function ensureImported(element, target) {

  if (element.ownerDocument !== target.ownerDocument) {
    try {
      // may fail on webkit
      return target.ownerDocument.importNode(element, true);
    } catch (e) {
      // ignore
    }
  }

  return element;
}

/**
 * appendTo utility
 */

/**
 * Append a node to a target element and return the appended node.
 *
 * @param  {SVGElement} element
 * @param  {SVGElement} target
 *
 * @return {SVGElement} the appended node
 */
function appendTo(element, target) {
  return target.appendChild(ensureImported(element, target));
}

/**
 * append utility
 */

/**
 * Append a node to an element
 *
 * @param  {SVGElement} element
 * @param  {SVGElement} node
 *
 * @return {SVGElement} the element
 */
function append(target, node) {
  appendTo(node, target);
  return target;
}

/**
 * attribute accessor utility
 */

var LENGTH_ATTR = 2;

var CSS_PROPERTIES = {
  'alignment-baseline': 1,
  'baseline-shift': 1,
  'clip': 1,
  'clip-path': 1,
  'clip-rule': 1,
  'color': 1,
  'color-interpolation': 1,
  'color-interpolation-filters': 1,
  'color-profile': 1,
  'color-rendering': 1,
  'cursor': 1,
  'direction': 1,
  'display': 1,
  'dominant-baseline': 1,
  'enable-background': 1,
  'fill': 1,
  'fill-opacity': 1,
  'fill-rule': 1,
  'filter': 1,
  'flood-color': 1,
  'flood-opacity': 1,
  'font': 1,
  'font-family': 1,
  'font-size': LENGTH_ATTR,
  'font-size-adjust': 1,
  'font-stretch': 1,
  'font-style': 1,
  'font-variant': 1,
  'font-weight': 1,
  'glyph-orientation-horizontal': 1,
  'glyph-orientation-vertical': 1,
  'image-rendering': 1,
  'kerning': 1,
  'letter-spacing': 1,
  'lighting-color': 1,
  'marker': 1,
  'marker-end': 1,
  'marker-mid': 1,
  'marker-start': 1,
  'mask': 1,
  'opacity': 1,
  'overflow': 1,
  'pointer-events': 1,
  'shape-rendering': 1,
  'stop-color': 1,
  'stop-opacity': 1,
  'stroke': 1,
  'stroke-dasharray': 1,
  'stroke-dashoffset': 1,
  'stroke-linecap': 1,
  'stroke-linejoin': 1,
  'stroke-miterlimit': 1,
  'stroke-opacity': 1,
  'stroke-width': LENGTH_ATTR,
  'text-anchor': 1,
  'text-decoration': 1,
  'text-rendering': 1,
  'unicode-bidi': 1,
  'visibility': 1,
  'word-spacing': 1,
  'writing-mode': 1
};


function getAttribute(node, name) {
  if (CSS_PROPERTIES[name]) {
    return node.style[name];
  } else {
    return node.getAttributeNS(null, name);
  }
}

function setAttribute(node, name, value) {
  var hyphenated = name.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase();

  var type = CSS_PROPERTIES[hyphenated];

  if (type) {
    // append pixel unit, unless present
    if (type === LENGTH_ATTR && typeof value === 'number') {
      value = String(value) + 'px';
    }

    node.style[hyphenated] = value;
  } else {
    node.setAttributeNS(null, name, value);
  }
}

function setAttributes(node, attrs) {

  var names = Object.keys(attrs), i, name;

  for (i = 0, name; (name = names[i]); i++) {
    setAttribute(node, name, attrs[name]);
  }
}

