Start extracting Tree component

packages/ui/src/components/DropMarker.tsx

@@ -0,0 +1,34 @@
+import classNames from 'classnames';
+import type { CSSProperties } from 'react';
+import { memo } from 'react';
+
+interface Props {
+  className?: string;
+  style?: CSSProperties;
+  orientation?: 'horizontal' | 'vertical';
+}
+
+export const DropMarker = memo(
+  function DropMarker({ className, style, orientation = 'horizontal' }: Props) {
+    return (
+      <div
+        style={style}
+        className={classNames(
+          className,
+          'absolute pointer-events-none z-50',
+          orientation === 'horizontal' && 'w-full',
+          orientation === 'vertical' && 'w-0 top-0 bottom-0',
+        )}
+      >
+        <div
+          className={classNames(
+            'absolute bg-primary rounded-full',
+            orientation === 'horizontal' && 'left-2 right-2 -bottom-[0.1rem] h-[0.2rem]',
+            orientation === 'vertical' && '-left-[0.1rem] top-0 bottom-0 w-[0.2rem]',
+          )}
+        />
+      </div>
+    );
+  },
+  () => true,
+);

packages/ui/src/index.ts

@@ -9,3 +9,5 @@ export { useIsFullscreen } from "./hooks/useIsFullscreen";
 export { useDebouncedValue } from "./hooks/useDebouncedValue";
 export { useDebouncedState } from "./hooks/useDebouncedState";
 export { HEADER_SIZE_MD, HEADER_SIZE_LG, WINDOW_CONTROLS_WIDTH } from "./lib/constants";
+export { DropMarker } from "./components/DropMarker";
+export { computeSideForDragMove } from "./lib/dnd";

packages/ui/src/lib/dnd.ts

@@ -0,0 +1,39 @@
+import type { DragMoveEvent } from '@dnd-kit/core';
+
+export function computeSideForDragMove(
+  id: string,
+  e: DragMoveEvent,
+  orientation: 'vertical' | 'horizontal' = 'vertical',
+): 'before' | 'after' | null {
+  if (e.over == null || e.over.id !== id) {
+    return null;
+  }
+  if (e.active.rect.current.initial == null) return null;
+
+  const overRect = e.over.rect;
+
+  if (orientation === 'horizontal') {
+    // For horizontal layouts (tabs side-by-side), use left/right logic
+    const activeLeft =
+      e.active.rect.current.translated?.left ?? e.active.rect.current.initial.left + e.delta.x;
+    const pointerX = activeLeft + e.active.rect.current.initial.width / 2;
+
+    const hoverLeft = overRect.left;
+    const hoverRight = overRect.right;
+    const hoverMiddleX = hoverLeft + (hoverRight - hoverLeft) / 2;
+
+    return pointerX < hoverMiddleX ? 'before' : 'after'; // 'before' = left, 'after' = right
+  } else {
+    // For vertical layouts, use top/bottom logic
+    const activeTop =
+      e.active.rect.current.translated?.top ?? e.active.rect.current.initial.top + e.delta.y;
+    const pointerY = activeTop + e.active.rect.current.initial.height / 2;
+
+    const hoverTop = overRect.top;
+    const hoverBottom = overRect.bottom;
+    const hoverMiddleY = (hoverBottom - hoverTop) / 2;
+    const hoverClientY = pointerY - hoverTop;
+
+    return hoverClientY < hoverMiddleY ? 'before' : 'after';
+  }
+}