import React, { useState } from 'react';
import axios from 'axios';
function UploadForm() {
  const [selectedFile, setSelectedFile] = useState(null);
  const [uploadProgress, setUploadProgress] = useState(0);
  const [uploadedFile, setUploadedFile] = useState(null);
  const handleFileSelect = (event) => {
    setSelectedFile(event.target.files[0]);
  };
  const handleSubmit = async (event) => {
    event.preventDefault();
    const formData = new FormData();
    formData.append('file', selectedFile);
    const config = {
      onUploadProgress: (progressEvent) => {
        const percentCompleted = Math.round(
          (progressEvent.loaded * 100) / progressEvent.total
        );
        setUploadProgress(percentCompleted);
      },
    };
    try {
      const response = await axios.post('/api/upload', formData, config);
      setUploadedFile(response.data.filename);
      setSelectedFile(null);
      setUploadProgress(0);
    } catch (error) {
      console.log(error);
    }
  };
  const handleDownload = async () => {
    try {
      const response = await axios.get(`/api/download?filename=${uploadedFile}`, {
        responseType: 'blob',
      });
      const url = window.URL.createObjectURL(new Blob([response.data]));
      const link = document.createElement('a');
      link.href = url;
      link.setAttribute('download', uploadedFile);
      document.body.appendChild(link);
      link.click();
    } catch (error) {
      console.log(error);
    }
  };
  return (
    <div>
      <form onSubmit={handleSubmit}>
        <input type="file" onChange={handleFileSelect} />
        <button type="submit">Upload</button>
      </form>
      {selectedFile && (
        <div>
          Uploading {selectedFile.name}: {uploadProgress}%
        </div>
      )}
      {uploadedFile && (
        <div>
          File uploaded: <a href="#" rel="external nofollow"  onClick={handleDownload}>{uploadedFile}</a>
        </div>
      )}
    </div>
  );
}
export default UploadForm;

const Koa = require("koa");
const Router = require("koa-router");
const koaBody = require("koa-body");
const cors = require("@koa/cors");
const fs = require("fs");
const path = require("path");
const app = new Koa();
const router = new Router();
// 配置跨域
app.use(cors());
// 配置Koa Body中間件以處理文件上傳
app.use(
  koaBody({
    multipart: true,
    formidable: {
      uploadDir: path.join(__dirname, "uploads"),
      keepExtensions: true,
    },
  })
);
// 上傳接口
router.post("/api/upload", async (ctx) => {
  const file = ctx.request.files.file;
  const filename = file.name;
  const filepath = file.path || file.filepath;
  // 計算文件大小
  const fileSizeInBytes = fs.statSync(filepath).size;
  const fileSizeInMegabytes = fileSizeInBytes / (1024 * 1024);
  ctx.body = {
    filename,
    size: fileSizeInMegabytes.toFixed(2),
  };
});
// 下載接口
router.get("/api/download", async (ctx) => {
  const filename = ctx.query.filename;
  const filepath = path.join(__dirname, "uploads", filename);
  const fileStream = fs.createReadStream(filepath);
  ctx.response.attachment(filename);
  ctx.body = fileStream;
});
app.use(router.routes());
app.use(router.allowedMethods());
// 啟動！
const port = process.env.PORT || 3001;
app.listen(port, () => {
  console.log(`Server started on port ${port}`);
});

// 前端
npm run start
//服務端
node server.js