Export bulk selected orders to CSV spreadsheet file

add_filter( 'bulk_actions-edit-shop_order', function( $actions ) {

	$actions['csv_download'] = 'Download spreadsheet file';

	return $actions;

}, 20 );

add_filter( 'handle_bulk_actions-edit-shop_order',
	function( $redirect_to, $action, $post_ids ) {

	if( $action !== 'csv_download' ) {
		return $redirect_to;
	}

	$args = [
		'csv_download' => 1,
		'post_ids' => implode( ',', $post_ids ),
	];

	return add_query_arg( $args, $redirect_to );

}, 10, 3 );

add_action( 'admin_init', function() {

	if( empty( $_REQUEST['csv_download'] ) ) {
		return;
	}
	$header = [
		'Date', 'OrderId', 'Customer', 'SKU', 'Product', 'Quantity', 'Price'
	];
	$data = [ $header ];
	$post_ids = explode( ',', $_REQUEST['post_ids'] );

	foreach( $post_ids as $order_id ) {

		$order = wc_get_order( $order_id );
		$order_data = $order->get_data();
		$order_items = $order->get_items();

		foreach( $order->get_items() as $order_item ) {

			$product_sku = '';
			$product_id = $order_item->get_product_id();

			if( $product_id ) {
				$product = wc_get_product( $product_id );
				$product_sku = $product->get_sku();
			}

			$data[] = [
				$order->get_date_created()->format( 'm/d/Y' ),
				$order_id,
				sprintf(
					'%s %s',
					$order_data['shipping']['first_name'],
					$order_data['shipping']['last_name']
				),
				$product_sku,
				$order_item['name'],
				$order_item['qty'],
				$order_item['line_total'],
			];
		}
	}

	// Output
	header( 'Content-Type: text/csv; charset=utf-8' );
	header( 'Content-Disposition: attachment; filename=orders.csv' );
	$out = fopen( 'php://output', 'w' );
	foreach( $data as $row ) {
		fputcsv( $out, $row );
	}
	fclose( $out );
	exit;

} );