const h = (name, props = {}, ...children) => {
    const element = document.createElement(name);

    for (const [key, value] of Object.entries(props))
        key.startsWith('on')
            ? element.addEventListener(key.substring(2), value)
            : element.setAttribute(key, value);

    for (const child of children)
        element.appendChild(
            typeof(child) === 'string'
                ? document.createTextNode(child)
                : child);

    return element;
};

const qs = s => document.querySelector(s);
const qsa = s => Array.from(document.querySelectorAll(s))

const on_command = command => {
    switch(command.type) {
    case 'alert': alert(command.message); break;
    case 'load_pdf': pdfjsLib.getDocument(command.url).promise.then(pdf => PDFViewerApplication.load(pdf)); break;
    }
};

let call_python;

new QWebChannel(qt.webChannelTransport, channel => {
    call_python = (argument, callback) =>
        channel.objects.bridge.call_python(JSON.stringify(argument),
            result => callback && callback(JSON.parse(result)));

    channel.objects.bridge.call_javascript.connect(
        result => on_command(JSON.parse(result)));

    call_python({'type': 'ready'});
});