A small plugin that enables tags on PDF files to create a simple press review archive using the theme's attachment archive template

press-review-archive.php

<?php
/**
 * Press Review Archive
 *
 * @package     press-review-archive
 * @author      Bernhard Kau
 * @license     GPLv3
 *
 * @wordpress-plugin
 * Plugin Name: Press Review Archive
 * Plugin URI: https://kau-boys.de
 * Description: A small plugin that enables tags on PDF files to create a simple press review archive using the theme's attachment archive template
 * Version: 0.1
 * Author: Bernhard Kau
 * Author URI: https://kau-boys.de
 * License: GPLv3
 * License URI: http://www.gnu.org/licenses/gpl-3.0.txt
 */

/**
 * Enable tags on attachments
 */
function press_review_archive_register_taxonomy_for_object_type() {
	register_taxonomy_for_object_type( 'post_tag', 'attachment' );
}

add_action( 'init', 'press_review_archive_register_taxonomy_for_object_type' );

/**
 * Adds a rewrite rule for the press review archive
 */
function press_review_archive_add_rewrite_rule() {
	add_rewrite_rule(
		'^pressespiegel(?:/(\d{4}))?(?:/(\d{2}))?(?:/(\d{2}))?/?',
		'index.php?tag=pressespiegel&year=$matches[1]&monthnum=$matches[2]&day=$matches[3]',
		'top'
	);
}

add_action( 'init', 'press_review_archive_add_rewrite_rule' );

/**
 * Change the main query to show only PDF files on the press review archive
 *
 * @param WP_Query $query The main query.
 */
function press_review_archive_pre_get_posts( WP_Query $query ) {
	if ( is_press_review_archive() ) {
		$query->set( 'post_type', 'attachment' );
		$query->set( 'post_mime_type', 'application/pdf' );
		$query->set( 'post_status', 'inherit' );
	}
}

add_action( 'pre_get_posts', 'press_review_archive_pre_get_posts' );

/**
 * Set the archive title and remove thr prefix.
 *
 * @param string $title The archive title.
 *
 * @return string
 */
function press_review_archive_get_the_archive_title( $title ) {
	if ( is_press_review_archive() ) {
		$tag   = get_term_by( 'slug', 'pressespiegel', 'post_tag' );
		$title = $tag->name;
	}

	return $title;
}

add_filter( 'get_the_archive_title', 'press_review_archive_get_the_archive_title' );

/**
 * Set the post thumbnail to large size for the press review archive
 *
 * @param string $p The attachment HTML output.
 *
 * @return string
 */
function press_review_archive_prepend_attachment( $p ) {
	if ( is_press_review_archive() ) {
		$p = '<p class="attachment">';
		$p .= wp_get_attachment_link( 0, 'large', false );
		$p .= '</p>';
	}

	return $p;
}

add_filter( 'prepend_attachment', 'press_review_archive_prepend_attachment' );

/**
 * A helper function to test if the currently requested page is a press review archive pae
 *
 * @return bool
 */
function is_press_review_archive() {
	return is_archive() && is_tag( 'pressespiegel' );
}