/// 相册创建/编辑表单页（UI-03 §4 页面 09-10 重设计）。
///
/// 创建（页面 09）：两分组（SectionHeader）——「Event details」（开始/
/// 结束时间 + 显式可见时区字段，缺省 Asia/Shanghai，不静默取设备时区）+
/// 「Description & languages」（默认语言必选 + zh-CN·en 双语 tab：标题/
/// 描述/场地/地址按语言各一份——契约 translations 的场地/地址是逐语言字
/// 段，不合并为共享输入）；无 Access 页签（开关取契约缺省）。
///
/// 编辑（页面 10）：顶部 Details / Access 页签共享同一份草稿——Details
/// 复用创建字段；Access 为四开关（upload/public/download/original）各配
/// 说明，原图下载受总下载开关约束（关闭时禁用且生效值为 false）；切页签
/// 不丢草稿、不写服务器。保存按钮固定 bottomNavigationBar——键盘打开时
/// 常驻可达；未保存离开经 PopScope 放弃确认。
///
/// 编辑提交经 [AlbumFormDraft.toUpdatePatch] 最小化 PATCH（仅变更字段）；
/// 无变更时保存禁用。成功 pop(true) 供调用方刷新列表/详情；失败保留输入。
library;

import 'dart:io' show File;

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/albums/album_format.dart';
import '../features/albums/album_form.dart';
import '../features/albums/models.dart';
import '../features/uploads/enqueue.dart';
import '../l10n/app_localizations.dart';
import '../ui/components/section_header.dart';
import '../ui/tokens.dart';

/// 创建（[existing] 为 null）/ 编辑相册表单。
class AlbumFormPage extends ConsumerStatefulWidget {
  const AlbumFormPage({this.existing, this.initialDraft, super.key});

  /// 编辑目标；null = 创建模式。
  final Album? existing;

  /// 初始草稿（测试注入/预填）；缺省从 [existing] 构建或全新（创建）。
  final AlbumFormDraft? initialDraft;

  @override
  ConsumerState<AlbumFormPage> createState() => _AlbumFormPageState();
}

class _AlbumFormPageState extends ConsumerState<AlbumFormPage>
    with TickerProviderStateMixin {
  static const String _zh = 'zh-CN';
  static const String _en = 'en';

  late final List<TextEditingController> _controllers;

  late final TextEditingController _zhTitle;
  late final TextEditingController _zhDescription;
  late final TextEditingController _zhVenue;
  late final TextEditingController _zhAddress;
  late final TextEditingController _enTitle;
  late final TextEditingController _enDescription;
  late final TextEditingController _enVenue;
  late final TextEditingController _enAddress;
  late final TextEditingController _timezone;

  late String _defaultLocale;
  DateTime? _startAt;
  DateTime? _endAt;
  late bool _uploadEnabled;
  late bool _publicEnabled;
  late bool _downloadEnabled;
  late bool _originalDownloadEnabled;

  /// 进入时的初始草稿快照（未保存变更判定基准）。
  late final AlbumFormDraft _initial;

  /// 语言 tab（Details 内 zh-CN/en 字段切换）。
  late final TabController _langTabs;
  int _langIndex = 0;

  /// Details/Access 主页签（仅编辑模式创建；创建模式无 Access）。
  TabController? _mainTabs;
  int _mainIndex = 0;

  List<AlbumFormError> _errors = const <AlbumFormError>[];
  bool _submitting = false;

  /// 用户选择的封面本机文件路径（null = 未选）。
  /// 创建模式：相册创建成功后上传；编辑模式：保存后上传。
  String? _coverFilePath;

  /// 用户选择的宣传图本机文件路径（null = 未选；上传时机同封面）。
  String? _bannerFilePath;

  /// 编辑模式下的现有宣传图 URL（asset 现状查询，异步加载即时预览）。
  String? _existingBannerUrl;

