<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>commons-io</groupId>
        <artifactId>commons-io</artifactId>
        <version>2.11.0</version>
    </dependency>
</dependencies>

@RestController
@RequestMapping("/api/upload")
public class ResumableUploadController {

    private static final String TEMP_DIR = "uploads/temp/";
    private static final String FINAL_DIR = "uploads/final/";

    /**
     * 檢查哪些分片已上傳（用于斷點(diǎn)續(xù)傳）
     */
    @GetMapping("/check")
    public Set<Integer> checkUploadedChunks(@RequestParam String fileMd5) {
        Set<Integer> uploaded = new HashSet<>();
        Path tempPath = Paths.get(TEMP_DIR, fileMd5);
        if (Files.exists(tempPath)) {
            try (Stream<Path> stream = Files.list(tempPath)) {
                stream.forEach(p -> {
                    String name = p.getFileName().toString();
                    if (name.matches("\\d+")) {
                        uploaded.add(Integer.parseInt(name));
                    }
                });
            } catch (IOException e) {
                // 日志記錄
            }
        }
        return uploaded;
    }

    /**
     * 上傳單個(gè)分片
     */
    @PostMapping("/chunk")
    public ResponseEntity<?> uploadChunk(
            @RequestParam String fileMd5,
            @RequestParam int chunkIndex,
            @RequestParam MultipartFile chunk) {

        try {
            Path tempDir = Paths.get(TEMP_DIR, fileMd5);
            Files.createDirectories(tempDir);
            Path chunkFile = tempDir.resolve(String.valueOf(chunkIndex));
            chunk.transferTo(chunkFile.toFile());
            return ResponseEntity.ok().build();
        } catch (IOException e) {
            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).build();
        }
    }

    /**
     * 合并所有分片為完整文件
     */
    @PostMapping("/merge")
    public ResponseEntity<?> mergeChunks(
            @RequestParam String fileMd5,
            @RequestParam String fileName,
            @RequestParam int totalChunks) {

        try {
            Path finalPath = Paths.get(FINAL_DIR, fileName);
            Files.createDirectories(finalPath.getParent());

            try (OutputStream out = Files.newOutputStream(finalPath)) {
                for (int i = 0; i < totalChunks; i++) {
                    Path chunk = Paths.get(TEMP_DIR, fileMd5, String.valueOf(i));
                    if (!Files.exists(chunk)) {
                        return ResponseEntity.badRequest()
                                .body("Missing chunk: " + i);
                    }
                    byte[] data = Files.readAllBytes(chunk);
                    out.write(data);
                }
            }

            // 清理臨時(shí)分片
            FileUtils.deleteDirectory(new File(TEMP_DIR + fileMd5));

            return ResponseEntity.ok(Map.of("success", true, "path", finalPath.toString()));
        } catch (IOException e) {
            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).build();
        }
    }
}

// 示例：上傳一個(gè)分片
const uploadChunk = async (fileMd5, index, blob) => {
  const formData = new FormData();
  formData.append('fileMd5', fileMd5);
  formData.append('chunkIndex', index);
  formData.append('chunk', blob);
  await fetch('/api/upload/chunk', { method: 'POST', body: formData });
};