Add backend inProgress status to prevent multiple exports from a sing…

…le user (in case of front-end interruption of the first).

Backend/Controllers/LiftController.cs

@@ -204,25 +204,45 @@ internal async Task<IActionResult> ExportLiftFile(string projectId, string userI
                 return new UnsupportedMediaTypeResult();
             }
 
-            // Ensure project exists and has words
+            // Ensure project exists
             var proj = _projectService.GetProject(projectId);
             if (proj is null)
             {
                 return new NotFoundObjectResult(projectId);
             }
-            var words = await _wordRepo.GetAllWords(projectId);
-            if (words.Count == 0)
+
+            // Check if another export started
+            if (_liftService.IsExportInProgress(userId))
             {
-                return new BadRequestResult();
+                return new ConflictResult();
             }
 
-            // Export the data to a zip, read into memory, and delete zip
-            var exportedFilepath = CreateLiftExport(projectId);
+            // Store in-progress status for the export
+            _liftService.SetExportInProgress(userId, true);
 
-            // Store the temporary path to the exported file for user to download later.
-            _liftService.StoreExport(userId, exportedFilepath);
-            await _notifyService.Clients.All.SendAsync("DownloadReady", userId);
-            return new OkObjectResult(projectId);
+            try
+            {
+                // Ensure project has words
+                var words = await _wordRepo.GetAllWords(projectId);
+                if (words.Count == 0)
+                {
+                    _liftService.SetExportInProgress(userId, false);
+                    return new BadRequestResult();
+                }
+
+                // Export the data to a zip, read into memory, and delete zip
+                var exportedFilepath = CreateLiftExport(projectId);
+
+                // Store the temporary path to the exported file for user to download later.
+                _liftService.StoreExport(userId, exportedFilepath);
+                await _notifyService.Clients.All.SendAsync("DownloadReady", userId);
+                return new OkObjectResult(projectId);
+            }
+            catch (Exception error)
+            {
+                _liftService.SetExportInProgress(userId, false);
+                throw error;
+            }
         }
 
         internal string CreateLiftExport(string projectId)

Backend/Interfaces/ILiftService.cs

@@ -14,5 +14,7 @@ ILexiconMerger<LiftObject, LiftEntry, LiftSense, LiftExample> GetLiftImporterExp
         void StoreExport(string key, string filePath);
         string? RetrieveExport(string key);
         bool DeleteExport(string key);
+        void SetExportInProgress(string key, bool isInProgress);
+        bool IsExportInProgress(string key);
     }
 }

Backend/Services/LiftApiServices.cs

@@ -89,6 +89,27 @@ public LiftService()
             _liftExports = new Dictionary<string, string>();
         }
 
+        private readonly string inProgress = "IN_PROGRESS";
+
+        /// <summary> Store status that a user's export is in-progress. </summary>
+        public void SetExportInProgress(string userId, bool isInProgress = true)
+        {
+            _liftExports.Remove(userId);
+            if (isInProgress)
+            {
+                _liftExports.Add(userId, inProgress);
+            }
+        }
+
+        /// <summary> Query whether user has an in-progress export. </summary>
+        public bool IsExportInProgress(string userId)
+        {
+            if (!_liftExports.ContainsKey(userId))
+            {
+                return false;
+            }
+            return _liftExports[userId] == inProgress;
+        }
 
         /// <summary> Store filePath for a user's Lift export. </summary>
         public void StoreExport(string userId, string filePath)
@@ -101,7 +122,7 @@ public void StoreExport(string userId, string filePath)
         /// <returns> Path to the Lift file on disk. </returns>
         public string? RetrieveExport(string userId)
         {
-            if (!_liftExports.ContainsKey(userId))
+            if (!_liftExports.ContainsKey(userId) || _liftExports[userId] == inProgress)
             {
                 return null;
             }