refactor: asset-store (#18938)

* refactor: asset-store

* Potential fix for code scanning alert no. 152: Prototype-polluting function

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

---------

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

web/src/lib/managers/timeline-manager/intersecting-asset.svelte.ts

@@ -0,0 +1,45 @@
+import type { CommonPosition } from '$lib/utils/layout-utils';
+import { TUNABLES } from '$lib/utils/tunables';
+import type { AssetDateGroup } from './asset-date-group.svelte';
+import type { TimelineAsset } from './types';
+
+const {
+  TIMELINE: { INTERSECTION_EXPAND_TOP, INTERSECTION_EXPAND_BOTTOM },
+} = TUNABLES;
+
+export class IntersectingAsset {
+  readonly #group: AssetDateGroup;
+
+  intersecting = $derived.by(() => {
+    if (!this.position) {
+      return false;
+    }
+
+    const store = this.#group.bucket.store;
+
+    const scrollCompensation = store.scrollCompensation;
+    const scrollCompensationHeightDelta = scrollCompensation?.heightDelta ?? 0;
+
+    const topWindow =
+      store.visibleWindow.top - store.headerHeight - INTERSECTION_EXPAND_TOP + scrollCompensationHeightDelta;
+    const bottomWindow =
+      store.visibleWindow.bottom + store.headerHeight + INTERSECTION_EXPAND_BOTTOM + scrollCompensationHeightDelta;
+    const positionTop = this.#group.absoluteDateGroupTop + this.position.top;
+    const positionBottom = positionTop + this.position.height;
+
+    const intersecting =
+      (positionTop >= topWindow && positionTop < bottomWindow) ||
+      (positionBottom >= topWindow && positionBottom < bottomWindow) ||
+      (positionTop < topWindow && positionBottom >= bottomWindow);
+    return intersecting;
+  });
+
+  position: CommonPosition | undefined = $state();
+  asset: TimelineAsset = <TimelineAsset>$state();
+  id: string | undefined = $derived(this.asset?.id);
+
+  constructor(group: AssetDateGroup, asset: TimelineAsset) {
+    this.#group = group;
+    this.asset = asset;
+  }
+}