<?php

/*
Plugin Name: Post Permalinks Redirect Fallback
Plugin URI: http://maciejbis.net
Description: A plugin that adjusts the functionality of this website
Version: 1.0
Author: Maciej Bis
Author URI: http://www.maciejbis.net
License: GPL2
*/

function bis_redirect_posts_from_404() {
    global $wp, $wpdb, $wp_query, $pm_query;

    if(is_404() && !empty($wp->request) && is_user_logged_in()) {

        // 1. Extract date parts
        preg_match('/(2[\d]+)\/([\d]{2})\//', $wp->request, $date_parts);

        if(empty($date_parts)) {
            return;
        }

        // 2. Extract the first & last two words
        $slug = basename($wp->request);
        $slug = esc_sql($slug);

        preg_match('/^([^-]+-[^-]+)(?:.*-([^-]+-[^-]+)$)?/', $slug, $words);

        if(!empty($words[2])) {
            $where_statement = sprintf('(post_name = "%s" OR post_name LIKE "%%%s%%" OR post_name LIKE "%%%s%%")', $slug, $words[1], $words[2]);
        } else if(!empty($words[2])) {
            $where_statement = sprintf('(post_name = "%s" OR post_name LIKE "%%%s%%")', $slug, $words[1]);
        } else {
            return;
        }

        // 3. Add the extracted date to the query
        $year = (int) $date_parts[1];
        $month = (int) $date_parts[2];
        $where_statement .= sprintf('AND (YEAR(post_date) = %d AND MONTH(post_date) = %d)', $year, $month);

        // 4. Limit the search results to posts with 'publish' status
        $where_statement .= "AND post_status = 'publish' AND post_type = 'post'";

        $post_id = $wpdb->get_var("
            SELECT ID FROM {$wpdb->posts}
            WHERE {$where_statement}
        ");

        if(!empty($post_id)) {
            $url = get_permalink($post_id);

            if(!empty($url)) {
                wp_safe_redirect($url, 301);
                exit();
            }
        }
    }
}
add_action('template_redirect', 'bis_redirect_posts_from_404', 1);