Function rewritePathsInTree

packages/app-core/src/lib/pane-layout.ts:227–277

(
  root: PaneLayout,
  fn: (path: string) => string | null
)

 * leaf (so the UI always has a pane to render).
 */
export function rewritePathsInTree(
  root: PaneLayout,
  fn: (path: string) => string | null
): PaneLayout {
  const result = mapLeaves(root, (leaf) => {
    const nextTabs: string[] = []
    const seen = new Set<string>()
    for (const tab of leaf.tabs) {
      const mapped = fn(tab)
      if (mapped == null) continue
      if (seen.has(mapped)) continue
      seen.add(mapped)
      nextTabs.push(mapped)
    }
    if (nextTabs.length === 0) return null
    const nextTabSet = new Set(nextTabs)
    const nextPinned: string[] = []
    const pinnedSeen = new Set<string>()
    for (const p of leaf.pinnedTabs) {
      const mapped = fn(p)
      if (mapped == null) continue
      if (!nextTabSet.has(mapped)) continue
      if (pinnedSeen.has(mapped)) continue
      pinnedSeen.add(mapped)
      nextPinned.push(mapped)
    }
    let nextActive: string | null = null
    if (leaf.activeTab) {
      const mappedActive = fn(leaf.activeTab)
      if (mappedActive && nextTabs.includes(mappedActive)) {
        nextActive = mappedActive
      }
    }
    if (!nextActive) nextActive = nextTabs[0]
    let nextPreview: string | null = null
    if (leaf.previewTab) {
      const mappedPreview = fn(leaf.previewTab)
      if (mappedPreview && nextTabs.includes(mappedPreview)) {
        nextPreview = mappedPreview
      }
    }
    return enforcePinnedPrefix({
      ...leaf,
      tabs: nextTabs,
      pinnedTabs: nextPinned,
      activeTab: nextActive,
      previewTab: nextPreview
    })
  })
  return result ?? makeLeaf()
}

/**
 * Classify where within a pane's bounding rect the cursor falls when