/// 登录页（UI-01 §4.5 主题统一，P3 计划 Task 3 基础）。
///
/// 账号/密码表单 → [ApiClient.login]（会话由客户端自动持久化到
/// SessionStore）→ 成功 pushReplacement /home；失败以内联 StateBadge
/// （图标 + 文案 + 错误色）展示错误码本地化文案（AUTH_RATE_LIMITED 文案
/// 自带「稍后再试」；网络/校验错误各有专属文案）。提交期间按钮进入
/// 加载态防重复提交。
library;

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../core/api_client.dart';
import '../core/app_exception.dart';
import '../core/error_l10n.dart';
import '../features/uploads/engine_scope.dart';
import '../l10n/app_localizations.dart';
import '../ui/components/state_badge.dart';
import '../ui/tokens.dart';

/// 登录页。
class LoginPage extends ConsumerStatefulWidget {
  const LoginPage({super.key});

  @override
  ConsumerState<LoginPage> createState() => _LoginPageState();
}

class _LoginPageState extends ConsumerState<LoginPage> {
  final _formKey = GlobalKey<FormState>();
  final _accountController = TextEditingController();
  final _passwordController = TextEditingController();

  bool _submitting = false;

  /// 最近一次提交失败文案（内联 StateBadge 展示；null = 无错误）。
  String? _errorText;

  @override
  void dispose() {
    _accountController.dispose();
    _passwordController.dispose();
    super.dispose();
  }

  Future<void> _submit() async {
    if (!_formKey.currentState!.validate()) return;
    setState(() {
      _submitting = true;
      _errorText = null;
    });
    final l10n = AppLocalizations.of(context);
    final navigator = Navigator.of(context);
    try {
      await ref.read(apiClientProvider).login(
            _accountController.text.trim(),
            _passwordController.text,
          );
      // 登录成功：刷新会话账号 → 引擎以新账号 scope start（Task 9 接线）。
      await ref.read(sessionAccountProvider.notifier).refresh();
      navigator.pushReplacementNamed('/home');
    } on AppException catch (error) {
      // 429（AUTH_RATE_LIMITED）等文案经错误码映射；登录页的
      // AUTH_INVALID_CREDENTIALS 即「账号或密码错误」。
      if (mounted) setState(() => _errorText = l10n.messageForError(error));
    } on Object {
      if (mounted) setState(() => _errorText = l10n.errorGeneric);
    } finally {
      if (mounted) setState(() => _submitting = false);
    }
  }

  @override
  Widget build(BuildContext context) {
    final l10n = AppLocalizations.of(context);
    return Scaffold(
      appBar: AppBar(title: Text(l10n.appName)),
      body: Center(
        child: ConstrainedBox(
          constraints: const BoxConstraints(maxWidth: 420),
          child: Padding(
            padding: const EdgeInsets.all(kSpace24),
            child: Form(
              key: _formKey,
              autovalidateMode: AutovalidateMode.onUserInteraction,
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                crossAxisAlignment: CrossAxisAlignment.stretch,
                children: [
                  TextFormField(
                    controller: _accountController,
                    autofillHints: const [AutofillHints.username],
                    decoration: InputDecoration(labelText: l10n.username),
                    validator: (value) =>
                        (value == null || value.trim().isEmpty)
                            ? l10n.fieldRequired
                            : null,
                  ),
                  const SizedBox(height: kSpace16),
                  TextFormField(
                    controller: _passwordController,
                    obscureText: true,
                    enableSuggestions: false,
                    autocorrect: false,
                    autofillHints: const [AutofillHints.password],
                    onFieldSubmitted: (_) => _submitting ? null : _submit(),
                    decoration: InputDecoration(labelText: l10n.password),
                    validator: (value) => (value == null || value.isEmpty)
                        ? l10n.fieldRequired
                        : null,
                  ),
                  if (_errorText != null) ...[
                    const SizedBox(height: kSpace16),
                    StateBadge(
                      variant: BadgeVariant.error,
                      label: _errorText!,
                    ),
                  ],
                  const SizedBox(height: kSpace24),
                  FilledButton(
                    onPressed: _submitting ? null : _submit,
                    child: _submitting
                        ? const SizedBox(
                            height: 20,
                            width: 20,
                            child: CircularProgressIndicator(strokeWidth: 2),
                          )
                        : Text(l10n.login),
                  ),
                  const SizedBox(height: kSpace12),
                  Text(
                    l10n.loginHint,
                    textAlign: TextAlign.center,
                    style: Theme.of(context).textTheme.bodySmall,
                  ),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }
}