  /// 编辑模式下的现有封面 URL（来自 AlbumSummary.cover，即时预览）。
  String? get _existingCoverUrl =>
      _coverFilePath == null ? (widget.existing?.cover?.url) : null;

  bool get _isCreate => widget.existing == null;

  @override
  void initState() {
    super.initState();
    // 编辑模式：加载现有宣传图预览（asset 现状查询；失败静默不阻塞表单）。
    if (widget.existing != null) {
      Future<void>.microtask(() async {
        try {
          final url = await ref
              .read(apiClientProvider)
              .fetchAlbumAssetUrl(widget.existing!.id, 'banner');
          if (mounted) setState(() => _existingBannerUrl = url);
        } on Object {
          // 预览加载失败不阻塞表单
        }
      });
    }
    final initial = widget.existing == null
        ? (widget.initialDraft ??
              AlbumFormDraft(
                zh: const AlbumTranslationDraft(locale: _zh),
                en: const AlbumTranslationDraft(locale: _en),
                defaultLocale: _zh,
                timezone: 'Asia/Shanghai',
              ))
        : (widget.initialDraft ?? AlbumFormDraft.fromAlbum(widget.existing!));
    _initial = initial;
    _zhTitle = TextEditingController(text: initial.zh.title);
    _zhDescription = TextEditingController(text: initial.zh.description);
    _zhVenue = TextEditingController(text: initial.zh.venue);
    _zhAddress = TextEditingController(text: initial.zh.address);
    _enTitle = TextEditingController(text: initial.en.title);
    _enDescription = TextEditingController(text: initial.en.description);
    _enVenue = TextEditingController(text: initial.en.venue);
    _enAddress = TextEditingController(text: initial.en.address);
    _timezone = TextEditingController(text: initial.timezone);
    _controllers = [
      _zhTitle,
      _zhDescription,
      _zhVenue,
      _zhAddress,
      _enTitle,
      _enDescription,
      _enVenue,
      _enAddress,
      _timezone,
    ];
    _defaultLocale = initial.defaultLocale;
    _startAt = initial.startAt;
    _endAt = initial.endAt;
    _uploadEnabled = initial.uploadEnabled;
    _publicEnabled = initial.publicEnabled;
    _downloadEnabled = initial.downloadEnabled;
    _originalDownloadEnabled = initial.originalDownloadEnabled;

    _langTabs = TabController(length: 2, vsync: this);
    // 仅编辑模式有主页签；内容区按 _mainIndex 手动切换（非 TabBarView），
    // 页签往返不重建字段——草稿共享、焦点不丢。
    if (!_isCreate) {
      _mainTabs = TabController(length: 2, vsync: this);
    }
  }

  @override
  void dispose() {
    _langTabs.dispose();
    _mainTabs?.dispose();
    for (final c in _controllers) {
      c.dispose();
    }
    super.dispose();
  }

  AlbumFormDraft _currentDraft() => AlbumFormDraft(
    zh: AlbumTranslationDraft(
      locale: _zh,
      title: _zhTitle.text,
      description: _zhDescription.text,
      venue: _zhVenue.text,
      address: _zhAddress.text,
    ),
    en: AlbumTranslationDraft(
      locale: _en,
      title: _enTitle.text,
      description: _enDescription.text,
      venue: _enVenue.text,
      address: _enAddress.text,
    ),
    defaultLocale: _defaultLocale,
    timezone: _timezone.text,
    startAt: _startAt,
    endAt: _endAt,
    uploadEnabled: _uploadEnabled,
    publicEnabled: _publicEnabled,
    downloadEnabled: _downloadEnabled,
    // 原图下载受总下载开关约束：下载关闭时生效值恒为 false。
    originalDownloadEnabled: _downloadEnabled && _originalDownloadEnabled,
  );

