High-performance Reddit to RedLib frontend redirector

redirector.js

// ==UserScript==
// @name         Reddit to RedLib Redirector
// @namespace    https://github.com/slashedzer0
// @version      1.1.0
// @description  High-performance Reddit to RedLib frontend redirector
// @author       slashedzer0
// @match        *://*.reddit.com/*
// @match        *://reddit.com/*
// @match        *://*/*
// @grant        none
// @run-at       document-start
// @noframes     true
// ==/UserScript==

(function() {
    'use strict';

    const REDLIB_BASE = 'https://redlib.perennialte.ch';
    const REDDIT_PATTERN = /^(?:(?:https?:)?\/\/)?(?:(?:www|old|new)\.)?reddit\.com(\/[^?#]*)?(\?[^#]*)?(#.*)?$/i;
    const redditHostRegex = /\breddit\.com$/i;
    const processedLinks = new Set();

    const convertToRedLib = (() => {
        const a = document.createElement('a');
        return (url) => {
            if (!url || url.includes(REDLIB_BASE)) return url;
            try {
                a.href = url;
                if (!REDDIT_PATTERN.test(url)) return url;
                return REDLIB_BASE + (a.pathname || '/') + a.search + a.hash;
            } catch {
                return url;
            }
        };
    })();

    const debounce = (fn, delay) => {
        let timeoutId;
        return (...args) => {
            clearTimeout(timeoutId);
            timeoutId = setTimeout(() => fn.apply(null, args), delay);
        };
    };

    const processLink = (link) => {
        if (!link || !link.href || processedLinks.has(link)) return;
        if (link.href.indexOf('reddit.com') !== -1) {
            const newHref = convertToRedLib(link.href);
            if (newHref !== link.href) {
                link.href = newHref;
                processedLinks.add(link);
            }
        }
    };

    const processLinks = debounce((links) => {
        const len = links.length;
        for (let i = 0; i < len; i++) {
            processLink(links[i]);
        }
    }, 50);

    const observerCallback = (mutations) => {
        const links = [];
        mutations.forEach(mutation => {
            if (mutation.type === 'childList') {
                const addedNodes = mutation.addedNodes;
                const addedNodesLen = addedNodes.length;
                for (let i = 0; i < addedNodesLen; i++) {
                    const node = addedNodes[i];
                    if (node.nodeType === 1) {
                        if (node.tagName === 'A') {
                            links.push(node);
                        } else if (node.getElementsByTagName) {
                            const nodeLinks = node.getElementsByTagName('a');
                            if (nodeLinks.length) {
                                links.push(...nodeLinks);
                            }
                        }
                    }
                }
            }
        });
        if (links.length) {
            processLinks(links);
        }
    };

    if (redditHostRegex.test(window.location.hostname)) {
        const redirectUrl = convertToRedLib(window.location.href);
        if (redirectUrl !== window.location.href) {
            window.stop();
            window.location.replace(redirectUrl);
        }
    }

    document.addEventListener('click', (e) => {
        const link = e.target.closest('a');
        if (!link || !link.href) return;
        if (link.href.indexOf('reddit.com') !== -1) {
            const newHref = convertToRedLib(link.href);
            if (newHref !== link.href) {
                e.preventDefault();
                window.location.href = newHref;
            }
        }
    }, { capture: true, passive: false });

    const observer = new MutationObserver(observerCallback);
    observer.observe(document.documentElement, {
        childList: true,
        subtree: true,
        attributes: false,
        characterData: false
    });

    processLinks(document.getElementsByTagName('a'));
})();