import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:go_router/go_router.dart';
import 'package:shuffle/core/l10n/l10n.dart';
import 'package:shuffle/core/routing/app_routes.dart';
import 'package:shuffle/core/theme/app_spacing.dart';
import 'package:shuffle/core/widgets/app_banner.dart';
import 'package:shuffle/core/widgets/app_checkbox_field.dart';
import 'package:shuffle/core/widgets/app_form_scaffold.dart';
import 'package:shuffle/core/widgets/app_password_field.dart';
import 'package:shuffle/core/widgets/app_primary_button.dart';
import 'package:shuffle/core/widgets/app_text_field.dart';
import 'package:shuffle/features/auth/domain/auth_failure.dart';
import 'package:shuffle/features/auth/domain/validation/display_name_rule.dart';
import 'package:shuffle/features/auth/domain/validation/email_format.dart';
import 'package:shuffle/features/auth/domain/validation/password_policy.dart';
import 'package:shuffle/features/auth/presentation/auth_failure_texts.dart';
import 'package:shuffle/features/auth/presentation/register/register_controller.dart';
import 'package:shuffle/features/auth/presentation/register/register_state.dart';
import 'package:shuffle/features/auth/presentation/widgets/auth_screen_title.dart';

/// Registration (`/register`, KTO-01 Kriterien 1 bis 4 und 10, QUE-04
/// Kriterium 1). Only shows state and forwards input to the
/// [RegisterController].
class RegisterScreen extends ConsumerStatefulWidget {
  const RegisterScreen({super.key});

  @override
  ConsumerState<RegisterScreen> createState() => _RegisterScreenState();
}

class _RegisterScreenState extends ConsumerState<RegisterScreen> {
  final _email = TextEditingController();
  final _password = TextEditingController();
  final _displayName = TextEditingController();
  final _emailFocus = FocusNode();
  final _passwordFocus = FocusNode();
  final _displayNameFocus = FocusNode();

  @override
  void initState() {
    super.initState();
    _emailFocus.addListener(
      () => _onFocusChange(_emailFocus, RegisterField.email),
    );
    _passwordFocus.addListener(() {
      if (_passwordFocus.hasFocus) {
        // The list of common passwords loads lazily on first use.
        unawaited(
          ref.read(registerControllerProvider.notifier).loadCommonPasswords(),
        );
      }
      _onFocusChange(_passwordFocus, RegisterField.password);
    });
    _displayNameFocus.addListener(
      () => _onFocusChange(_displayNameFocus, RegisterField.displayName),
    );
  }

  void _onFocusChange(FocusNode node, RegisterField field) {
    if (!node.hasFocus) {
      ref.read(registerControllerProvider.notifier).fieldBlurred(field);
    }
  }

  @override
  void dispose() {
    _email.dispose();
    _password.dispose();
    _displayName.dispose();
    _emailFocus.dispose();
    _passwordFocus.dispose();
    _displayNameFocus.dispose();
    super.dispose();
  }

  Future<void> _submit() async {
    final controller = ref.read(registerControllerProvider.notifier);
    final succeeded = await controller.submit();
    if (!mounted || !succeeded) {
      return;
    }
    final email = EmailFormat.normalize(
      ref.read(registerControllerProvider).email,
    );
    TextInput.finishAutofillContext();
    context.go(AppRoutes.registerCheckEmail, extra: email);
  }

  Future<void> _openLegal(LegalDocument document) async {
    final opened = await ref
        .read(registerControllerProvider.notifier)
        .openLegalDocument(document);
    if (!mounted || opened) {
      return;
    }
    ScaffoldMessenger.of(
      context,
    ).showSnackBar(SnackBar(content: Text(context.l10n.authErrorUnexpected)));
  }

  void _requestFocus(RegisterField? field) {
    final node = switch (field) {
      RegisterField.email => _emailFocus,
      RegisterField.password => _passwordFocus,
      RegisterField.displayName => _displayNameFocus,
      _ => null,
    };
    node?.requestFocus();
  }

  @override
  Widget build(BuildContext context) {
    ref.listen(registerControllerProvider, (previous, next) {
      if (previous?.focusRequest != next.focusRequest) {
        _requestFocus(next.focusField);
      }
    });
    final state = ref.watch(registerControllerProvider);
    final controller = ref.read(registerControllerProvider.notifier);
    final l10n = context.l10n;
    final busy = state.isSubmitting;

