1 files changed, 85 insertions, 0 deletions
diff --git a/apps/web/src/timeline/group-move/snap.ts b/apps/web/src/timeline/group-move/snap.ts
new file mode 100644
index 00000000..32c0a2f1
--- /dev/null
+++ b/apps/web/src/timeline/group-move/snap.ts
@@ -0,0 +1,85 @@
+import type { SceneTracks } from "@/timeline";
+import {
+	buildTimelineSnapPoints,
+	getTimelineSnapThresholdInTicks,
+	resolveTimelineSnap,
+	type SnapPoint,
+} from "@/timeline/snapping";
+import { getElementEdgeSnapPoints } from "@/timeline/element-snap-source";
+import { getPlayheadSnapPoints } from "@/timeline/playhead-snap-source";
+import { getAnimationKeyframeSnapPointsForTimeline } from "@/animation/timeline-snap-points";
+import type { MoveGroup } from "./types";
+
+export function snapGroupEdges({
+	group,
+	anchorStartTime,
+	tracks,
+	playheadTime,
+	zoomLevel,
+}: {
+	group: MoveGroup;
+	anchorStartTime: number;
+	tracks: SceneTracks;
+	playheadTime: number;
+	zoomLevel: number;
+}): {
+	snappedAnchorStartTime: number;
+	snapPoint: SnapPoint | null;
+} {
+	const excludeElementIds = new Set(
+		group.members.map((member) => member.elementId),
+	);
+	const snapPoints = buildTimelineSnapPoints({
+		sources: [
+			() => getElementEdgeSnapPoints({ tracks, excludeElementIds }),
+			() => getPlayheadSnapPoints({ playheadTime }),
+			() =>
+				getAnimationKeyframeSnapPointsForTimeline({
+					tracks,
+					excludeElementIds,
+				}),
+		],
+	});
+	const maxSnapDistance = getTimelineSnapThresholdInTicks({ zoomLevel });
+
+	let closestSnapDistance = Infinity;
+	let snappedAnchorStartTime = anchorStartTime;
+	let snapPoint: SnapPoint | null = null;
+
+	for (const member of group.members) {
+		const memberStartTime = anchorStartTime + member.timeOffset;
+		const memberStartSnap = resolveTimelineSnap({
+			targetTime: memberStartTime,
+			snapPoints,
+			maxSnapDistance,
+		});
+		if (
+			memberStartSnap.snapPoint &&
+			memberStartSnap.snapDistance < closestSnapDistance
+		) {
+			closestSnapDistance = memberStartSnap.snapDistance;
+			snappedAnchorStartTime = memberStartSnap.snappedTime - member.timeOffset;
+			snapPoint = memberStartSnap.snapPoint;
+		}
+
+		const memberEndSnap = resolveTimelineSnap({
+			targetTime: memberStartTime + member.duration,
+			snapPoints,
+			maxSnapDistance,
+		});
+		if (
+			memberEndSnap.snapPoint &&
+			memberEndSnap.snapDistance < closestSnapDistance
+		) {
+			closestSnapDistance = memberEndSnap.snapDistance;
+			snappedAnchorStartTime =
+				memberEndSnap.snappedTime - member.duration - member.timeOffset;
+			snapPoint = memberEndSnap.snapPoint;
+		}
+	}
+
+	return {
+		snappedAnchorStartTime,
+		snapPoint,
+	};
+}