innerSliderUtils.js

import React from "react";

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

export const safePreventDefault = event => {
  const passiveEvents = ["onTouchStart", "onTouchMove", "onWheel"];
  if (!passiveEvents.includes(event._reactName)) {
    event.preventDefault();
  }
}

export const getOnDemandLazySlides = spec => {
  let onDemandSlides = [];
  let startIndex = lazyStartIndex(spec);
  let 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 => {
  let requiredSlides = [];
  let startIndex = lazyStartIndex(spec);
  let 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) => {
  var xDist, yDist, r, swipeAngle;
  xDist = touchObject.startX - touchObject.curX;
  yDist = touchObject.startY - touchObject.curY;
  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) => {
  let newObject = {};
  keys.forEach(key => (newObject[key] = spec[key]));
  return newObject;
};

// get initialized state
export const initializedState = spec => {
  // spec also contains listRef, trackRef
  let slideCount = React.Children.count(spec.children);
  const listNode = spec.listRef;
  let listWidth = Math.ceil(getWidth(listNode));
  const trackNode = spec.trackRef && spec.trackRef.node;
  let 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;
  }
  let slideHeight =
    listNode && getHeight(listNode.querySelector('[data-index="0"]'));
  let 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 || [];
  let slidesToLoad = getOnDemandLazySlides({
    ...spec,
    currentSlide,
    lazyLoadedList
  });
  lazyLoadedList = lazyLoadedList.concat(slidesToLoad);

  let 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,
    finalSlide,
    animationLeft,
    finalLeft;
  let state = {},
    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) => {
  var indexOffset, previousInt, slideOffset, unevenOffset, targetSlide;
  const {
    slidesToScroll,
    slidesToShow,
    slideCount,
    currentSlide,
    targetSlide: previousTargetSlide,
    lazyLoad,
    infinite
  } = spec;
  unevenOffset = slideCount % slidesToScroll !== 0;
  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) {
      let 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,
    state = {};
  let 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))
  );
  let 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;

  let dotCount = Math.ceil(slideCount / slidesToScroll);
  let 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 {};
  }
  let minSwipe = verticalSwiping
    ? listHeight / touchThreshold
    : listWidth / touchThreshold;
  let swipeDirection = getSwipeDirection(touchObject, verticalSwiping);
  // reset the state of touch related state variables.
  let 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.
    let currentLeft = getTrackLeft(spec);
    state["trackStyle"] = getTrackAnimateCSS({ ...spec, left: currentLeft });
  }
  return state;
};
export const getNavigableIndexes = spec => {
  let max = spec.infinite ? spec.slideCount * 2 : spec.slideCount;
  let breakpoint = spec.infinite ? spec.slidesToShow * -1 : 0;
  let counter = spec.infinite ? spec.slidesToShow * -1 : 0;
  let 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 (let 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;
  if (!spec.vertical) {
    trackWidth = getTotalSlides(spec) * spec.slideWidth;
  } else {
    const trackChildren = spec.unslick
      ? spec.slideCount
      : spec.slideCount + 2 * spec.slidesToShow;
    trackHeight = trackChildren * spec.slideHeight;
  }
  let style = {
    opacity: 1,
    transition: "",
    WebkitTransition: ""
  };
  if (spec.useTransform) {
    let WebkitTransform = !spec.vertical
      ? "translate3d(" + spec.left + "px, 0px, 0px)"
      : "translate3d(0px, " + spec.left + "px, 0px)";
    let transform = !spec.vertical
      ? "translate3d(" + spec.left + "px, 0px, 0px)"
      : "translate3d(0px, " + spec.left + "px, 0px)";
    let 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;
  if (trackHeight) style.height = trackHeight;

  // 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"
  ]);
  let 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;

  var slideOffset = 0;
  var targetLeft;
  var targetSlide;
  var 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) {
    var targetSlideIndex;
    const trackElem = trackRef && trackRef.node;
    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
  );