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84 lines
3.3 KiB
JavaScript
84 lines
3.3 KiB
JavaScript
/**
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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import { useMemo } from 'react';
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function treeifyTOC(flatTOC) {
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const headings = flatTOC.map((heading) => ({
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...heading,
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parentIndex: -1,
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children: [],
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}));
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// Keep track of which previous index would be the current heading's direct
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// parent. Each entry <i> is the last index of the `headings` array at heading
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// level <i>. We will modify these indices as we iterate through all headings.
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// e.g. if an ### H3 was last seen at index 2, then prevIndexForLevel[3] === 2
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// indices 0 and 1 will remain unused.
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const prevIndexForLevel = Array(7).fill(-1);
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headings.forEach((curr, currIndex) => {
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// Take the last seen index for each ancestor level. the highest index will
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// be the direct ancestor of the current heading.
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const ancestorLevelIndexes = prevIndexForLevel.slice(2, curr.level);
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curr.parentIndex = Math.max(...ancestorLevelIndexes);
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// Mark that curr.level was last seen at the current index.
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prevIndexForLevel[curr.level] = currIndex;
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});
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const rootNodes = [];
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// For a given parentIndex, add each Node into that parent's `children` array
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headings.forEach((heading) => {
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const { parentIndex, ...rest } = heading;
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if (parentIndex >= 0) {
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headings[parentIndex].children.push(rest);
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}
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else {
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rootNodes.push(rest);
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}
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});
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return rootNodes;
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}
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/**
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* Takes a flat TOC list (from the MDX loader) and treeifies it into what the
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* TOC components expect. Memoized for performance.
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*/
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export function useTreeifiedTOC(toc) {
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return useMemo(() => treeifyTOC(toc), [toc]);
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}
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function filterTOC({ toc, minHeadingLevel, maxHeadingLevel, }) {
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function isValid(item) {
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return item.level >= minHeadingLevel && item.level <= maxHeadingLevel;
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}
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return toc.flatMap((item) => {
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const filteredChildren = filterTOC({
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toc: item.children,
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minHeadingLevel,
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maxHeadingLevel,
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});
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if (isValid(item)) {
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return [
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{
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...item,
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children: filteredChildren,
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},
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];
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}
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return filteredChildren;
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});
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}
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/**
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* Takes a flat TOC list (from the MDX loader) and treeifies it into what the
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* TOC components expect, applying the `minHeadingLevel` and `maxHeadingLevel`.
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* Memoized for performance.
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*
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* **Important**: this is not the same as `useTreeifiedTOC(toc.filter(...))`,
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* because we have to filter the TOC after it has been treeified. This is mostly
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* to ensure that weird TOC structures preserve their semantics. For example, an
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* h3-h2-h4 sequence should not be treeified as an "h3 > h4" hierarchy with
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* min=3, max=4, but should rather be "[h3, h4]" (since the h2 heading has split
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* the two headings and they are not parent-children)
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*/
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export function useFilteredAndTreeifiedTOC({ toc, minHeadingLevel, maxHeadingLevel, }) {
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return useMemo(() => filterTOC({ toc: treeifyTOC(toc), minHeadingLevel, maxHeadingLevel }), [toc, minHeadingLevel, maxHeadingLevel]);
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}
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//# sourceMappingURL=tocUtils.js.map
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