ant-design-vue/components/vc-slick/utils/innerSliderUtils.js

// import supportsPassive from '../../../_util/supportsPassive';

export function clamp(number, lowerBound, upperBound) {
  return Math.max(lowerBound, Math.min(number, upperBound));
}

export const safePreventDefault = event => {
  const passiveEvents = ['touchstart', 'touchmove', 'wheel'];
  if (!passiveEvents.includes(event.type)) {
    event.preventDefault();
  }
};

export const getOnDemandLazySlides = spec => {
  const onDemandSlides = [];
  const startIndex = lazyStartIndex(spec);
  const endIndex = lazyEndIndex(spec);
  for (let slideIndex = startIndex; slideIndex < endIndex; slideIndex++) {
    if (spec.lazyLoadedList.indexOf(slideIndex) < 0) {
      onDemandSlides.push(slideIndex);
    }
  }
  return onDemandSlides;
};

// return list of slides that need to be present
export const getRequiredLazySlides = spec => {
  const requiredSlides = [];
  const startIndex = lazyStartIndex(spec);
  const endIndex = lazyEndIndex(spec);
  for (let slideIndex = startIndex; slideIndex < endIndex; slideIndex++) {
    requiredSlides.push(slideIndex);
  }
  return requiredSlides;
};

// startIndex that needs to be present
export const lazyStartIndex = spec => spec.currentSlide - lazySlidesOnLeft(spec);
export const lazyEndIndex = spec => spec.currentSlide + lazySlidesOnRight(spec);
export const lazySlidesOnLeft = spec =>
  spec.centerMode
    ? Math.floor(spec.slidesToShow / 2) + (parseInt(spec.centerPadding) > 0 ? 1 : 0)
    : 0;
export const lazySlidesOnRight = spec =>
  spec.centerMode
    ? Math.floor((spec.slidesToShow - 1) / 2) + 1 + (parseInt(spec.centerPadding) > 0 ? 1 : 0)
    : spec.slidesToShow;

// get width of an element
export const getWidth = elem => (elem && elem.offsetWidth) || 0;
export const getHeight = elem => (elem && elem.offsetHeight) || 0;
export const getSwipeDirection = (touchObject, verticalSwiping = false) => {
  let swipeAngle;
  const xDist = touchObject.startX - touchObject.curX;
  const yDist = touchObject.startY - touchObject.curY;
  const r = Math.atan2(yDist, xDist);
  swipeAngle = Math.round((r * 180) / Math.PI);
  if (swipeAngle < 0) {
    swipeAngle = 360 - Math.abs(swipeAngle);
  }
  if ((swipeAngle <= 45 && swipeAngle >= 0) || (swipeAngle <= 360 && swipeAngle >= 315)) {
    return 'left';
  }
  if (swipeAngle >= 135 && swipeAngle <= 225) {
    return 'right';
  }
  if (verticalSwiping === true) {
    if (swipeAngle >= 35 && swipeAngle <= 135) {
      return 'up';
    } else {
      return 'down';
    }
  }

  return 'vertical';
};

// whether or not we can go next
export const canGoNext = spec => {
  let canGo = true;
  if (!spec.infinite) {
    if (spec.centerMode && spec.currentSlide >= spec.slideCount - 1) {
      canGo = false;
    } else if (
      spec.slideCount <= spec.slidesToShow ||
      spec.currentSlide >= spec.slideCount - spec.slidesToShow
    ) {
      canGo = false;
    }
  }
  return canGo;
};

// given an object and a list of keys, return new object with given keys
export const extractObject = (spec, keys) => {
  const newObject = {};
  keys.forEach(key => (newObject[key] = spec[key]));
  return newObject;
};

