From 93776944b901b2fad7bef8961771dc674938f6a2 Mon Sep 17 00:00:00 2001
From: hsiegeln <37154749+hsiegeln@users.noreply.github.com>
Date: Thu, 2 Apr 2026 18:35:27 +0200
Subject: [PATCH] refactor: extract keyboard handlers to reduce cognitive
 complexity (S3776)

Extract per-key arrow handler logic into standalone functions outside the
component in SidebarTree.tsx and TreeView.tsx, reducing handleKeyDown
cognitive complexity from 31 to below the 15-unit maximum.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 .../composites/TreeView/TreeView.tsx          | 115 ++++++++----------
 .../layout/Sidebar/SidebarTree.tsx            | 111 ++++++++---------
 2 files changed, 106 insertions(+), 120 deletions(-)

diff --git a/src/design-system/composites/TreeView/TreeView.tsx b/src/design-system/composites/TreeView/TreeView.tsx
index f16d2fa..056dc46 100644
--- a/src/design-system/composites/TreeView/TreeView.tsx
+++ b/src/design-system/composites/TreeView/TreeView.tsx
@@ -31,6 +31,52 @@ function flattenVisibleNodes(
   return result
 }
 
+// ── Keyboard nav helpers ─────────────────────────────────────────────────────
+
+function handleArrowDown(visibleNodes: FlatNode[], currentIndex: number, focusNode: (id: string) => void) {
+  const next = visibleNodes[currentIndex + 1]
+  if (next) focusNode(next.node.id)
+}
+
+function handleArrowUp(visibleNodes: FlatNode[], currentIndex: number, focusNode: (id: string) => void) {
+  const prev = visibleNodes[currentIndex - 1]
+  if (prev) focusNode(prev.node.id)
+}
+
+function handleArrowRight(
+  current: FlatNode | undefined,
+  currentIndex: number,
+  expandedSet: Set<string>,
+  visibleNodes: FlatNode[],
+  handleToggle: (id: string) => void,
+  focusNode: (id: string) => void,
+) {
+  if (!current) return
+  const hasChildren = current.node.children && current.node.children.length > 0
+  if (!hasChildren) return
+  if (!expandedSet.has(current.node.id)) {
+    handleToggle(current.node.id)
+  } else {
+    const next = visibleNodes[currentIndex + 1]
+    if (next) focusNode(next.node.id)
+  }
+}
+
+function handleArrowLeft(
+  current: FlatNode | undefined,
+  expandedSet: Set<string>,
+  handleToggle: (id: string) => void,
+  focusNode: (id: string) => void,
+) {
+  if (!current) return
+  const hasChildren = current.node.children && current.node.children.length > 0
+  if (hasChildren && expandedSet.has(current.node.id)) {
+    handleToggle(current.node.id)
+  } else if (current.parentId !== null) {
+    focusNode(current.parentId)
+  }
+}
+
 interface TreeViewProps {
   nodes: TreeNode[]
   onSelect?: (id: string) => void
@@ -105,68 +151,13 @@ export function TreeView({
       const current = visibleNodes[currentIndex]
 
       switch (e.key) {
-        case 'ArrowDown': {
-          e.preventDefault()
-          const next = visibleNodes[currentIndex + 1]
-          if (next) focusNode(next.node.id)
-          break
-        }
-        case 'ArrowUp': {
-          e.preventDefault()
-          const prev = visibleNodes[currentIndex - 1]
-          if (prev) focusNode(prev.node.id)
-          break
-        }
-        case 'ArrowRight': {
-          e.preventDefault()
-          if (!current) break
-          const hasChildren = current.node.children && current.node.children.length > 0
-          if (hasChildren) {
-            if (!expandedSet.has(current.node.id)) {
-              // Expand it
-              handleToggle(current.node.id)
-            } else {
-              // Move to first child (it will be the next visible node)
-              const next = visibleNodes[currentIndex + 1]
-              if (next) focusNode(next.node.id)
-            }
-          }
-          break
-        }
-        case 'ArrowLeft': {
-          e.preventDefault()
-          if (!current) break
-          const hasChildren = current.node.children && current.node.children.length > 0
-          if (hasChildren && expandedSet.has(current.node.id)) {
-            // Collapse
-            handleToggle(current.node.id)
-          } else if (current.parentId !== null) {
-            // Move to parent
-            focusNode(current.parentId)
-          }
-          break
-        }
-        case 'Enter': {
-          e.preventDefault()
-          if (current) {
-            onSelect?.(current.node.id)
-          }
-          break
-        }
-        case 'Home': {
-          e.preventDefault()
-          if (visibleNodes.length > 0) {
-            focusNode(visibleNodes[0].node.id)
-          }
-          break
-        }
-        case 'End': {
-          e.preventDefault()
-          if (visibleNodes.length > 0) {
-            focusNode(visibleNodes[visibleNodes.length - 1].node.id)
-          }
-          break
-        }
+        case 'ArrowDown': { e.preventDefault(); handleArrowDown(visibleNodes, currentIndex, focusNode); break }
+        case 'ArrowUp': { e.preventDefault(); handleArrowUp(visibleNodes, currentIndex, focusNode); break }
+        case 'ArrowRight': { e.preventDefault(); handleArrowRight(current, currentIndex, expandedSet, visibleNodes, handleToggle, focusNode); break }
+        case 'ArrowLeft': { e.preventDefault(); handleArrowLeft(current, expandedSet, handleToggle, focusNode); break }
+        case 'Enter': { e.preventDefault(); if (current) onSelect?.(current.node.id); break }
+        case 'Home': { e.preventDefault(); if (visibleNodes.length > 0) focusNode(visibleNodes[0].node.id); break }
+        case 'End': { e.preventDefault(); if (visibleNodes.length > 0) focusNode(visibleNodes[visibleNodes.length - 1].node.id); break }
       }
     },
     // eslint-disable-next-line react-hooks/exhaustive-deps
diff --git a/src/design-system/layout/Sidebar/SidebarTree.tsx b/src/design-system/layout/Sidebar/SidebarTree.tsx
index fce531a..4fa9770 100644
--- a/src/design-system/layout/Sidebar/SidebarTree.tsx
+++ b/src/design-system/layout/Sidebar/SidebarTree.tsx
@@ -124,6 +124,52 @@ function filterNodes(
   return { filtered: walk(nodes), matchedParentIds }
 }
 
