Transfers: say so when a drop or a download is refused because the screen is busy

src/DodoSSH.Client.Shell/ViewModels/TransfersViewModel.cs

@@ -2289,6 +2289,10 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
 
     // ---- Moving files ----
 
+    /// <summary>What a transfer asked for while another command is still running is told.</summary>
+    private const string StillBusy =
+        "Still working on the last request. Nothing was queued — try again when it has finished.";
+
     /// <summary>Queues the chosen remote file for download into the local directory showing.</summary>
     [RelayCommand]
     private void Download()
@@ -2306,7 +2310,8 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
                 await QueueDownloadsAsync(rows, CancellationToken.None).ConfigureAwait(true);
 
                 ClearRemoteChecks();
-            });
+            },
+            StillBusy);
     }
 
     /// <summary>Queues the chosen local file for upload into the remote directory showing.</summary>
@@ -2328,7 +2333,8 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
                 await QueueUploadsAsync(paths, CancellationToken.None).ConfigureAwait(true);
 
                 ClearLocalChecks();
-            });
+            },
+            StillBusy);
     }
 
     /// <summary>Unticks everything on the host's side.</summary>
@@ -2393,13 +2399,15 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     internal void QueueUploads(IReadOnlyList<string> paths) =>
         _ = RunAsync(
             "Working out what to upload…",
-            () => QueueUploadsAsync(paths, CancellationToken.None));
+            () => QueueUploadsAsync(paths, CancellationToken.None),
+            StillBusy);
 
     /// <inheritdoc cref="QueueUploads" />
     internal void QueueDownloads(IReadOnlyList<RemoteEntryRowViewModel> rows) =>
         _ = RunAsync(
             "Working out what to download…",
-            () => QueueDownloadsAsync(rows, CancellationToken.None));
+            () => QueueDownloadsAsync(rows, CancellationToken.None),
+            StillBusy);
 
     internal async Task QueueUploadsAsync(IReadOnlyList<string> paths, CancellationToken cancellationToken)
     {
@@ -2580,7 +2588,8 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
 
         _ = RunAsync(
             "Working out what to upload…",
-            () => QueueUploadsAsync(paths, CancellationToken.None));
+            () => QueueUploadsAsync(paths, CancellationToken.None),
+            StillBusy);
     }
 
     /// <summary>
@@ -4154,11 +4163,21 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     /// The same funnel <c>VaultViewModel</c> uses, and here for the same reason: every command on this screen
     /// can fail with a path the server refused, and one that forgot to clear the busy flag would leave the
     /// pane permanently disabled.
+    /// <para>
+    /// <paramref name="refusedWhileBusy"/> is for the commands somebody can fire while another is running —
+    /// a drop, or the download and upload buttons pressed twice — which used to vanish without a word: the
+    /// files were not queued and nothing said so. A command given one says why it did nothing instead.
+    /// </para>
     /// </remarks>
-    private async Task RunAsync(string busyMessage, Func<Task> work)
+    private async Task RunAsync(string busyMessage, Func<Task> work, string? refusedWhileBusy = null)
     {
         if (IsBusy)
         {
+            if (refusedWhileBusy is not null)
+            {
+                Status = refusedWhileBusy;
+            }
+
             return;
         }