diff --git a/app/src/main/java/foundation/e/drive/services/ObserverService.java b/app/src/main/java/foundation/e/drive/services/ObserverService.java
index e57f135e1d21e537b17ac9ad9eb54073bf1e84f4..b80f40662a5907607c1b52f18a304c1a4ec40734 100644
--- a/app/src/main/java/foundation/e/drive/services/ObserverService.java
+++ b/app/src/main/java/foundation/e/drive/services/ObserverService.java
@@ -47,11 +47,13 @@ import foundation.e.drive.receivers.DebugCmdReceiver;
 import foundation.e.drive.utils.AppConstants;
 import foundation.e.drive.utils.CommonUtils;
 import foundation.e.drive.utils.DavClientProvider;
+import foundation.e.drive.utils.FileDiffUtils.Action;
 import foundation.e.drive.utils.ServiceExceptionHandler;
 import foundation.e.drive.utils.SynchronizationServiceConnection;
 
 import static com.owncloud.android.lib.resources.files.FileUtils.PATH_SEPARATOR;
 import static foundation.e.drive.utils.AppConstants.INITIALIZATION_HAS_BEEN_DONE;
+import static foundation.e.drive.utils.FileDiffUtils.getActionForFileDiff;
 
 import androidx.annotation.Nullable;
 
@@ -380,41 +382,30 @@ public class ObserverService extends Service implements OnRemoteOperationListene
                     continue;
                 }
 
-                Log.v(TAG, "syncedFileState.getRemotePath() :"+syncedFileState.getRemotePath() );
-
-                //If syncedFileState match the remote file
                 if (remoteFilePath.equals(syncedFileState.getRemotePath())) {
                     Log.d(TAG, "correspondant found for "+remoteFilePath );
                     correspondant_found = true;
 
-                    if (syncedFileState.isLastEtagStored() //there is an etag stored
-                        && (!remoteFile.getEtag().equals(syncedFileState.getLastETAG()) //If etag has changed
-                        || syncedFileState.getLocalLastModified() == 0L)) { //File hasn't been downloaded
-
-                        Log.v(TAG, "etag and localLastModified are valids for "+remoteFilePath );
+                    final Action action = getActionForFileDiff(remoteFile, syncedFileState);
+                    if (action == Action.Download) {
 
-                        //compare size with local file
-                        if (remoteFile.getLength() == new File(syncedFileState.getLocalPath()).length()) { //length is 0 is file doesn't exist
-                            Log.v(TAG, "file size are the same for local and remote, just update syncedFileState etag");
+                        Log.i(TAG, "Add download operation for file " + syncedFileState.getId());
+                        this.syncRequests.put(syncedFileState.getId(), new DownloadRequest(remoteFile, syncedFileState));
 
-                            syncedFileState.setLastETAG(remoteFile.getEtag());
-                            int affectedRows = DbHelper.manageSyncedFileStateDB(syncedFileState, "UPDATE", this);
-                            Log.v(TAG, affectedRows + " syncedFileState.s row in DB has been updated.");
-                        } else {
-                            Log.i(TAG, "Add download operation for file "+syncedFileState.getId());
+                    } else if (action == Action.updateDB) {
 
-                            this.syncRequests.put(syncedFileState.getId(), new DownloadRequest(remoteFile, syncedFileState));
-                        }
+                        syncedFileState.setLastETAG(remoteFile.getEtag());
+                        final int affectedRows = DbHelper.manageSyncedFileStateDB(syncedFileState, "UPDATE", this);
+                        if (affectedRows == 0) Log.e(TAG, "Error while updating eTag in DB for: " + remoteFilePath);
                     }
-                    syncedFileListIterator.remove(); //we can delete syncedFile from list because its correspondant has already been found and handled
+                    syncedFileListIterator.remove();
                     break;
                 }
             }
 
-            if ( correspondant_found )continue;
+            if (correspondant_found) continue;
 
-            //If we get here, RemoteFile is a new file to download
-            Log.v(TAG, "SyncedFileState corresponding to remoteFile not found.");
+            Log.v(TAG, remoteFilePath + "is a new file");
 
             //Extract parent folder's path of remote file
             final String parentOfKnownPath = remoteFilePath.substring(0, remoteFilePath.lastIndexOf(FileUtils.PATH_SEPARATOR) + 1);
diff --git a/app/src/main/java/foundation/e/drive/utils/FileDiffUtils.java b/app/src/main/java/foundation/e/drive/utils/FileDiffUtils.java
new file mode 100644
index 0000000000000000000000000000000000000000..1edaa713f3434537216ac0028ef454233348f44b
--- /dev/null
+++ b/app/src/main/java/foundation/e/drive/utils/FileDiffUtils.java
@@ -0,0 +1,84 @@
+/*
+ * Copyright © ECORP SAS 2022.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the GNU Public License v3.0
+ * which accompanies this distribution, and is available at
+ * http://www.gnu.org/licenses/gpl.html
+ */
+
+package foundation.e.drive.utils;
+
+import com.owncloud.android.lib.resources.files.model.RemoteFile;
+
+import java.io.File;
+
+import foundation.e.drive.models.SyncedFileState;
+
+/**
+ * This class encapsulate code to compare syncedFile & Remote file
+ * but also RemoteFolder and SyncedFolder
+ * @author vincent Bourgmayer
+ */
+public class FileDiffUtils {
+
+    public enum Action {
+        Upload,
+        Download,
+        Remove,
+        skip,
+        updateDB
+    }
+
+
+    /**
+     * Define what to do of RemoteFile for which we know the Database equivalent
+     * @param remoteFile RemoteFile
+     * @param fileState SyncedFileState instance
+     * @return Action from Enum
+     */
+    public static Action getActionForFileDiff(RemoteFile remoteFile, SyncedFileState fileState) {
+        if (hasAlreadyBeenDownloaded(fileState) && !hasEtagChanged(remoteFile, fileState)) {
+            return Action.skip;
+        }
+
+        final File localFile = new File(fileState.getLocalPath());
+
+        if (isRemoteSizeSameAsLocalSize(remoteFile, localFile)) {
+            return Action.updateDB;
+        }
+
+        return Action.Download;
+    }
+
+    /**
+     * Compare RemoteFile's eTag with the one stored in Database
+     * @param file RemoteFile
+     * @param fileState last store file's state
+     * @return true if ETag
+     */
+    private static boolean hasEtagChanged(RemoteFile file, SyncedFileState fileState) {
+        //if SyncedFileState has no Etag then it hasn't been uploaded and so must not exist on server
+        return fileState.isLastEtagStored() && !file.getEtag().equals(fileState.getLastETAG());
+    }
+
+    /**
+     * Indicate if the file has already been downloaded
+     * or detected on the device
+     * @param fileState SyncedFileState containing data from Database
+     * @return true if localLastModified store in Database == 0
+     */
+    private static boolean hasAlreadyBeenDownloaded(SyncedFileState fileState) {
+        return fileState.getLocalLastModified() == 0l;
+    }
+
+    /**
+     *
+     * @param remoteFile RemoteFile instance
+     * @param localFile File instance
+     * @return true if remote file size is same as local file size
+     */
+    private static boolean isRemoteSizeSameAsLocalSize(RemoteFile remoteFile, File localFile) {
+        // if local file doesn't exist its size will be 0
+        return remoteFile.getLength() == localFile.length();
+    }
+}