(() => {
    const positionEl = document.querySelector('.cwl-guide-prev-next .right');
    const btn        = document.getElementsByName('next-step')[0];

    const INTERVAL       = 80;   // 75 wont work
    const SLEEP_DURATION = 2000; // might be increased; ~1.8s is my avg load

    let currentStep = 1;
    let currentPage = 1;

    const targetPage = prompt('please enter target page', 2);

    if(targetPage <= 1) {
        alert('that\'s a no from me dawg');
        return;
    }

    const updateETA = (step, limit) => {
        const newETA = Math.round(((targetPage - currentPage) * SLEEP_DURATION + (limit - step) * INTERVAL - SLEEP_DURATION) / 1000);

        etaBtn.innerText = `ETA: ~${newETA}s`;
    };

    const doSteps = async () => {
        if(currentPage < targetPage) {
            const [step, limit] = positionEl.innerText.split(' / ');
            updateETA(step, limit);

            // reset step on next page
            if(step === 1) {
                currentStep = 1;
            }

            // step limit reached, next page up
            if(step === limit) {
                currentPage += 1;

                pageBtn.innerText = 'loading...';

                // click to force-load in case its something that needs loading
                btn.click();

                // remove interval to prevent queueing
                clearInterval(interval);

                // sleep SLEEP_DURATION seconds to await potential data load
                await new Promise(resolve => setTimeout(resolve, SLEEP_DURATION));

                pageBtn.innerText = `Page ${currentPage}`;

                // restart paused interval
                interval = setInterval(doSteps, INTERVAL);
                return;
            }


            btn.click();
            return;
        }

        clearInterval(interval);
        etaBtn.remove();
    }

    let interval = setInterval(doSteps, INTERVAL);

    // some UI info
    const pageBtn = document.createElement('button');
    const etaBtn  = document.createElement('button');

    pageBtn.innerText = 'Page 1';
    etaBtn.innerText  = 'ETA: ?s';

    [pageBtn, etaBtn].forEach(injectedBtn => {
        injectedBtn.type = 'button';
        injectedBtn.style.marginRight = '1rem';
        injectedBtn.disabled = true;
        ['injected-btn', 'btn-small'].forEach(className => injectedBtn.classList.add(className));
        btn.insertAdjacentElement('afterend', injectedBtn);
    });
})();