// get initialized state
export const initializedState = spec => {
  // spec also contains listRef, trackRef
  const slideCount = spec.children.length;
  const listNode = spec.listRef;
  const listWidth = Math.ceil(getWidth(listNode));
  const trackNode = spec.trackRef;
  const trackWidth = Math.ceil(getWidth(trackNode));
  let slideWidth;
  if (!spec.vertical) {
    let centerPaddingAdj = spec.centerMode && parseInt(spec.centerPadding) * 2;
    if (typeof spec.centerPadding === 'string' && spec.centerPadding.slice(-1) === '%') {
      centerPaddingAdj *= listWidth / 100;
    }
    slideWidth = Math.ceil((listWidth - centerPaddingAdj) / spec.slidesToShow);
  } else {
    slideWidth = listWidth;
  }
  const slideHeight = listNode && getHeight(listNode.querySelector('[data-index="0"]'));
  const listHeight = slideHeight * spec.slidesToShow;
  let currentSlide = spec.currentSlide === undefined ? spec.initialSlide : spec.currentSlide;
  if (spec.rtl && spec.currentSlide === undefined) {
    currentSlide = slideCount - 1 - spec.initialSlide;
  }
  let lazyLoadedList = spec.lazyLoadedList || [];
  const slidesToLoad = getOnDemandLazySlides({ ...spec, currentSlide, lazyLoadedList }, spec);
  lazyLoadedList = lazyLoadedList.concat(slidesToLoad);

  const state = {
    slideCount,
    slideWidth,
    listWidth,
    trackWidth,
    currentSlide,
    slideHeight,
    listHeight,
    lazyLoadedList,
  };

  if (spec.autoplaying === null && spec.autoplay) {
    state['autoplaying'] = 'playing';
  }

  return state;
};

export const slideHandler = spec => {
  const {
    waitForAnimate,
    animating,
    fade,
    infinite,
    index,
    slideCount,
    lazyLoad,
    currentSlide,
    centerMode,
    slidesToScroll,
    slidesToShow,
    useCSS,
  } = spec;
  let { lazyLoadedList } = spec;
  if (waitForAnimate && animating) return {};
  let animationSlide = index;
  let finalSlide;
  let animationLeft;
  let finalLeft;
  let state = {};
  let nextState = {};
  const targetSlide = infinite ? index : clamp(index, 0, slideCount - 1);
  if (fade) {
    if (!infinite && (index < 0 || index >= slideCount)) return {};
    if (index < 0) {
      animationSlide = index + slideCount;
    } else if (index >= slideCount) {
      animationSlide = index - slideCount;
    }
    if (lazyLoad && lazyLoadedList.indexOf(animationSlide) < 0) {
      lazyLoadedList = lazyLoadedList.concat(animationSlide);
    }
    state = {
      animating: true,
      currentSlide: animationSlide,
      lazyLoadedList,
      targetSlide: animationSlide,
    };
    nextState = { animating: false, targetSlide: animationSlide };
  } else {
    finalSlide = animationSlide;
    if (animationSlide < 0) {
      finalSlide = animationSlide + slideCount;
      if (!infinite) finalSlide = 0;
      else if (slideCount % slidesToScroll !== 0) {
        finalSlide = slideCount - (slideCount % slidesToScroll);
      }
    } else if (!canGoNext(spec) && animationSlide > currentSlide) {
      animationSlide = finalSlide = currentSlide;
    } else if (centerMode && animationSlide >= slideCount) {
      animationSlide = infinite ? slideCount : slideCount - 1;
      finalSlide = infinite ? 0 : slideCount - 1;
    } else if (animationSlide >= slideCount) {
      finalSlide = animationSlide - slideCount;
      if (!infinite) finalSlide = slideCount - slidesToShow;
      else if (slideCount % slidesToScroll !== 0) finalSlide = 0;
    }

    if (!infinite && animationSlide + slidesToShow >= slideCount) {
      finalSlide = slideCount - slidesToShow;
    }

