// This is the carousel implemented in idiomatic javascript

// Converts NodeLists to Arrays
function toArray(x) {
    return Array.prototype.slice.call(x);
};

// Returns array of elements that match css query nested to parent
function queryChildren(parent, query) {
    return toArray(Element.prototype.querySelectorAll.call(parent, query));
};

// Returns array of elements that match css query
function queryAll(query) {
    return toArray(document.querySelectorAll(query));
};

// Sets the hidden property of elements based on new index
function to(index, children) {
    children.forEach((function(x, i) {
        x.hidden = i !== index;
    }));
};

// Gets the current index of carousel
function index(children) {
    return (Array.prototype.findIndex.call(children, (function(x) {
        return !(x.hidden);
    })) || 0);
};

// Moves to next slide in carousel with wrapping
function rotate(children) {
    return to(((1 + index(children)) % children.length), children);
};

// Rotate carousels once every three seconds
queryAll("[data-carousel]").forEach((function(x) {
    return window.setInterval(rotate.bind(window, queryChildren(x, "[data-carousel-slide]")), 3000);
}));