/**
 * @license
 * Copyright (C) 2017 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.
 */
import '../../shared/gr-js-api-interface/gr-js-api-interface.js';
import {importHref} from '../../../scripts/import-href.js';
import {updateStyles} from '@polymer/polymer/lib/mixins/element-mixin.js';
import {GestureEventListeners} from '@polymer/polymer/lib/mixins/gesture-event-listeners.js';
import {LegacyElementMixin} from '@polymer/polymer/lib/legacy/legacy-element-mixin.js';
import {PolymerElement} from '@polymer/polymer/polymer-element.js';
import {htmlTemplate} from './gr-external-style_html.js';
import {pluginEndpoints} from '../../shared/gr-js-api-interface/gr-plugin-endpoints.js';
import {pluginLoader} from '../../shared/gr-js-api-interface/gr-plugin-loader.js';

/** @extends PolymerElement */
class GrExternalStyle extends GestureEventListeners(
    LegacyElementMixin(
        PolymerElement)) {
  static get template() { return htmlTemplate; }

  static get is() { return 'gr-external-style'; }

  static get properties() {
    return {
      name: String,
      _urlsImported: {
        type: Array,
        value() { return []; },
      },
      _stylesApplied: {
        type: Array,
        value() { return []; },
      },
    };
  }

  _importHref(url, resolve, reject) {
    // It is impossible to mock es6-module imported function.
    // The _importHref function is mocked in test.
    importHref(url, resolve, reject);
  }

  /**
   * @suppress {checkTypes}
   */
  _import(url) {
    if (this._urlsImported.includes(url)) { return Promise.resolve(); }
    this._urlsImported.push(url);
    return new Promise((resolve, reject) => {
      this._importHref(url, resolve, reject);
    });
  }

  _applyStyle(name) {
    if (this._stylesApplied.includes(name)) { return; }
    this._stylesApplied.push(name);

    const s = document.createElement('style');
    s.setAttribute('include', name);
    const cs = document.createElement('custom-style');
    cs.appendChild(s);
    // When using Shadow DOM <custom-style> must be added to the <body>.
    // Within <gr-external-style> itself the styles would have no effect.
    const topEl = document.getElementsByTagName('body')[0];
    topEl.insertBefore(cs, topEl.firstChild);
    updateStyles();
  }

  _importAndApply() {
    Promise.all(pluginEndpoints.getPlugins(this.name).map(
        pluginUrl => this._import(pluginUrl))
    ).then(() => {
      const moduleNames = pluginEndpoints.getModules(this.name);
      for (const name of moduleNames) {
        this._applyStyle(name);
      }
    });
  }

  /** @override */
  attached() {
    super.attached();
    this._importAndApply();
  }

  /** @override */
  ready() {
    super.ready();
    pluginLoader.awaitPluginsLoaded().then(() => this._importAndApply());
  }
}

customElements.define(GrExternalStyle.is, GrExternalStyle);