Add custom data to cart & order in WooCommerce using filters

add_filter( 'woocommerce_product_get_stock_quantity' ,'custom_get_stock_quantity', 10, 2 );
add_filter( 'woocommerce_product_variation_get_stock_quantity' ,'custom_get_stock_quantity', 10, 2 );
function custom_get_stock_quantity( $value, $product ) {
    $value = 15; // <== Just for testing
    return $value;
}

<script>
jQuery( document ).ready(function($){
	$(document).on('click','.elementor-location-popup a', function(event){
		elementorProFrontend.modules.popup.closePopup( {}, event);
	})
});
</script>

function search_by_sku( $search, &$query_vars ) {
    global $wpdb;
    if(isset($query_vars->query['s']) && !empty($query_vars->query['s'])){
        $args = array(
            'posts_per_page'  => -1,
            'post_type'       => 'product',
            'meta_query' => array(
                array(
                    'key' => '_sku',
                    'value' => $query_vars->query['s'],
                    'compare' => 'LIKE'
                )
            )
        );
        $posts = get_posts($args);
        if(empty($posts)) return $search;
        $get_post_ids = array();
        foreach($posts as $post){
            $get_post_ids[] = $post->ID;
        }
        if(sizeof( $get_post_ids ) > 0 ) {
                $search = str_replace( 'AND (((', "AND ((({$wpdb->posts}.ID IN (" . implode( ',', $get_post_ids ) . ")) OR (", $search);
        }
    }
    return $search;
    
}
    add_filter( 'posts_search', 'search_by_sku', 999, 2 );

/***** Shorten Post/Page link  *****/
//============================
add_filter( 'get_shortlink', function ( $shortlink ) {
    return $shortlink;
});

//******--- Remove Font Awesome ---*****
//===============================
add_action( 'elementor/frontend/after_register_styles',function() {
	foreach( [ 'solid', 'regular', 'brands' ] as $style ) {
		wp_deregister_style( 'elementor-icons-fa-' . $style );
	}
}, 20 );

//*****---  Remove Eicons:  ---*****
//==========================
add_action( 'wp_enqueue_scripts', 'remove_default_stylesheet', 20 ); 
function remove_default_stylesheet() { 
	wp_deregister_style( 'elementor-icons' ); 
}

input { -webkit-user-select:text;}

if ( is_single() ) {
  $current_post_id = get_queried_object_id();
  $current_category_id = get_the_category( $current_post_id )[0]->cat_ID;

  $args = array(
    'category' => $current_category_id,
    'post__not_in' => array( $current_post_id ),
    'posts_per_page' => 3,
  );

  $related_posts = new WP_Query( $args );

  if ( $related_posts->have_posts() ) {
    echo '<h2>Related Posts:</h2>';
    while ( $related_posts->have_posts() ) {
      $related_posts->the_post();
      echo '<a href="' . get_the_permalink() . '">' . get_the_title() . '</a><br>';
    }
    wp_reset_postdata();
  }
}

add_filter( 'woocommerce_email_attachments', 'attach_downloadable_files_to_customer_completed_email', 10, 3 );
function attach_downloadable_files_to_customer_completed_email( $attachments, $email_id, $order ) {
    if( isset( $email_id ) && $email_id === 'customer_completed_order' ){
        // Loop through order items
        foreach( $order->get_items() as $item ) {
            $product = $item->get_product(); // The product Object

            if ( $product->is_downloadable() && ( $downloads = $product->get_downloads() ) ) {
                // Loop through product downloads
                foreach( $downloads as $download ) {
                    $attachments[] = $download->get_file();
                }
            }
        }
    }
    return $attachments;
}

function custom_price_shortcode_callback( $atts ) {

    $atts = shortcode_atts( array(
        'id' => null,
    ), $atts, 'product_price' );

    $html = '';

    if( intval( $atts['id'] ) > 0 && function_exists( 'wc_get_product' ) ){
        // Get an instance of the WC_Product object
        $product = wc_get_product( intval( $atts['id'] ) );

        // Get the product prices
        $price         = wc_get_price_to_display( $product, array( 'price' => $product->get_price() ) ); // Get the active price
        $regular_price = wc_get_price_to_display( $product, array( 'price' => $product->get_regular_price() ) ); // Get the regular price
        $sale_price    = wc_get_price_to_display( $product, array( 'price' => $product->get_sale_price() ) ); // Get the sale price

        // Your price CSS styles
        $style1 = 'style="font-size:40px;color:#e79a99;font-weight:bold;"';
        $style2 = 'style="font-size:25px;color:#e79a99"';

