const NS = {
    xrd: 'http://docs.oasis-open.org/ns/xri/xrd-1.0',
    roster: 'jabber:iq:roster',
    disco_items: 'http://jabber.org/protocol/disco#items',
    disco_info: 'http://jabber.org/protocol/disco#info',
    dataforms: 'jabber:x:data',
    pubsub: 'http://jabber.org/protocol/pubsub',
    pubsub_owner: 'http://jabber.org/protocol/pubsub#owner',
    avatar_metadata: 'urn:xmpp:avatar:metadata',
    avatar_data: 'urn:xmpp:avatar:data',
    nickname: 'http://jabber.org/protocol/nick',
};

function nsResolver(prefix) {
    return NS[prefix] || null;
}

function parseXPath(elem, xpath, result)
{
    if (result === undefined)
        result = XPathResult.FIRST_ORDERED_NODE_TYPE;
    const value = elem.getRootNode().evaluate(xpath, elem, nsResolver, result, null);
    if (result == XPathResult.FIRST_ORDERED_NODE_TYPE)
        return value.singleNodeValue;
    return value;
}

function configurePEPField(node, key, value, cb, err_cb) {
    return $iq({type: 'set'})
        .c('pubsub', {xmlns: 'http://jabber.org/protocol/pubsub#owner'})
            .c('configure', {node: node})
                .c('x', {xmlns: 'jabber:x:data', type: 'submit'})
                    .c('field', {'var': 'FORM_TYPE', type: 'hidden'})
                        .c('value')
                            .t('http://jabber.org/protocol/pubsub#node_config')
                            .up()
                        .up()
                    .c('field', {'var': key})
                        .c('value')
                            .t(value)
                            .up()
                        .up();
}