  /// 未保存变更判定：编辑 = 与原相册有差异（PATCH 非空）；创建 = 与初始
  /// 草稿有任何字段差异（用户实际输入过内容才算脏）。
  bool get _isDirty {
    if (_isCreate) {
      final current = _currentDraft();
      final init = _initial;
      return current.zh.title != init.zh.title ||
          current.zh.description != init.zh.description ||
          current.zh.venue != init.zh.venue ||
          current.zh.address != init.zh.address ||
          current.en.title != init.en.title ||
          current.en.description != init.en.description ||
          current.en.venue != init.en.venue ||
          current.en.address != init.en.address ||
          current.defaultLocale != init.defaultLocale ||
          current.timezone != init.timezone ||
          current.startAt != init.startAt ||
          current.endAt != init.endAt ||
          current.uploadEnabled != init.uploadEnabled ||
          current.publicEnabled != init.publicEnabled ||
          current.downloadEnabled != init.downloadEnabled ||
          current.originalDownloadEnabled != init.originalDownloadEnabled;
    }
    return _currentDraft().toUpdatePatch(widget.existing!) != null;
  }

  /// 编辑模式：与原值无任何差异时禁用保存（PATCH minProperties 1）。
  bool get _canSubmit {
    if (_submitting) return false;
    if (_isCreate) return true;
    return _currentDraft().toUpdatePatch(widget.existing!) != null;
  }

  Future<void> _submit() async {
    final draft = _currentDraft();
    final errors = draft.validate();
    if (errors.isNotEmpty) {
      // Details 字段校验失败：跳回 Details 页签展示错误（Access 页签无
      // 可校验字段）。
      setState(() {
        _errors = errors;
        if (_mainTabs != null && _mainIndex != 0) {
          _mainTabs!.index = 0;
          _mainIndex = 0;
        }
      });
      return;
    }
    setState(() {
      _submitting = true;
      _errors = const <AlbumFormError>[];
    });
    final l10n = AppLocalizations.of(context);
    final messenger = ScaffoldMessenger.of(context);
    final navigator = Navigator.of(context);
    try {
      late final String albumId;
      if (_isCreate) {
        final album = await ref
            .read(apiClientProvider)
            .createAlbum(draft.toCreateRequest());
        albumId = album.id;
      } else {
        final patch = draft.toUpdatePatch(widget.existing!);
        if (patch == null &&
            _coverFilePath == null &&
            _bannerFilePath == null) {
          navigator.pop(false);
          return;
        }
        if (patch != null) {
          await ref
              .read(apiClientProvider)
              .updateAlbum(widget.existing!.id, patch);
        }
        albumId = widget.existing!.id;
      }
      // 封面上传：相册保存成功后执行；失败不阻塞表单结果（封面可后补）。
      if (_coverFilePath != null) {
        try {
          await ref
              .read(apiClientProvider)
              .uploadAlbumCoverFromFile(albumId, _coverFilePath!);
        } on Object {
          // 封面失败仅提示，不影响相册保存结果。
          messenger.showSnackBar(
            SnackBar(content: Text(l10n.coverUploadFailed)),
          );
        }
      }
      // 宣传图上传：同封面——保存成功后执行，失败不阻塞表单结果。
      if (_bannerFilePath != null) {
        try {
          await ref
              .read(apiClientProvider)
              .uploadAlbumAssetFromFile(
                albumId,
                kind: 'banner',
                filePath: _bannerFilePath!,
              );
        } on Object {
          messenger.showSnackBar(
            SnackBar(content: Text(l10n.bannerUploadFailed)),
          );
        }
      }
      navigator.pop(true);
    } on AppException catch (error) {
      // 保存失败：保留输入，仅提示。
      messenger.showSnackBar(
        SnackBar(content: Text(l10n.messageForError(error))),
      );
    } on Object {
      messenger.showSnackBar(SnackBar(content: Text(l10n.errorGeneric)));
    } finally {
      if (mounted) setState(() => _submitting = false);
    }
  }

