docs: add nested list stories

apps/stories/stories/react/Sortable/NestedLists/NestedLists.stories.tsx

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+import type {Meta, StoryObj} from '@storybook/react';
+
+import {NestedLists} from './NestedLists.tsx';
+
+const meta: Meta<typeof NestedLists> = {
+  title: 'React/Sortable/Nested lists',
+  component: NestedLists,
+};
+
+export default meta;
+type Story = StoryObj<typeof NestedLists>;
+
+export const Example: Story = {
+  name: 'Example',
+  args: {
+    debug: false,
+  },
+};
+
+export const Debug: Story = {
+  name: 'Debug',
+  args: {
+    debug: true,
+  },
+};

apps/stories/stories/react/Sortable/NestedLists/NestedLists.tsx

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+import React, {useRef, useState} from 'react';
+import type {PropsWithChildren} from 'react';
+import {CollisionPriority} from '@dnd-kit/abstract';
+import {DragDropProvider, useDroppable} from '@dnd-kit/react';
+import {useSortable} from '@dnd-kit/react/sortable';
+import {defaultPreset} from '@dnd-kit/dom';
+import {Debug} from '@dnd-kit/dom/plugins/debug';
+
+import {Actions, Container, Item, Handle} from '../../components/index.ts';
+import {cloneDeep} from '../../../utilities/cloneDeep.ts';
+import {deepMove} from './deepMove.ts';
+
+interface Props {
+  debug?: boolean;
+}
+
+interface Card {
+  id: string;
+  type: 'card';
+}
+
+export interface Group {
+  id: string;
+  type: 'group';
+  items: Node[];
+}
+
+export type Root = {
+  id: 'root';
+  type: 'root';
+  items: Node[];
+};
+
+export type Node = Root | Card | Group;
+
+interface SortableCardProps {
+  id: string;
+  group: string;
+  index: number;
+  style?: React.CSSProperties;
+}
+
+const COLORS: Record<string, string> = {
+  A: '#7193f1',
+  B: '#FF851B',
+  A1: '#2ECC40',
+};
+
+const DeepRender = ({content, group}: {content: Node[]; group: string}) => {
+  return content.map((item, index) => {
+    if (item.type === 'card') {
+      return (
+        <SortableCard key={item.id} id={item.id} group={group} index={index} />
+      );
+    }
+
+    return (
+      <SortableGroup
+        accentColor={COLORS[group]}
+        key={item.id}
+        id={item.id}
+        index={index}
+        group={group}
+      >
+        <DeepRender content={item.items} group={item.id} />
+      </SortableGroup>
+    );
+  });
+};
+
+export function NestedLists({debug}: Props) {
+  const [data, setData] = useState<Root>({
+    id: 'root',
+    type: 'root',
+    items: [
+      {
+        type: 'group',
+        id: 'A',
+        items: [
+          {
+            type: 'group',
+            id: 'A1',
+            items: [
+              {type: 'card', id: 'A1.1'},
+              {type: 'card', id: 'A1.2'},
+              {type: 'card', id: 'A1.3'},
+            ],
+          },
+          {type: 'card', id: 'A2'},
+          {type: 'card', id: 'A3'},
+        ],
+      },
+      {
+        type: 'group',
+        id: 'B',
+        items: [
+          {type: 'card', id: 'B1'},
+          {type: 'card', id: 'B2'},
+          {type: 'card', id: 'B3'},
+        ],
+      },
+    ],
+  });
+
+  const snapshot = useRef(cloneDeep(data));
+
+  return (
+    <DragDropProvider
+      plugins={debug ? [...defaultPreset.plugins, Debug] : undefined}
+      onDragStart={() => {
+        snapshot.current = cloneDeep(data);
+      }}
+      onDragOver={(event) => {
+        event.preventDefault();
+
+        setData((data) => {
+          return deepMove(data, event.operation) as Root;
+        });
+      }}
+      onDragEnd={(event) => {
+        if (event.canceled) {
+          setData(snapshot.current);
+        }
+      }}
+    >
+      <Root>
+        <DeepRender content={data.items} group={'root'} />
+      </Root>
+    </DragDropProvider>
+  );
+}
+
+function SortableCard({
+  id,
+  group,
+  index,
+  style,
+}: PropsWithChildren<SortableCardProps>) {
+  const {ref, isDragSource} = useSortable({
+    id,
+    group,
+    accept: ['card', 'group'],
+    type: 'card',
+    feedback: 'clone',
+    index,
+    data: {group},
+  });
+
+  return (
+    <Item
+      ref={ref}
+      accentColor={COLORS[group]}
+      shadow={isDragSource}
+      style={style}
+    >
+      {id}
+    </Item>
+  );
+}
+
+interface SortableGroupProps {
+  accentColor?: string;
+  id: string;
+  index: number;
+  group: string;
+  scrollable?: boolean;
+  style?: React.CSSProperties;
+}
+
+function SortableGroup({
+  accentColor,
+  children,
+  id,
+  index,
+  group,
+  style,
+}: PropsWithChildren<SortableGroupProps>) {
+  const {handleRef, ref} = useSortable({
+    id,
+    accept: ['group', 'card'],
+    collisionPriority: CollisionPriority.Low,
+    type: 'group',
+    group,
+    feedback: 'clone',
+    index,
+    data: {group},
+  });
+
+  return (
+    <Container
+      accentColor={accentColor}
+      ref={ref}
+      label={`${id}`}
+      actions={
+        <Actions>
+          <Handle ref={handleRef} />
+        </Actions>
+      }
+      style={style}
+    >
+      {children}
+    </Container>
+  );
+}
+
+function Root({children}: PropsWithChildren<{}>) {
+  const {ref} = useDroppable({
+    id: 'root',
+    collisionPriority: CollisionPriority.Low,
+    type: 'root',
+    disabled: true,
+  });
+
+  return (
+    <div
+      style={{
+        display: 'flex',
+        gap: 20,
+      }}
+      ref={ref}
+    >
+      {children}
+    </div>
+  );
+}

