Archipelago — open-source initial import

aiui/packages/app/src/composables/useScrollMemory.ts

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+import { onMounted, onUnmounted, type Ref } from 'vue'
+
+const scrollPositions = new Map<string, number>()
+
+export function useScrollMemory(key: string, elementRef: Ref<HTMLElement | null>) {
+  function savePosition() {
+    const el = elementRef.value
+    if (el) {
+      scrollPositions.set(key, el.scrollTop)
+    }
+  }
+
+  function restorePosition() {
+    const el = elementRef.value
+    if (!el) return
+    const saved = scrollPositions.get(key)
+    if (saved !== undefined) {
+      requestAnimationFrame(() => {
+        el.scrollTop = saved
+      })
+    }
+  }
+
+  onMounted(() => {
+    restorePosition()
+    const el = elementRef.value
+    if (el) {
+      el.addEventListener('scroll', savePosition, { passive: true })
+    }
+  })
+
+  onUnmounted(() => {
+    savePosition()
+    const el = elementRef.value
+    if (el) {
+      el.removeEventListener('scroll', savePosition)
+    }
+  })
+
+  return { savePosition, restorePosition }
+}