import 'dart:async';
import 'dart:js_interop';

import 'package:flutter/foundation.dart';

import 'spelling_tts_backend.dart';

SpellingTtsBackend createSpellingTtsBackend() => _WebSpeechBackend();

@JS('speechSynthesis')
external SpeechSynthesis get _speechSynthesis;

@JS()
extension type SpeechSynthesis._(JSObject _) implements JSObject {
  external void speak(SpeechSynthesisUtterance utterance);
  external void cancel();
}

@JS()
extension type SpeechSynthesisUtterance._(JSObject _) implements JSObject {
  external SpeechSynthesisUtterance();

  external String text;
  external String lang;
  external double rate;
  external double pitch;

  @JS('onend')
  external set onEnd(JSFunction? listener);

  @JS('onerror')
  external set onError(JSFunction? listener);
}

class _WebSpeechBackend implements SpellingTtsBackend {
  Completer<void>? _pending;

  @override
  Future<void> speak(String text, {String? title}) async {
    final String trimmed = text.trim();
    if (trimmed.isEmpty) {
      return;
    }

    if (title != null && title.isNotEmpty) {
      debugPrint('Spelling TTS utterance title: $title');
    }

    await stop();

    final Completer<void> done = Completer<void>();
    _pending = done;

    final SpeechSynthesisUtterance utterance = SpeechSynthesisUtterance();
    utterance.text = trimmed;
    utterance.lang = 'en-US';
    utterance.rate = 0.85;
    utterance.pitch = 1.0;
    utterance.onEnd = (() {
      if (!done.isCompleted) {
        done.complete();
      }
    }).toJS;
    utterance.onError = ((JSAny event) {
      debugPrint('Spelling web TTS error: $event');
      if (!done.isCompleted) {
        done.complete();
      }
    }).toJS;

    try {
      _speechSynthesis.speak(utterance);
      await done.future.timeout(
        const Duration(seconds: 30),
        onTimeout: () {
          debugPrint('Spelling web TTS timed out');
        },
      );
    } catch (e, st) {
      debugPrint('Spelling web TTS failed: $e\n$st');
      if (!done.isCompleted) {
        done.complete();
      }
    } finally {
      if (identical(_pending, done)) {
        _pending = null;
      }
    }
  }

  @override
  Future<void> stop() async {
    final Completer<void>? pending = _pending;
    _pending = null;
    try {
      _speechSynthesis.cancel();
    } catch (e, st) {
      debugPrint('Spelling web TTS stop failed: $e\n$st');
    }
    pending?.complete();
  }
}