const sleep = function(n = 0) {
    return new Promise((resolve, reject) => {
        setTimeout(() => resolve({ resolvedAfterNSeconds: n }), n * 1000);
    });
};

async function unCollapseVids(){
    const arrows = document.querySelectorAll('span.udi-angle-down');
    arrows.forEach(arrow => arrow.click());
    await sleep(5);
};

function goThrowVideos(){
    const timeStep = 3000;
    const vids = document.querySelectorAll('div[data-purpose="curriculum-section-container"] ul li.curriculum-item-link--curriculum-item--KX9MD > div');

    let index = 0;
    let goToNextVid = true;
    let lastUrl = '';

    const intrvl = setInterval(() => {
        if(index >= vids.length) clearInterval(intrvl);

        if(goToNextVid){
            const vid = vids[index];
            vid.click();

            goToNextVid = false;
            index++;
        } else {
            const video = document.querySelector('video');
            const url = video && video.src;

            if (url && url !== lastUrl) {
                download(url);
                setTimeout(() => { goToNextVid = true }, timeStep*2);
                lastUrl = url;
            }
        }
    }, timeStep);
}


function download (url) {
    let a = document.createElement('a');
    a.href = url;
    a.textContent = 'download';
    a.target = '_blank';
    a.download = '';
    a.style.display = 'none';

    document.body.appendChild(a);
    a.click();
}

unCollapseVids().then(() => goThrowVideos())