@atlaskit/breadcrumbs/dist/es2019/components/internal/use-overflow-collapse.js

Breadcrumbs are a navigation system used to show a user's location in a site or app.

import { useCallback, useEffect, useLayoutEffect as useRealLayoutEffect, useRef, useState } from 'react';

// The ellipsis trigger is a compact IconButton (24px) plus the trailing separator (24px).
const ELLIPSIS_WIDTH_ESTIMATE = 48;

// Measurements need layout timing in the browser, but should be a no-op for SSR.
const useLayoutEffect = typeof window === 'undefined' ? useEffect : useRealLayoutEffect;
function setsEqual(a, b) {
  if (a.size !== b.size) {
    return false;
  }
  for (const v of a) {
    if (!b.has(v)) {
      return false;
    }
  }
  return true;
}
function getMiddleOutCollapseOrder(itemCount) {
  const lastIndex = itemCount - 1;
  const middleIndex = Math.floor((itemCount - 1) / 2);
  const collapseOrder = [];
  if (middleIndex > 0 && middleIndex < lastIndex) {
    collapseOrder.push(middleIndex);
  }
  for (let distance = 1; distance < itemCount; distance++) {
    const leftIndex = middleIndex - distance;
    const rightIndex = middleIndex + distance;
    if (leftIndex > 0) {
      collapseOrder.push(leftIndex);
    }
    if (rightIndex < lastIndex) {
      collapseOrder.push(rightIndex);
    }
  }
  return collapseOrder;
}

// eslint-disable-next-line @repo/internal/react/require-jsdoc
export default function useOverflowCollapse(itemCount) {
  const itemRefs = useRef([]);
  const containerRef = useRef(null);
  const naturalWidths = useRef([]);
  const naturalWidthsReady = useRef(false);
  const [naturalWidthsReadyState, setNaturalWidthsReadyState] = useState(false);
  const [collapsedIndices, setCollapsedIndices] = useState(new Set());

  // Intentionally runs after each render until refs have committed and natural widths are measured.
  // eslint-disable-next-line react-hooks/exhaustive-deps
  useLayoutEffect(() => {
    if (naturalWidthsReady.current) {
      return;
    }
    const widths = itemRefs.current.map(el => {
      var _el$offsetWidth;
      return (_el$offsetWidth = el === null || el === void 0 ? void 0 : el.offsetWidth) !== null && _el$offsetWidth !== void 0 ? _el$offsetWidth : 0;
    });
    if (widths.some(w => w > 0)) {
      naturalWidths.current = widths;
      naturalWidthsReady.current = true;
      setNaturalWidthsReadyState(true);
    }
  });
  const recalculate = useCallback(() => {
    const container = containerRef.current;
    if (!container || !naturalWidthsReady.current) {
      return;
    }
    const availableWidth = container.offsetWidth;
    const widths = naturalWidths.current;
    if (itemCount <= 2) {
      setCollapsedIndices(prev => prev.size === 0 ? prev : new Set());
      return;
    }
    const totalWidth = widths.reduce((sum, w) => sum + w, 0);
    if (totalWidth <= availableWidth) {
      setCollapsedIndices(prev => prev.size === 0 ? prev : new Set());
      return;
    }
    let usedWidth = totalWidth;
    const newCollapsed = new Set();
    for (const index of getMiddleOutCollapseOrder(itemCount)) {
      var _widths$index;
      if (newCollapsed.size === 0) {
        usedWidth += ELLIPSIS_WIDTH_ESTIMATE;
      }
      newCollapsed.add(index);
      usedWidth -= (_widths$index = widths[index]) !== null && _widths$index !== void 0 ? _widths$index : 0;
      if (usedWidth <= availableWidth) {
        break;
      }
    }

    // At the smallest sizes, even first + ellipsis + last may not fit.
    // In that case, also collapse the first item so only ellipsis + last is shown.
    // Note: this branch is only reachable when itemCount > 2 (the early return above
    // handles itemCount <= 2), so collapsing index 0 here always leaves at least one
    // visible item (the last) plus the ellipsis trigger.
    if (usedWidth > availableWidth) {
      newCollapsed.add(0);
    }
    setCollapsedIndices(prev => setsEqual(prev, newCollapsed) ? prev : newCollapsed);
  }, [itemCount]);
  const registerItem = useCallback(index => el => {
    itemRefs.current[index] = el;
  }, []);
  const observerRef = useRef(null);
  const registerContainer = useCallback(el => {
    var _observerRef$current;
    // Disconnect any existing observer
    (_observerRef$current = observerRef.current) === null || _observerRef$current === void 0 ? void 0 : _observerRef$current.disconnect();
    containerRef.current = el;
    if (!el) {
      return;
    }
    if (typeof ResizeObserver === 'undefined') {
      return;
    }

    // Set up ResizeObserver immediately when container mounts
    const observer = new ResizeObserver(() => {
      recalculate();
    });
    observer.observe(el);
    observerRef.current = observer;
  }, [recalculate]);
  useEffect(() => {
    if (naturalWidthsReadyState) {
      recalculate();
    }
  }, [naturalWidthsReadyState, recalculate]);

  // Cleanup observer on unmount
  useEffect(() => {
    return () => {
      var _observerRef$current2;
      (_observerRef$current2 = observerRef.current) === null || _observerRef$current2 === void 0 ? void 0 : _observerRef$current2.disconnect();
    };
  }, []);
  useEffect(() => {
    naturalWidthsReady.current = false;
    naturalWidths.current = [];
    setNaturalWidthsReadyState(false);
    setCollapsedIndices(new Set());
  }, [itemCount]);
  return {
    collapsedIndices,
    naturalWidthsReady: naturalWidthsReadyState,
    registerItem,
    registerContainer
  };
}