// ==UserScript==
// @name         Decode Buttondown emails to remove tracking
// @namespace    http://tampermonkey.net/
// @version      2025-09-20
// @description  Replace the URL of links in Buttondown emails with the actual link target, bypassing Buttondown’s redirector (which probably does some tracking stuff)
// @author       Lucas Werkmeister
// @match        https://buttondown.com/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=buttondown.com
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    const UUID = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/;

    for (const link of document.querySelectorAll('a[href^="https://buttondown-"]')) {
        const originalUrl = link.href;
        const match = originalUrl.match(/^https:\/\/buttondown-[0-9][0-9][0-9][0-9].com\/c\/([A-Za-z0-9+/]+)/);
        if (!match) {
            console.info('Not updating', link, 'because it does not look like a tracking link');
            continue;
        }
        const payload = atob(match[1]); // decode base64
        const parts = payload.split('|');
        if (parts.length !== 4) {
            console.warn('Not updating', link, 'because the payload has the wrong length (expected four pipe-separated parts):', payload);
            continue;
        }
        const [uuid1, uuid2, url, web] = parts;
        if (!UUID.test(uuid1) || !UUID.test(uuid2) || web !== 'web') {
            console.warn('Not updating', link, 'because the payload looks unexpected:', payload);
            continue;
        }
        link.href = url;
    }
})();