    animationLeft = getTrackLeft({ ...spec, slideIndex: animationSlide });
    finalLeft = getTrackLeft({ ...spec, slideIndex: finalSlide });
    if (!infinite) {
      if (animationLeft === finalLeft) animationSlide = finalSlide;
      animationLeft = finalLeft;
    }
    if (lazyLoad) {
      lazyLoadedList = lazyLoadedList.concat(
        getOnDemandLazySlides({ ...spec, currentSlide: animationSlide }),
      );
    }
    if (!useCSS) {
      state = {
        currentSlide: finalSlide,
        trackStyle: getTrackCSS({ ...spec, left: finalLeft }),
        lazyLoadedList,
        targetSlide,
      };
    } else {
      state = {
        animating: true,
        currentSlide: finalSlide,
        trackStyle: getTrackAnimateCSS({ ...spec, left: animationLeft }),
        lazyLoadedList,
        targetSlide,
      };
      nextState = {
        animating: false,
        currentSlide: finalSlide,
        trackStyle: getTrackCSS({ ...spec, left: finalLeft }),
        swipeLeft: null,
        targetSlide,
      };
    }
  }
  return { state, nextState };
};

export const changeSlide = (spec, options) => {
  let previousInt, slideOffset, targetSlide;
  const {
    slidesToScroll,
    slidesToShow,
    slideCount,
    currentSlide,
    targetSlide: previousTargetSlide,
    lazyLoad,
    infinite,
  } = spec;
  const unevenOffset = slideCount % slidesToScroll !== 0;
  const indexOffset = unevenOffset ? 0 : (slideCount - currentSlide) % slidesToScroll;

  if (options.message === 'previous') {
    slideOffset = indexOffset === 0 ? slidesToScroll : slidesToShow - indexOffset;
    targetSlide = currentSlide - slideOffset;
    if (lazyLoad && !infinite) {
      previousInt = currentSlide - slideOffset;
      targetSlide = previousInt === -1 ? slideCount - 1 : previousInt;
    }
    if (!infinite) {
      targetSlide = previousTargetSlide - slidesToScroll;
    }
  } else if (options.message === 'next') {
    slideOffset = indexOffset === 0 ? slidesToScroll : indexOffset;
    targetSlide = currentSlide + slideOffset;
    if (lazyLoad && !infinite) {
      targetSlide = ((currentSlide + slidesToScroll) % slideCount) + indexOffset;
    }
    if (!infinite) {
      targetSlide = previousTargetSlide + slidesToScroll;
    }
  } else if (options.message === 'dots') {
    // Click on dots
    targetSlide = options.index * options.slidesToScroll;
  } else if (options.message === 'children') {
    // Click on the slides
    targetSlide = options.index;

    if (infinite) {
      const direction = siblingDirection({ ...spec, targetSlide });
      if (targetSlide > options.currentSlide && direction === 'left') {
        targetSlide = targetSlide - slideCount;
      } else if (targetSlide < options.currentSlide && direction === 'right') {
        targetSlide = targetSlide + slideCount;
      }
    }
  } else if (options.message === 'index') {
    targetSlide = Number(options.index);
  }
  return targetSlide;
};
export const keyHandler = (e, accessibility, rtl) => {
  if (e.target.tagName.match('TEXTAREA|INPUT|SELECT') || !accessibility) {
    return '';
  }
  if (e.keyCode === 37) return rtl ? 'next' : 'previous';
  if (e.keyCode === 39) return rtl ? 'previous' : 'next';
  return '';
};

