Improve debugging information

 # Changelog
 
+## 3.7.2
+
+- Improve debugging information
+
 ## 3.7.1
 
 - Fix missing chars with pdfjs

+import 'dart:math' as math;
+
+import 'package:meta/meta.dart';
+
+import '../stream.dart';
+
+mixin PdfDiagnostic {
+  static const _maxSize = 300;
+
+  final _properties = <String>[];
+
+  int? _offset;
+
+  Stopwatch? _stopwatch;
+
+  int get elapsedStopwatch => _stopwatch?.elapsedMicroseconds ?? 0;
+
+  @protected
+  @mustCallSuper
+  void debugFill(String value) {
+    assert(() {
+      if (_properties.isEmpty) {
+        _properties.add('');
+        _properties.add('-' * 78);
+        _properties.add('$runtimeType');
+      }
+      _properties.add(value);
+      return true;
+    }());
+  }
+
+  void setInsertion(PdfStream os) {
+    assert(() {
+      _offset = os.offset;
+      os.putComment(' ' * _maxSize);
+      return true;
+    }());
+  }
+
+  void writeDebug(PdfStream os) {
+    assert(() {
+      if (_offset != null) {
+        final o = PdfStream();
+        _properties.forEach(o.putComment);
+        _properties.forEach(print);
+        final b = o.output();
+        os.setBytes(
+          _offset!,
+          b.sublist(0, math.min(_maxSize + 2, b.lengthInBytes - 1)),
+        );
+      }
+      return true;
+    }());
+  }
+
+  void startStopwatch() {
+    _stopwatch ??= Stopwatch();
+    _stopwatch!.start();
+  }
+
+  void stopStopwatch() {
+    _stopwatch?.stop();
+  }
+}

@@ -69,6 +69,12 @@ class PdfImage extends PdfXObject {
       orientation,
     );
 
+    assert(() {
+      im.startStopwatch();
+      im.debugFill('RAW RGB${alpha ? 'A' : ''} Image ${width}x$height');
+      return true;
+    }());
+
     im.params['/BitsPerComponent'] = const PdfNum(8);
     im.params['/Name'] = PdfName(im.name);
     im.params['/ColorSpace'] = const PdfName('/DeviceRGB');
@@ -95,6 +101,10 @@ class PdfImage extends PdfXObject {
     }
 
     im.buf.putBytes(out);
+    assert(() {
+      im.stopStopwatch();
+      return true;
+    }());
     return im;
   }
 
@@ -112,6 +122,11 @@ class PdfImage extends PdfXObject {
       orientation ?? info.orientation,
     );
 
+    assert(() {
+      im.startStopwatch();
+      im.debugFill('Jpeg Image ${info.width}x${info.height}');
+      return true;
+    }());
     im.params['/BitsPerComponent'] = const PdfNum(8);
     im.params['/Name'] = PdfName(im.name);
     im.params['/Intent'] = const PdfName('/RelativeColorimetric');
@@ -124,6 +139,10 @@ class PdfImage extends PdfXObject {
     }
 
     im.buf.putBytes(image);
+    assert(() {
+      im.stopStopwatch();
+      return true;
+    }());
     return im;
   }
 
@@ -178,6 +197,11 @@ class PdfImage extends PdfXObject {
       orientation,
     );
 
+    assert(() {
+      im.startStopwatch();
+      im.debugFill('Image alpha channel ${width}x$height');
+      return true;
+    }());
     im.params['/BitsPerComponent'] = const PdfNum(8);
     im.params['/Name'] = PdfName(im.name);
     im.params['/ColorSpace'] = const PdfName('/DeviceGray');
@@ -193,6 +217,10 @@ class PdfImage extends PdfXObject {
     }
 
     im.buf.putBytes(out);
+    assert(() {
+      im.stopStopwatch();
+      return true;
+    }());
     return im;
   }
 
@@ -204,6 +232,10 @@ class PdfImage extends PdfXObject {
   ) : super(pdfDocument, '/Image', isBinary: true) {
     params['/Width'] = PdfNum(_width);
     params['/Height'] = PdfNum(_height);
+    assert(() {
+      debugFill('Orientation: $orientation');
+      return true;
+    }());
   }
 
   final int _width;

@@ -19,9 +19,10 @@ import 'package:meta/meta.dart';
 import '../data_types.dart';
 import '../document.dart';
 import '../stream.dart';
+import 'diagnostic.dart';
 
