WooCommerce Booking, get the unavailable rentals by date

wc_booking_unavailable_rentals_by_date.php

<?php

$dateTimeStart = new DateTime($timestamp_start);
$dateTimeEnd   = new DateTime($timestamp_end);
$unavailable_ids = wc_booking_unavailable_rentals_by_date($dateTimeStart, $dateTimeEnd);

// get all unavailable rentals by date
function wc_booking_unavailable_rentals_by_date($dateStart, $dateEnd) {
	$filtered_rentals = array();
	$unavailable_ids = array();

	$start = array(
		'y' => $dateStart->format('Y'),
		'm' => intval($dateStart->format('m')),
		'd' => intval($dateStart->format('d')),
		'ymd' => $dateStart->format('Ymd')
	);

	$end = array(
		'y' => $dateEnd->format('Y'),
		'm' => intval($dateEnd->format('m')),
		'd' => intval($dateEnd->format('d')),
		'ymd' => $dateEnd->format('Ymd')
	);

	// WP Query
	$the_query = new WP_Query(array(
		'post_type' => 'product',
    		'posts_per_page' => -1, // -1 mean show all data
    		'post_status' => 'publish', 
	));

	// loop
	while ($the_query->have_posts()) : $the_query->the_post();
		$id = get_the_ID();
		$title = get_the_title();

		$product_obj = new WC_Product_Booking($id);
		$avability = $product_obj->get_availability_rules();		

		foreach ($avability as $root) {
			if(! isset($root[1]) || ! is_array($root[1])) continue;

			foreach ($root[1] as $year => $value) {
				if($year >= $start['y'] && $year <= $end['y']) {
					if(! is_array($value)) continue;

					foreach ($value as $month => $value2) {
						if(! is_array($value2)) continue;

						foreach ($value2 as $day => $is_available) {
							if($is_available) continue;

							$date_val = new DateTime("$year-$month-$day");

							if(! isset($filtered_rentals[$id]['name'])) {
								$filtered_rentals[$id]['name'] = $title;
							}

							$filtered_rentals[$id]['date'][] = $date_val->format('Ymd');
						}
					}
				}
			}
		}

	endwhile;
	wp_reset_query();

	// filter the filtered_rentals by date range
	foreach ($filtered_rentals as $key => $value) {
		if(! is_array($value)) continue;

		foreach ($value as $key2 => $value2) {
			if($key2 != 'date') continue; 

			foreach ($value2 as $key3 => $dateint) {				
				if($dateint >= $start['ymd'] && $dateint <= $end['ymd']) {
					$unavailable_ids[] = $key;
					break;
				}
			}
		}
	}

	return $unavailable_ids;
}