function hidden(node) {
    return node.style.display === 'none';
}

function visible(node) {
    while (node) {
        if (node === document.body) {
            break;
        }
        if (hidden(node)) {
            return false;
        }
        node = node.parentNode;
    }
    return true;
}

function focusable(node) {
    const nodeName = node.nodeName.toLowerCase();
    const tabIndex = parseInt(node.getAttribute('tabindex'), 10);
    const hasTabIndex = !isNaN(tabIndex) && tabIndex > -1;

    if (visible(node)) {
        if (['input', 'select', 'textarea', 'button'].indexOf(nodeName) > -1) {
            return !node.disabled;
        } else if (nodeName === 'a') {
            return (node.getAttribute('href') || hasTabIndex);
        }
        return hasTabIndex;
    }
}

export function getFocusNodeList(node) {
    const res = [].slice.call(node.querySelectorAll('*'), 0).filter((child) => {
        return focusable(child);
    });
    if (focusable(node)) {
        res.unshift(node);
    }
    return res;
}

let lastFocusElement = null;

export function saveLastFocusNode() {
    lastFocusElement = document.activeElement;
}

export function clearLastFocusNode() {
    lastFocusElement = null;
}

export function backLastFocusNode() {
    if (lastFocusElement) {
        try {
            // 元素可能已经被移动了
            lastFocusElement.focus();

            /* eslint-disable no-empty */
        } catch (e) {
            // empty
        }
        /* eslint-enable no-empty */
    }
}

export function limitTabRange(node, e) {
    if (e.keyCode === 9) {
        const tabNodeList = getFocusNodeList(node);
        const lastTabNode = tabNodeList[e.shiftKey ? 0 : tabNodeList.length - 1];
        const leavingTab = (lastTabNode === document.activeElement || node === document.activeElement);

        if (leavingTab) {
            const target = tabNodeList[e.shiftKey ? tabNodeList.length - 1 : 0];
            target.focus();
            e.preventDefault();
        }
    }
}