package com.app;

import java.io.IOException;
import java.net.MalformedURLException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;
import java.util.List;
import java.util.stream.Collectors;

import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.stereotype.Service;
import org.springframework.util.StringUtils;
import org.springframework.web.multipart.MultipartFile;

@Service
public class FileService {

    private final Path fileStorageLocation;

    public FileService() {
        this.fileStorageLocation = Paths.get("uploads").toAbsolutePath().normalize();
        try {
            Files.createDirectories(this.fileStorageLocation);
        } catch (Exception ex) {
            throw new RuntimeException("Could not create the directory where the uploaded files will be stored.", ex);
        }
    }

    /**
     * Saves the uploaded file to the specified location.
     * @param file MultipartFile to be saved
     */
    public void saveFile(MultipartFile file) {
        String fileName = StringUtils.cleanPath(file.getOriginalFilename());
        try {
            Path targetLocation = this.fileStorageLocation.resolve(fileName);
            Files.copy(file.getInputStream(), targetLocation, StandardCopyOption.REPLACE_EXISTING);
        } catch (IOException ex) {
            throw new RuntimeException("Could not store file " + fileName + ". Please try again!", ex);
        }
    }

    /**
     * Loads a file as a Resource for downloading.
     * @param fileName the name of the file to be loaded
     * @return Resource representing the file
     */
    public Resource loadFile(String fileName) {
        try {
            Path filePath = this.fileStorageLocation.resolve(fileName).normalize();
            Resource resource = new UrlResource(filePath.toUri());
            if (resource.exists()) {
                return resource;
            } else {
                throw new RuntimeException("File not found " + fileName);
            }
        } catch (MalformedURLException ex) {
            throw new RuntimeException("File not found " + fileName, ex);
        }
    }

    /**
     * Retrieves all file names from the storage location.
     * @return List of file names
     */
    public List<String> getAllFiles() {
        try {
            return Files.walk(this.fileStorageLocation, 1)
                    .filter(path -> !path.equals(this.fileStorageLocation))
                    .map(this.fileStorageLocation::relativize)
                    .map(Path::toString)
                    .collect(Collectors.toList());
        } catch (IOException ex) {
            throw new RuntimeException("Could not list the files!", ex);
        }
    }
}

package com.app;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.multipart.MultipartFile;

@Controller
public class FileController {

    @Autowired
    private FileService fileService;

    /**
     * Displays the index page with a list of uploaded files.
     * @param model the model to pass data to the view
     * @return the name of the HTML template to be rendered
     */
    @GetMapping("/")
    public String getIndex(Model model) {
        List<String> fileNames = fileService.getAllFiles();
        model.addAttribute("files", fileNames);
        return "index";
    }

    /**
     * Handles file upload requests.
     * @param file the file to be uploaded
     * @param model the model to pass data to the view
     * @return the redirect URL to the index page
     */
    @PostMapping("/upload")
    public String uploadFile(@RequestParam("file") MultipartFile file, Model model) {
        fileService.saveFile(file);
        model.addAttribute("message", "File uploaded successfully!");
        return "redirect:/";
    }

    /**
     * Handles file download requests.
     * @param fileName the name of the file to be downloaded
     * @return the ResponseEntity containing the file resource
     */
    @GetMapping("/download/{fileName:.+}")
    public ResponseEntity<Resource> downloadFile(@PathVariable String fileName) {
        Resource resource = fileService.loadFile(fileName);
        return ResponseEntity.ok()
                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + resource.getFilename() + "\"")
                .body(resource);
    }
}