Rewrite/redirect URLs

url-rewriter.user.js

// ==UserScript==
// @name        url-rewriter
// @namespace   https://github.com/olmokramer
// @description Rewrite current url or urls on the page
// @match       *://*/*
// @run-at      document-start
// @version     2
// @author      Olmo Kramer
// ==/UserScript==

(function() {
	'use strict';

	function youtube2hooktube(url) {
		url.host = 'hooktube.com';

		if (url.pathname.slice(0, 7) == '/embed/') {
			return url;
		}

		if (url.pathname.slice(0, 6) != '/watch') {
			const vid_id = url.pathname.slice(1);
			const search = url.search;

			url.pathname = '/watch'
			url.search = `?v=${vid_id}`;

			if (search) {
				url.search += `&${search.slice(1)}`;
			}
		}

		return url;
	}

	function wikiwand2wikipedia(url) {
		const [, lang, topic] = url.pathname.split('/');

		if (lang) {
			url.host = `${lang}.wikipedia.org`;
		} else {
			url.host = `en.wikipedia.org`;
		}

		if (topic) {
			url.pathname = `/wiki/${topic}`;

			if (url.hash) {
				url.hash = url.hash.slice(2);
			}
		} else {
			url.pathname = '';
		}

		return url;
	}

	const domains = {
		'www.youtube.com': youtube2hooktube,
		'youtu.be': youtube2hooktube,
		'youtube-nocookie.com': youtube2hooktube,
		'www.wikiwand.com': wikiwand2wikipedia,
	};

	const seen_urls = {};

	function rewriteURL(url, transform) {
		if (!(url in seen_urls)) {
			seen_urls[url] = transform(new URL(url)).href;
		}

		return seen_urls[url];
	}

	function rewriteAttr(attr, domain, transform) {
		const selector = `[${attr}*="${domain}"]`;

		for (let el of document.querySelectorAll(selector)) {
			const old_url = el.getAttribute(attr);
			const new_url = rewriteURL(old_url, transform);
			
			if (old_url != new_url) {
				el.setAttribute(attr, rewriteURL(old_url, transform));
			}
		}
	}

	function rewriteURLs() {
		for (let attr of ['href', 'src']) {
			for (let [domain, transform] of Object.entries(domains)) {
				rewriteAttr(attr, domain, transform);
			}
		}
	}

	if (window.location.host in domains) {
		window.location.href = rewriteURL(window.location.href, domains[window.location.host]);
		return;
	}

	document.addEventListener('DOMContentLoaded', function() {
		new MutationObserver(function OnMutate() {
			rewriteURLs(domains);
		}).observe(document.body, {
			attributes: true,
			childList: true,
			subtree: true,
		});

		rewriteURLs(domains);
	});
})();