    return AppFormScaffold(
      key: const Key('register_screen'),
      child: AutofillGroup(
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            AuthScreenTitle(l10n.authRegisterTitle),
            if (state.bannerFailure case final failure?) ...[
              const SizedBox(height: AppSpacing.lg),
              _FailureBanner(
                key: const Key('register_banner'),
                failure: failure,
                onRetry: busy ? null : _submit,
              ),
            ],
            const SizedBox(height: AppSpacing.xl),
            AppTextField(
              key: const Key('register_email'),
              label: l10n.authFieldEmailLabel,
              controller: _email,
              focusNode: _emailFocus,
              keyboardType: TextInputType.emailAddress,
              textInputAction: TextInputAction.next,
              autofillHints: const [AutofillHints.email],
              autocorrect: false,
              enableSuggestions: false,
              enabled: !busy,
              errorText: _emailError(l10n, state),
              onChanged: controller.emailChanged,
            ),
            const SizedBox(height: AppSpacing.lg),
            AppPasswordField(
              key: const Key('register_password'),
              label: l10n.authFieldPasswordLabel,
              showPasswordLabel: l10n.authPasswordShow,
              hidePasswordLabel: l10n.authPasswordHide,
              controller: _password,
              focusNode: _passwordFocus,
              isNewPassword: true,
              textInputAction: TextInputAction.next,
              enabled: !busy,
              ruleHint: l10n.authPasswordRule,
              errorText: _passwordError(l10n, state),
              onChanged: controller.passwordChanged,
            ),
            const SizedBox(height: AppSpacing.lg),
            AppTextField(
              key: const Key('register_display_name'),
              label: l10n.authFieldDisplayNameLabel,
              controller: _displayName,
              focusNode: _displayNameFocus,
              textInputAction: TextInputAction.done,
              textCapitalization: TextCapitalization.words,
              autofillHints: const [AutofillHints.nickname],
              maxLength: DisplayNameRule.maxLength,
              showCounter: true,
              counterText: l10n.authDisplayNameCounter(
                state.displayNameLength,
                DisplayNameRule.maxLength,
              ),
              enabled: !busy,
              errorText: _displayNameError(l10n, state),
              onChanged: controller.displayNameChanged,
              onSubmitted: (_) {
                if (!busy) {
                  unawaited(_submit());
                }
              },
            ),
            const SizedBox(height: AppSpacing.lg),
            AppCheckboxField(
              key: const Key('register_age_checkbox'),
              value: state.ageConfirmed,
              label: l10n.authCheckboxAgeLabel,
              enabled: !busy,
              errorText: state.shownAgeError ? l10n.authAgeNotConfirmed : null,
              onChanged: (value) =>
                  controller.ageConfirmedChanged(value: value),
            ),
            AppCheckboxField.rich(
              key: const Key('register_terms_checkbox'),
              value: state.termsAccepted,
              enabled: !busy,
              segments: _termsSegments(l10n),
              errorText: state.shownTermsError
                  ? l10n.authTermsNotAccepted
                  : null,
              onChanged: (value) =>
                  controller.termsAcceptedChanged(value: value),
            ),
            const SizedBox(height: AppSpacing.xl),
            AppPrimaryButton(
              key: const Key('register_submit'),
              label: l10n.authRegisterSubmit,
              loadingLabel: l10n.authSubmitting,
              isLoading: busy,
              onPressed: _submit,
            ),
            const SizedBox(height: AppSpacing.sm),
            TextButton(
              key: const Key('register_login_link'),
              onPressed: busy ? null : () => context.go(AppRoutes.login),
              child: Text(l10n.authRegisterHaveAccount),
            ),
          ],
        ),
      ),
    );
  }

  List<AppLabelSegment> _termsSegments(AppLocalizations l10n) {
    final suffix = l10n.authCheckboxTermsSuffix;
    return [
      AppLabelSegment.text('${l10n.authCheckboxTermsPrefix} '),
      AppLabelSegment.link(
        l10n.authCheckboxTermsPrivacyLink,
        () => _openLegal(LegalDocument.privacy),
      ),
      AppLabelSegment.text(' ${l10n.authCheckboxTermsMiddle} '),
      AppLabelSegment.link(
        l10n.authCheckboxTermsTermsLink,
        () => _openLegal(LegalDocument.terms),
      ),
      if (suffix.isNotEmpty) AppLabelSegment.text(' $suffix'),
    ];
  }

  String? _emailError(AppLocalizations l10n, RegisterState state) {
    if (state.serverEmailInvalid || state.shownEmailError != null) {
      return l10n.authErrorEmailInvalid;
    }
    return null;
  }

  String? _passwordError(AppLocalizations l10n, RegisterState state) {
    if (state.serverPasswordReasons case final reasons?) {
      return weakPasswordMessage(l10n, reasons);
    }
    if (state.shownPasswordRequired) {
      return l10n.authPasswordRequired;
    }
    return switch (state.shownPasswordError) {
      PasswordTooShort(:final missing) => l10n.authPasswordTooShort(missing),
      PasswordCommon() => l10n.authPasswordCommon,
      null => null,
    };
  }

  String? _displayNameError(AppLocalizations l10n, RegisterState state) =>
      switch (state.shownDisplayNameError) {
        DisplayNameError.empty => l10n.authDisplayNameEmpty,
        DisplayNameError.tooLong => l10n.authDisplayNameTooLong(
          DisplayNameRule.maxLength,
        ),
        // U+200B: same message as "invalid" (Spec #1 § 5.4).
        DisplayNameError.invalidCharacter => l10n.authDisplayNameInvalid,
        null => null,
      };
}

class _FailureBanner extends StatelessWidget {
  const _FailureBanner({
    required this.failure,
    required this.onRetry,
    super.key,
  });

  final AuthFailure failure;
  final VoidCallback? onRetry;

  @override
  Widget build(BuildContext context) {
    final l10n = context.l10n;
    final retryable = failure is NetworkFailure || failure is Unexpected;
    return AppBanner(
      type: AppBannerType.error,
      typeLabel: l10n.authBannerTypeError,
      message: authFailureMessage(l10n, failure),
      actionLabel: retryable && onRetry != null ? l10n.authActionRetry : null,
      onAction: retryable ? onRetry : null,
    );
  }
}