const namespace = 'itf-sticky';
const events = [
  'resize',
  'scroll',
  'touchstart',
  'touchmove',
  'touchend',
  'pageshow',
  'load',
];

const batchStyle = (el, style = {}, className = {}) => {
  for (let k in style) {
    el.style[k] = style[k];
  }
  for (let k in className) {
    if (className[k] && !el.classList.contains(k)) {
      el.classList.add(k);
    } else if (!className[k] && el.classList.contains(k)) {
      el.classList.remove(k);
    }
  }
};

class Sticky {
  constructor(el, vm) {
    this.el = el;
    this.vm = vm;
    this.unsubscribers = [];
    this.isPending = false;
    this.state = {
      isTopSticky: null,
      isBottomSticky: null,
      height: null,
      width: null,
      xOffset: null,
    };

    this.lastState = {
      top: null,
      bottom: null,
      sticked: false,
    };

    const offset = this.getAttribute('sticky-offset') || {};
    const side = this.getAttribute('sticky-side') || 'top';
    const zIndex = this.getAttribute('sticky-z-index') || '10';
    const onStick = this.getAttribute('on-stick') || null;

    this.options = {
      topOffset: Number(offset.top) || 0,
      bottomOffset: Number(offset.bottom) || 0,
      shouldTopSticky: side === 'top' || side === 'both',
      shouldBottomSticky: side === 'bottom' || side === 'both',
      zIndex: zIndex,
      onStick: onStick,
    };
  }

  doBind() {
    if (this.unsubscribers.length > 0) {
      return;
    }
    const { el, vm } = this;
    vm.$nextTick(() => {
      this.placeholderEl = document.createElement('div');
      this.containerEl = this.getContainerEl();
      el.parentNode.insertBefore(this.placeholderEl, el);
      events.forEach(event => {
        const fn = this.update.bind(this);
        this.unsubscribers.push(() => window.removeEventListener(event, fn));
        this.unsubscribers.push(() =>
          this.containerEl.removeEventListener(event, fn),
        );
        window.addEventListener(event, fn, { passive: true });
        this.containerEl.addEventListener(event, fn, { passive: true });
      });
    });
  }

  doUnbind() {
    this.unsubscribers.forEach(fn => fn());
    this.unsubscribers = [];
    this.resetElement();
  }

  update() {
    if (!this.isPending) {
      requestAnimationFrame(() => {
        this.isPending = false;
        this.recomputeState();
        this.updateElements();
      });
      this.isPending = true;
    }
  }

  isTopSticky() {
    if (!this.options.shouldTopSticky) return false;
    const fromTop = this.state.placeholderElRect.top;
    const fromBottom = this.state.containerElRect.bottom;

    const topBreakpoint = this.options.topOffset;
    const bottomBreakpoint = this.options.bottomOffset;

    return fromTop <= topBreakpoint && fromBottom >= bottomBreakpoint;
  }

  isBottomSticky() {
    if (!this.options.shouldBottomSticky) return false;
    const fromBottom =
      window.innerHeight - this.state.placeholderElRect.top - this.state.height;
    const fromTop = window.innerHeight - this.state.containerElRect.top;

    const topBreakpoint = this.options.topOffset;
    const bottomBreakpoint = this.options.bottomOffset;

    return fromBottom <= bottomBreakpoint && fromTop >= topBreakpoint;
  }

  recomputeState() {
    this.state = Object.assign({}, this.state, {
      height: this.getHeight(),
      width: this.getWidth(),
      xOffset: this.getXOffset(),
      placeholderElRect: this.getPlaceholderElRect(),
      containerElRect: this.getContainerElRect(),
    });
    this.state.isTopSticky = this.isTopSticky();
    this.state.isBottomSticky = this.isBottomSticky();
  }

  fireEvents() {
    if (
      typeof this.options.onStick === 'function' &&
      (this.lastState.top !== this.state.isTopSticky ||
        this.lastState.bottom !== this.state.isBottomSticky ||
        this.lastState.sticked !==
        (this.state.isTopSticky || this.state.isBottomSticky))
    ) {
      this.lastState = {
        top: this.state.isTopSticky,
        bottom: this.state.isBottomSticky,
        sticked: this.state.isBottomSticky || this.state.isTopSticky,
      };
      this.options.onStick(this.lastState);
    }
  }

