IS MU Fix disabled assignment button

is-fix-assignment.user.js

// ==UserScript==
// @name         IS course assignment
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Fix disabled button for course assignment
// @author       Jan Pokorný
// @match        https://is.muni.cz/auth/student/*
// @grant        GM_setValue
// @grant        GM_getValue
// @grant        GM_xmlhttpRequest
// @connect      muni.cz
// ==/UserScript==

(function() {
    'use strict';

    function GM_fetch(url) {
        return new Promise((resolve, reject) => GM_xmlhttpRequest({
            url: url,
            method: "GET",
            onload: resolve,
            onerror: reject
        }));
    }

    const urlFinders = [
        async function cached(courseURL) {
            return GM_getValue("courseUrl:" + courseURL, null);
        },
        async function courseDescription(courseURL) {
            const {responseText} = await GM_fetch(courseURL.replace("/el/", "/predmet/") + "?lang=en");
            const descRegex = /<DT><B>Teacher's information<\/B><\/DT>\s*<DD>(.*?)<\/DD>/;
            const urlRegex = /https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/;

            try {
                return responseText.match(descRegex)[1].match(urlRegex)[0];
            } catch {
                return null;
            }
        },
        async function materials(courseURL) {
            return courseURL + "um/";
        }
    ];

    async function fixButton(button, courseURL) {
        for(const urlFinder of urlFinders) {
            const url = await urlFinder(courseURL);
            if(url !== null) {
                button.classList.remove("disabled");
                button.href = url;
                button.childNodes[2].nodeValue = "Materiály";
                GM_setValue("courseUrl:" + courseURL, url);
                break;
            }
        }
    }

    function domChange(mutationsList) {
        for(const mutation of mutationsList) {
            const button = mutation.target.querySelector(".student_row_c > .column:first-child > .disabled.button.large");
            const courseURL = mutation.target.querySelector('.student_row_b a[href^="/auth/el"]').href;
            if(button != null) fixButton(button, courseURL);
        }
    }

    const observer = new MutationObserver(domChange);

    const courseBlocks = document.querySelectorAll(".predmet_conteiner"); // yep, "conteiner"
    for(const courseBlock of courseBlocks) {
        observer.observe(courseBlock.children[1], { childList: true });
    }

})();