+// ── Keyboard nav helpers ─────────────────────────────────────────────────────
+
+function handleArrowDown(visibleNodes: FlatNode[], currentIndex: number, focusNode: (id: string) => void) {
+  const next = visibleNodes[currentIndex + 1]
+  if (next) focusNode(next.node.id)
+}
+
+function handleArrowUp(visibleNodes: FlatNode[], currentIndex: number, focusNode: (id: string) => void) {
+  const prev = visibleNodes[currentIndex - 1]
+  if (prev) focusNode(prev.node.id)
+}
+
+function handleArrowRight(
+  current: FlatNode | undefined,
+  currentIndex: number,
+  expandedSet: Set<string>,
+  visibleNodes: FlatNode[],
+  handleToggle: (id: string) => void,
+  focusNode: (id: string) => void,
+) {
+  if (!current) return
+  const hasChildren = current.node.children && current.node.children.length > 0
+  if (!hasChildren) return
+  if (!expandedSet.has(current.node.id)) {
+    handleToggle(current.node.id)
+  } else {
+    const next = visibleNodes[currentIndex + 1]
+    if (next) focusNode(next.node.id)
+  }
+}
+
+function handleArrowLeft(
+  current: FlatNode | undefined,
+  expandedSet: Set<string>,
+  handleToggle: (id: string) => void,
+  focusNode: (id: string) => void,
+) {
+  if (!current) return
+  const hasChildren = current.node.children && current.node.children.length > 0
+  if (hasChildren && expandedSet.has(current.node.id)) {
+    handleToggle(current.node.id)
+  } else if (current.parentId !== null) {
+    focusNode(current.parentId)
+  }
+}
+
 // ── SidebarTree ──────────────────────────────────────────────────────────────
 
 export function SidebarTree({
@@ -222,64 +268,13 @@ export function SidebarTree({
       const current = visibleNodes[currentIndex]
 
       switch (e.key) {
-        case 'ArrowDown': {
-          e.preventDefault()
-          const next = visibleNodes[currentIndex + 1]
-          if (next) focusNode(next.node.id)
-          break
-        }
-        case 'ArrowUp': {
-          e.preventDefault()
-          const prev = visibleNodes[currentIndex - 1]
-          if (prev) focusNode(prev.node.id)
-          break
-        }
-        case 'ArrowRight': {
-          e.preventDefault()
-          if (!current) break
-          const hasChildren = current.node.children && current.node.children.length > 0
-          if (hasChildren) {
-            if (!expandedSet.has(current.node.id)) {
-              handleToggle(current.node.id)
-            } else {
-              const next = visibleNodes[currentIndex + 1]
-              if (next) focusNode(next.node.id)
-            }
-          }
-          break
-        }
-        case 'ArrowLeft': {
-          e.preventDefault()
-          if (!current) break
-          const hasChildren = current.node.children && current.node.children.length > 0
-          if (hasChildren && expandedSet.has(current.node.id)) {
-            handleToggle(current.node.id)
-          } else if (current.parentId !== null) {
-            focusNode(current.parentId)
-          }
-          break
-        }
-        case 'Enter': {
-          e.preventDefault()
-          if (current?.node.path) {
-            navigate(current.node.path)
-          }
-          break
-        }
-        case 'Home': {
-          e.preventDefault()
-          if (visibleNodes.length > 0) {
-            focusNode(visibleNodes[0].node.id)
-          }
-          break
-        }
-        case 'End': {
-          e.preventDefault()
-          if (visibleNodes.length > 0) {
-            focusNode(visibleNodes[visibleNodes.length - 1].node.id)
-          }
-          break
-        }
+        case 'ArrowDown': { e.preventDefault(); handleArrowDown(visibleNodes, currentIndex, focusNode); break }
+        case 'ArrowUp': { e.preventDefault(); handleArrowUp(visibleNodes, currentIndex, focusNode); break }
+        case 'ArrowRight': { e.preventDefault(); handleArrowRight(current, currentIndex, expandedSet, visibleNodes, handleToggle, focusNode); break }
+        case 'ArrowLeft': { e.preventDefault(); handleArrowLeft(current, expandedSet, handleToggle, focusNode); break }
+        case 'Enter': { e.preventDefault(); if (current?.node.path) navigate(current.node.path); break }
+        case 'Home': { e.preventDefault(); if (visibleNodes.length > 0) focusNode(visibleNodes[0].node.id); break }
+        case 'End': { e.preventDefault(); if (visibleNodes.length > 0) focusNode(visibleNodes[visibleNodes.length - 1].node.id); break }
       }
     },
     // eslint-disable-next-line react-hooks/exhaustive-deps