@freezed
class AuthState with _$AuthState {
/// Welcome page/User has not entered the phone number
const factory AuthState.initial() = _Initial;

/// When something is happening. 
const factory AuthState.loading(String msg) = _Loading;

/// when waiting for user to enter phone number
const factory AuthState.waitingForUserInput() = _WaitingForUserInput;

/// when the code has been sent to the user
const factory AuthState.codeSent(String verificationId) = _CodeSent;

/// when the user successfully signs in
const factory AuthState.gotFirebaseUser(
  User user,
) = _GotFirebaseUser;

/// if you're planning to intergrate an external backend with a custom user model
const factory AuthState.success(User firebaseUser, CustomUser user) =
    _Success;

/// when firebase SMS auto-retrieval times out
const factory AuthState.codeRetreivalTimedOut() = _CodeTimedOut;

/// when an error occurred during phone number verification.
const factory AuthState.verificationError(
  FirebaseAuthException firebaseAuthException, {
  String? verificationId,
  String? message,
}) = _VerificationError;

/// when an invalid-phone-number error occurs during phone number verification
const factory AuthState.invalidPhoneNumber(
  FirebaseAuthException firebaseAuthException,
  Function(String) retry,
  String message,
) = _InvalidPhoneNumber;
const factory AuthState.unknownError(Object error, StackTrace? stackTrace) =
    _UnknownError;
}

  @override
  Widget build(BuildContext context, ScopedReader watch) {
    final authState = watch(phoneVerificationStateProvider);
    final authStateNotifier = watch(phoneVerificationStateProvider.notifier);
    return authState.when(
      initial: () => WelcomePage(
        onAcceptButtonPressed: () {
          authStateNotifier.acceptToUsePhone;
        },
      ),
      loading: (msg) => LoadingWidget(msg: msg),
      waitingForUserInput: () => PhoneInputWidget(
        verifyFunction: (validatedPhone) {
          authStateNotifier.verifyPhoneNumber(validatedPhone);
        },
      ),
      codeSent: (verificationId) => SMSCodeInputWidget(
        onTap: (smsCode) {
          authStateNotifier.verifyCode(smsCode, verificationId);
        },
      ),
      gotFirebaseUser: (user) => whenAuthentcated(user),
      success: (firebaseUser, customUser) => whenAuthentcated(firebaseUser),
      codeRetreivalTimedOut: () => CodeRetrievalTimedOutWidget(
        onTryAgain: () => authStateNotifier.retry,
      ),
      verificationError: (_, verificationId, msg) => InvalidCodeWidget(
        verificationId: verificationId,
        invalidCodeMsg: msg,
        onEnterNewCode: () {
          if (verificationId != null) {
            authStateNotifier.reEnterVerificationCode(verificationId);
          }
        },
        onUseDifferentPhone: () => authStateNotifier.retry,
      ),
      invalidPhoneNumber: (_, retryFn, _) => InvalidPhoneNumberWidget(
        onChangePhoneNumber: () {
          authStateNotifier.retry;
        },
      ),
      unknownError: (error, stackTrace) => GenericErrorWidget(
        error: error,
        message: 'Unknown Error occured',
        retryWidget: ElevatedButton(
          onPressed: () {
            authStateNotifier.retry;
          },
          child: Container(
            child: const Text('Start again'),
            alignment: Alignment.center,
            width: Adaptive.w(40),
          ),
        ),
      ),
    );
  }