  /// 未保存变更 → 放弃确认；确认后直接 pop（绕过 PopScope 拦截）。
  Future<void> _confirmDiscard() async {
    final l10n = AppLocalizations.of(context);
    final discard = await showDialog<bool>(
      context: context,
      builder: (_) => AlertDialog(
        title: Text(l10n.unsavedChangesTitle),
        content: Text(l10n.unsavedChangesBody),
        actions: [
          TextButton(
            onPressed: () => Navigator.of(context).pop(false),
            child: Text(l10n.keepEditing),
          ),
          FilledButton(
            onPressed: () => Navigator.of(context).pop(true),
            child: Text(l10n.discardChanges),
          ),
        ],
      ),
    );
    if (discard == true && mounted) {
      Navigator.of(context).pop();
    }
  }

  /// 日期 + 时间选择器 → 相册时区墙钟 → UTC 瞬间。
  Future<void> _pickDateTime({required bool isStart}) async {
    final tzName = _timezone.text.trim();
    final initial = (isStart ? _startAt : _endAt) ?? _startAt ?? DateTime.now();
    final wall = tryToAlbumZone(initial, tzName) ?? initial.toUtc();
    final pickedDate = await showDatePicker(
      context: context,
      initialDate: wall,
      firstDate: DateTime(2000),
      lastDate: DateTime(2100),
    );
    if (pickedDate == null || !mounted) return;
    // UI06（用户需求 2026-09-23）：只选日期不带时间——开始=当天 00:00，
    // 结束=当天 23:59（活动整天语义；契约仍为 datetime，仅交互粒度变化）。
    final naive = DateTime(
      pickedDate.year,
      pickedDate.month,
      pickedDate.day,
      isStart ? 0 : 23,
      isStart ? 0 : 59,
    );
    final utc = albumWallClockToUtc(naive, tzName);
    setState(() {
      if (isStart) {
        _startAt = utc;
      } else {
        _endAt = utc;
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    final l10n = AppLocalizations.of(context);
    final mainTabs = _mainTabs;
    return PopScope(
      // 有未保存变更时拦截系统返回/aybePop；保存成功后的程序化 pop 不受
      // 影响（Navigator.pop 绕过 canPop）。
      canPop: !_isDirty,
      onPopInvokedWithResult: (didPop, _) {
        if (didPop) return;
        _confirmDiscard();
      },
      child: Scaffold(
        appBar: AppBar(
          title: Text(_isCreate ? l10n.createAlbumTitle : l10n.editAlbumTitle),
          // 编辑模式：Details / Access 页签（共享同一草稿）。
          bottom: mainTabs == null
              ? null
              : TabBar(
                  controller: mainTabs,
                  onTap: (index) => setState(() => _mainIndex = index),
                  tabs: [
                    Tab(text: l10n.formDetailsTab),
                    Tab(text: l10n.formAccessTab),
                  ],
                ),
        ),
        // 保存按钮固定底部：键盘打开时常驻可达（§4.5）。
        bottomNavigationBar: SafeArea(
          minimum: const EdgeInsets.fromLTRB(
            kSpace16,
            kSpace8,
            kSpace16,
            kSpace12,
          ),
          child: FilledButton(
            onPressed: _canSubmit ? _submit : null,
            child: _submitting
                ? const SizedBox(
                    height: 20,
                    width: 20,
                    child: CircularProgressIndicator(strokeWidth: 2),
                  )
                : Text(_isCreate ? l10n.createAlbumSubmit : l10n.saveChanges),
          ),
        ),
        body: mainTabs == null
            ? _detailsForm(l10n)
            : _mainIndex == 0
            ? _detailsForm(l10n)
            : _accessPanel(l10n),
      ),
    );
  }

