// Defines the framerate of autoscroller
setInterval(autoScroll, 50);

/**
 * Auto scrolls all elements with class autoscroll
 */
function autoScroll () {
    Array.from (document.getElementsByClassName("autoscroll")).forEach((objDiv) => {
        // Skip non-scrollable
        if (objDiv.scrollHeight - objDiv.clientHeight == 0) return;

        // Wait timeout until scroll direction change
        let scrollpause = parseInt(objDiv.dataset.scrollpause);
        if (scrollpause != NaN && scrollpause > 0) {
            scrollpause --;
            objDiv.dataset.scrollpause = scrollpause;

            return;
        }

        // Step either forward or backwards by one
        let direction = 1;
        if (objDiv.dataset.scrolldirection == "up") direction = -1;
        objDiv.scrollTop += direction;

        // If this is the first scroll step after, remove the scrollpause tag
        if (scrollpause != NaN && scrollpause == 0) {
            delete objDiv.dataset.scrollpause;
            return;
        }

        // Reached the bottom, turn around
        if (objDiv.scrollTop == objDiv.scrollHeight - objDiv.clientHeight) {
            objDiv.dataset.scrolldirection = "up";
            objDiv.dataset.scrollpause     = 50;
        }

        // Reached the top, turn around
        if (objDiv.scrollTop == 0) {
            delete objDiv.dataset.scrolldirection;
            objDiv.dataset.scrollpause = 50;
        }
    });
}