import React, { useCallback } from 'react';
import {
  ReactFlow,
  Background,
  useNodesState,
  useEdgesState,
  addEdge,
  getOutgoers,
  useReactFlow,
  ReactFlowProvider,
} from '@xyflow/react';
 
import '@xyflow/react/dist/style.css';
 
import {
  nodes as initialNodes,
  edges as initialEdges,
} from './initialElements';
 
const Flow = () => {
  const [nodes, setNodes, onNodesChange] = useNodesState(initialNodes);
  const [edges, setEdges, onEdgesChange] = useEdgesState(initialEdges);
 
  const { getNodes, getEdges } = useReactFlow();
 
  const isValidConnection = useCallback(
    (connection) => {
      // we are using getNodes and getEdges helpers here
      // to make sure we create isValidConnection function only once
      const nodes = getNodes();
      const edges = getEdges();
      const target = nodes.find((node) => node.id === connection.target);
      const hasCycle = (node, visited = new Set()) => {
        if (visited.has(node.id)) return false;
 
        visited.add(node.id);
 
        for (const outgoer of getOutgoers(node, nodes, edges)) {
          if (outgoer.id === connection.source) return true;
          if (hasCycle(outgoer, visited)) return true;
        }
      };
 
      if (target.id === connection.source) return false;
      return !hasCycle(target);
    },
    [getNodes, getEdges],
  );
 
  const onConnect = useCallback((params) =>
    setEdges((els) => addEdge(params, els)),
  );
 
  return (
    <ReactFlow
      nodes={nodes}
      edges={edges}
      onNodesChange={onNodesChange}
      onEdgesChange={onEdgesChange}
      onConnect={onConnect}
      isValidConnection={isValidConnection}
      fitView
    >
      <Background />
    </ReactFlow>
  );
};
 
export default () => (
  <ReactFlowProvider>
    <Flow />
  </ReactFlowProvider>
);