import { nextTick } from 'vue';
import { inBrowser, getScrollParent } from '@vant/use';
import {
  remove,
  on,
  off,
  throttle,
  supportWebp,
  getDPR,
  getBestSelectionFromSrcset,
  isObject,
  hasIntersectionObserver,
  modeType,
  ImageCache,
} from './util';
import ReactiveListener from './listener';

const DEFAULT_URL =
  'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7';
const DEFAULT_EVENTS = [
  'scroll',
  'wheel',
  'mousewheel',
  'resize',
  'animationend',
  'transitionend',
  'touchmove',
];
const DEFAULT_OBSERVER_OPTIONS = {
  rootMargin: '0px',
  threshold: 0,
};

export default function () {
  return class Lazy {
    constructor({
      preLoad,
      error,
      throttleWait,
      preLoadTop,
      dispatchEvent,
      loading,
      attempt,
      silent = true,
      scale,
      listenEvents,
      filter,
      adapter,
      observer,
      observerOptions,
    }) {
      this.mode = modeType.event;
      this.ListenerQueue = [];
      this.TargetIndex = 0;
      this.TargetQueue = [];
      this.options = {
        silent,
        dispatchEvent: !!dispatchEvent,
        throttleWait: throttleWait || 200,
        preLoad: preLoad || 1.3,
        preLoadTop: preLoadTop || 0,
        error: error || DEFAULT_URL,
        loading: loading || DEFAULT_URL,
        attempt: attempt || 3,
        scale: scale || getDPR(scale),
        ListenEvents: listenEvents || DEFAULT_EVENTS,
        hasbind: false,
        supportWebp: supportWebp(),
        filter: filter || {},
        adapter: adapter || {},
        observer: !!observer,
        observerOptions: observerOptions || DEFAULT_OBSERVER_OPTIONS,
      };
      this._initEvent();
      this._imageCache = new ImageCache({ max: 200 });
      this.lazyLoadHandler = throttle(
        this._lazyLoadHandler.bind(this),
        this.options.throttleWait
      );

      this.setMode(this.options.observer ? modeType.observer : modeType.event);
    }

    /**
     * update config
     * @param  {Object} config params
     * @return
     */
    config(options = {}) {
      Object.assign(this.options, options);
    }

    /**
     * output listener's load performance
     * @return {Array}
     */
    performance() {
      return this.ListenerQueue.map((item) => item.performance());
    }

    /*
     * add lazy component to queue
     * @param  {Vue} vm lazy component instance
     * @return
     */
    addLazyBox(vm) {
      this.ListenerQueue.push(vm);
      if (inBrowser) {
        this._addListenerTarget(window);
        this._observer && this._observer.observe(vm.el);
        if (vm.$el && vm.$el.parentNode) {
          this._addListenerTarget(vm.$el.parentNode);
        }
      }
    }

    /*
     * add image listener to queue
     * @param  {DOM} el
     * @param  {object} binding vue directive binding
     * @param  {vnode} vnode vue directive vnode
     * @return
     */
    add(el, binding, vnode) {
      if (this.ListenerQueue.some((item) => item.el === el)) {
        this.update(el, binding);
        return nextTick(this.lazyLoadHandler);
      }

      const value = this._valueFormatter(binding.value);
      let { src } = value;

      nextTick(() => {
        src = getBestSelectionFromSrcset(el, this.options.scale) || src;
        this._observer && this._observer.observe(el);

        const container = Object.keys(binding.modifiers)[0];
        let $parent;

        if (container) {
          $parent = vnode.context.$refs[container];
          // if there is container passed in, try ref first, then fallback to getElementById to support the original usage
          $parent = $parent
            ? $parent.$el || $parent
            : document.getElementById(container);
        }

        if (!$parent) {
          $parent = getScrollParent(el);
        }

        const newListener = new ReactiveListener({
          bindType: binding.arg,
          $parent,
          el,
          src,
          loading: value.loading,
          error: value.error,
          cors: value.cors,
          elRenderer: this._elRenderer.bind(this),
          options: this.options,
          imageCache: this._imageCache,
        });

        this.ListenerQueue.push(newListener);

        if (inBrowser) {
          this._addListenerTarget(window);
          this._addListenerTarget($parent);
        }

        this.lazyLoadHandler();
        nextTick(() => this.lazyLoadHandler());
      });
    }

