2 files changed, 229 insertions, 0 deletions
diff --git a/apps/web/src/hooks/timeline/use-scroll-position.ts b/apps/web/src/hooks/timeline/use-scroll-position.ts
new file mode 100644
index 00000000..ad2c6374
--- /dev/null
+++ b/apps/web/src/hooks/timeline/use-scroll-position.ts
@@ -0,0 +1,52 @@
+import { useEffect, useState, useRef } from "react";
+
+interface UseScrollPositionReturn {
+	scrollLeft: number;
+	viewportWidth: number;
+}
+
+export function useScrollPosition({
+	scrollRef,
+}: {
+	scrollRef: React.RefObject<HTMLElement | null>;
+}): UseScrollPositionReturn {
+	const [scrollLeft, setScrollLeft] = useState(0);
+	const [viewportWidth, setViewportWidth] = useState(0);
+	const rafIdRef = useRef<number | null>(null);
+
+	useEffect(() => {
+		const scrollElement = scrollRef.current;
+		if (!scrollElement) return;
+
+		const updatePosition = () => {
+			if (rafIdRef.current !== null) {
+				cancelAnimationFrame(rafIdRef.current);
+			}
+
+			rafIdRef.current = requestAnimationFrame(() => {
+				setScrollLeft(scrollElement.scrollLeft);
+				setViewportWidth(scrollElement.clientWidth);
+				rafIdRef.current = null;
+			});
+		};
+
+		const resizeObserver = new ResizeObserver(() => {
+			updatePosition();
+		});
+
+		updatePosition();
+
+		scrollElement.addEventListener("scroll", updatePosition, { passive: true });
+		resizeObserver.observe(scrollElement);
+
+		return () => {
+			scrollElement.removeEventListener("scroll", updatePosition);
+			resizeObserver.disconnect();
+			if (rafIdRef.current !== null) {
+				cancelAnimationFrame(rafIdRef.current);
+			}
+		};
+	}, [scrollRef]);
+
+	return { scrollLeft, viewportWidth };
+}
diff --git a/apps/web/src/hooks/use-preview-interaction.ts b/apps/web/src/hooks/use-preview-interaction.ts
new file mode 100644
index 00000000..6aeb0c9b
--- /dev/null
+++ b/apps/web/src/hooks/use-preview-interaction.ts
@@ -0,0 +1,177 @@
+import { useCallback, useRef, useState } from "react";
+import { useEditor } from "@/hooks/use-editor";
+import { useSyncExternalStore } from "react";
+import type { Transform, TimelineTrack } from "@/types/timeline";
+
+interface DragState {
+	startX: number;
+	startY: number;
+	tracksSnapshot: TimelineTrack[];
+	elements: Array<{
+		trackId: string;
+		elementId: string;
+		initialTransform: Transform;
+	}>;
+}
+
+export function usePreviewInteraction({
+	canvasRef,
+}: {
+	canvasRef: React.RefObject<HTMLCanvasElement | null>;
+}) {
+	const editor = useEditor();
+	const [isDragging, setIsDragging] = useState(false);
+	const dragStateRef = useRef<DragState | null>(null);
+
+	const selectedElements = useSyncExternalStore(
+		(listener) => editor.selection.subscribe(listener),
+		() => editor.selection.getSelectedElements(),
+	);
+
+	const getCanvasCoordinates = useCallback(
+		({ clientX, clientY }: { clientX: number; clientY: number }) => {
+			if (!canvasRef.current) return { x: 0, y: 0 };
+
+			const rect = canvasRef.current.getBoundingClientRect();
+			const logicalWidth = canvasRef.current.width;
+			const logicalHeight = canvasRef.current.height;
+			const scaleX = logicalWidth / rect.width;
+			const scaleY = logicalHeight / rect.height;
+
+			const canvasX = (clientX - rect.left) * scaleX;
+			const canvasY = (clientY - rect.top) * scaleY;
+
+			return { x: canvasX, y: canvasY };
+		},
+		[canvasRef],
+	);
+
+	const handlePointerDown = useCallback(
+		(event: React.PointerEvent) => {
+			if (selectedElements.length === 0) return;
+
+			const elementsWithTracks = editor.timeline.getElementsWithTracks({
+				elements: selectedElements,
+			});
+
+			const draggableElements = elementsWithTracks.filter(
+				({ element }) =>
+					element.type === "video" ||
+					element.type === "image" ||
+					element.type === "text" ||
+					element.type === "sticker",
+			);
+
+			if (draggableElements.length === 0) return;
+
+			const startPos = getCanvasCoordinates({
+				clientX: event.clientX,
+				clientY: event.clientY,
+			});
+
+			dragStateRef.current = {
+				startX: startPos.x,
+				startY: startPos.y,
+				tracksSnapshot: editor.timeline.getTracks(),
+				elements: draggableElements.map(({ track, element }) => ({
+					trackId: track.id,
+					elementId: element.id,
+					initialTransform: (element as { transform: Transform }).transform,
+				})),
+			};
+
+			setIsDragging(true);
+			event.currentTarget.setPointerCapture(event.pointerId);
+		},
+		[selectedElements, editor, getCanvasCoordinates],
+	);
+
+	const handlePointerMove = useCallback(
+		(event: React.PointerEvent) => {
+			if (!dragStateRef.current || !isDragging) return;
+
+			const currentPos = getCanvasCoordinates({
+				clientX: event.clientX,
+				clientY: event.clientY,
+			});
+
+			const deltaX = currentPos.x - dragStateRef.current.startX;
+			const deltaY = currentPos.y - dragStateRef.current.startY;
+
+			for (const { trackId, elementId, initialTransform } of dragStateRef
+				.current.elements) {
+				const newPosition = {
+					x: initialTransform.position.x + deltaX,
+					y: initialTransform.position.y + deltaY,
+				};
+
+				editor.timeline.updateElements({
+					updates: [
+						{
+							trackId,
+							elementId,
+							updates: {
+								transform: {
+									...initialTransform,
+									position: newPosition,
+								},
+							},
+						},
+					],
+					pushHistory: false,
+				});
+			}
+		},
+		[isDragging, getCanvasCoordinates, editor],
+	);
+
+	const handlePointerUp = useCallback(
+		(event: React.PointerEvent) => {
+			if (!dragStateRef.current || !isDragging) return;
+
+			const currentPos = getCanvasCoordinates({
+				clientX: event.clientX,
+				clientY: event.clientY,
+			});
+
+			const deltaX = currentPos.x - dragStateRef.current.startX;
+			const deltaY = currentPos.y - dragStateRef.current.startY;
+
+			// revert to pre-drag state so the command captures the correct undo snapshot
+			editor.timeline.updateTracks(dragStateRef.current.tracksSnapshot);
+
+			const updates = dragStateRef.current.elements.map(
+				({ trackId, elementId, initialTransform }) => {
+					const newPosition = {
+						x: initialTransform.position.x + deltaX,
+						y: initialTransform.position.y + deltaY,
+					};
+
+					return {
+						trackId,
+						elementId,
+						updates: {
+							transform: {
+								...initialTransform,
+								position: newPosition,
+							},
+						},
+					};
+				},
+			);
+
+			editor.timeline.updateElements({ updates });
+
+			dragStateRef.current = null;
+			setIsDragging(false);
+			event.currentTarget.releasePointerCapture(event.pointerId);
+		},
+		[isDragging, getCanvasCoordinates, editor],
+	);
+
+	return {
+		onPointerDown: handlePointerDown,
+		onPointerMove: handlePointerMove,
+		onPointerUp: handlePointerUp,
+	};
+}