<?php
/**
 * Plugin Name:       4zero4
 * Plugin URI:        https://wordpress.org/plugins/4zero4/
 * Description:       Turns "page not found" (404) errors into a helpful search: when a visitor hits a missing URL, they are redirected to the site search for terms derived from the requested address.
 * Version:           1.2
 * Requires at least: 6.5
 * Requires PHP:      7.4
 * Author:            DevFabio
 * Author URI:        https://profiles.wordpress.org/devfabio/
 * License:           GPL-2.0-or-later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 * Text Domain:       4zero4
 *
 * @package FourZeroFour
 */

// Exit if accessed directly.
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

define( 'P4ZERO4_VERSION', '1.2' );

/**
 * On a 404, redirect the visitor to the site search for terms derived from the
 * requested (missing) URL.
 *
 * Example: a request for "/my-old-product-name/" that no longer resolves becomes
 * a search for "my old product name", so the visitor lands on relevant content
 * instead of a dead end.
 *
 * The redirect is a temporary 302 (not a permanent 301): the original URL may
 * become valid again, so it must not be cached as permanently moved.
 *
 * @return void
 */
function p4zero4_redirect() {
	// Only act on front-end 404 page views, never in admin, feeds or REST.
	if ( ! is_404() || is_admin() || is_feed() || ( defined( 'REST_REQUEST' ) && REST_REQUEST ) ) {
		return;
	}

	// Only follow normal navigation (GET/HEAD); ignore POST and other methods.
	$method = isset( $_SERVER['REQUEST_METHOD'] ) ? strtoupper( sanitize_text_field( wp_unslash( $_SERVER['REQUEST_METHOD'] ) ) ) : 'GET';
	if ( 'GET' !== $method && 'HEAD' !== $method ) {
		return;
	}

	// Read the requested URI safely (unslash + sanitize the superglobal).
	$request_uri = isset( $_SERVER['REQUEST_URI'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '';
	if ( '' === $request_uri ) {
		return;
	}

	// Keep only the path component (drop any query string or fragment).
	$path = (string) wp_parse_url( $request_uri, PHP_URL_PATH );
	if ( '' === $path ) {
		return;
	}

	// Use the last non-empty path segment as the basis for the search terms.
	$segments = array_values( array_filter( explode( '/', trim( $path, '/' ) ) ) );
	$slug     = $segments ? (string) end( $segments ) : '';
	if ( '' === $slug ) {
		return;
	}

	// Drop common file extensions (e.g. "page.html" -> "page").
	$slug = (string) preg_replace( '/\.(html?|php|aspx?|jsp)$/i', '', $slug );

	// Turn a slug like "my-missing-page" into the phrase "my missing page".
	$terms = trim( str_replace( array( '-', '_', '+', '.' ), ' ', urldecode( $slug ) ) );

	/**
	 * Filters the search terms derived from the missing URL.
	 *
	 * Return an empty string to skip the redirect for this request.
	 *
	 * @since 1.2
	 *
	 * @param string $terms The terms extracted from the requested URL.
	 * @param string $path  The requested URL path.
	 */
	$terms = apply_filters( 'p4zero4_search_terms', $terms, $path );
	if ( ! is_string( $terms ) || '' === trim( $terms ) ) {
		return;
	}

	$redirect_url = get_search_link( $terms );

	/**
	 * Filters the destination URL the visitor is redirected to.
	 *
	 * Return an empty value to cancel the redirect for this request.
	 *
	 * @since 1.2
	 *
	 * @param string $redirect_url The search results URL.
	 * @param string $terms        The search terms.
	 * @param string $path         The requested URL path.
	 */
	$redirect_url = apply_filters( 'p4zero4_redirect_url', $redirect_url, $terms, $path );
	if ( empty( $redirect_url ) ) {
		return;
	}

	/**
	 * Filters the HTTP status code used for the redirect.
	 *
	 * Defaults to 302 (temporary). Use 301 only if you are sure the mapping is
	 * permanent, as browsers cache 301 responses aggressively.
	 *
	 * @since 1.2
	 *
	 * @param int $status The HTTP status code.
	 */
	$status = (int) apply_filters( 'p4zero4_redirect_status', 302 );

	wp_safe_redirect( $redirect_url, $status );
	exit;
}
add_action( 'template_redirect', 'p4zero4_redirect' );