[super_editor_markdown] - serialization fixes (Resolves #712) (#713)

Author: matthew-carroll

super_editor_markdown/lib/src/markdown.dart

@@ -1,5 +1,6 @@
 import 'dart:convert';
 
+import 'package:flutter/widgets.dart';
 import 'package:markdown/markdown.dart' as md;
 import 'package:super_editor/super_editor.dart';
 
@@ -411,7 +412,7 @@ class _InlineMarkdownToDocument implements md.NodeVisitor {
   }
 }
 
-extension on AttributedText {
+extension Markdown on AttributedText {
   String toMarkdown() {
     final serializer = AttributedTextMarkdownSerializer();
     return serializer.serialize(this);
@@ -420,38 +421,29 @@ extension on AttributedText {
 
 /// Serializes an [AttributedText] into markdown format
 class AttributedTextMarkdownSerializer extends AttributionVisitor {
-  late String _text;
-  int _spanStart = 0;
-  final _buffer = StringBuffer();
+  late String _fullText;
+  late StringBuffer _buffer;
+  late int _bufferCursor;
 
   String serialize(AttributedText attributedText) {
-    _text = attributedText.text;
+    _fullText = attributedText.text;
+    _buffer = StringBuffer();
+    _bufferCursor = 0;
     attributedText.visitAttributions(this);
     return _buffer.toString();
   }
 
   @override
-  void visitAttributions(AttributedText fullText, int index, Set<Attribution> startingAttributions, Set<Attribution> endingAttributions) {
-    // Add end markers.
-    if (endingAttributions.isNotEmpty) {
-      final markdownStyles = _sortAndSerializeAttributions(endingAttributions, AttributionVisitEvent.end);
-      // Links are different from the plain styles since they are both not NamedAttributions (and therefore
-      // can't be checked using equality comparison) and asymmetrical in markdown.
-      final linkMarker = _encodeLinkMarker(endingAttributions, AttributionVisitEvent.end);
-
-      // +1 on end index because this visitor has inclusive indices
-      // whereas substring() expects an exclusive ending index.
-      _buffer
-        ..write(fullText.text.substring(_spanStart, index + 1))
-        ..write(markdownStyles)
-        ..write(linkMarker);
-
-      // When we reach the end of an attribution we need to hold the start of the next span,
-      // because if the last span has no attributions we will not visit any other index with
-      // a start marker.
-      // After we visit all the indexes we add the remaining text to the buffer.
-      _spanStart = index + 1;
-    }
+  void visitAttributions(
+    AttributedText fullText,
+    int index,
+    Set<Attribution> startingAttributions,
+    Set<Attribution> endingAttributions,
+  ) {
+    // Write out the text between the end of the last markers, and these new markers.
+    _buffer.write(
+      fullText.text.substring(_bufferCursor, index),
+    );
 
     // Add start markers.
     if (startingAttributions.isNotEmpty) {
@@ -461,19 +453,34 @@ class AttributedTextMarkdownSerializer extends AttributionVisitor {
       final linkMarker = _encodeLinkMarker(startingAttributions, AttributionVisitEvent.start);
 
       _buffer
-        ..write(fullText.text.substring(_spanStart, index))
         ..write(linkMarker)
         ..write(markdownStyles);
+    }
+
+    // Write out the character at this index.
+    _buffer.write(_fullText[index]);
+    _bufferCursor = index + 1;
+
+    // Add end markers.
+    if (endingAttributions.isNotEmpty) {
+      final markdownStyles = _sortAndSerializeAttributions(endingAttributions, AttributionVisitEvent.end);
+      // Links are different from the plain styles since they are both not NamedAttributions (and therefore
+      // can't be checked using equality comparison) and asymmetrical in markdown.
+      final linkMarker = _encodeLinkMarker(endingAttributions, AttributionVisitEvent.end);
 
-      _spanStart = index;
+      // +1 on end index because this visitor has inclusive indices
+      // whereas substring() expects an exclusive ending index.
+      _buffer
+        ..write(markdownStyles)
+        ..write(linkMarker);
     }
   }
 