        // Formatting price settings (for the wc_price() function)
        $args = array(
            'ex_tax_label'       => false,
            'currency'           => 'EUR',
            'decimal_separator'  => '.',
            'thousand_separator' => ' ',
            'decimals'           => 2,
            'price_format'       => '%2$s %1$s',
        );

        // Formatting html output
        if( ! empty( $sale_price ) && $sale_price != 0 && $sale_price < $regular_price )
            $html = "<del $style2>" . wc_price( $regular_price, $args ) . "</del> <ins $style1>" . wc_price( $sale_price, $args ) . "</ins>"; // Sale price is set
        else
            $html = "<ins $style1>" . wc_price( $price, $args ) . "</ins>"; // No sale price set
    }
    return $html;
 }
 add_shortcode( 'product_price', 'custom_price_shortcode_callback' );

<?php

add_filter( 'woocommerce_product_data_tabs', 'b2b_add_user_product_per_user_tab' ); 
function b2b_add_user_product_per_user_tab( $tabs ) {
    $tabs['product-per-user'] = array( 
        'label' => __( 'Assign User', 'woocommerce' ), 
        'target' => 'product_per_user', 
        'class' => array( 'show_if_simple', 'show_if_variable' ), 
    ); 
    return $tabs; 
}

add_action('woocommerce_product_data_panels', 'b2b_product_per_user_panel');
function b2b_product_per_user_panel() {
    global $post;
    // Note the 'id' attribute needs to match the 'target' parameter set above
	?>
    <div id='product_per_user' class='panel woocommerce_options_panel'>
        <?php $redeemable_stores = (array) get_post_meta( $post->ID, '_redeem_in_stores', true );?>
        <p class='form-field _redeem_in_stores'>
            <label for='_redeem_in_stores'><?php _e( 'Redeemable in stores', 'woocommerce' ); ?></label>
            <select name='_redeem_in_stores[]' class='wc-enhanced-select' multiple='multiple' style='width: 80%;'>
                <option <?php selected( in_array( 'AL', $redeemable_stores ) ); ?> value='AL'>Alabama</option>
                <option <?php selected( in_array( 'NY', $redeemable_stores ) ); ?> value='NY'>New York</option>
                <option <?php selected( in_array( 'TX', $redeemable_stores ) ); ?> value='TX'>Texas</option>
                <option <?php selected( in_array( 'WY', $redeemable_stores ) ); ?> value='WY'>Wyoming</option>
            </select>
            <img class='help_tip' data-tip="<?php _e( 'Select the stores where this gift card is redeemable.', 'woocommerce' ); ?>" src='<?php echo esc_url( WC()->plugin_url() ); ?>/assets/images/help.png' height='16' width='16'>
        </p>
    </div>
    <?php
}

/**
 * Save the custom fields.
 */
function save_product_per_user_field( $post_id ) {
	if ( isset( $_POST['_redeem_in_stores'] ) ) :
		update_post_meta( $post_id, '_redeem_in_stores', (array) $_POST['_redeem_in_stores'] );
	endif;
}
add_action( 'woocommerce_process_product_meta_simple', 'save_product_per_user_field' );
add_action( 'woocommerce_process_product_meta_variable', 'save_product_per_user_field' );

<?php

$args = array(
  'role'    => 'customer',
  'orderby' => 'user_nicename',   
  'order'   => 'ASC'
);
$users = get_users( $args );

echo '<ul>';
foreach ( $users as $user ) {
	echo '<li>' . esc_html( $user->display_name ) . '[' . esc_html( $user->user_email ) . ']</li>';
}
echo '</ul>';

<?php

add_filter( 'woocommerce_product_query_meta_query', 'show_only_products_with_specific_metakey', 10, 2 );
function show_only_products_with_specific_metakey( $meta_query, $query ) {
    // Only on shop pages
    if( ! is_shop() ) return $meta_query;

    $meta_query[] = array(
        'key'     => '_allowed_user',
        'value'   => get_current_user_id(),
    );
    return $meta_query;
}

function b2b_redirect_if_product_is_not_for_user() {
    if ( is_product() ) {
        $allowed_user = get_post_meta( get_the_ID(), '_allowed_user', true );
        if ( $allowed_user != get_current_user_id() ) {
            wp_redirect( site_url( '/shop' ), 301 );
        }
    }
}

add_action('template_redirect', 'b2b_redirect_if_product_is_not_for_user');