import 'package:shuffle/core/l10n/l10n.dart';
import 'package:shuffle/features/auth/domain/auth_failure.dart';
import 'package:shuffle/features/auth/domain/validation/password_policy.dart';

/// User-facing text of an [AuthFailure] (Spec #1 § 4.4, texts from
/// `docs/design/auth-screens.md`).
///
/// `emailSendLimited` has no text of its own: screens treat it as success
/// (F12) or convert it to `rateLimited` beforehand.
String authFailureMessage(AppLocalizations l10n, AuthFailure failure) =>
    switch (failure) {
      InvalidCredentials() => l10n.authErrorInvalidCredentials,
      EmailNotConfirmed() => l10n.authErrorEmailNotConfirmed,
      EmailSendLimited() || RateLimited() => l10n.authErrorRateLimited,
      WeakPassword(:final reasons) => weakPasswordMessage(l10n, reasons),
      SamePassword() => l10n.authErrorSamePassword,
      LinkInvalidOrExpired() => l10n.authErrorLinkInvalidOrExpired,
      InvalidEmail() => l10n.authErrorEmailInvalid,
      RegistrationRejected() => l10n.authErrorRegistrationRejected,
      NetworkFailure() => l10n.authErrorNetwork,
      Unexpected() => l10n.authErrorUnexpected,
    };

/// One sentence per distinct reason; an empty list gets the generic text.
String weakPasswordMessage(
  AppLocalizations l10n,
  List<WeakPasswordReason> reasons,
) {
  final texts = <String>{
    for (final reason in reasons)
      switch (reason) {
        WeakPasswordReason.length => l10n.authErrorWeakPasswordLength,
        WeakPasswordReason.pwned => l10n.authErrorWeakPasswordPwned,
        WeakPasswordReason.characters ||
        WeakPasswordReason.unknown => l10n.authErrorWeakPasswordCharacters,
      },
  };
  return texts.isEmpty ? l10n.authErrorWeakPasswordCharacters : texts.join(' ');
}

/// Failures the user can fix by simply trying again (offline, unexpected).
extension AuthFailureRetry on AuthFailure {
  bool get isRetryable => this is NetworkFailure || this is Unexpected;
}

/// Text of the password field error, shared by registration and reset.
///
/// Order: server answer, `same_password`, "required", then the local policy
/// [error] (only passed when it should be shown).
String? passwordFieldError(
  AppLocalizations l10n, {
  required PasswordError? error,
  required bool required,
  List<WeakPasswordReason>? serverReasons,
  bool serverSamePassword = false,
}) {
  if (serverReasons != null) {
    return weakPasswordMessage(l10n, serverReasons);
  }
  if (serverSamePassword) {
    return l10n.authErrorSamePassword;
  }
  if (required) {
    return l10n.authPasswordRequired;
  }
  return switch (error) {
    PasswordTooShort(:final missing) => l10n.authPasswordTooShort(missing),
    PasswordCommon() => l10n.authPasswordCommon,
    null => null,
  };
}

/// The only message shown is the "n missing" count, which changes with every
/// keystroke: screens announce it only when the field is left.
bool isPasswordLengthHintOnly({
  required PasswordError? error,
  required bool required,
  List<WeakPasswordReason>? serverReasons,
  bool serverSamePassword = false,
}) =>
    serverReasons == null &&
    !serverSamePassword &&
    !required &&
    error is PasswordTooShort;