frontend: refactor of the new build viewer

extracting the logic into composables

frontend/utils/buildHelpers.ts

@@ -0,0 +1,69 @@
+import { isEmpty } from './helpers'
+
+/**
+ * Trims the build tree to only show the first path
+ * Removes alternate build paths to keep the UI clean
+ */
+export function trimBuilds(builds: Builds): void {
+  if (!builds?.tree?.children) return
+
+  // Keep only the first child (primary build path)
+  builds.tree.children.splice(1, builds.tree.children.length - 1)
+
+  // Also trim grandchildren to first path only
+  if (builds.tree.children[0]?.children) {
+    builds.tree.children[0].children.splice(1, builds.tree.children[0].children.length - 1)
+  }
+}
+
+/**
+ * Removes late game items that appear in the core build tree
+ * Prevents duplicate items from being shown
+ */
+export function trimLateGameItems(builds: Builds): void {
+  if (!builds?.tree || isEmpty(builds.lateGame)) return
+
+  const coreItemIds = new Set<number>()
+
+  // Collect all item IDs from the tree
+  function collectItemIds(tree: ItemTree): void {
+    if (tree.data !== undefined) {
+      coreItemIds.add(tree.data)
+    }
+    for (const child of tree.children || []) {
+      collectItemIds(child)
+    }
+  }
+
+  collectItemIds(builds.tree)
+
+  // Remove late game items that appear in core
+  builds.lateGame = builds.lateGame.filter((item) => !coreItemIds.has(item.data))
+}
+
+/**
+ * Gets the index of the build with the highest pickrate
+ */
+export function getHighestPickrateBuildIndex(
+  runes: Array<{ pickrate: number }>
+): number {
+  if (runes.length === 0) return 0
+
+  return runes.reduce((maxIdx, rune, idx, arr) =>
+    rune.pickrate > arr[maxIdx].pickrate ? idx : maxIdx,
+    0
+  )
+}
+
+/**
+ * Gets the first core item for each build variant
+ */
+export function getFirstCoreItems(
+  runes: unknown[],
+  builds: Builds
+): number[] {
+  return runes.map(() => {
+    const tree = builds?.tree
+    return tree?.children?.[0]?.data ?? tree?.data ?? 0
+  })
+}