/**
 * @license
 * Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
 * This code may only be used under the BSD style license found at
 * http://polymer.github.io/LICENSE.txt
 * The complete set of authors may be found at
 * http://polymer.github.io/AUTHORS.txt
 * The complete set of contributors may be found at
 * http://polymer.github.io/CONTRIBUTORS.txt
 * Code distributed by Google as part of the polymer project is also
 * subject to an additional IP rights grant found at
 * http://polymer.github.io/PATENTS.txt
 */

import {directive, isPrimitive, NodePart, Part} from '../lit-html.js';

/**
 * Renders the result as HTML, rather than text.
 *
 * Note, this is unsafe to use with any user-provided input that hasn't been
 * sanitized or escaped, as it may lead to cross-site-scripting
 * vulnerabilities.
 */

const previousValues = new WeakMap<NodePart, string>();

export const unsafeHTML = directive((value: any) => (part: Part): void => {
  if (!(part instanceof NodePart)) {
    throw new Error('unsafeHTML can only be used in text bindings');
  }
  // Dirty check primitive values
  const previousValue = previousValues.get(part);
  if (previousValue === value && isPrimitive(value)) {
    return;
  }

  // Use a <template> to parse HTML into Nodes
  const tmp = document.createElement('template');
  tmp.innerHTML = value;
  part.setValue(document.importNode(tmp.content, true));
  previousValues.set(part, value);
});