// File: frontend/app/workflow/page.tsx
// Description: 工作流编辑器页面，添加侧边栏用于拖放节点

'use client';

import React, { useState, useCallback, useRef, DragEvent } from 'react'; // 添加 useRef, DragEvent
import ReactFlow, {
  ReactFlowProvider,
  MiniMap,
  Controls,
  Background,
  useNodesState,
  useEdgesState,
  addEdge,
  Node,
  Edge,
  Connection,
  Position,
  MarkerType,
  NodeChange,
  EdgeChange,
  applyNodeChanges,
  applyEdgeChanges,
  useReactFlow, // 导入 useReactFlow hook
  XYPosition,
  BackgroundVariant, // 导入 XYPosition 类型
} from 'reactflow';
import { MessageSquareText, BrainCircuit, Database, LogOut, Play } from 'lucide-react'; // 导入一些节点图标

import 'reactflow/dist/style.css';

// --- 初始节点和边数据 (可以清空或保留示例) ---
const initialNodes: Node[] = [
//   { id: '1', type: 'inputNode', data: { label: '开始' }, position: { x: 100, y: 100 } },
];
const initialEdges: Edge[] = [];

// --- 定义可拖拽的节点类型 ---
const nodeTypesForPalette = [
    { type: 'inputNode', label: '输入', icon: MessageSquareText, defaultData: { text: '用户输入...' } },
    { type: 'llmNode', label: 'LLM 调用', icon: BrainCircuit, defaultData: { model: 'gpt-3.5-turbo', prompt: '...' } },
    { type: 'ragNode', label: 'RAG 查询', icon: Database, defaultData: { query: '...', knowledgeBase: 'default' } },
    { type: 'outputNode', label: '输出', icon: LogOut, defaultData: { result: null } },
    { type: 'startNode', label: '开始流程', icon: Play, defaultData: {} }, // 添加一个开始节点类型
];

// --- 侧边栏组件 ---
const Sidebar = () => {
  // 拖拽开始时设置数据
  const onDragStart = (event: DragEvent, nodeType: string, defaultData: any) => {
    // 将节点类型和默认数据存储在 dataTransfer 中
    const nodeInfo = JSON.stringify({ nodeType, defaultData });
    event.dataTransfer.setData('application/reactflow', nodeInfo);
    event.dataTransfer.effectAllowed = 'move';
    console.log(`Drag Start: ${nodeType}`);
  };

  return (
    <aside className="w-64 bg-white dark:bg-gray-800 p-4 border-r dark:border-gray-700 shadow-md overflow-y-auto">
      <h3 className="text-lg font-semibold mb-4 text-gray-800 dark:text-gray-200">节点面板</h3>
      <p className="text-xs text-gray-500 dark:text-gray-400 mb-4">将节点拖拽到右侧画布</p>
      <div className="space-y-2">
        {nodeTypesForPalette.map((nodeInfo) => (
          <div
            key={nodeInfo.type}
            className="p-3 border dark:border-gray-600 rounded-lg cursor-grab flex items-center gap-2 bg-gray-50 dark:bg-gray-700 hover:bg-gray-100 dark:hover:bg-gray-600 transition-colors"
            onDragStart={(event) => onDragStart(event, nodeInfo.type, nodeInfo.defaultData)}
            draggable // 设置为可拖拽
          >
            <nodeInfo.icon size={18} className="text-gray-600 dark:text-gray-300 flex-shrink-0" />
            <span className="text-sm text-gray-700 dark:text-gray-200">{nodeInfo.label}</span>
          </div>
        ))}
      </div>
    </aside>
  );
};


// --- 工作流编辑器组件 ---
function WorkflowEditor() {
  const reactFlowWrapper = useRef<HTMLDivElement>(null); // Ref 指向 React Flow 容器
  const [nodes, setNodes] = useState<Node[]>(initialNodes);
  const [edges, setEdges] = useState<Edge[]>(initialEdges);
  const { project } = useReactFlow(); // 使用 hook 获取 project 方法

  const onNodesChange = useCallback(
    (changes: NodeChange[]) => setNodes((nds) => applyNodeChanges(changes, nds)),
    [setNodes]
  );
  const onEdgesChange = useCallback(
    (changes: EdgeChange[]) => setEdges((eds) => applyEdgeChanges(changes, eds)),
    [setEdges]
  );
  const onConnect = useCallback(
    (connection: Connection) => setEdges((eds) => addEdge({ ...connection, markerEnd: { type: MarkerType.ArrowClosed } }, eds)),
    [setEdges]
  );