/**
 * Gets or sets raw attributes on a node.
 *
 * @param  {SVGElement} node
 * @param  {Object} [attrs]
 * @param  {String} [name]
 * @param  {String} [value]
 *
 * @return {String}
 */
function attr(node, name, value) {
  if (typeof name === 'string') {
    if (value !== undefined) {
      setAttribute(node, name, value);
    } else {
      return getAttribute(node, name);
    }
  } else {
    setAttributes(node, name);
  }

  return node;
}

/**
 * Clear utility
 */
function index(arr, obj) {
  if (arr.indexOf) {
    return arr.indexOf(obj);
  }


  for (var i = 0; i < arr.length; ++i) {
    if (arr[i] === obj) {
      return i;
    }
  }

  return -1;
}

var re = /\s+/;

var toString = Object.prototype.toString;

function defined(o) {
  return typeof o !== 'undefined';
}

/**
 * Wrap `el` in a `ClassList`.
 *
 * @param {Element} el
 * @return {ClassList}
 * @api public
 */

function classes(el) {
  return new ClassList(el);
}

function ClassList(el) {
  if (!el || !el.nodeType) {
    throw new Error('A DOM element reference is required');
  }
  this.el = el;
  this.list = el.classList;
}

/**
 * Add class `name` if not already present.
 *
 * @param {String} name
 * @return {ClassList}
 * @api public
 */

ClassList.prototype.add = function(name) {

  // classList
  if (this.list) {
    this.list.add(name);
    return this;
  }

  // fallback
  var arr = this.array();
  var i = index(arr, name);
  if (!~i) {
    arr.push(name);
  }

  if (defined(this.el.className.baseVal)) {
    this.el.className.baseVal = arr.join(' ');
  } else {
    this.el.className = arr.join(' ');
  }

  return this;
};

/**
 * Remove class `name` when present, or
 * pass a regular expression to remove
 * any which match.
 *
 * @param {String|RegExp} name
 * @return {ClassList}
 * @api public
 */

ClassList.prototype.remove = function(name) {
  if ('[object RegExp]' === toString.call(name)) {
    return this.removeMatching(name);
  }

  // classList
  if (this.list) {
    this.list.remove(name);
    return this;
  }

  // fallback
  var arr = this.array();
  var i = index(arr, name);
  if (~i) {
    arr.splice(i, 1);
  }
  this.el.className.baseVal = arr.join(' ');
  return this;
};

/**
 * Remove all classes matching `re`.
 *
 * @param {RegExp} re
 * @return {ClassList}
 * @api private
 */

ClassList.prototype.removeMatching = function(re) {
  var arr = this.array();
  for (var i = 0; i < arr.length; i++) {
    if (re.test(arr[i])) {
      this.remove(arr[i]);
    }
  }
  return this;
};

/**
 * Toggle class `name`, can force state via `force`.
 *
 * For browsers that support classList, but do not support `force` yet,
 * the mistake will be detected and corrected.
 *
 * @param {String} name
 * @param {Boolean} force
 * @return {ClassList}
 * @api public
 */

ClassList.prototype.toggle = function(name, force) {
  // classList
  if (this.list) {
    if (defined(force)) {
      if (force !== this.list.toggle(name, force)) {
        this.list.toggle(name); // toggle again to correct
      }
    } else {
      this.list.toggle(name);
    }
    return this;
  }

  // fallback
  if (defined(force)) {
    if (!force) {
      this.remove(name);
    } else {
      this.add(name);
    }
  } else {
    if (this.has(name)) {
      this.remove(name);
    } else {
      this.add(name);
    }
  }

  return this;
};

/**
 * Return an array of classes.
 *
 * @return {Array}
 * @api public
 */

ClassList.prototype.array = function() {
  var className = this.el.getAttribute('class') || '';
  var str = className.replace(/^\s+|\s+$/g, '');
  var arr = str.split(re);
  if ('' === arr[0]) {
    arr.shift();
  }
  return arr;
};

/**
 * Check if class `name` is present.
 *
 * @param {String} name
 * @return {ClassList}
 * @api public
 */

ClassList.prototype.has =
ClassList.prototype.contains = function(name) {
  return (
    this.list ?
      this.list.contains(name) :
      !! ~index(this.array(), name)
  );
};

function remove(element) {
  var parent = element.parentNode;

  if (parent) {
    parent.removeChild(element);
  }

  return element;
}

/**
 * Clear utility
 */

/**
 * Removes all children from the given element
 *
 * @param  {DOMElement} element
 * @return {DOMElement} the element (for chaining)
 */
function clear(element) {
  var child;

  while ((child = element.firstChild)) {
    remove(child);
  }

  return element;
}

function clone(element) {
  return element.cloneNode(true);
}

var ns = {
  svg: 'http://www.w3.org/2000/svg'
};

