WordPress - Redirect 404s that end in a post's name

rowley-redirect.php

<?php
/**
 * Plugin Name:     Rowley Redirect
 * Description:     Redirect old links for posts to the current link
 * Author:          Ryan Hoover
 * Author URI:      https://github.com/ryanshoover
 * Version:         0.1
 */

/**
 * Redirect 404s that end in the post name
 *
 * If a request comes in that is a 404, but the last
 * subdirectory is a post's slug, then redirect to
 * that post's actual link
 */
function rowley_redirect_category_post_links() {
	// If this isn't a 404 error page, abort
	if ( 404 != get_query_var( 'error' ) ) {
		return;
	}
	// Get the request path's parts
	$request_parts = explode( '/', $_SERVER['REQUEST_URI'] );
	$request_parts = array_filter( $request_parts );
	// If we don't have any parts, abort
	if ( empty( $request_parts ) ) {
		return;
	}
	// Find the post that has the matching slug
	$post_slug = array_pop( $request_parts );
	$post = get_page_by_path( $post_slug, null, 'post' );
	// If we didn't find a post, abort
	if ( empty( $post ) ) {
		return;
	}
	// Redirect to the post's actual link
	wp_safe_redirect( get_permalink( $post->ID ) );
	exit;
}

add_action( 'wp', 'rowley_redirect_category_post_links' );