feat: improve dialogue speech recognition and AI intervention

kouyu_english/lib/core/voice_service.dart

@@ -14,6 +14,42 @@ class VoiceService {
   VoiceService._();
   static final instance = VoiceService._();
 
+  /// Reverses the inverse text normalization (ITN) performed by system speech
+  /// recognisers, which convert spoken numbers like "one" into "1".
+  /// For an English-learning app the learner needs the spelled-out words.
+  static String reverseItn(String text) {
+    // Standalone digit → word. Uses word-boundary anchors so "12" or "100" are
+    // left alone (those are unlikely to be single-word utterances the learner
+    // intended as words).
+    const digitToWord = {
+      '0': 'zero',
+      '1': 'one',
+      '2': 'two',
+      '3': 'three',
+      '4': 'four',
+      '5': 'five',
+      '6': 'six',
+      '7': 'seven',
+      '8': 'eight',
+      '9': 'nine',
+      '10': 'ten',
+      '11': 'eleven',
+      '12': 'twelve',
+      '13': 'thirteen',
+      '14': 'fourteen',
+      '15': 'fifteen',
+      '16': 'sixteen',
+      '17': 'seventeen',
+      '18': 'eighteen',
+      '19': 'nineteen',
+      '20': 'twenty',
+    };
+    return text.replaceAllMapped(
+      RegExp(r'\b(\d{1,2})\b'),
+      (m) => digitToWord[m.group(1)!] ?? m.group(0)!,
+    );
+  }
+
   final FlutterTts _tts = FlutterTts();
   final SpeechToText _stt = SpeechToText();
   final AudioRecorder _recorder = AudioRecorder();
@@ -228,7 +264,7 @@ class VoiceService {
 
       await _stt.listen(
         onResult: (result) =>
-            onResult(result.recognizedWords, result.finalResult),
+            onResult(reverseItn(result.recognizedWords), result.finalResult),
         listenOptions: SpeechListenOptions(
           localeId: targetLocaleId,
           listenFor: const Duration(seconds: 30),