refactor: consolidate output folder resolution and prefix handling

Move ParseDrawingNumber + GetDrawingOutputFolder into Export() before
the document-type switch so folder resolution happens once. Extract
PrependPrefix helper in PartExporter to deduplicate the prefix guard.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ExportDXF/Services/DxfExportService.cs

@@ -63,6 +63,9 @@ namespace ExportDXF.Services
 
             var startTime = DateTime.Now;
 
+            var drawingNumber = ParseDrawingNumber(context);
+            var outputFolder = _fileExportService.GetDrawingOutputFolder(drawingNumber);
+
             try
             {
                 _solidWorksService.EnableUserControl(false);
@@ -70,15 +73,15 @@ namespace ExportDXF.Services
                 switch (context.ActiveDocument.DocumentType)
                 {
                     case DocumentType.Part:
-                        ExportPart(context);
+                        ExportPart(context, outputFolder);
                         break;
 
                     case DocumentType.Assembly:
-                        ExportAssembly(context);
+                        ExportAssembly(context, outputFolder);
                         break;
 
                     case DocumentType.Drawing:
-                        ExportDrawing(context);
+                        ExportDrawing(context, drawingNumber, outputFolder);
                         break;
 
                     default:
@@ -98,7 +101,7 @@ namespace ExportDXF.Services
 
         #region Export Methods by Document Type
 
-        private void ExportPart(ExportContext context)
+        private void ExportPart(ExportContext context, string outputFolder)
         {
             LogProgress(context, "Active document is a Part");
 
@@ -109,11 +112,10 @@ namespace ExportDXF.Services
                 return;
             }
 
-            // Export directly to the output folder
-            _partExporter.ExportSinglePart(part, _fileExportService.OutputFolder, context);
+            _partExporter.ExportSinglePart(part, outputFolder, context);
         }
 
-        private void ExportAssembly(ExportContext context)
+        private void ExportAssembly(ExportContext context, string outputFolder)
         {
             LogProgress(context, "Active document is an Assembly");
             LogProgress(context, "Fetching components...");
@@ -135,11 +137,10 @@ namespace ExportDXF.Services
 
             LogProgress(context, $"Found {items.Count} item(s).");
 
-            // Export directly to the output folder
-            ExportItems(items, _fileExportService.OutputFolder, context);
+            ExportItems(items, outputFolder, context);
         }
 
-        private void ExportDrawing(ExportContext context)
+        private void ExportDrawing(ExportContext context, string drawingNumber, string drawingOutputFolder)
         {
             LogProgress(context, "Active document is a Drawing");
             LogProgress(context, "Finding BOM tables...");
@@ -161,12 +162,6 @@ namespace ExportDXF.Services
 
             LogProgress(context, $"Found {items.Count} component(s)");
 
-            // Determine drawing number for file naming
-            var drawingNumber = ParseDrawingNumber(context);
-
-            // Resolve output folder: /{outputDir}/{equipmentNo}/{drawingNo}/ or flat fallback
-            var drawingOutputFolder = _fileExportService.GetDrawingOutputFolder(drawingNumber);
-
             // Export drawing to PDF
             var tempDir = CreateTempWorkDir();
             _drawingExporter.ExportToPdf(drawing, tempDir, context);

ExportDXF/Services/PartExporter.cs

@@ -32,6 +32,13 @@ namespace ExportDXF.Services
 
     public class PartExporter : IPartExporter
     {
+        private readonly IFileExportService _fileExportService;
+
+        public PartExporter(IFileExportService fileExportService)
+        {
+            _fileExportService = fileExportService ?? throw new ArgumentNullException(nameof(fileExportService));
+        }
+
         public void ExportSinglePart(PartDoc part, string saveDirectory, ExportContext context)
         {
             if (part == null)
@@ -99,12 +106,22 @@ namespace ExportDXF.Services
 
             var templateDrawing = context.GetOrCreateTemplateDrawing();
 
+            // Stash existing file before overwriting
+            item.StashedFilePath = _fileExportService.StashFile(savePath);
+
             if (ExportPartToDxf(part, item.Component.ReferencedConfiguration, savePath, context))
             {
                 item.FileName = Path.GetFileNameWithoutExtension(savePath);
+                item.ContentHash = Utilities.ContentHasher.ComputeDxfContentHash(savePath);
             }
             else
             {
+                // Export failed - restore stashed file if we have one
+                if (item.StashedFilePath != null && File.Exists(item.StashedFilePath))
+                {
+                    File.Move(item.StashedFilePath, savePath, overwrite: true);
+                    item.StashedFilePath = null;
+                }
                 LogExportFailure(item, context);
             }
         }
@@ -274,7 +291,8 @@ namespace ExportDXF.Services
             var isDefaultConfig = string.Equals(config, "default", StringComparison.OrdinalIgnoreCase);
 
             var name = isDefaultConfig ? title : $"{title} [{config}]";
-            return prefix + name;
+
+            return PrependPrefix(name, prefix);
         }
 
         private string GetItemFileName(Item item, string prefix)
@@ -282,9 +300,7 @@ namespace ExportDXF.Services
             prefix = prefix?.Replace("\"", "''") ?? string.Empty;
 
             if (string.IsNullOrWhiteSpace(item.ItemNo))
-            {
-                return prefix + item.PartName;
-            }
+                return PrependPrefix(item.PartName, prefix);
 
             var num = item.ItemNo.PadLeft(2, '0');
             // Expected format: {DrawingNo} PT{ItemNo}
@@ -293,6 +309,17 @@ namespace ExportDXF.Services
                 : $"{prefix} PT{num}";
         }
 
+        private string PrependPrefix(string name, string prefix)
+        {
+            if (string.IsNullOrEmpty(prefix))
+                return name;
+
+            if (name.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
+                return name;
+
+            return prefix + name;
+        }
+
         private void LogExportFailure(Item item, ExportContext context)
         {
             var desc = item.Description?.ToLower() ?? string.Empty;