/**
 * DOM parsing utility
 */

var SVG_START = '<svg xmlns="' + ns.svg + '"';

function parse(svg) {

  var unwrap = false;

  // ensure we import a valid svg document
  if (svg.substring(0, 4) === '<svg') {
    if (svg.indexOf(ns.svg) === -1) {
      svg = SVG_START + svg.substring(4);
    }
  } else {
    // namespace svg
    svg = SVG_START + '>' + svg + '</svg>';
    unwrap = true;
  }

  var parsed = parseDocument(svg);

  if (!unwrap) {
    return parsed;
  }

  var fragment = document.createDocumentFragment();

  var parent = parsed.firstChild;

  while (parent.firstChild) {
    fragment.appendChild(parent.firstChild);
  }

  return fragment;
}

function parseDocument(svg) {

  var parser;

  // parse
  parser = new DOMParser();
  parser.async = false;

  return parser.parseFromString(svg, 'text/xml');
}

/**
 * Create utility for SVG elements
 */


/**
 * Create a specific type from name or SVG markup.
 *
 * @param {String} name the name or markup of the element
 * @param {Object} [attrs] attributes to set on the element
 *
 * @returns {SVGElement}
 */
function create(name, attrs) {
  var element;

  if (name.charAt(0) === '<') {
    element = parse(name).firstChild;
    element = document.importNode(element, true);
  } else {
    element = document.createElementNS(ns.svg, name);
  }

  if (attrs) {
    attr(element, attrs);
  }

  return element;
}

/**
 * Events handling utility
 */

function on(node, event, listener, useCapture) {
  node.addEventListener(event, listener, useCapture);
}

function off(node, event, listener, useCapture) {
  node.removeEventListener(event, listener, useCapture);
}

/**
 * Geometry helpers
 */

// fake node used to instantiate svg geometry elements
var node = create('svg');

function extend(object, props) {
  var i, k, keys = Object.keys(props);

  for (i = 0; (k = keys[i]); i++) {
    object[k] = props[k];
  }

  return object;
}


function createPoint(x, y) {
  var point = node.createSVGPoint();

  switch (arguments.length) {
  case 0:
    return point;
  case 2:
    x = {
      x: x,
      y: y
    };
    break;
  }

  return extend(point, x);
}

/**
 * Create matrix via args.
 *
 * @example
 *
 * createMatrix({ a: 1, b: 1 });
 * createMatrix();
 * createMatrix(1, 2, 0, 0, 30, 20);
 *
 * @return {SVGMatrix}
 */
function createMatrix(a, b, c, d, e, f) {
  var matrix = node.createSVGMatrix();

  switch (arguments.length) {
  case 0:
    return matrix;
  case 1:
    return extend(matrix, a);
  case 6:
    return extend(matrix, {
      a: a,
      b: b,
      c: c,
      d: d,
      e: e,
      f: f
    });
  }
}

function createTransform(matrix) {
  if (matrix) {
    return node.createSVGTransformFromMatrix(matrix);
  } else {
    return node.createSVGTransform();
  }
}

/**
 * Serialization util
 */

var TEXT_ENTITIES = /([&<>]{1})/g;
var ATTR_ENTITIES = /([\n\r"]{1})/g;

var ENTITY_REPLACEMENT = {
  '&': '&amp;',
  '<': '&lt;',
  '>': '&gt;',
  '"': '\''
};

function escape(str, pattern) {

  function replaceFn(match, entity) {
    return ENTITY_REPLACEMENT[entity] || entity;
  }

  return str.replace(pattern, replaceFn);
}

function serialize(node, output) {

  var i, len, attrMap, attrNode, childNodes;

  switch (node.nodeType) {
  // TEXT
  case 3:
    // replace special XML characters
    output.push(escape(node.textContent, TEXT_ENTITIES));
    break;

