var candidateSelectors = [
  'input',
  'select',
  'textarea',
  'a[href]',
  'button',
  '[tabindex]',
  'audio[controls]',
  'video[controls]',
  '[contenteditable]:not([contenteditable="false"])',
];
var candidateSelector = candidateSelectors.join(',');

var matches = typeof Element === 'undefined'
  ? function () {}
  : Element.prototype.matches || Element.prototype.msMatchesSelector || Element.prototype.webkitMatchesSelector;

function tabbable(el, options) {
  options = options || {};

  var regularTabbables = [];
  var orderedTabbables = [];

  var candidates = el.querySelectorAll(candidateSelector);

  if (options.includeContainer) {
    if (matches.call(el, candidateSelector)) {
      candidates = Array.prototype.slice.apply(candidates);
      candidates.unshift(el);
    }
  }

  var i, candidate, candidateTabindex;
  for (i = 0; i < candidates.length; i++) {
    candidate = candidates[i];

    if (!isNodeMatchingSelectorTabbable(candidate)) continue;

    candidateTabindex = getTabindex(candidate);
    if (candidateTabindex === 0) {
      regularTabbables.push(candidate);
    } else {
      orderedTabbables.push({
        documentOrder: i,
        tabIndex: candidateTabindex,
        node: candidate,
      });
    }
  }

  var tabbableNodes = orderedTabbables
    .sort(sortOrderedTabbables)
    .map(function(a) { return a.node })
    .concat(regularTabbables);

  return tabbableNodes;
}

tabbable.isTabbable = isTabbable;
tabbable.isFocusable = isFocusable;

function isNodeMatchingSelectorTabbable(node) {
  if (
    !isNodeMatchingSelectorFocusable(node)
    || isNonTabbableRadio(node)
    || getTabindex(node) < 0
  ) {
    return false;
  }
  return true;
}

function isTabbable(node) {
  if (!node) throw new Error('No node provided');
  if (matches.call(node, candidateSelector) === false) return false;
  return isNodeMatchingSelectorTabbable(node);
}

function isNodeMatchingSelectorFocusable(node) {
  if (
    node.disabled
    || isHiddenInput(node)
    || isHidden(node)
  ) {
    return false;
  }
  return true;
}

var focusableCandidateSelector = candidateSelectors.concat('iframe').join(',');
function isFocusable(node) {
  if (!node) throw new Error('No node provided');
  if (matches.call(node, focusableCandidateSelector) === false) return false;
  return isNodeMatchingSelectorFocusable(node);
}

function getTabindex(node) {
  var tabindexAttr = parseInt(node.getAttribute('tabindex'), 10);
  if (!isNaN(tabindexAttr)) return tabindexAttr;
  // Browsers do not return `tabIndex` correctly for contentEditable nodes;
  // so if they don't have a tabindex attribute specifically set, assume it's 0.
  if (isContentEditable(node)) return 0;
  return node.tabIndex;
}

function sortOrderedTabbables(a, b) {
  return a.tabIndex === b.tabIndex ? a.documentOrder - b.documentOrder : a.tabIndex - b.tabIndex;
}

function isContentEditable(node) {
  return node.contentEditable === 'true';
}

function isInput(node) {
  return node.tagName === 'INPUT';
}

function isHiddenInput(node) {
  return isInput(node) && node.type === 'hidden';
}

function isRadio(node) {
  return isInput(node) && node.type === 'radio';
}

function isNonTabbableRadio(node) {
  return isRadio(node) && !isTabbableRadio(node);
}

function getCheckedRadio(nodes) {
  for (var i = 0; i < nodes.length; i++) {
    if (nodes[i].checked) {
      return nodes[i];
    }
  }
}

function isTabbableRadio(node) {
  if (!node.name) return true;
  // This won't account for the edge case where you have radio groups with the same
  // in separate forms on the same page.
  var radioSet = node.ownerDocument.querySelectorAll('input[type="radio"][name="' + node.name + '"]');
  var checked = getCheckedRadio(radioSet);
  return !checked || checked === node;
}

function isHidden(node) {
  // offsetParent being null will allow detecting cases where an element is invisible or inside an invisible element,
  // as long as the element does not use position: fixed. For them, their visibility has to be checked directly as well.
  return node.offsetParent === null || getComputedStyle(node).visibility === 'hidden';
}

module.exports = tabbable;