refactor(examples): switch examples from cra to nextjs

examples/nextjs/pages/Provider/Sidebar.tsx

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+import React from 'react';
+import { useStore, useStoreApi } from '@react-flow/core';
+
+import styles from './provider.module.css';
+
+const Sidebar = () => {
+  const store = useStoreApi();
+  const nodeInternals = useStore((store) => store.nodeInternals);
+  const transform = useStore((store) => store.transform);
+
+  const selectAll = () => {
+    nodeInternals.forEach((node) => (node.selected = true));
+    store.setState({ nodeInternals: new Map(nodeInternals) });
+  };
+
+  return (
+    <aside className={styles.aside}>
+      <div className={styles.description}>
+        This is an example of how you can access the internal state outside of
+        the ReactFlow component.
+      </div>
+      <div className={styles.title}>Zoom & pan transform</div>
+      <div className={styles.transform}>
+        [{transform[0].toFixed(2)}, {transform[1].toFixed(2)},{' '}
+        {transform[2].toFixed(2)}]
+      </div>
+      <div className={styles.title}>Nodes</div>
+      {Array.from(nodeInternals).map(([, node]) => (
+        <div key={node.id}>
+          Node {node.id} - x: {node.position.x.toFixed(2)}, y:{' '}
+          {node.position.y.toFixed(2)}
+        </div>
+      ))}
+
+      <div className={styles.selectall}>
+        <button onClick={selectAll}>select all nodes</button>
+      </div>
+    </aside>
+  );
+};
+
+export default Sidebar;

examples/nextjs/pages/Provider/index.tsx

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+import React, { MouseEvent } from 'react';
+import ReactFlow, {
+  ReactFlowProvider,
+  addEdge,
+  Node,
+  Controls,
+  Connection,
+  Edge,
+  ConnectionMode,
+  useNodesState,
+  useEdgesState,
+  ReactFlowInstance,
+} from '@react-flow/core';
+
+import Sidebar from './Sidebar';
+
+import styles from './provider.module.css';
+
+const onNodeClick = (_: MouseEvent, node: Node) => console.log('click', node);
+const onInit = (reactFlowInstance: ReactFlowInstance) =>
+  console.log('pane ready:', reactFlowInstance);
+
+const initialNodes: Node[] = [
+  {
+    id: '1',
+    type: 'input',
+    data: { label: 'Node 1' },
+    position: { x: 250, y: 5 },
+  },
+  { id: '2', data: { label: 'Node 2' }, position: { x: 100, y: 100 } },
+  { id: '3', data: { label: 'Node 3' }, position: { x: 400, y: 100 } },
+  { id: '4', data: { label: 'Node 4' }, position: { x: 400, y: 200 } },
+];
+
+const initialEdges: Edge[] = [
+  { id: 'e1-2', source: '1', target: '2', animated: true },
+  { id: 'e1-3', source: '1', target: '3' },
+];
+
+const ProviderFlow = () => {
+  const [nodes, , onNodesChange] = useNodesState(initialNodes);
+  const [edges, setEdges, onEdgesChange] = useEdgesState(initialEdges);
+  const onConnect = (params: Edge | Connection) =>
+    setEdges((els) => addEdge(params, els));
+
+  return (
+    <div className={styles.providerflow}>
+      <ReactFlowProvider>
+        <Sidebar />
+        <div className={styles.wrapper}>
+          <ReactFlow
+            nodes={nodes}
+            edges={edges}
+            onNodesChange={onNodesChange}
+            onEdgesChange={onEdgesChange}
+            onNodeClick={onNodeClick}
+            onConnect={onConnect}
+            onInit={onInit}
+            connectionMode={ConnectionMode.Loose}
+          >
+            <Controls />
+          </ReactFlow>
+        </div>
+      </ReactFlowProvider>
+    </div>
+  );
+};
+
+export default ProviderFlow;

examples/nextjs/pages/Provider/provider.module.css

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+.providerflow {
+  flex-direction: column;
+  display: flex;
+  height: 100%;
+}
+
+.aside {
+  border-right: 1px solid #eee;
+  padding: 15px 10px;
+  font-size: 12px;
+  background: #fcfcfc;
+}
+
+.description {
+  margin-bottom: 10px;
+}
+
+.title {
+  font-weight: 700;
+  margin-bottom: 5px;
+}
+
+.transform {
+  margin-bottom: 20px;
+}
+
+.wrapper {
+  flex-grow: 1;
+  height: 100%;
+}
+
+.selectall {
+  margin-top: 10px;
+}
+
+@media screen and (min-width: 768px) {
+  .providerflow {
+    flex-direction: row;
+  }
+
+  .aside {
+    width: 20%;
+    max-width: 250px;
+  }
+}