  // ELEMENT
  case 1:
    output.push('<', node.tagName);

    if (node.hasAttributes()) {
      attrMap = node.attributes;
      for (i = 0, len = attrMap.length; i < len; ++i) {
        attrNode = attrMap.item(i);
        output.push(' ', attrNode.name, '="', escape(attrNode.value, ATTR_ENTITIES), '"');
      }
    }

    if (node.hasChildNodes()) {
      output.push('>');
      childNodes = node.childNodes;
      for (i = 0, len = childNodes.length; i < len; ++i) {
        serialize(childNodes.item(i), output);
      }
      output.push('</', node.tagName, '>');
    } else {
      output.push('/>');
    }
    break;

  // COMMENT
  case 8:
    output.push('<!--', escape(node.nodeValue, TEXT_ENTITIES), '-->');
    break;

  // CDATA
  case 4:
    output.push('<![CDATA[', node.nodeValue, ']]>');
    break;

  default:
    throw new Error('unable to handle node ' + node.nodeType);
  }

  return output;
}

/**
 * innerHTML like functionality for SVG elements.
 * based on innerSVG (https://code.google.com/p/innersvg)
 */


function set(element, svg) {

  var parsed = parse(svg);

  // clear element contents
  clear(element);

  if (!svg) {
    return;
  }

  if (!isFragment(parsed)) {
    // extract <svg> from parsed document
    parsed = parsed.documentElement;
  }

  var nodes = slice(parsed.childNodes);

  // import + append each node
  for (var i = 0; i < nodes.length; i++) {
    appendTo(nodes[i], element);
  }

}

function get(element) {
  var child = element.firstChild,
      output = [];

  while (child) {
    serialize(child, output);
    child = child.nextSibling;
  }

  return output.join('');
}

function isFragment(node) {
  return node.nodeName === '#document-fragment';
}

function innerSVG(element, svg) {

  if (svg !== undefined) {

    try {
      set(element, svg);
    } catch (e) {
      throw new Error('error parsing SVG: ' + e.message);
    }

    return element;
  } else {
    return get(element);
  }
}


function slice(arr) {
  return Array.prototype.slice.call(arr);
}

/**
 * Selection utilities
 */

function select(node, selector) {
  return node.querySelector(selector);
}

function selectAll(node, selector) {
  var nodes = node.querySelectorAll(selector);

  return [].map.call(nodes, function(element) {
    return element;
  });
}

/**
 * prependTo utility
 */

/**
 * Prepend a node to a target element and return the prepended node.
 *
 * @param  {SVGElement} node
 * @param  {SVGElement} target
 *
 * @return {SVGElement} the prepended node
 */
function prependTo(node, target) {
  return target.insertBefore(ensureImported(node, target), target.firstChild || null);
}

/**
 * prepend utility
 */

/**
 * Prepend a node to a target element
 *
 * @param  {SVGElement} target
 * @param  {SVGElement} node
 *
 * @return {SVGElement} the target element
 */
function prepend(target, node) {
  prependTo(node, target);
  return target;
}

/**
 * Replace utility
 */

function replace(element, replacement) {
  element.parentNode.replaceChild(ensureImported(replacement, element), element);
  return replacement;
}

/**
 * transform accessor utility
 */

function wrapMatrix(transformList, transform) {
  if (transform instanceof SVGMatrix) {
    return transformList.createSVGTransformFromMatrix(transform);
  }

  return transform;
}


function setTransforms(transformList, transforms) {
  var i, t;

  transformList.clear();

  for (i = 0; (t = transforms[i]); i++) {
    transformList.appendItem(wrapMatrix(transformList, t));
  }
}

/**
 * Get or set the transforms on the given node.
 *
 * @param {SVGElement} node
 * @param  {SVGTransform|SVGMatrix|Array<SVGTransform|SVGMatrix>} [transforms]
 *
 * @return {SVGTransform} the consolidated transform
 */
function transform(node, transforms) {
  var transformList = node.transform.baseVal;

  if (transforms) {

    if (!Array.isArray(transforms)) {
      transforms = [ transforms ];
    }

    setTransforms(transformList, transforms);
  }

  return transformList.consolidate();
}

export { append, appendTo, attr, classes, clear, clone, create, innerSVG, prepend, prependTo, remove, replace, transform, on, off, createPoint, createMatrix, createTransform, select, selectAll };