feat:add last-modified-at for both file and folder

backend/src/main/java/cloudpage/dto/FileDto.java

@@ -12,4 +12,5 @@ public class FileDto {
     private String path;
     private long size;
     private String mimeType;
+    private long lastModifiedAt;
 }

backend/src/main/java/cloudpage/dto/FolderDto.java

@@ -1,11 +1,11 @@
 package cloudpage.dto;
 
+import java.util.List;
+
 import lombok.AllArgsConstructor;
 import lombok.Getter;
 import lombok.Setter;
 
-import java.util.List;
-
 @Getter
 @Setter
 @AllArgsConstructor
@@ -14,4 +14,5 @@ public class FolderDto {
     private String path;
     private List<FolderDto> folders;
     private List<FileDto> files;
-}
+    private long lastModifiedAt;
+}

backend/src/main/java/cloudpage/service/FolderService.java

@@ -1,12 +1,5 @@
 package cloudpage.service;
 
-import cloudpage.dto.FileDto;
-import cloudpage.dto.FolderDto;
-import cloudpage.exceptions.FileDeletionException;
-import cloudpage.exceptions.InvalidPathException;
-import cloudpage.exceptions.UnauthorizedAccessException;
-import org.springframework.stereotype.Service;
-
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -16,6 +9,13 @@
 import java.util.List;
 import java.util.stream.Collectors;
 
+import org.springframework.stereotype.Service;
+
+import cloudpage.dto.FileDto;
+import cloudpage.dto.FolderDto;
+import cloudpage.exceptions.FileDeletionException;
+import cloudpage.exceptions.InvalidPathException;
+
 @Service
 public class FolderService {
 
@@ -82,15 +82,27 @@ private FolderDto readFolder(Path path) throws IOException {
                                 filePath.getFileName().toString(),
                                 filePath.toAbsolutePath().toString(),
                                 attrs.size(),
-                                Files.probeContentType(filePath)
+                                Files.probeContentType(filePath),
+                                attrs.lastModifiedTime().toMillis()
                         );
                     } catch (IOException e) {
                         throw new FileDeletionException("Failed to read: " + filePath + "with exception : " + e.getMessage());
                     }
                 })
                 .collect(Collectors.toList());
 
-        return new FolderDto(path.getFileName().toString(), path.toAbsolutePath().toString(), subfolders, files);
+        try {
+            BasicFileAttributes folderAttrs = Files.readAttributes(path, BasicFileAttributes.class);
+            return new FolderDto(
+                    path.getFileName().toString(), 
+                    path.toAbsolutePath().toString(), 
+                    subfolders, 
+                    files,
+                    folderAttrs.lastModifiedTime().toMillis()
+            );
+        } catch (IOException e) {
+            throw new FileDeletionException("Failed to read folder attributes: " + path + " with exception: " + e.getMessage());
+        }
     }
 
     public void validatePath(String rootPath, Path path) {
@@ -104,4 +116,4 @@ private void validateRoot(Path root) {
             throw new InvalidPathException("Root folder does not exist or is not a directory: " + root);
         }
     }
-}
+}