Normalize composer annotations after text mutations

lib/app/components/custom_text_editing_controllers.dart

@@ -17,7 +17,6 @@ import "package:languagetool_textfield/core/enums/mistake_type.dart";
 import 'package:languagetool_textfield/languagetool_textfield.dart';
 import "package:languagetool_textfield/utils/closed_range.dart";
 import "package:languagetool_textfield/utils/keep_latest_response_service.dart";
-import 'package:tuple/tuple.dart';
 import 'package:bluebubbles/utils/logger/logger.dart';
 
 class Mentionable {
@@ -41,6 +40,70 @@ class Mentionable {
   String toString() => displayName;
 }
 
+/// Repairs the annotation partition after keyboards or IMEs report an editing
+/// delta that does not line up exactly with the previous selection.
+///
+/// Composer annotations are expected to cover the text once, without gaps or
+/// overlaps. Preserve valid formatting, clip overlaps, and fill uncovered text
+/// with a plain annotation.
+void normalizeComposerAnnotationCoverage(
+    List<Annotation> annotations, int textLength) {
+  if (textLength <= 0) {
+    annotations.clear();
+    return;
+  }
+
+  final candidates = annotations.where((annotation) {
+    if (annotation.range.length < 2) return false;
+    final start = annotation.range[0].clamp(0, textLength).toInt();
+    final end = annotation.range[1].clamp(0, textLength).toInt();
+    annotation.range = [start, end];
+    return end > start;
+  }).toList()
+    ..sort((a, b) {
+      final startComparison = a.range[0].compareTo(b.range[0]);
+      return startComparison != 0
+          ? startComparison
+          : a.range[1].compareTo(b.range[1]);
+    });
+
+  final repaired = <Annotation>[];
+  var pointer = 0;
+
+  void append(Annotation annotation) {
+    final last = repaired.lastOrNull;
+    if (last != null &&
+        last.range[1] == annotation.range[0] &&
+        last.eqUnranged(annotation)) {
+      last.range[1] = annotation.range[1];
+    } else {
+      repaired.add(annotation);
+    }
+  }
+
+  for (final annotation in candidates) {
+    final end = annotation.range[1];
+    if (end <= pointer) continue;
+
+    final start = max(pointer, annotation.range[0]);
+    if (start > pointer) {
+      append(Annotation(range: [pointer, start]));
+    }
+
+    annotation.range = [start, end];
+    append(annotation);
+    pointer = end;
+  }
+
+  if (pointer < textLength) {
+    append(Annotation(range: [pointer, textLength]));
+  }
+
+  annotations
+    ..clear()
+    ..addAll(repaired);
+}
+
 class SpellCheckTextEditingController extends TextEditingController {
   SpellCheckTextEditingController({super.text, this.focusNode}) {
     assert(focusNode != null || !(kIsDesktop || kIsWeb));
@@ -509,30 +572,7 @@ class MentionTextEditingController extends SpellCheckTextEditingController {
   bool changeLock = false;
 
   void validateRange() {
-    annotations.sort((a, b) => a.range[0].compareTo(b.range[0]));
-    if (text.isEmpty) {
-      assert(annotations.isEmpty);
-    }
-    Annotation? lastAnnotation;
-    var pointer = 0;
-    while (pointer < text.length) {
-      var annotation = annotations.firstWhere((a) => a.range[0] == pointer);
-      // do we overlap with any other annotation?
-      assert(!annotations.any((a) => ((a.range[0] >= annotation.range[0] && a.range[0] < annotation.range[1]) ||
-          (a.range[1] > annotation.range[0] && a.range[1] <= annotation.range[1])) && annotation != a));
-      // we cannot have zero length
-      assert(annotation.range[0] != annotation.range[1]);
-      pointer = annotation.range[1];
-
-      if (lastAnnotation?.eqUnranged(annotation) ?? false) {
-        lastAnnotation!.range[1] = annotation.range[1]; // merge equal annotations
-        annotations.remove(annotation);
-      } else {
-        lastAnnotation = annotation;
-      }
-    }
-    assert(pointer == text.length);
-    assert(lastAnnotation == annotations.lastOrNull);
+    normalizeComposerAnnotationCoverage(annotations, text.length);
   }
 
   List<Annotation> annotationsForRange(TextSelection range) {

test/components/custom_text_editing_controllers_test.dart

@@ -0,0 +1,58 @@
+import 'package:bluebubbles/app/components/custom_text_editing_controllers.dart';
+import 'package:bluebubbles/database/global/message_part.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('normalizeComposerAnnotationCoverage', () {
+    test('fills a transient gap without discarding valid formatting', () {
+      final annotations = [
+        Annotation(range: [0, 3], bold: true),
+        Annotation(range: [5, 8], italic: true),
+      ];
+
+      normalizeComposerAnnotationCoverage(annotations, 10);
+
+      expect(annotations.map((annotation) => annotation.range), [
+        [0, 3],
+        [3, 5],
+        [5, 8],
+        [8, 10],
+      ]);
+      expect(annotations.first.bold, isTrue);
+      expect(annotations[2].italic, isTrue);
+    });
+
+    test('clips overlaps into a single complete partition', () {
+      final annotations = [
+        Annotation(range: [-2, 4], bold: true),
+        Annotation(range: [2, 8], italic: true),
+        Annotation(range: [8, 20]),
+      ];
+
+      normalizeComposerAnnotationCoverage(annotations, 10);
+
+      expect(annotations.map((annotation) => annotation.range), [
+        [0, 4],
+        [4, 8],
+        [8, 10],
+      ]);
+      expect(annotations.first.bold, isTrue);
+      expect(annotations[1].italic, isTrue);
+    });
+
+    test('merges adjacent plain ranges and clears empty text', () {
+      final annotations = [
+        Annotation(range: [0, 2]),
+        Annotation(range: [2, 4]),
+      ];
+
+      normalizeComposerAnnotationCoverage(annotations, 4);
+      expect(annotations.map((annotation) => annotation.range), [
+        [0, 4],
+      ]);
+
+      normalizeComposerAnnotationCoverage(annotations, 0);
+      expect(annotations, isEmpty);
+    });
+  });
+}