 /// Base Object used in the PDF file
-abstract class PdfObject<T extends PdfDataType> {
+abstract class PdfObject<T extends PdfDataType> with PdfDiagnostic {
   /// This is usually called by extensors to this class, and sets the
   /// Pdf Object Type
   PdfObject(
@@ -60,15 +61,6 @@ abstract class PdfObject<T extends PdfDataType> {
   /// The write method should call this before writing anything to the
   /// OutputStream. This will send the standard header for each object.
   void _writeStart(PdfStream os) {
-    assert(() {
-      if (pdfDocument.verbose) {
-        os.putComment('');
-        os.putComment('-' * 78);
-        os.putComment('$runtimeType');
-      }
-      return true;
-    }());
-
     os.putString('$objser $objgen obj\n');
   }
 

@@ -17,6 +17,7 @@
 import 'data_types.dart';
 import 'document.dart';
 import 'obj/catalog.dart';
+import 'obj/diagnostic.dart';
 import 'obj/encryption.dart';
 import 'obj/info.dart';
 import 'obj/object.dart';
@@ -25,7 +26,7 @@ import 'stream.dart';
 import 'xref.dart';
 
 /// PDF document writer
-class PdfOutput {
+class PdfOutput with PdfDiagnostic {
   /// This creates a Pdf [PdfStream]
   PdfOutput(this.os, this.version, this.verbose) {
     String v;
@@ -42,20 +43,16 @@ class PdfOutput {
     os.putBytes(const <int>[0x25, 0xC2, 0xA5, 0xC2, 0xB1, 0xC3, 0xAB, 0x0A]);
     assert(() {
       if (verbose) {
-        _stopwatch = Stopwatch()..start();
-        os.putComment('');
-        os.putComment('Verbose dart_pdf');
-        os.putComment('Creation date: ${DateTime.now()}');
-        _comment = os.offset;
-        os.putBytes(List<int>.filled(120, 0x20));
+        setInsertion(os);
+        startStopwatch();
+        debugFill('Verbose dart_pdf');
+        debugFill('Producer https://github.com/DavBfr/dart_pdf');
+        debugFill('Creation date: ${DateTime.now()}');
       }
       return true;
     }());
   }
 
-  late final Stopwatch _stopwatch;
-  var _comment = 0;
-
   /// Pdf version to output
   final PdfVersion version;
 
@@ -98,7 +95,23 @@ class PdfOutput {
     }
 
     xref.add(PdfXref(ob.objser, os.offset));
+    assert(() {
+      if (verbose) {
+        ob.setInsertion(os);
+        ob.startStopwatch();
+      }
+      return true;
+    }());
     ob.write(os);
+    assert(() {
+      if (verbose) {
+        ob.stopStopwatch();
+        ob.debugFill(
+            'Creation time: ${ob.elapsedStopwatch / Duration.microsecondsPerSecond} seconds');
+        ob.writeDebug(os);
+      }
+      return true;
+    }());
   }
 
   /// This closes the Stream, writing the xref table
@@ -171,15 +184,13 @@ class PdfOutput {
 
     assert(() {
       if (verbose) {
-        _stopwatch.stop();
-        final h = PdfStream();
-        h.putComment(
-            'Creation time: ${_stopwatch.elapsed.inMicroseconds / Duration.microsecondsPerSecond} seconds');
-        h.putComment('File size: ${os.offset} bytes');
-        h.putComment('Pages: ${rootID!.pdfDocument.pdfPageList.pages.length}');
-        h.putComment('Objects: ${xref.offsets.length}');
-
-        os.setBytes(_comment, h.output());
+        stopStopwatch();
+        debugFill(
+            'Creation time: ${elapsedStopwatch / Duration.microsecondsPerSecond} seconds');
+        debugFill('File size: ${os.offset} bytes');
+        debugFill('Pages: ${rootID!.pdfDocument.pdfPageList.pages.length}');
+        debugFill('Objects: ${xref.offsets.length}');
+        writeDebug(os);
       }
       return true;
     }());

@@ -3,7 +3,7 @@ description: A pdf producer for Dart. It can create pdf files for both web or fl
 homepage: https://github.com/DavBfr/dart_pdf/tree/master/pdf
 repository: https://github.com/DavBfr/dart_pdf
 issue_tracker: https://github.com/DavBfr/dart_pdf/issues
-version: 3.7.1
+version: 3.7.2
 
 environment:
   sdk: ">=2.12.0 <3.0.0"