import createList from '../builders/build-list.mjs';
import { isHorizontal } from '../utils.mjs';
import { AUTO_ALIGNMENT, CENTERED_ALIGNMENT, END_ALIGNMENT, START_ALIGNMENT, SMART_ALIGNMENT } from '../defaults.mjs';

const FixedSizeList = createList({
  name: "ElFixedSizeList",
  getItemOffset: ({ itemSize }, index) => index * itemSize,
  getItemSize: ({ itemSize }) => itemSize,
  getEstimatedTotalSize: ({ total, itemSize }) => itemSize * total,
  getOffset: ({ height, total, itemSize, layout, width }, index, alignment, scrollOffset) => {
    const size = isHorizontal(layout) ? width : height;
    const lastItemOffset = Math.max(0, total * itemSize - size);
    const maxOffset = Math.min(lastItemOffset, index * itemSize);
    const minOffset = Math.max(0, (index + 1) * itemSize - size);
    if (alignment === SMART_ALIGNMENT) {
      if (scrollOffset >= minOffset - size && scrollOffset <= maxOffset + size) {
        alignment = AUTO_ALIGNMENT;
      } else {
        alignment = CENTERED_ALIGNMENT;
      }
    }
    switch (alignment) {
      case START_ALIGNMENT: {
        return maxOffset;
      }
      case END_ALIGNMENT: {
        return minOffset;
      }
      case CENTERED_ALIGNMENT: {
        const middleOffset = Math.round(minOffset + (maxOffset - minOffset) / 2);
        if (middleOffset < Math.ceil(size / 2)) {
          return 0;
        } else if (middleOffset > lastItemOffset + Math.floor(size / 2)) {
          return lastItemOffset;
        } else {
          return middleOffset;
        }
      }
      case AUTO_ALIGNMENT:
      default: {
        if (scrollOffset >= minOffset && scrollOffset <= maxOffset) {
          return scrollOffset;
        } else if (scrollOffset < minOffset) {
          return minOffset;
        } else {
          return maxOffset;
        }
      }
    }
  },
  getStartIndexForOffset: ({ total, itemSize }, offset) => Math.max(0, Math.min(total - 1, Math.floor(offset / itemSize))),
  getStopIndexForStartIndex: ({ height, total, itemSize, layout, width }, startIndex, scrollOffset) => {
    const offset = startIndex * itemSize;
    const size = isHorizontal(layout) ? width : height;
    const numVisibleItems = Math.ceil((size + scrollOffset - offset) / itemSize);
    return Math.max(0, Math.min(total - 1, startIndex + numVisibleItems - 1));
  },
  initCache() {
    return void 0;
  },
  clearCache: true,
  validateProps() {
  }
});

export { FixedSizeList as default };
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