  /// 封面选择器：16:9 可点击区域。编辑模式显示现有封面预览。
  Widget _buildCoverPicker(AppLocalizations l10n) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Text(l10n.coverPicker, style: Theme.of(context).textTheme.titleMedium),
        const SizedBox(height: kSpace8),
        InkWell(
          onTap: _submitting ? null : _pickCoverImage,
          borderRadius: BorderRadius.circular(kRadiusInput),
          child: Container(
            height: 180,
            width: double.infinity,
            decoration: BoxDecoration(
              color: Theme.of(context).colorScheme.surfaceContainerHighest,
              borderRadius: BorderRadius.circular(kRadiusInput),
              border: Border.all(
                color: Theme.of(context).colorScheme.outlineVariant,
                width: 1,
              ),
            ),
            child: ClipRRect(
              borderRadius: BorderRadius.circular(kRadiusInput),
              child: _coverFilePath != null
                  ? Image.file(
                      File(_coverFilePath!),
                      fit: BoxFit.cover,
                      errorBuilder: (_, _, _) => _coverPlaceholder(l10n),
                    )
                  : _existingCoverUrl != null
                  ? Image.network(
                      _existingCoverUrl!,
                      fit: BoxFit.cover,
                      errorBuilder: (_, _, _) => _coverPlaceholder(l10n),
                    )
                  : _coverPlaceholder(l10n),
            ),
          ),
        ),
        const SizedBox(height: kSpace4),
        Text(
          _coverFilePath != null ? l10n.coverSelected : l10n.coverPickerHint,
          style: Theme.of(context).textTheme.bodySmall?.copyWith(
            color: Theme.of(context).colorScheme.onSurfaceVariant,
          ),
        ),
      ],
    );
  }

  Widget _coverPlaceholder(AppLocalizations l10n) => Column(
    mainAxisAlignment: MainAxisAlignment.center,
    children: [
      Icon(
        Icons.add_photo_alternate_outlined,
        size: 48,
        color: Theme.of(context).colorScheme.primary,
      ),
      const SizedBox(height: kSpace8),
      Text(
        l10n.coverPickerHint,
        style: Theme.of(context).textTheme.bodySmall?.copyWith(
          color: Theme.of(context).colorScheme.onSurfaceVariant,
        ),
      ),
    ],
  );

  Future<void> _pickCoverImage() async {
    final path = await ref.read(singleImagePickerProvider)();
    if (path != null) {
      setState(() => _coverFilePath = path);
    }
  }

  Future<void> _pickBannerImage() async {
    final path = await ref.read(singleImagePickerProvider)();
    if (path != null) {
      setState(() => _bannerFilePath = path);
    }
  }

  /// 宣传图（banner）选择器：3:1 横幅可点击区域；编辑模式显示现有 banner。
  Widget _buildBannerPicker(AppLocalizations l10n) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Text(l10n.bannerPicker, style: Theme.of(context).textTheme.titleMedium),
        const SizedBox(height: kSpace8),
        InkWell(
          onTap: _submitting ? null : _pickBannerImage,
          borderRadius: BorderRadius.circular(kRadiusInput),
          child: Container(
            height: 120,
            width: double.infinity,
            decoration: BoxDecoration(
              color: Theme.of(context).colorScheme.surfaceContainerHighest,
              borderRadius: BorderRadius.circular(kRadiusInput),
              border: Border.all(
                color: Theme.of(context).colorScheme.outlineVariant,
                width: 1,
              ),
            ),
            child: ClipRRect(
              borderRadius: BorderRadius.circular(kRadiusInput),
              child: _bannerFilePath != null
                  ? Image.file(
                      File(_bannerFilePath!),
                      fit: BoxFit.cover,
                      errorBuilder: (_, _, _) => _bannerPlaceholder(l10n),
                    )
                  : _existingBannerUrl != null
                  ? Image.network(
                      _existingBannerUrl!,
                      fit: BoxFit.cover,
                      errorBuilder: (_, _, _) => _bannerPlaceholder(l10n),
                    )
                  : _bannerPlaceholder(l10n),
            ),
          ),
        ),
        const SizedBox(height: kSpace4),
        Text(
          _bannerFilePath != null ? l10n.bannerSelected : l10n.bannerPickerHint,
          style: Theme.of(context).textTheme.bodySmall?.copyWith(
            color: Theme.of(context).colorScheme.onSurfaceVariant,
          ),
        ),
      ],
    );
  }