    /**
     * update image src
     * @param  {DOM} el
     * @param  {object} vue directive binding
     * @return
     */
    update(el, binding, vnode) {
      const value = this._valueFormatter(binding.value);
      let { src } = value;
      src = getBestSelectionFromSrcset(el, this.options.scale) || src;

      const exist = this.ListenerQueue.find((item) => item.el === el);
      if (!exist) {
        this.add(el, binding, vnode);
      } else {
        exist.update({
          src,
          error: value.error,
          loading: value.loading,
        });
      }
      if (this._observer) {
        this._observer.unobserve(el);
        this._observer.observe(el);
      }
      this.lazyLoadHandler();
      nextTick(() => this.lazyLoadHandler());
    }

    /**
     * remove listener form list
     * @param  {DOM} el
     * @return
     */
    remove(el) {
      if (!el) return;
      this._observer && this._observer.unobserve(el);
      const existItem = this.ListenerQueue.find((item) => item.el === el);
      if (existItem) {
        this._removeListenerTarget(existItem.$parent);
        this._removeListenerTarget(window);
        remove(this.ListenerQueue, existItem);
        existItem.$destroy();
      }
    }

    /*
     * remove lazy components form list
     * @param  {Vue} vm Vue instance
     * @return
     */
    removeComponent(vm) {
      if (!vm) return;
      remove(this.ListenerQueue, vm);
      this._observer && this._observer.unobserve(vm.el);
      if (vm.$parent && vm.$el.parentNode) {
        this._removeListenerTarget(vm.$el.parentNode);
      }
      this._removeListenerTarget(window);
    }

    setMode(mode) {
      if (!hasIntersectionObserver && mode === modeType.observer) {
        mode = modeType.event;
      }

      this.mode = mode; // event or observer

      if (mode === modeType.event) {
        if (this._observer) {
          this.ListenerQueue.forEach((listener) => {
            this._observer.unobserve(listener.el);
          });
          this._observer = null;
        }

        this.TargetQueue.forEach((target) => {
          this._initListen(target.el, true);
        });
      } else {
        this.TargetQueue.forEach((target) => {
          this._initListen(target.el, false);
        });
        this._initIntersectionObserver();
      }
    }

    /*
     *** Private functions ***
     */

    /*
     * add listener target
     * @param  {DOM} el listener target
     * @return
     */
    _addListenerTarget(el) {
      if (!el) return;
      let target = this.TargetQueue.find((target) => target.el === el);
      if (!target) {
        target = {
          el,
          id: ++this.TargetIndex,
          childrenCount: 1,
          listened: true,
        };
        this.mode === modeType.event && this._initListen(target.el, true);
        this.TargetQueue.push(target);
      } else {
        target.childrenCount++;
      }
      return this.TargetIndex;
    }

    /*
     * remove listener target or reduce target childrenCount
     * @param  {DOM} el or window
     * @return
     */
    _removeListenerTarget(el) {
      this.TargetQueue.forEach((target, index) => {
        if (target.el === el) {
          target.childrenCount--;
          if (!target.childrenCount) {
            this._initListen(target.el, false);
            this.TargetQueue.splice(index, 1);
            target = null;
          }
        }
      });
    }

    /*
     * add or remove eventlistener
     * @param  {DOM} el DOM or Window
     * @param  {boolean} start flag
     * @return
     */
    _initListen(el, start) {
      this.options.ListenEvents.forEach((evt) =>
        (start ? on : off)(el, evt, this.lazyLoadHandler)
      );
    }