export const swipeStart = (e, swipe, draggable) => {
  e.target.tagName === 'IMG' && safePreventDefault(e);
  if (!swipe || (!draggable && e.type.indexOf('mouse') !== -1)) return '';
  return {
    dragging: true,
    touchObject: {
      startX: e.touches ? e.touches[0].pageX : e.clientX,
      startY: e.touches ? e.touches[0].pageY : e.clientY,
      curX: e.touches ? e.touches[0].pageX : e.clientX,
      curY: e.touches ? e.touches[0].pageY : e.clientY,
    },
  };
};
export const swipeMove = (e, spec) => {
  // spec also contains, trackRef and slideIndex
  const {
    scrolling,
    animating,
    vertical,
    swipeToSlide,
    verticalSwiping,
    rtl,
    currentSlide,
    edgeFriction,
    edgeDragged,
    onEdge,
    swiped,
    swiping,
    slideCount,
    slidesToScroll,
    infinite,
    touchObject,
    swipeEvent,
    listHeight,
    listWidth,
  } = spec;
  if (scrolling) return;
  if (animating) return safePreventDefault(e);
  if (vertical && swipeToSlide && verticalSwiping) safePreventDefault(e);
  let swipeLeft;
  let state = {};
  const curLeft = getTrackLeft(spec);
  touchObject.curX = e.touches ? e.touches[0].pageX : e.clientX;
  touchObject.curY = e.touches ? e.touches[0].pageY : e.clientY;
  touchObject.swipeLength = Math.round(
    Math.sqrt(Math.pow(touchObject.curX - touchObject.startX, 2)),
  );
  const verticalSwipeLength = Math.round(
    Math.sqrt(Math.pow(touchObject.curY - touchObject.startY, 2)),
  );
  if (!verticalSwiping && !swiping && verticalSwipeLength > 10) {
    return { scrolling: true };
  }
  if (verticalSwiping) touchObject.swipeLength = verticalSwipeLength;
  let positionOffset = (!rtl ? 1 : -1) * (touchObject.curX > touchObject.startX ? 1 : -1);
  if (verticalSwiping) {
    positionOffset = touchObject.curY > touchObject.startY ? 1 : -1;
  }