apps/stories/stories/react/Sortable/NestedLists/deepMove.ts

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+import {DragOperation} from '@dnd-kit/abstract';
+import {cloneDeep} from '../../../utilities/cloneDeep.ts';
+import {Group, Node, Root} from './NestedLists.tsx';
+
+export function deepMove<T extends Root = Root>(
+  root: T,
+  operation: DragOperation
+): T {
+  const {source, target} = operation;
+  if (!source || !target) return root;
+
+  const sourceGroupId = source.data.group;
+  const targetGroupId = target.data.group;
+
+  console.debug(
+    `Moving ${source.id} from ${sourceGroupId} to ${target.id} in ${targetGroupId}`
+  );
+
+  if (sourceGroupId === targetGroupId && source.id === target.id) {
+    return root;
+  }
+
+  if (source.id === targetGroupId) {
+    return root;
+  }
+
+  const clone = cloneDeep(root);
+
+  // Helper function to find a group by its ID
+  function findGroup(node: Node, groupId: string): Root | Group | null {
+    if (node.type === 'group' || node.type === 'root') {
+      if (node.id === groupId) {
+        return node;
+      }
+
+      for (const child of node.items) {
+        const result = findGroup(child, groupId);
+        if (result) {
+          return result;
+        }
+      }
+    }
+
+    return null;
+  }
+
+  // Find the source group
+  const sourceGroup = findGroup(clone, sourceGroupId);
+  if (!sourceGroup) {
+    throw new Error(`Source group ${sourceGroupId} not found`);
+  }
+
+  // Find and remove the source item from the source group
+  const sourceIndex = sourceGroup.items.findIndex(
+    (item) => item.id === source.id
+  );
+  if (sourceIndex === -1) {
+    throw new Error(
+      `Source item ${source.id} not found in group ${sourceGroupId}`
+    );
+  }
+  const [sourceItem] = sourceGroup.items.splice(sourceIndex, 1);
+
+  if (!targetGroupId) {
+    if (target.type === 'root') {
+      clone.items.splice(clone.items.length, 0, sourceItem);
+    } else if (target.type === 'group') {
+      const targetGroup = findGroup(clone, target.id as string);
+
+      if (!targetGroup) {
+        throw new Error(`Target group ${target.id} not found`);
+      }
+
+      targetGroup.items.splice(targetGroup.items.length, 0, sourceItem);
+    }
+
+    return clone;
+  }
+
+  // Find the target group
+  const targetGroup = findGroup(clone, targetGroupId);
+  if (!targetGroup) {
+    return root;
+  }
+
+  // Find the index of the target item in the target group
+  const targetIndex = targetGroup.items.findIndex(
+    (item) => item.id === target.id
+  );
+
+  if (targetIndex === -1) {
+    throw new Error(
+      `Target item ${target.id} not found in group ${targetGroupId}`
+    );
+  }
+
+  const position = operation.position.current;
+
+  let isBelowTarget = false;
+
+  // Because of the nested nature of groups and cards, we need to use special positioning logic
+  if (target.shape) {
+    if (targetGroupId === 'root') {
+      if (target.type === 'group') {
+        isBelowTarget = position.x < target.shape.center.x;
+      } else {
+        isBelowTarget = position.x > target.shape.center.x;
+      }
+    } else {
+      if (target.type === 'group') {
+        isBelowTarget = position.y < target.shape.center.y;
+      } else {
+        isBelowTarget = position.y > target.shape.center.y;
+      }
+    }
+  }
+
+  targetGroup.items.splice(
+    isBelowTarget ? targetIndex : targetIndex + 1,
+    0,
+    sourceItem
+  );
+
+  return clone;
+}