Function useJsonCollapse

packages/emcn/src/components/code/code.tsx:337–397

* Custom hook for managing JSON collapse state and computations. * * @param lines - Array of code lines * @param showCollapseColumn - Whether collapse functionality is enabled * @param language - Programming language for syntax detection * @returns Object containing collapse state and handlers

(
  lines: string[],
  showCollapseColumn: boolean,
  language: string
)

 * @returns Object containing collapse state and handlers
 */
function useJsonCollapse(
  lines: string[],
  showCollapseColumn: boolean,
  language: string
): {
  collapsedLines: Set<number>
  collapsibleLines: Set<number>
  collapsibleRegions: Map<number, CollapsibleRegion>
  collapsedStringLines: Set<number>
  visibleLineIndices: number[]
  toggleCollapse: (lineIndex: number) => void
} {
  const [collapsedLines, setCollapsedLines] = useState<Set<number>>(() => new Set())

  const collapsibleRegions = useMemo(() => {
    if (!showCollapseColumn || language !== 'json') return new Map<number, CollapsibleRegion>()
    return findCollapsibleRegions(lines)
  }, [lines, showCollapseColumn, language])

  const collapsibleLines = useMemo(() => new Set(collapsibleRegions.keys()), [collapsibleRegions])

  // Track which collapsed lines are string type (need truncation, not hiding)
  const collapsedStringLines = useMemo(() => {
    const stringLines = new Set<number>()
    for (const lineIdx of collapsedLines) {
      const region = collapsibleRegions.get(lineIdx)
      if (region?.type === 'string') {
        stringLines.add(lineIdx)
      }
    }
    return stringLines
  }, [collapsedLines, collapsibleRegions])

  const visibleLineIndices = useMemo(() => {
    if (!showCollapseColumn) {
      return Array.from({ length: lines.length }, (_, i) => i)
    }
    return computeVisibleLineIndices(lines.length, collapsedLines, collapsibleRegions)
  }, [lines.length, collapsedLines, collapsibleRegions, showCollapseColumn])

  const toggleCollapse = useCallback((lineIndex: number) => {
    setCollapsedLines((prev) => {
      const next = new Set(prev)
      if (next.has(lineIndex)) {
        next.delete(lineIndex)
      } else {
        next.add(lineIndex)
      }
      return next
    })
  }, [])

  return {
    collapsedLines,
    collapsibleLines,
    collapsibleRegions,
    collapsedStringLines,
    visibleLineIndices,