  const dotCount = Math.ceil(slideCount / slidesToScroll);
  const swipeDirection = getSwipeDirection(spec.touchObject, verticalSwiping);
  let touchSwipeLength = touchObject.swipeLength;
  if (!infinite) {
    if (
      (currentSlide === 0 && (swipeDirection === 'right' || swipeDirection === 'down')) ||
      (currentSlide + 1 >= dotCount && (swipeDirection === 'left' || swipeDirection === 'up')) ||
      (!canGoNext(spec) && (swipeDirection === 'left' || swipeDirection === 'up'))
    ) {
      touchSwipeLength = touchObject.swipeLength * edgeFriction;
      if (edgeDragged === false && onEdge) {
        onEdge(swipeDirection);
        state['edgeDragged'] = true;
      }
    }
  }
  if (!swiped && swipeEvent) {
    swipeEvent(swipeDirection);
    state['swiped'] = true;
  }
  if (!vertical) {
    if (!rtl) {
      swipeLeft = curLeft + touchSwipeLength * positionOffset;
    } else {
      swipeLeft = curLeft - touchSwipeLength * positionOffset;
    }
  } else {
    swipeLeft = curLeft + touchSwipeLength * (listHeight / listWidth) * positionOffset;
  }
  if (verticalSwiping) {
    swipeLeft = curLeft + touchSwipeLength * positionOffset;
  }
  state = {
    ...state,
    touchObject,
    swipeLeft,
    trackStyle: getTrackCSS({ ...spec, left: swipeLeft }),
  };
  if (
    Math.abs(touchObject.curX - touchObject.startX) <
    Math.abs(touchObject.curY - touchObject.startY) * 0.8
  ) {
    return state;
  }
  if (touchObject.swipeLength > 10) {
    state['swiping'] = true;
    safePreventDefault(e);
  }
  return state;
};
export const swipeEnd = (e, spec) => {
  const {
    dragging,
    swipe,
    touchObject,
    listWidth,
    touchThreshold,
    verticalSwiping,
    listHeight,
    swipeToSlide,
    scrolling,
    onSwipe,
    targetSlide,
    currentSlide,
    infinite,
  } = spec;
  if (!dragging) {
    if (swipe) safePreventDefault(e);
    return {};
  }
  const minSwipe = verticalSwiping ? listHeight / touchThreshold : listWidth / touchThreshold;
  const swipeDirection = getSwipeDirection(touchObject, verticalSwiping);
  // reset the state of touch related state variables.
  const state = {
    dragging: false,
    edgeDragged: false,
    scrolling: false,
    swiping: false,
    swiped: false,
    swipeLeft: null,
    touchObject: {},
  };
  if (scrolling) {
    return state;
  }
  if (!touchObject.swipeLength) {
    return state;
  }
  if (touchObject.swipeLength > minSwipe) {
    safePreventDefault(e);
    if (onSwipe) {
      onSwipe(swipeDirection);
    }
    let slideCount, newSlide;
    let activeSlide = infinite ? currentSlide : targetSlide;
    switch (swipeDirection) {
      case 'left':
      case 'up':
        newSlide = activeSlide + getSlideCount(spec);
        slideCount = swipeToSlide ? checkNavigable(spec, newSlide) : newSlide;
        state['currentDirection'] = 0;
        break;
      case 'right':
      case 'down':
        newSlide = activeSlide - getSlideCount(spec);
        slideCount = swipeToSlide ? checkNavigable(spec, newSlide) : newSlide;
        state['currentDirection'] = 1;
        break;
      default:
        slideCount = activeSlide;
    }
    state['triggerSlideHandler'] = slideCount;
  } else {
    // Adjust the track back to it's original position.
    const currentLeft = getTrackLeft(spec);
    state['trackStyle'] = getTrackAnimateCSS({ ...spec, left: currentLeft });
  }
  return state;
};
export const getNavigableIndexes = spec => {
  const max = spec.infinite ? spec.slideCount * 2 : spec.slideCount;
  let breakpoint = spec.infinite ? spec.slidesToShow * -1 : 0;
  let counter = spec.infinite ? spec.slidesToShow * -1 : 0;
  const indexes = [];
  while (breakpoint < max) {
    indexes.push(breakpoint);
    breakpoint = counter + spec.slidesToScroll;
    counter += Math.min(spec.slidesToScroll, spec.slidesToShow);
  }
  return indexes;
};
export const checkNavigable = (spec, index) => {
  const navigables = getNavigableIndexes(spec);
  let prevNavigable = 0;
  if (index > navigables[navigables.length - 1]) {
    index = navigables[navigables.length - 1];
  } else {
    for (const n in navigables) {
      if (index < navigables[n]) {
        index = prevNavigable;
        break;
      }
      prevNavigable = navigables[n];
    }
  }
  return index;
};
export const getSlideCount = spec => {
  const centerOffset = spec.centerMode ? spec.slideWidth * Math.floor(spec.slidesToShow / 2) : 0;
  if (spec.swipeToSlide) {
    let swipedSlide;
    const slickList = spec.listRef;
    const slides = (slickList.querySelectorAll && slickList.querySelectorAll('.slick-slide')) || [];
    Array.from(slides).every(slide => {
      if (!spec.vertical) {
        if (slide.offsetLeft - centerOffset + getWidth(slide) / 2 > spec.swipeLeft * -1) {
          swipedSlide = slide;
          return false;
        }
      } else {
        if (slide.offsetTop + getHeight(slide) / 2 > spec.swipeLeft * -1) {
          swipedSlide = slide;
          return false;
        }
      }

      return true;
    });

    if (!swipedSlide) {
      return 0;
    }
    const currentIndex =
      spec.rtl === true ? spec.slideCount - spec.currentSlide : spec.currentSlide;
    const slidesTraversed = Math.abs(swipedSlide.dataset.index - currentIndex) || 1;
    return slidesTraversed;
  } else {
    return spec.slidesToScroll;
  }
};

