Warn when saving snippet information looses data

When saving snippet information that contains characters not supported
in the selected output encoding a warning message now appears to inform
that the saved or previewed text differs from the original.

This usually happens when saving Markdown or plain text in the default
ANSI encoding.

Fixes #165

Author: delphidabbler

Src/USaveInfoMgr.pas

@@ -35,6 +35,10 @@   TSaveInfoMgr = class(TNoPublicConstructObject)
       fSaveDlg: TSaveSourceDlg;
       fSourceFileInfo: TSourceFileInfo;
 
+    ///  <summary>Displays a warning message about data loss if
+    ///  <c>ExpectedStr</c> doesn't match <c>EncodedStr</c>.</summary>
+    class procedure WarnIfDataLoss(const ExpectedStr, EncodedStr: string);
+
     ///  <summary>Returns encoded data containing a RTF representation of
     ///  information about the snippet represented by the given view.</summary>
     class function GenerateRichText(View: IView; const AUseHiliting: Boolean):
@@ -140,6 +144,7 @@ implementation
   Hiliter.UGlobals,
   UIOUtils,
   UMarkdownSnippetDoc,
+  UMessageBox,
   UOpenDialogHelper,
   UPreferences,
   URTFSnippetDoc,
@@ -231,18 +236,20 @@ function TSaveInfoMgr.GenerateHTML(const AUseHiliting: Boolean;
 function TSaveInfoMgr.GenerateMarkdown: TEncodedData;
 var
   Doc: TMarkdownSnippetDoc;
-  GeneratedData: TEncodedData;
+  ExpectedMarkown: string;
 begin
   Assert(Supports(fView, ISnippetView),
-    ClassName + '.GeneratePlainText: View is not a snippet view');
+    ClassName + '.GenerateMarkdown: View is not a snippet view');
   Doc := TMarkdownSnippetDoc.Create(
     (fView as ISnippetView).Snippet.Kind <> skFreeform
   );
   try
-    GeneratedData := Doc.Generate((fView as ISnippetView).Snippet);
-    Result := TEncodedData.Create(
-      GeneratedData.ToString, fSaveDlg.SelectedEncoding
-    );
+    // Generate Markdown using default UTF-16 encoding
+    ExpectedMarkown := Doc.Generate((fView as ISnippetView).Snippet).ToString;
+    // Convert Markdown to encoding to that selected in save dialogue box
+    Result := TEncodedData.Create(ExpectedMarkown, fSaveDlg.SelectedEncoding);
+    // Check for data loss in required encoding
+    WarnIfDataLoss(ExpectedMarkown, Result.ToString);
   finally
     Doc.Free;
   end;
@@ -266,19 +273,23 @@ function TSaveInfoMgr.GenerateOutput(const FileType: TSourceFileType):
 
 function TSaveInfoMgr.GeneratePlainText: TEncodedData;
 var
-  Doc: TTextSnippetDoc;        // object that generates RTF document
-  HiliteAttrs: IHiliteAttrs;  // syntax highlighter formatting attributes
-  GeneratedData: TEncodedData;
+  Doc: TTextSnippetDoc;        // object that generates plain text document
+  HiliteAttrs: IHiliteAttrs;   // syntax highlighter formatting attributes
+  ExpectedText: string;        // expected plain text
 begin
   Assert(Supports(fView, ISnippetView),
     ClassName + '.GeneratePlainText: View is not a snippet view');
   HiliteAttrs := THiliteAttrsFactory.CreateNulAttrs;
   Doc := TTextSnippetDoc.Create;
   try
-    GeneratedData := Doc.Generate((fView as ISnippetView).Snippet);
+    // Generate text using default UTF-16 encoding
+    ExpectedText := Doc.Generate((fView as ISnippetView).Snippet).ToString;
+    // Convert encoding to that selected in save dialogue box
     Result := TEncodedData.Create(
-      GeneratedData.ToString, fSaveDlg.SelectedEncoding
+      ExpectedText, fSaveDlg.SelectedEncoding
     );
+    // Check for data loss in required encoding
+    WarnIfDataLoss(ExpectedText, Result.ToString);
   finally
     Doc.Free;
   end;
@@ -448,4 +459,15 @@ function TSaveInfoMgr.SelectedFileType: TSourceFileType;
   Result := fSourceFileInfo.FileTypeFromFilterIdx(fSaveDlg.FilterIndex);
 end;
 
+class procedure TSaveInfoMgr.WarnIfDataLoss(const ExpectedStr,
+  EncodedStr: string);
+resourcestring
+  sEncodingError = 'The selected snippet contains characters that can''t be '
+    + 'represented in the chosen file encoding.' + sLineBreak + sLineBreak
+    + 'Please compare the output to the snippet displayed in the Details pane.';
+begin
+  if ExpectedStr <> EncodedStr then
+    TMessageBox.Warning(nil, sEncodingError);
+end;
+
 end.