import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import java.io.File;
import java.io.RandomAccessFile;
import java.nio.file.Path;
import java.nio.file.Paths;

@RestController
public class VideoDownloadController {

    private static final String VIDEO_BASE_PATH = "/path/to/your/videos";

    @GetMapping("/video/{filename}")
    public ResponseEntity<Resource> downloadVideo(@PathVariable String filename, HttpServletRequest request) {
        try {
            Path videoPath = Paths.get(VIDEO_BASE_PATH, filename);
            Resource video = new UrlResource(videoPath.toUri());

            if (video.exists()) {
                long fileLength = video.contentLength();
                String range = request.getHeader("Range");
                long start = 0, end = fileLength - 1;

                if (range != null) {
                    String[] ranges = range.replace("bytes=", "").split("-");
                    start = Long.parseLong(ranges[0]);
                    end = ranges.length > 1 ? Long.parseLong(ranges[1]) : end;
                }

                // Set the content type and attachment header.
                String contentType = request.getServletContext().getMimeType(video.getFile().getAbsolutePath());
                HttpHeaders headers = new HttpHeaders();
                headers.add(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + video.getFilename() + "\"");
                headers.add(HttpHeaders.ACCEPT_RANGES, "bytes");
                headers.add(HttpHeaders.CONTENT_RANGE, "bytes " + start + "-" + end + "/" + fileLength);
                headers.add(HttpHeaders.CONTENT_LENGTH, String.valueOf(end - start + 1));
                headers.setContentType(MediaType.parseMediaType(contentType));

                // Create resource that represents the part of the video file.
                RandomAccessFile raf = new RandomAccessFile(video.getFile(), "r");
                raf.seek(start);
                Resource partialVideo = new InputStreamResource(new CustomFileInputStream(raf, end - start + 1));

                return ResponseEntity.status(HttpStatus.PARTIAL_CONTENT)
                                     .headers(headers)
                                     .body(partialVideo);
            } else {
                return ResponseEntity.notFound().build();
            }
        } catch (Exception e) {
            return ResponseEntity.internalServerError().build();
        }
    }

    private static class CustomFileInputStream extends InputStream {
        private final RandomAccessFile raf;
        private final long end;

        public CustomFileInputStream(RandomAccessFile raf, long end) {
            this.raf = raf;
            this.end = end;
        }

        @Override
        public int read() throws IOException {
            if (raf.getFilePointer() <= end) {
                return raf.read();
            }
            return -1;
        }

        @Override
        public int read(byte[] b, int off, int len) throws IOException {
            if (raf.getFilePointer() <= end) {
                return raf.read(b, off, len);
            }
            return -1;
        }

        @Override
        public void close() throws IOException {
            raf.close();
        }
    }
}