  // 处理画布上的拖拽悬停事件
  const onDragOver = useCallback((event: DragEvent) => {
    event.preventDefault(); // 必须阻止默认行为才能触发 onDrop
    event.dataTransfer.dropEffect = 'move'; // 设置放置效果
  }, []);

  // 处理画布上的放置事件
  const onDrop = useCallback(
    (event: DragEvent) => {
      event.preventDefault(); // 阻止默认行为（如打开文件）

      if (!reactFlowWrapper.current) {
        return;
      }

      // 从 dataTransfer 中获取节点信息
      const nodeInfoString = event.dataTransfer.getData('application/reactflow');
      if (!nodeInfoString) {
        console.warn("No reactflow data found in dataTransfer");
        return;
      }

      let nodeInfo;
      try {
        nodeInfo = JSON.parse(nodeInfoString);
      } catch (error) {
        console.error("Failed to parse node info from dataTransfer", error);
        return;
      }

      const { nodeType, defaultData } = nodeInfo;
      if (!nodeType) {
         console.warn("Node type not found in dataTransfer");
         return;
      }

      // 获取鼠标相对于 React Flow 画布的位置
      // 需要计算鼠标位置相对于 reactFlowWrapper 的偏移量
      const reactFlowBounds = reactFlowWrapper.current.getBoundingClientRect();
      const position = project({
        x: event.clientX - reactFlowBounds.left,
        y: event.clientY - reactFlowBounds.top,
      });

      // 创建新节点
      const newNode: Node = {
        id: `${nodeType}-${Date.now()}`, // 使用更唯一的 ID
        type: nodeType, // 设置节点类型
        position,
        data: { label: `${nodeType} node`, ...defaultData }, // 合并默认数据
        // 根据节点类型设置 Handle 位置 (可选，也可以在自定义节点内部定义)
        sourcePosition: Position.Bottom,
        targetPosition: Position.Top,
      };

      console.log('Node dropped:', newNode);
      // 将新节点添加到状态中
      setNodes((nds) => nds.concat(newNode));
    },
    [project, setNodes] // 依赖 project 方法和 setNodes
  );

  // --- (可选) 注册自定义节点类型 ---
  // const nodeTypes = useMemo(() => ({
  //   inputNode: CustomInputNode,
  //   llmNode: LLMNode,
  //   ragNode: RAGNode,
  //   outputNode: CustomOutputNode,
  //   startNode: StartNode,
  // }), []);

  return (
    <div className="flex flex-col h-full bg-white dark:bg-gray-800 rounded-lg shadow-md overflow-hidden">
      <h1 className="text-xl font-semibold p-4 border-b dark:border-gray-700 text-gray-800 dark:text-gray-200">
        工作流编辑器
      </h1>
      {/* 主容器使用 Flexbox */}
      <div className="flex flex-1 overflow-hidden">
        {/* 侧边栏 */}
        <Sidebar />
        {/* React Flow 画布容器 */}
        <div className="flex-1 h-full" ref={reactFlowWrapper}> {/* 添加 ref */}
          <ReactFlow
            nodes={nodes}
            edges={edges}
            onNodesChange={onNodesChange}
            onEdgesChange={onEdgesChange}
            onConnect={onConnect}
            onDragOver={onDragOver} // 添加 onDragOver
            onDrop={onDrop}         // 添加 onDrop
            // nodeTypes={nodeTypes}
            fitView
            className="bg-gray-50 dark:bg-gray-900"
          >
            <Controls />
            <MiniMap nodeStrokeWidth={3} zoomable pannable />
            <Background gap={16} color="#ccc" variant={BackgroundVariant.Dots} />
          </ReactFlow>
        </div>
      </div>
    </div>
  );
}

// --- 主页面组件，包含 Provider ---
export default function WorkflowPage() {
  return (
    <ReactFlowProvider>
      <WorkflowEditor />
    </ReactFlowProvider>
  );
}