polygerrit-ui/app/elements/plugins/gr-styles-api/gr-styles-api.js

/**
 * @license
 * Copyright (C) 2019 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

let styleObjectCount = 0;

/** @constructor */
function GrStyleObject(rulesStr) {
  this._rulesStr = rulesStr;
  this._className = `__pg_js_api_class_${styleObjectCount}`;
  styleObjectCount++;
}

/**
 * Creates a new unique CSS class and injects it in a root node of the element
 * if it hasn't been added yet. A root node is an document or is the
 * associated shadowRoot. This class can be added to any element with the same
 * root node.
 *
 * @param {HTMLElement} element The element to get class name for.
 * @return {string} Appropriate class name for the element is returned
 */
GrStyleObject.prototype.getClassName = function(element) {
  let rootNode = Polymer.Settings.useShadow
    ? element.getRootNode() : document.body;
  if (rootNode === document) {
    rootNode = document.head;
  }
  if (!rootNode.__pg_js_api_style_tags) {
    rootNode.__pg_js_api_style_tags = {};
  }
  if (!rootNode.__pg_js_api_style_tags[this._className]) {
    const styleTag = document.createElement('style');
    styleTag.innerHTML = `.${this._className} { ${this._rulesStr} }`;
    rootNode.appendChild(styleTag);
    rootNode.__pg_js_api_style_tags[this._className] = true;
  }
  return this._className;
};

/**
 * Apply shared style to the element.
 *
 * @param {HTMLElement} element The element to apply style for
 */
GrStyleObject.prototype.apply = function(element) {
  element.classList.add(this.getClassName(element));
};

export function GrStylesApi() {
}

/**
 * Creates a new GrStyleObject with specified style properties.
 *
 * @param {string} ruleStr with style properties.
 * @return {GrStyleObject}
 */
GrStylesApi.prototype.css = function(ruleStr) {
  return new GrStyleObject(ruleStr);
};