Wordpress - Get Related Posts IDS

// PRIORITY: TAGS BEFORE CATEGORIES

function appeal_get_related_posts() {
	$post_array = array();
	global $post;
	$tags = wp_get_post_tags( $post->ID );
	if ( $tags ) {
		$first_tag = $tags[0]->term_id;
		$args = array(
			'tag__in' => array( $first_tag ),
			'post__not_in' => array( $post->ID ),
			'posts_per_page' => 5,
			'ignore_sticky_posts' => 1,
		);
		$my_query = new WP_Query( $args );
		if ( $my_query->have_posts() ) {
			while ( $my_query->have_posts() ) {
				$my_query->the_post();
				$post_array[] = get_the_ID();
			}
		}
	} elseif ( empty( $post_array ) ) {
		$cats = get_the_category( $post->ID );
		if ( $cats ) {
			$first_cat = $cats[0]->cat_ID;
			$args = array(
				'cat' => $first_cat,
				'post__not_in' => array( $post->ID ),
				'posts_per_page' => 5,
				'ignore_sticky_posts' => 1,
			);
			$my_query = new WP_Query( $args );
			if ( $my_query->have_posts() ) {
				while ( $my_query->have_posts() ) {
					$my_query->the_post();
					$post_array[] = get_the_ID();
				}
			}
		}
	}

	if ( ! empty( $post_array ) ) {
		wp_reset_query();
	}

	return $post_array;
}