Untitled

<?php

/**
 * Plugin Name: Book and Chapter Plugin
 * Description: A nice project using books and chapters
 */

class BookAndChapter
{

    public function __construct()
    {
        add_action('init', array($this, 'init'));
    }

    public function init()
    {
        add_filter('the_content', array($this, 'show_book_in_chapter_thumbnail'));
        add_filter('the_content', array($this, 'show_book_in_chapter'));
        add_filter('post_type_link', array($this, 'chapter_cpt_slug_fix'), 1, 2);
        add_filter('the_content', array($this, 'show_relate_book_by_meta'));
        add_filter('the_content', array($this, 'show_relate_book_by_taxonomy'));
    }



    public function chapter_cpt_slug_fix($post_link, $chapter)
    {
        if (get_post_type($chapter) == 'chapter') {
            $book_id = get_post_meta($chapter->ID, 'book_id', true);
            $book = get_post($book_id);
            $post_link = str_replace('%book%', $book->post_name, $post_link);
        }
        return $post_link;
    }

    public function show_book_in_chapter_thumbnail($the_content)
    {
        if (is_singular('chapter')) {
            $book_id = get_post_meta(get_the_ID(), 'book_id', true);
            $image = get_the_post_thumbnail($book_id, 'medium');
            $the_content = " <p> $image </p> " . $the_content;
        }
        return $the_content;
    }

    public function show_relate_book_by_meta($content)
    {
        if (is_singular('book')) {
            $book_id = get_the_ID();
            $genre = get_post_meta($book_id, 'genre', true);
            $args = [
                'post_type' => 'book',
                'post__not_in' => [$book_id],
                'meta_key' => 'genre',
                'meta_value' => $genre
            ];
            $books = get_posts($args);

            if ($books) {
                $content .= '<h2>Related Books By Meta Field</h2>';
                $content .= '<ul>';
                foreach ($books as $book) {
                    $content .= '<li><a href="' . get_permalink($book->ID) . '">' . $book->post_title . '</a></li>';
                }
                $content .= '</ul>';
            }
        }
        return $content;
    }

    public function show_book_in_chapter($content)
    {
        if (is_singular('book')) {
            $content .= '<h2>Book Content</h2>';
            $get_chapter = get_posts(array(
                'post_type' => 'chapter',
                'meta_query' => array(
                    array(
                        'key' => 'book_id',
                        'value' => get_the_ID(),
                        'compare' => '='
                    )
                ),
                'meta_key' => 'chapter_number',
                'orderby' => 'meta_value_num',
                'order' => 'ASC'
            ));
            if ($get_chapter) {
                $content .= '<ul>';
                foreach ($get_chapter as $chapter) {
                    $content .= '<li><a href="' . get_permalink($chapter->ID) . '">' . $chapter->post_title . '</a></li>';
                }
                $content .= '</ul>';
            } else {
                $content .= '<b>No Chapter Found</b>';
            }
        }
        return $content;
    }

    public function show_relate_book_by_taxonomy($content)
    {
        if (is_singular('book')) {
            $book_id = get_the_ID();
            $genres = wp_get_post_terms($book_id, 'book_genre');
            if (!empty($genres)) {
                $genre = $genres[0]->term_id;
                $args = [
                    'post_type' => 'book',
                    'post__not_in' => [$book_id],
                    'tax_query' => [
                        [
                            'taxonomy' => 'book_genre',
                            'field' => 'term_id',
                            'terms' => $genre
                        ]
                    ]
                ];
                $books = get_posts($args);

                if ($books) {
                    $content .= '<h2>Related Books By Taxonomy</h2>';
                    $content .= '<ul>';
                    foreach ($books as $book) {
                        $content .= '<li><a href="' . get_permalink($book->ID) . '">' . $book->post_title . '</a></li>';
                    }
                    $content .= '</ul>';
                }
            }
        }
        return $content;
    }
}

new BookAndChapter();