Auto-hide pooltest at the beginning of the semester

    <main>

        <h1>Was möchtest du tun?</h1>

        <a href="./test.html?id=practice" class="btn big">Linux üben</a>

        <a href="./test.html?id=pooltest" class="btn primary big">Den Pooltest ablegen</a>

        <a href="./test.html?id=pooltest" class="btn primary big" id="pooltest-start-btn">Den Pooltest ablegen</a>

    </main>

    <a href="https://gitlab.cl.uni-heidelberg.de/technik/teaching/yalikejazz" class="ribbon" target="_blank">Quelltext</a>

    <script type="module" src="./js/index.mjs"></script>

const now = Date.now()

/**

 * @param {Date} now Now

 * @returns The first of the current month, as date object

 */

function getFirstOfMonth(now) {

    return new Date(now.getFullYear(), now.getMonth(), 1)

}

document.querySelectorAll("[data-hidden-until]").forEach(element => {

    const hiddenUntil = Date.parse(element.dataset.hiddenUntil)

function addDays(date, daysToAdd) {

    return new Date(date.getFullYear(), date.getMonth(), date.getDate() + daysToAdd)

}

    element.style.display = now < hiddenUntil ? "none" : "inherit"

})

const now = new Date()

// Yes, the date uses zero-based indexing for months...

const APRIL = 3

const OCTOBER = 9

const SATURDAY = 6 // Saturday is the 6th day of the week, with Sunday being the 0th

if(now.getMonth() === APRIL || now.getMonth() === OCTOBER) {

    // We have a new semester now, so we want to hide the pool test until the Saturday before the lectures start.

    // Lectures start more or less in the middle of the month, so the following logic works out what date this saturday is.

    const first = getFirstOfMonth(now)

    const firstWeekday = first.getDay()

    const unlockDate = firstWeekday === SATURDAY ? addDays(first, 14) : addDays(first, 13 - firstWeekday)

    if(now.getDate() < unlockDate.getDate()) {

        document.querySelector("#pooltest-start-btn").style.display = "none"

    }

}