import { window } from 'ssr-window';
import Utils from '../../utils/utils';
import Support from '../../utils/support';

const Observer = {
  func: window.MutationObserver || window.WebkitMutationObserver,
  attach(target, options = {}) {
    const swiper = this;

    const ObserverFunc = Observer.func;
    const observer = new ObserverFunc((mutations) => {
      // The observerUpdate event should only be triggered
      // once despite the number of mutations.  Additional
      // triggers are redundant and are very costly
      if (mutations.length === 1) {
        swiper.emit('observerUpdate', mutations[0]);
        return;
      }
      const observerUpdate = function observerUpdate() {
        swiper.emit('observerUpdate', mutations[0]);
      };

      if (window.requestAnimationFrame) {
        window.requestAnimationFrame(observerUpdate);
      } else {
        window.setTimeout(observerUpdate, 0);
      }
    });

    observer.observe(target, {
      attributes: typeof options.attributes === 'undefined' ? true : options.attributes,
      childList: typeof options.childList === 'undefined' ? true : options.childList,
      characterData: typeof options.characterData === 'undefined' ? true : options.characterData,
    });

    swiper.observer.observers.push(observer);
  },
  init() {
    const swiper = this;
    if (!Support.observer || !swiper.params.observer) return;
    if (swiper.params.observeParents) {
      const containerParents = swiper.$el.parents();
      for (let i = 0; i < containerParents.length; i += 1) {
        swiper.observer.attach(containerParents[i]);
      }
    }
    // Observe container
    swiper.observer.attach(swiper.$el[0], { childList: swiper.params.observeSlideChildren });

    // Observe wrapper
    swiper.observer.attach(swiper.$wrapperEl[0], { attributes: false });
  },
  destroy() {
    const swiper = this;
    swiper.observer.observers.forEach((observer) => {
      observer.disconnect();
    });
    swiper.observer.observers = [];
  },
};

export default {
  name: 'observer',
  params: {
    observer: false,
    observeParents: false,
    observeSlideChildren: false,
  },
  create() {
    const swiper = this;
    Utils.extend(swiper, {
      observer: {
        init: Observer.init.bind(swiper),
        attach: Observer.attach.bind(swiper),
        destroy: Observer.destroy.bind(swiper),
        observers: [],
      },
    });
  },
  on: {
    init() {
      const swiper = this;
      swiper.observer.init();
    },
    destroy() {
      const swiper = this;
      swiper.observer.destroy();
    },
  },
};