export const checkSpecKeys = (spec, keysArray) =>
  keysArray.reduce((value, key) => value && spec.hasOwnProperty(key), true)
    ? null
    : console.error('Keys Missing:', spec);

export const getTrackCSS = spec => {
  checkSpecKeys(spec, ['left', 'variableWidth', 'slideCount', 'slidesToShow', 'slideWidth']);
  let trackWidth, trackHeight;
  const trackChildren = spec.slideCount + 2 * spec.slidesToShow;
  if (!spec.vertical) {
    trackWidth = getTotalSlides(spec) * spec.slideWidth;
  } else {
    trackHeight = trackChildren * spec.slideHeight;
  }
  let style = {
    opacity: 1,
    transition: '',
    WebkitTransition: '',
  };
  if (spec.useTransform) {
    const WebkitTransform = !spec.vertical
      ? 'translate3d(' + spec.left + 'px, 0px, 0px)'
      : 'translate3d(0px, ' + spec.left + 'px, 0px)';
    const transform = !spec.vertical
      ? 'translate3d(' + spec.left + 'px, 0px, 0px)'
      : 'translate3d(0px, ' + spec.left + 'px, 0px)';
    const msTransform = !spec.vertical
      ? 'translateX(' + spec.left + 'px)'
      : 'translateY(' + spec.left + 'px)';
    style = {
      ...style,
      WebkitTransform,
      transform,
      msTransform,
    };
  } else {
    if (spec.vertical) {
      style['top'] = spec.left;
    } else {
      style['left'] = spec.left;
    }
  }
  if (spec.fade) style = { opacity: 1 };
  if (trackWidth) style.width = trackWidth + 'px';
  if (trackHeight) style.height = trackHeight + 'px';

  // Fallback for IE8
  if (window && !window.addEventListener && window.attachEvent) {
    if (!spec.vertical) {
      style.marginLeft = spec.left + 'px';
    } else {
      style.marginTop = spec.left + 'px';
    }
  }

  return style;
};
export const getTrackAnimateCSS = spec => {
  checkSpecKeys(spec, [
    'left',
    'variableWidth',
    'slideCount',
    'slidesToShow',
    'slideWidth',
    'speed',
    'cssEase',
  ]);
  const style = getTrackCSS(spec);
  // useCSS is true by default so it can be undefined
  if (spec.useTransform) {
    style.WebkitTransition = '-webkit-transform ' + spec.speed + 'ms ' + spec.cssEase;
    style.transition = 'transform ' + spec.speed + 'ms ' + spec.cssEase;
  } else {
    if (spec.vertical) {
      style.transition = 'top ' + spec.speed + 'ms ' + spec.cssEase;
    } else {
      style.transition = 'left ' + spec.speed + 'ms ' + spec.cssEase;
    }
  }
  return style;
};
export const getTrackLeft = spec => {
  if (spec.unslick) {
    return 0;
  }

  checkSpecKeys(spec, [
    'slideIndex',
    'trackRef',
    'infinite',
    'centerMode',
    'slideCount',
    'slidesToShow',
    'slidesToScroll',
    'slideWidth',
    'listWidth',
    'variableWidth',
    'slideHeight',
  ]);

  const {
    slideIndex,
    trackRef,
    infinite,
    centerMode,
    slideCount,
    slidesToShow,
    slidesToScroll,
    slideWidth,
    listWidth,
    variableWidth,
    slideHeight,
    fade,
    vertical,
  } = spec;

  let slideOffset = 0;
  let targetLeft;
  let targetSlide;
  let verticalOffset = 0;

