feat: support formula in DeltaMarkdownDecoder (#1155)

lib/src/core/legacy/built_in_attribute_keys.dart

@@ -3,7 +3,7 @@
 ///   bold, italic,
 ///   underline, strikethrough,
 ///   textColor, highlightColor,
-///   href
+///   href, formula
 ///
 /// Supported global rendering types:
 ///   heading: h1, h2, h3, h4, h5, h6, ...
@@ -20,6 +20,7 @@ class BuiltInAttributeKey {
   static String highlightColor = 'highlightColor';
   static String code = 'code';
   static String href = 'href';
+  static String formula = 'formula';
 
   static String subtype = 'subtype';
   static String heading = 'heading';

lib/src/plugins/markdown/decoder/custom_syntaxes/formula_syntax.dart

@@ -0,0 +1,18 @@
+import 'package:markdown/markdown.dart' as md;
+
+class FormulaInlineSyntax extends md.InlineSyntax {
+  FormulaInlineSyntax() : super(r'(?<!\$)\$(?!\$)([\s\S]+?)(?<!\$)\$(?!\$)');
+
+  @override
+  bool onMatch(md.InlineParser parser, Match match) {
+    final formula = match.group(1);
+    if (formula == null || formula.isEmpty) {
+      return false;
+    }
+
+    final element = md.Element('formula', [md.Text('\$')]);
+    element.attributes['formula'] = formula;
+    parser.addNode(element);
+    return true;
+  }
+}

lib/src/plugins/markdown/decoder/delta_markdown_decoder.dart

@@ -6,6 +6,8 @@ import 'package:appflowy_editor/src/core/legacy/built_in_attribute_keys.dart';
 import 'package:appflowy_editor/src/plugins/markdown/decoder/custom_syntaxes/underline_syntax.dart';
 import 'package:markdown/markdown.dart' as md;
 
+import 'custom_syntaxes/formula_syntax.dart';
+
 class DeltaMarkdownDecoder extends Converter<String, Delta>
     implements md.NodeVisitor {
   final _delta = Delta();
@@ -20,6 +22,7 @@ class DeltaMarkdownDecoder extends Converter<String, Delta>
   Delta convert(String input) {
     final inlineSyntaxes = [
       UnderlineInlineSyntax(),
+      FormulaInlineSyntax(),
       ...customInlineSyntaxes,
     ];
     final document = md.Document(
@@ -73,6 +76,8 @@ class DeltaMarkdownDecoder extends Converter<String, Delta>
       _attributes[BuiltInAttributeKey.href] = element.attributes['href'];
     } else if (element.tag == 'u') {
       _attributes[BuiltInAttributeKey.underline] = true;
+    } else if (element.tag == 'formula') {
+      _attributes[BuiltInAttributeKey.formula] = element.attributes['formula'];
     } else {
       element.attributes.forEach((key, value) {
         try {
@@ -97,6 +102,8 @@ class DeltaMarkdownDecoder extends Converter<String, Delta>
       _attributes.remove(BuiltInAttributeKey.href);
     } else if (element.tag == 'u') {
       _attributes.remove(BuiltInAttributeKey.underline);
+    } else if (element.tag == 'formula') {
+      _attributes.remove(BuiltInAttributeKey.formula);
     } else {
       for (final key in element.attributes.keys) {
         _attributes.remove(key);

lib/src/plugins/markdown/decoder/document_markdown_decoder.dart

@@ -5,6 +5,8 @@ import 'package:appflowy_editor/src/plugins/markdown/decoder/custom_syntaxes/und
 import 'package:collection/collection.dart';
 import 'package:markdown/markdown.dart' as md;
 
+import 'custom_syntaxes/formula_syntax.dart';
+
 class DocumentMarkdownDecoder extends Converter<String, Document> {
   DocumentMarkdownDecoder({
     this.markdownElementParsers = const [],
@@ -21,6 +23,7 @@ class DocumentMarkdownDecoder extends Converter<String, Document> {
       extensionSet: md.ExtensionSet.gitHubFlavored,
       inlineSyntaxes: [
         ...inlineSyntaxes,
+        FormulaInlineSyntax(),
         UnderlineInlineSyntax(),
       ],
       encodeHtml: false,

test/plugins/markdown/decoder/delta_markdown_decoder_test.dart

@@ -121,5 +121,20 @@ void main() async {
       final result = DeltaMarkdownDecoder().convert(markdown);
       expect(result, delta);
     });
+
+    test('formula', () {
+      const markdown = 'This is a math equation \$E = MC ^ 2\$';
+      final delta = Delta(
+        operations: [
+          TextInsert('This is a math equation '),
+          TextInsert(
+            '\$',
+            attributes: {BuiltInAttributeKey.formula: 'E = MC ^ 2'},
+          ),
+        ],
+      );
+      final result = DeltaMarkdownDecoder().convert(markdown);
+      expect(result, delta);
+    });
   });
 }