  updateElements() {
    const placeholderStyle = { paddingTop: 0 };
    const elStyle = {
      position: 'static',
      top: 'auto',
      bottom: 'auto',
      left: 'auto',
      width: 'auto',
      zIndex: this.options.zIndex,
    };
    const placeholderClassName = { 'vue-sticky-placeholder': true };
    const elClassName = {
      'vue-sticky-el': true,
      'top-sticky': false,
      'bottom-sticky': false,
    };

    if (this.state.isTopSticky) {
      elStyle.position = 'fixed';
      elStyle.top = this.options.topOffset + 'px';
      elStyle.left = this.state.xOffset + 'px';
      elStyle.width = this.state.width + 'px';
      const bottomLimit =
        this.state.containerElRect.bottom -
        this.state.height -
        this.options.bottomOffset -
        this.options.topOffset;
      if (bottomLimit < 0) {
        elStyle.top = bottomLimit + this.options.topOffset + 'px';
      }
      placeholderStyle.paddingTop = this.state.height + 'px';
      elClassName['top-sticky'] = true;
    } else if (this.state.isBottomSticky) {
      elStyle.position = 'fixed';
      elStyle.bottom = this.options.bottomOffset + 'px';
      elStyle.left = this.state.xOffset + 'px';
      elStyle.width = this.state.width + 'px';
      const topLimit =
        window.innerHeight -
        this.state.containerElRect.top -
        this.state.height -
        this.options.bottomOffset -
        this.options.topOffset;
      if (topLimit < 0) {
        elStyle.bottom = topLimit + this.options.bottomOffset + 'px';
      }
      placeholderStyle.paddingTop = this.state.height + 'px';
      elClassName['bottom-sticky'] = true;
    } else {
      placeholderStyle.paddingTop = 0;
    }

    batchStyle(this.el, elStyle, elClassName);
    batchStyle(this.placeholderEl, placeholderStyle, placeholderClassName);

    this.fireEvents();
  }

  resetElement() {
    ['position', 'top', 'bottom', 'left', 'width', 'zIndex'].forEach(attr => {
      this.el.style.removeProperty(attr);
    });
    this.el.classList.remove('bottom-sticky', 'top-sticky');
    const { parentNode } = this.placeholderEl;
    if (parentNode) {
      parentNode.removeChild(this.placeholderEl);
    }
  }

  getContainerEl() {
    let node = this.el.parentNode;
    while (
      node &&
      node.tagName !== 'HTML' &&
      node.tagName !== 'BODY' &&
      node.nodeType === 1
      ) {
      if (node.hasAttribute('sticky-container')) {
        return node;
      }
      node = node.parentNode;
    }
    return this.el.parentNode;
  }

  getXOffset() {
    return this.placeholderEl.getBoundingClientRect().left;
  }

  getWidth() {
    return this.placeholderEl.getBoundingClientRect().width;
  }

  getHeight() {
    return this.el.getBoundingClientRect().height;
  }

  getPlaceholderElRect() {
    return this.placeholderEl.getBoundingClientRect();
  }

  getContainerElRect() {
    return this.containerEl.getBoundingClientRect();
  }

  getAttribute(name) {
    const expr = this.el.getAttribute(name);
    let result = undefined;
    if (expr) {
      if (this.vm[expr]) {
        result = this.vm[expr];
      } else {
        try {
          result = eval(`(${expr})`);
        } catch (error) {
          result = expr;
        }
      }
    }
    return result;
  }
}

export default {
  inserted(el, bind, vnode) {
    if (typeof bind.value === 'undefined' || bind.value) {
      el[namespace] = new Sticky(el, vnode.context);
      el[namespace].doBind();
    }
  },
  unbind(el, bind, vnode) {
    if (el[namespace]) {
      el[namespace].doUnbind();
      el[namespace] = undefined;
    }
  },
  componentUpdated(el, bind, vnode) {
    if (typeof bind.value === 'undefined' || bind.value) {
      if (!el[namespace]) {
        el[namespace] = new Sticky(el, vnode.context);
      }
      el[namespace].doBind();
    } else {
      if (el[namespace]) {
        el[namespace].doUnbind();
      }
    }
  },
};