  if (fade || spec.slideCount === 1) {
    return 0;
  }

  let slidesToOffset = 0;
  if (infinite) {
    slidesToOffset = -getPreClones(spec); // bring active slide to the beginning of visual area
    // if next scroll doesn't have enough children, just reach till the end of original slides instead of shifting slidesToScroll children
    if (slideCount % slidesToScroll !== 0 && slideIndex + slidesToScroll > slideCount) {
      slidesToOffset = -(slideIndex > slideCount
        ? slidesToShow - (slideIndex - slideCount)
        : slideCount % slidesToScroll);
    }
    // shift current slide to center of the frame
    if (centerMode) {
      slidesToOffset += parseInt(slidesToShow / 2);
    }
  } else {
    if (slideCount % slidesToScroll !== 0 && slideIndex + slidesToScroll > slideCount) {
      slidesToOffset = slidesToShow - (slideCount % slidesToScroll);
    }
    if (centerMode) {
      slidesToOffset = parseInt(slidesToShow / 2);
    }
  }
  slideOffset = slidesToOffset * slideWidth;
  verticalOffset = slidesToOffset * slideHeight;

  if (!vertical) {
    targetLeft = slideIndex * slideWidth * -1 + slideOffset;
  } else {
    targetLeft = slideIndex * slideHeight * -1 + verticalOffset;
  }

  if (variableWidth === true) {
    let targetSlideIndex;
    const trackElem = trackRef;
    targetSlideIndex = slideIndex + getPreClones(spec);
    targetSlide = trackElem && trackElem.childNodes[targetSlideIndex];
    targetLeft = targetSlide ? targetSlide.offsetLeft * -1 : 0;
    if (centerMode === true) {
      targetSlideIndex = infinite ? slideIndex + getPreClones(spec) : slideIndex;
      targetSlide = trackElem && trackElem.children[targetSlideIndex];
      targetLeft = 0;
      for (let slide = 0; slide < targetSlideIndex; slide++) {
        targetLeft -=
          trackElem && trackElem.children[slide] && trackElem.children[slide].offsetWidth;
      }
      targetLeft -= parseInt(spec.centerPadding);
      targetLeft += targetSlide && (listWidth - targetSlide.offsetWidth) / 2;
    }
  }

  return targetLeft;
};

export const getPreClones = spec => {
  if (spec.unslick || !spec.infinite) {
    return 0;
  }
  if (spec.variableWidth) {
    return spec.slideCount;
  }
  return spec.slidesToShow + (spec.centerMode ? 1 : 0);
};

export const getPostClones = spec => {
  if (spec.unslick || !spec.infinite) {
    return 0;
  }
  return spec.slideCount;
};

export const getTotalSlides = spec =>
  spec.slideCount === 1 ? 1 : getPreClones(spec) + spec.slideCount + getPostClones(spec);
export const siblingDirection = spec => {
  if (spec.targetSlide > spec.currentSlide) {
    if (spec.targetSlide > spec.currentSlide + slidesOnRight(spec)) {
      return 'left';
    }
    return 'right';
  } else {
    if (spec.targetSlide < spec.currentSlide - slidesOnLeft(spec)) {
      return 'right';
    }
    return 'left';
  }
};

export const slidesOnRight = ({ slidesToShow, centerMode, rtl, centerPadding }) => {
  // returns no of slides on the right of active slide
  if (centerMode) {
    let right = (slidesToShow - 1) / 2 + 1;
    if (parseInt(centerPadding) > 0) right += 1;
    if (rtl && slidesToShow % 2 === 0) right += 1;
    return right;
  }
  if (rtl) {
    return 0;
  }
  return slidesToShow - 1;
};

export const slidesOnLeft = ({ slidesToShow, centerMode, rtl, centerPadding }) => {
  // returns no of slides on the left of active slide
  if (centerMode) {
    let left = (slidesToShow - 1) / 2 + 1;
    if (parseInt(centerPadding) > 0) left += 1;
    if (!rtl && slidesToShow % 2 === 0) left += 1;
    return left;
  }
  if (rtl) {
    return slidesToShow - 1;
  }
  return 0;
};

export const canUseDOM = () =>
  !!(typeof window !== 'undefined' && window.document && window.document.createElement);