1 files changed, 87 insertions, 0 deletions
diff --git a/apps/web/src/lib/timeline/group-move/build-group.ts b/apps/web/src/lib/timeline/group-move/build-group.ts
new file mode 100644
index 00000000..16d720eb
--- /dev/null
+++ b/apps/web/src/lib/timeline/group-move/build-group.ts
@@ -0,0 +1,87 @@
+import type { ElementRef, SceneTracks } from "@/lib/timeline";
+import { findTrackInSceneTracks } from "@/lib/timeline/track-element-update";
+import type { GroupMember, MoveGroup } from "./types";
+import { getTrackPlacementById } from "./track-placement";
+
+export function buildMoveGroup({
+	anchorRef,
+	selectedElements,
+	tracks,
+}: {
+	anchorRef: ElementRef;
+	selectedElements: ElementRef[];
+	tracks: SceneTracks;
+}): MoveGroup | null {
+	const anchorTrack = findTrackInSceneTracks({
+		tracks,
+		trackId: anchorRef.trackId,
+	});
+	const anchorElement = anchorTrack?.elements.find(
+		(element) => element.id === anchorRef.elementId,
+	);
+	const anchorPlacement = getTrackPlacementById({
+		tracks,
+		trackId: anchorRef.trackId,
+	});
+	if (!anchorTrack || !anchorElement || !anchorPlacement) {
+		return null;
+	}
+
+	const seen = new Set<string>();
+	const orderedRefs = [anchorRef, ...selectedElements].filter((elementRef) => {
+		if (seen.has(elementRef.elementId)) {
+			return false;
+		}
+
+		seen.add(elementRef.elementId);
+		return true;
+	});
+
+	const members = orderedRefs.flatMap((elementRef): GroupMember[] => {
+		const track = findTrackInSceneTracks({
+			tracks,
+			trackId: elementRef.trackId,
+		});
+		const element = track?.elements.find(
+			(trackElement) => trackElement.id === elementRef.elementId,
+		);
+		const placement = getTrackPlacementById({
+			tracks,
+			trackId: elementRef.trackId,
+		});
+		if (!track || !element || !placement) {
+			return [];
+		}
+
+		return [
+			{
+				trackId: track.id,
+				elementId: element.id,
+				elementType: element.type,
+				duration: element.duration,
+				timeOffset: element.startTime - anchorElement.startTime,
+				trackSection: placement.section,
+				sectionIndex: placement.sectionIndex,
+				displayIndex: placement.displayIndex,
+			},
+		];
+	});
+
+	if (members.length === 0) {
+		return null;
+	}
+
+	const anchor = members.find(
+		(member) =>
+			member.trackId === anchorRef.trackId &&
+			member.elementId === anchorRef.elementId,
+	);
+	if (!anchor) {
+		return null;
+	}
+
+	return {
+		anchor,
+		members,
+	};
+}