    _initEvent() {
      this.Event = {
        listeners: {
          loading: [],
          loaded: [],
          error: [],
        },
      };

      this.$on = (event, func) => {
        if (!this.Event.listeners[event]) this.Event.listeners[event] = [];
        this.Event.listeners[event].push(func);
      };

      this.$once = (event, func) => {
        const on = (...args) => {
          this.$off(event, on);
          func.apply(this, args);
        };
        this.$on(event, on);
      };

      this.$off = (event, func) => {
        if (!func) {
          if (!this.Event.listeners[event]) return;
          this.Event.listeners[event].length = 0;
          return;
        }
        remove(this.Event.listeners[event], func);
      };

      this.$emit = (event, context, inCache) => {
        if (!this.Event.listeners[event]) return;
        this.Event.listeners[event].forEach((func) => func(context, inCache));
      };
    }

    /**
     * find nodes which in viewport and trigger load
     * @return
     */
    _lazyLoadHandler() {
      const freeList = [];
      this.ListenerQueue.forEach((listener) => {
        if (!listener.el || !listener.el.parentNode) {
          freeList.push(listener);
        }
        const catIn = listener.checkInView();
        if (!catIn) return;
        listener.load();
      });
      freeList.forEach((item) => {
        remove(this.ListenerQueue, item);
        item.$destroy();
      });
    }

    /**
     * init IntersectionObserver
     * set mode to observer
     * @return
     */
    _initIntersectionObserver() {
      if (!hasIntersectionObserver) {
        return;
      }

      this._observer = new IntersectionObserver(
        this._observerHandler.bind(this),
        this.options.observerOptions
      );

      if (this.ListenerQueue.length) {
        this.ListenerQueue.forEach((listener) => {
          this._observer.observe(listener.el);
        });
      }
    }

    /**
     * init IntersectionObserver
     * @return
     */
    _observerHandler(entries) {
      entries.forEach((entry) => {
        if (entry.isIntersecting) {
          this.ListenerQueue.forEach((listener) => {
            if (listener.el === entry.target) {
              if (listener.state.loaded)
                return this._observer.unobserve(listener.el);
              listener.load();
            }
          });
        }
      });
    }

    /**
     * set element attribute with image'url and state
     * @param  {object} lazyload listener object
     * @param  {string} state will be rendered
     * @param  {bool} inCache  is rendered from cache
     * @return
     */
    _elRenderer(listener, state, cache) {
      if (!listener.el) return;
      const { el, bindType } = listener;

      let src;
      switch (state) {
        case 'loading':
          src = listener.loading;
          break;
        case 'error':
          src = listener.error;
          break;
        default:
          ({ src } = listener);
          break;
      }

      if (bindType) {
        el.style[bindType] = 'url("' + src + '")';
      } else if (el.getAttribute('src') !== src) {
        el.setAttribute('src', src);
      }

      el.setAttribute('lazy', state);

      this.$emit(state, listener, cache);
      this.options.adapter[state] &&
        this.options.adapter[state](listener, this.options);

      if (this.options.dispatchEvent) {
        const event = new CustomEvent(state, {
          detail: listener,
        });
        el.dispatchEvent(event);
      }
    }

    /**
     * generate loading loaded error image url
     * @param {string} image's src
     * @return {object} image's loading, loaded, error url
     */
    _valueFormatter(value) {
      let src = value;
      let { loading, error } = this.options;

      // value is object
      if (isObject(value)) {
        if (
          process.env.NODE_ENV !== 'production' &&
          !value.src &&
          !this.options.silent
        ) {
          console.error('[@vant/lazyload] miss src with ' + value);
        }

        ({ src } = value);
        loading = value.loading || this.options.loading;
        error = value.error || this.options.error;
      }
      return {
        src,
        loading,
        error,
      };
    }
  };
}