  Widget _bannerPlaceholder(AppLocalizations l10n) => Column(
    mainAxisAlignment: MainAxisAlignment.center,
    children: [
      Icon(
        Icons.panorama_outlined,
        size: 40,
        color: Theme.of(context).colorScheme.primary,
      ),
      const SizedBox(height: kSpace8),
      Text(
        l10n.bannerPickerHint,
        style: Theme.of(context).textTheme.bodySmall?.copyWith(
          color: Theme.of(context).colorScheme.onSurfaceVariant,
        ),
      ),
    ],
  );

  /// Details（= 创建表单）：封面选择 + 分组字段 + 校验错误汇总。
  Widget _detailsForm(AppLocalizations l10n) {
    return Form(
      child: SingleChildScrollView(
        child: Padding(
          padding: const EdgeInsets.all(kSpace16),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: [
              // ── 封面选择（16:9 可点击区域） ─────────────────
              _buildCoverPicker(l10n),
              const SizedBox(height: kSpace16),

              // ── 宣传图选择（3:1 横幅；编辑模式显示现有 banner）──
              _buildBannerPicker(l10n),
              const SizedBox(height: kSpace24),

              // ── 分组 1：Event details ──────────────────────────
              SectionHeader(title: l10n.formEventDetails),
              const SizedBox(height: kSpace12),
              _dateTimeRow(isStart: true),
              _dateTimeRow(isStart: false),
              const SizedBox(height: kSpace8),
              TextFormField(
                controller: _timezone,
                onChanged: (_) => setState(() {}),
                decoration: InputDecoration(labelText: l10n.albumTimezone),
              ),
              const SizedBox(height: kSpace24),

              // ── 分组 2：Description & languages ───────────────
              SectionHeader(title: l10n.formDescriptionLanguages),
              const SizedBox(height: kSpace12),
              Text('${l10n.formDefaultLanguage} *'),
              const SizedBox(height: kSpace8),
              SegmentedButton<String>(
                segments: [
                  ButtonSegment(value: _zh, label: Text(l10n.localeChinese)),
                  ButtonSegment(value: _en, label: Text(l10n.localeEnglish)),
                ],
                selected: {_defaultLocale},
                onSelectionChanged: (selection) =>
                    setState(() => _defaultLocale = selection.first),
              ),
              const SizedBox(height: kSpace12),
              TabBar(
                controller: _langTabs,
                onTap: (index) => setState(() => _langIndex = index),
                tabs: [
                  Tab(text: l10n.localeChinese),
                  Tab(text: l10n.localeEnglish),
                ],
              ),
              const SizedBox(height: kSpace12),
              if (_langIndex == 0)
                _translationFields(
                  title: _zhTitle,
                  description: _zhDescription,
                  venue: _zhVenue,
                  address: _zhAddress,
                  isDefault: _defaultLocale == _zh,
                )
              else
                _translationFields(
                  title: _enTitle,
                  description: _enDescription,
                  venue: _enVenue,
                  address: _enAddress,
                  isDefault: _defaultLocale == _en,
                ),
              if (_errors.isNotEmpty) ...[
                const SizedBox(height: kSpace8),
                ..._errors.map(
                  (e) => Padding(
                    padding: const EdgeInsets.only(bottom: 4),
                    child: Text(
                      _errorText(l10n, e),
                      style: TextStyle(
                        color: Theme.of(context).colorScheme.error,
                      ),
                    ),
                  ),
                ),
              ],
              const SizedBox(height: kSpace24),
            ],
          ),
        ),
      ),
    );
  }

