function prepareClasses(entries, prefix) {
  const resultClasses = [];
  entries.forEach(item => {
    if (typeof item === 'object') {
      Object.keys(item).forEach(classNames => {
        if (item[classNames]) {
          resultClasses.push(prefix + classNames);
        }
      });
    } else if (typeof item === 'string') {
      resultClasses.push(prefix + item);
    }
  });
  return resultClasses;
}

export default function addClasses() {
  const swiper = this;
  const {
    classNames,
    params,
    rtl,
    el,
    device
  } = swiper; // prettier-ignore

  const suffixes = prepareClasses(['initialized', params.direction, {
    'free-mode': swiper.params.freeMode && params.freeMode.enabled
  }, {
    'autoheight': params.autoHeight
  }, {
    'rtl': rtl
  }, {
    'grid': params.grid && params.grid.rows > 1
  }, {
    'grid-column': params.grid && params.grid.rows > 1 && params.grid.fill === 'column'
  }, {
    'android': device.android
  }, {
    'ios': device.ios
  }, {
    'css-mode': params.cssMode
  }, {
    'centered': params.cssMode && params.centeredSlides
  }, {
    'watch-progress': params.watchSlidesProgress
  }], params.containerModifierClass);
  classNames.push(...suffixes);
  el.classList.add(...classNames);
  swiper.emitContainerClasses();
}