'shop_order', 'wc-processing' ));

        // Collect the order IDs and add products to the pick list
        foreach($order_ids as $an_order_id) {

            // Collect all order line items matching IDs of pending orders
            $order_line_items = $wpdb->get_results( $wpdb->prepare("SELECT * FROM {$wpdb->prefix}woocommerce_order_items WHERE order_id = %d AND order_item_type = %s;", $an_order_id->ID, 'line_item'));

            // Extract the order line item
            foreach($order_line_items as $line_item) {

                // Add it to the array
                $pair = array($line_item->order_item_name, $line_item->order_item_id);
                array_push($output_stack, $line_item->order_item_name); // Now we've got a list of line items
                array_push($output_stack_ids, $pair); // Now we've got a list of line ids

            }
        }

        // Count the number of occurrences of each value
        $occurrences = (array_count_values($output_stack));

        // Print output
        echo '<table><tr><td><strong>SKU</strong></td><td><strong>Thumbnail</strong></td><td style="width: 100px;"><strong>Quantity</strong></td><td><strong>Product</strong></td></tr>';

        if(count($occurrences) > 0){

            $cumulative_count = 0;

            // Loop through each different product in our list
            foreach ($occurrences as $product_name => $quantity) {

                // Reset cumulative_count for each product
                $cumulative_count = 0;

                // Initialize product_id, sku, and thumbnail for the current product
                $product_id = null;
                $sku = null;
                $thumbnail = null;

                // Go through the list of ALL line items from earlier
                foreach ($output_stack_ids as $the_line_item) {

                    // We only want to cumulatively add the quantity if the line item name matches the current product name in the list of unique products
                    if ($product_name == $the_line_item[0]) {

                        // Fetch product_id from wp_wc_order_product_lookup using order_item_id
                        $product_id = $wpdb->get_var($wpdb->prepare("SELECT product_id FROM {$wpdb->prefix}wc_order_product_lookup WHERE order_item_id = %d", $the_line_item[1]));

                        // Fetch sku from wp_postmeta using product_id
                        $sku = $wpdb->get_var($wpdb->prepare("SELECT meta_value FROM {$wpdb->prefix}postmeta WHERE post_id = %d AND meta_key = '_sku'", $product_id));

                        // Fetch thumbnail URL from wp_postmeta using product_id
                        $thumbnail_id = get_post_thumbnail_id($product_id);
                        $thumbnail_url = wp_get_attachment_image_src($thumbnail_id, 'thumbnail');
                        $thumbnail = $thumbnail_url ? $thumbnail_url[0] : '';

                        // Reset the quantity to zero, because we don't need to know the number of instances if we're counting stock
                        $quantity = 0;

                        // For each unique line item, we want to retrieve the quantity
                        $order_line_item_quantity = $wpdb->get_results($wpdb->prepare("SELECT meta_value FROM {$wpdb->prefix}woocommerce_order_itemmeta WHERE meta_key = %s AND order_item_id = %d", "_qty", $the_line_item[1]));

                        // We've now got the quantity for each line item. Add them all together.
                        foreach ($order_line_item_quantity as $item_quantity) {
                            // The total quantity is the combined _qty of each instance of a unique line item
                            $cumulative_count = $cumulative_count + ($item_quantity->meta_value);
                        }

                    }
                }

                // Store the data in the output_diplay_array
                $output_diplay_array[] = array(
                    'order_item_id' => $the_line_item[1],
                    'product_id' => $product_id,
                    'sku' => $sku,
                    'thumbnail' => $thumbnail,
                    'quantity' => $cumulative_count,
                    'product_name' => $product_name
                );
            }

            // Output the results in a table
            foreach ($output_diplay_array as $data) {
                echo '<tr><td style="border-bottom: 1px solid #ccc; padding: 10px;">' . $data['sku'] . '</td><td style="border-bottom: 1px solid #ccc; padding: 10px;"><img src="' . $data['thumbnail'] . '" width="50" height="50"></td><td style="border-bottom: 1px solid #ccc; padding: 10px;">x <b>' . $data['quantity'] . '</b></td><td style="border-bottom: 1px solid #ccc; padding: 10px;">' . $data['product_name'] . '</td></tr>';
            }

            echo '</table>';

            // Some house cleaning
            $wpdb->flush();
        }

    ?>

    <br /><a href="javascript:window.print()"><button type="button" class="orderprintbutton">Print</button>

</div>

<?php }
add_action('admin_menu', 'register_pending_order_summary_page', 99);

// Function to apply print styling to the page
add_action('admin_head', 'dashboard_print_view');

function dashboard_print_view() {
    echo '<style>
   @media print {
    #adminmenu{display: none!important;}
    div#adminmenuback {display: none!important;}
    #wpcontent {margin-left: 5%!important;}
    #wpfooter {display: none!important;}
    .orderprintbutton {display: none!important;"}
    #screen-meta {display: none!important;}
}
  </style>';
}