   @override
   void onVisitEnd() {
     // When the last span has no attributions, we still have text that wasn't added to the buffer yet.
-    if (_spanStart <= _text.length - 1) {
-      _buffer.write(_text.substring(_spanStart));
+    if (_bufferCursor <= _fullText.length - 1) {
+      _buffer.write(_fullText.substring(_bufferCursor));
     }
   }
 

super_editor_markdown/test/attributed_text_markdown_test.dart

@@ -0,0 +1,95 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:super_editor/super_editor.dart';
+import 'package:super_editor_markdown/src/markdown.dart';
+
+void main() {
+  group("AttributedText markdown serializes", () {
+    test("un-styled text", () {
+      expect(
+        AttributedText(text: "This is unstyled text.").toMarkdown(),
+        "This is unstyled text.",
+      );
+    });
+
+    test("single character styles", () {
+      expect(
+        AttributedText(
+          text: "This is single character styles.",
+          spans: AttributedSpans(
+            attributions: [
+              SpanMarker(attribution: boldAttribution, offset: 8, markerType: SpanMarkerType.start),
+              SpanMarker(attribution: boldAttribution, offset: 8, markerType: SpanMarkerType.end),
+              SpanMarker(attribution: italicsAttribution, offset: 23, markerType: SpanMarkerType.start),
+              SpanMarker(attribution: italicsAttribution, offset: 23, markerType: SpanMarkerType.end),
+            ],
+          ),
+        ).toMarkdown(),
+        "This is **s**ingle characte*r* styles.",
+      );
+    });
+
+    test("bold text", () {
+      expect(
+        AttributedText(
+          text: "This is bold text.",
+          spans: AttributedSpans(
+            attributions: [
+              SpanMarker(attribution: boldAttribution, offset: 8, markerType: SpanMarkerType.start),
+              SpanMarker(attribution: boldAttribution, offset: 11, markerType: SpanMarkerType.end),
+            ],
+          ),
+        ).toMarkdown(),
+        "This is **bold** text.",
+      );
+    });
+
+    test("italics text", () {
+      expect(
+        AttributedText(
+          text: "This is italics text.",
+          spans: AttributedSpans(
+            attributions: [
+              SpanMarker(attribution: italicsAttribution, offset: 8, markerType: SpanMarkerType.start),
+              SpanMarker(attribution: italicsAttribution, offset: 14, markerType: SpanMarkerType.end),
+            ],
+          ),
+        ).toMarkdown(),
+        "This is *italics* text.",
+      );
+    });
+
+    test("multiple styles across the same span", () {
+      expect(
+        AttributedText(
+          text: "This is multiple styled text.",
+          spans: AttributedSpans(
+            attributions: [
+              SpanMarker(attribution: boldAttribution, offset: 8, markerType: SpanMarkerType.start),
+              SpanMarker(attribution: boldAttribution, offset: 22, markerType: SpanMarkerType.end),
+              SpanMarker(attribution: italicsAttribution, offset: 8, markerType: SpanMarkerType.start),
+              SpanMarker(attribution: italicsAttribution, offset: 22, markerType: SpanMarkerType.end),
+            ],
+          ),
+        ).toMarkdown(),
+        "This is ***multiple styled*** text.",
+      );
+    });
+
+    test("partially overlapping styles", () {
+      expect(
+        AttributedText(
+          text: "This is overlapping styles.",
+          spans: AttributedSpans(
+            attributions: [
+              SpanMarker(attribution: boldAttribution, offset: 8, markerType: SpanMarkerType.start),
+              SpanMarker(attribution: boldAttribution, offset: 13, markerType: SpanMarkerType.end),
+              SpanMarker(attribution: italicsAttribution, offset: 11, markerType: SpanMarkerType.start),
+              SpanMarker(attribution: italicsAttribution, offset: 18, markerType: SpanMarkerType.end),
+            ],
+          ),
+        ).toMarkdown(),
+        "This is **ove*rla**pping* styles.",
+      );
+    });
+  });
+}