1 files changed, 135 insertions, 0 deletions
diff --git a/apps/web/src/timeline/components/selection-hit-testing.ts b/apps/web/src/timeline/components/selection-hit-testing.ts
new file mode 100644
index 00000000..da5617c6
--- /dev/null
+++ b/apps/web/src/timeline/components/selection-hit-testing.ts
@@ -0,0 +1,135 @@
+import type { TimelineTrack } from "@/timeline";
+import { timelineTimeToPixels } from "@/timeline/pixel-utils";
+import {
+	TIMELINE_CONTENT_TOP_PADDING_PX,
+} from "./layout";
+import { getCumulativeHeightBefore, getTrackHeight } from "./track-layout";
+
+type TimelineElementRef = { trackId: string; elementId: string };
+
+interface SelectionRectangle {
+	left: number;
+	top: number;
+	right: number;
+	bottom: number;
+}
+
+function getNormalizedRectangle({
+	startPos,
+	endPos,
+}: {
+	startPos: { x: number; y: number };
+	endPos: { x: number; y: number };
+}): SelectionRectangle {
+	return {
+		left: Math.min(startPos.x, endPos.x),
+		top: Math.min(startPos.y, endPos.y),
+		right: Math.max(startPos.x, endPos.x),
+		bottom: Math.max(startPos.y, endPos.y),
+	};
+}
+
+function getSelectionRectangleInContent({
+	container,
+	scrollContainer,
+	startPos,
+	endPos,
+}: {
+	container: HTMLElement;
+	scrollContainer: HTMLDivElement | null;
+	startPos: { x: number; y: number };
+	endPos: { x: number; y: number };
+}): SelectionRectangle {
+	const containerRect = container.getBoundingClientRect();
+	const scrollRect = scrollContainer?.getBoundingClientRect() ?? containerRect;
+	const scrollLeft = scrollContainer?.scrollLeft ?? 0;
+	const scrollTop = scrollContainer?.scrollTop ?? 0;
+
+	const adjustedStart = {
+		x: startPos.x - containerRect.left + scrollLeft,
+		y: startPos.y - scrollRect.top + scrollTop,
+	};
+	const adjustedEnd = {
+		x: endPos.x - containerRect.left + scrollLeft,
+		y: endPos.y - scrollRect.top + scrollTop,
+	};
+
+	return getNormalizedRectangle({
+		startPos: adjustedStart,
+		endPos: adjustedEnd,
+	});
+}
+
+function isRectangleIntersecting({
+	elementRectangle,
+	selectionRectangle,
+}: {
+	elementRectangle: SelectionRectangle;
+	selectionRectangle: SelectionRectangle;
+}): boolean {
+	return !(
+		elementRectangle.right < selectionRectangle.left ||
+		elementRectangle.left > selectionRectangle.right ||
+		elementRectangle.bottom < selectionRectangle.top ||
+		elementRectangle.top > selectionRectangle.bottom
+	);
+}
+
+export function resolveTimelineElementIntersections({
+	container,
+	scrollContainer,
+	tracks,
+	zoomLevel,
+	startPos,
+	currentPos,
+}: {
+	container: HTMLElement;
+	scrollContainer: HTMLDivElement | null;
+	tracks: TimelineTrack[];
+	zoomLevel: number;
+	startPos: { x: number; y: number };
+	currentPos: { x: number; y: number };
+}): TimelineElementRef[] {
+	const selectionRectangle = getSelectionRectangleInContent({
+		container,
+		scrollContainer,
+		startPos,
+		endPos: currentPos,
+	});
+	const selectedElements: TimelineElementRef[] = [];
+
+	for (const [trackIndex, track] of tracks.entries()) {
+		const trackTop = getCumulativeHeightBefore({
+			tracks,
+			trackIndex,
+		});
+		const trackHeight = getTrackHeight({ type: track.type });
+		const elementTop = TIMELINE_CONTENT_TOP_PADDING_PX + trackTop;
+		const elementBottom = elementTop + trackHeight;
+
+		for (const element of track.elements) {
+			const elementLeft = timelineTimeToPixels({ time: element.startTime, zoomLevel });
+			const elementRight = timelineTimeToPixels({ time: element.startTime + element.duration, zoomLevel });
+			const elementRectangle = {
+				left: elementLeft,
+				top: elementTop,
+				right: elementRight,
+				bottom: elementBottom,
+			};
+
+			if (
+				isRectangleIntersecting({
+					elementRectangle,
+					selectionRectangle,
+				})
+			) {
+				selectedElements.push({
+					trackId: track.id,
+					elementId: element.id,
+				});
+			}
+		}
+	}
+
+	return selectedElements;
+}