Ajax back and forth

Ajax-back-and-forth.php

<?php
class FF_Track {

public function __construct {
    add_action( 'wp_ajax_nopriv_ajax_music', array($this, 'ajax_music') );
    add_action( 'wp_ajax_ajax_music', array($this, 'ajax_music') );

    add_action( 'wp_ajax_nopriv_ajax_next_music', array($this, 'ajax_next_music') );
    add_action( 'wp_ajax_ajax_next_music', array($this, 'ajax_next_music') );
 }

 public function ajax_music(){
        $id = $_POST['id'];
        $type = $_POST['type'];
        $post_type = get_post_type($id);

        // Update post views
        if( 'music' == $post_type || 'product' == $post_type ){
            do_action( 'ff_save_views', $id);
        }
        
        if( FF()->validate_nonce() ){
			if ($type == 'user') {
				$tracks_get =	$this->get_user_music_list($id);
			} elseif ($type == 'fm_genre') {
				$genre_array= wp_get_object_terms( $id, 'track_genre');
				if ( ! empty( $genre_array ) ) {
					if ( ! is_wp_error( $genre_array ) ) {
						$genre = $genre_array[0];
						print_r($genre);
						$genre_id = $genre->term_id;
						$posts_array = get_posts(
							array(
								'posts_per_page' => -1,
								'post_type' => 'track',
								'tax_query' => array(
									array(
										'taxonomy' => 'track_genre',
										'field' => 'term_id',
										'terms' => $genre_id,
									)
								)
							)
						);
						foreach($posts_array as $post ){
							$id = $post->ID ;
						}
					}
				}
				$tracks_get = $this->get_music_list($id);
			} else {
				$tracks_get = $this->get_music_list($id);
			}
            FF()->response(array(
                'status' => 'success',
                'tracks' => $tracks_get,
            ));
        }
    }

	public function ajax_next_music($id) {

		$type = 'fm_genre';
		$post_type = get_post_type($id);

		// Update post views
		if ('music' == $post_type || 'product' == $post_type) {
			do_action('ff_save_views', $id);
		}

		if (FF()->validate_nonce()) {
			if ($type == 'fm_genre') {
				$genre_array = wp_get_object_terms($id, 'track_genre');
				if (!empty($genre_array)) {
					if (!is_wp_error($genre_array)) {
						$genre = $genre_array[0];
						$genre_id = $genre->term_id;
						$posts_array = get_posts(
							array(
								'posts_per_page' => -1,
								'post_type' => 'track',
								'tax_query' => array(
									array(
										'taxonomy' => 'track_genre',
										'field' => 'term_id',
										'terms' => $genre_id,
									)
								)
							)
						);
						foreach ($posts_array as $post) {
							if ($post->ID != $id) {
								$tid = $post->ID;
								print_r($tid);
							}
						}
					}
				}
			}
			FF()->response(array(
				'status' => 'success',
				'id' => $tid,
			));
		}
	}
  
}