fix: the cursor is inaccuracy when the text contains special emoji

lib/src/core/document/text_delta.dart

@@ -4,23 +4,11 @@ import 'dart:math';
 import 'package:flutter/foundation.dart';
 
 import 'package:appflowy_editor/src/core/document/attributes.dart';
+import 'package:flutter/services.dart';
 
 // constant number: 2^53 - 1
 const int _maxInt = 9007199254740991;
 
-List<int> stringIndexes(String text) {
-  final indexes = List<int>.filled(text.length, 0);
-  final iterator = text.runes.iterator;
-
-  while (iterator.moveNext()) {
-    for (var i = 0; i < iterator.currentSize; i++) {
-      indexes[iterator.rawIndex + i] = iterator.rawIndex;
-    }
-  }
-
-  return indexes;
-}
-
 abstract class TextOperation {
   Attributes? get attributes;
   int get length;
@@ -163,7 +151,6 @@ class Delta extends Iterable<TextOperation> {
 
   final List<TextOperation> _operations;
   String? _plainText;
-  List<int>? _runeIndexes;
 
   void addAll(Iterable<TextOperation> textOperations) {
     textOperations.forEach(add);
@@ -399,10 +386,10 @@ class Delta extends Iterable<TextOperation> {
     if (pos == 0) {
       return pos - 1;
     }
-    _plainText ??=
-        _operations.whereType<TextInsert>().map((op) => op.text).join();
-    _runeIndexes ??= stringIndexes(_plainText!);
-    return _runeIndexes![pos - 1];
+    final content = toPlainText();
+    final boundary = CharacterBoundary(content);
+    final index = boundary.getLeadingTextBoundaryAt(pos - 1);
+    return index ?? 0;
   }
 
   /// This method will return the position of the next rune.
@@ -413,19 +400,13 @@ class Delta extends Iterable<TextOperation> {
   ///
   /// This method can help you to compute the position of the next character.
   int nextRunePosition(int pos) {
-    final stringContent = toPlainText();
-    if (pos >= stringContent.length - 1) {
-      return stringContent.length;
-    }
-    _runeIndexes ??= stringIndexes(_plainText!);
-
-    for (var i = pos + 1; i < _runeIndexes!.length; i++) {
-      if (_runeIndexes![i] != pos) {
-        return _runeIndexes![i];
-      }
+    final content = toPlainText();
+    if (pos >= content.length - 1) {
+      return content.length;
     }
-
-    return stringContent.length;
+    final boundary = CharacterBoundary(content);
+    final index = boundary.getTrailingTextBoundaryAt(pos);
+    return index ?? content.length;
   }
 
   String toPlainText() {

test/core/document/text_delta_test.dart

@@ -325,11 +325,48 @@ void main() {
       });
     });
     group('runes', () {
-      test("stringIndexes", () {
-        final indexes = stringIndexes('😊');
-        expect(indexes[0], 0);
-        expect(indexes[1], 0);
+      test('emoji next rune', () {
+        final text = '😊👫👩‍👩‍👧‍👧👨‍👨‍👧👩‍👧🧑‍🚀'; // 6 emojis
+        final delta = Delta()..insert(text);
+        final pos = [0];
+        for (var i = 0; i < 6; i++) {
+          pos.add(delta.nextRunePosition(pos.last));
+        }
+        expect(pos, [0, 2, 4, 15, 23, 28, 33]);
       });
+
+      test('text next rune', () {
+        final text = 'Hello你好こんにちは안녕하세요';
+        final delta = Delta()..insert(text);
+        var pos = 0;
+        for (var i = 0; i < text.length; i++) {
+          expect(pos, i);
+          pos = delta.nextRunePosition(pos);
+        }
+        expect(pos, text.length);
+      });
+
+      test('emoji previous rune', () {
+        final text = '😊👫👩‍👩‍👧‍👧👨‍👨‍👧👩‍👧🧑‍🚀'; // 6 emojis
+        final delta = Delta()..insert(text);
+        final pos = [text.length];
+        for (var i = 0; i < 6; i++) {
+          pos.add(delta.prevRunePosition(pos.last));
+        }
+        expect(pos.reversed, [0, 2, 4, 15, 23, 28, 33]);
+      });
+
+      test('text previous rune', () {
+        final text = 'Hello你好こんにちは안녕하세요';
+        final delta = Delta()..insert(text);
+        var pos = text.length;
+        for (var i = text.length; i > 0; i--) {
+          expect(pos, i);
+          pos = delta.prevRunePosition(pos);
+        }
+        expect(pos, 0);
+      });
+
       test("next rune 1", () {
         final delta = Delta()..insert('😊');
         expect(delta.nextRunePosition(0), 2);
@@ -342,6 +379,10 @@ void main() {
         final delta = Delta()..insert('😊陈');
         expect(delta.nextRunePosition(2), 3);
       });
+      test("next rune 4", () {
+        final delta = Delta()..insert('😊陈');
+        expect(delta.nextRunePosition(2), 3);
+      });
       test("prev rune 1", () {
         final delta = Delta()..insert('😊陈');
         expect(delta.prevRunePosition(2), 0);