GetPaid Wordpress plugin: Code snippet to list users who've purchased an item (or any of its children)

getpaid-item-purchases.php

<?php
add_action( 'add_meta_boxes', 'add_getpaid_item_invoices_meta_box', 50 );

function add_getpaid_item_invoices_meta_box() {
	add_meta_box( 'wpinv_item_invoices', __( 'Item Purchases', 'invoicing' ), 'show_getpaid_item_purchases', 'wpi_item', 'normal' );
}

function show_getpaid_item_purchases( $post ) {
	// get this post and all children
    $posts = get_children( array(
		'post_parent'    => $post->ID,
		'post_type'      => 'wpi_item'
	) );
    $posts[] = $post;


    $post_ids = array_map( function( $post ) {
        return $post->ID;
    }, $posts );

	print_invoice_details_table_start();
	
	// search through all invoices and find those that contain this item
	$max_pages = -1;
	for ($page = 1; $max_pages < 0 || $page <= $max_pages; $page++) {
		$invoices = wpinv_get_invoices( array(
			'limit' => false,
			'paginate' => true,
			'page' => $page,
		) );
	
		$max_pages = $invoices->max_num_pages;
		foreach ( $invoices->invoices as $inv ) {
			foreach ( $inv->get_items() as $n => $inv_item ) {
				if ( in_array( $inv_item->get_id(), $post_ids ) ) {
					print_invoice_details_table_row( $inv, $n, $inv_item );
				}
			}
		}
	}
	
	print_invoice_details_table_end();
}

function print_invoice_details_table_row( $inv, $n, $item ) {
	$user_id = $inv->get_user_id();
	$user_info = get_userdata( $user_id );
	$user_url = esc_url( add_query_arg( 'user_id', $user_id, admin_url( 'user-edit.php' ) ) );
	
	?>
			<tr class="item item-<?php echo ( $n % 2 == 0 ? 'even' : 'odd' ); ?>">
                <td class="title">
                    <a href="<?php echo $user_url; ?>" target="_blank"><?php echo $user_info->display_name; ?></a>
                </td>
				<td class="title">
                    <a href="<?php echo get_edit_post_link( $item->get_id() ); ?>" target="_blank"><?php echo esc_html( $item->get_name() ); ?></a>
                </td>
                <td class="qty">
					<?php
						echo $item->get_quantity();
					?>
                </td>
				<td class="title">
                    <a href="<?php echo get_permalink( $inv->get_id() ); ?>" target="_blank"><?php echo esc_html( $inv->get_number() ); ?></a>
                </td>
                <!-- <td class="total">
					<?php
						echo wpinv_the_price( $inv->get_total(), $inv->get_currency() );
					?>
                </td> -->
            </tr>
	<?php
	
}

function print_invoice_details_table_start() {
?>
<div class="wpinv-items-wrap" id="wpinv_items_wrap">
    <table id=" wpinv_items" class="wpinv-items" cellspacing="0" cellpadding="0">
        <thead>
            <tr>
                <th class="title">Customer</th>
                <th class="title">Ticket</th>
                <th class="qty">Quantity</th>
                <th class="title">Invoice</th>
                <!-- <th class="total">Invoice Price</th> -->
            </tr>
        </thead>

        <tbody class="wpinv-line-items">
<?php
}

function print_invoice_details_table_end() {
?>
			</tbody>
    </table>
</div>
<?php
}
?>