  /// Access 页签（仅编辑）：四开关各配说明；原图下载受总下载约束。
  Widget _accessPanel(AppLocalizations l10n) {
    final theme = Theme.of(context);
    final descStyle = theme.textTheme.bodySmall?.copyWith(
      color: theme.colorScheme.onSurfaceVariant,
    );
    return ListView(
      padding: const EdgeInsets.all(kSpace16),
      children: [
        SwitchListTile(
          contentPadding: EdgeInsets.zero,
          title: Text(l10n.formAllowUploads),
          subtitle: Text(l10n.formAllowUploadsDesc, style: descStyle),
          value: _uploadEnabled,
          onChanged: (v) => setState(() => _uploadEnabled = v),
        ),
        SwitchListTile(
          contentPadding: EdgeInsets.zero,
          title: Text(l10n.formPublicAccess),
          subtitle: Text(l10n.formPublicAccessDesc, style: descStyle),
          value: _publicEnabled,
          onChanged: (v) => setState(() => _publicEnabled = v),
        ),
        SwitchListTile(
          contentPadding: EdgeInsets.zero,
          title: Text(l10n.formAllowDownloads),
          subtitle: Text(l10n.formAllowDownloadsDesc, style: descStyle),
          value: _downloadEnabled,
          onChanged: (v) => setState(() => _downloadEnabled = v),
        ),
        SwitchListTile(
          contentPadding: EdgeInsets.zero,
          title: Text(l10n.formOriginalDownloads),
          subtitle: Text(l10n.formOriginalDownloadsDesc, style: descStyle),
          // 总下载关闭 → 原图下载禁用（生效值恒 false，重开下载恢复原值）。
          value: _downloadEnabled && _originalDownloadEnabled,
          onChanged: !_downloadEnabled
              ? null
              : (v) => setState(() => _originalDownloadEnabled = v),
        ),
      ],
    );
  }

  Widget _translationFields({
    required TextEditingController title,
    required TextEditingController description,
    required TextEditingController venue,
    required TextEditingController address,
    required bool isDefault,
  }) {
    final l10n = AppLocalizations.of(context);
    return Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: [
        TextFormField(
          controller: title,
          onChanged: (_) => setState(() {}),
          decoration: InputDecoration(
            labelText: isDefault ? '${l10n.albumTitle} *' : l10n.albumTitle,
          ),
        ),
        const SizedBox(height: 12),
        TextFormField(
          controller: description,
          onChanged: (_) => setState(() {}),
          maxLines: 2,
          decoration: InputDecoration(labelText: l10n.albumDescription),
        ),
        const SizedBox(height: 12),
        TextFormField(
          controller: venue,
          onChanged: (_) => setState(() {}),
          decoration: InputDecoration(labelText: l10n.albumVenue),
        ),
        const SizedBox(height: 12),
        TextFormField(
          controller: address,
          onChanged: (_) => setState(() {}),
          decoration: InputDecoration(labelText: l10n.albumAddress),
        ),
      ],
    );
  }

  /// 开始（必填）/ 结束（可选、可清除）时间行；展示按当前时区输入换算。
  Widget _dateTimeRow({required bool isStart}) {
    final l10n = AppLocalizations.of(context);
    final theme = Theme.of(context);
    final value = isStart ? _startAt : _endAt;
    // 只显日期（选择粒度为日期；时间由开始/结束日的 00:00/23:59 语义承载）。
    final wallShown = value == null
        ? null
        : (tryToAlbumZone(value, _timezone.text.trim()) ?? value.toUtc());
    final formatted = wallShown == null
        ? null
        : '${wallShown.year}/${wallShown.month}/${wallShown.day}';
    return Padding(
      padding: const EdgeInsets.only(bottom: 12),
      child: InkWell(
        onTap: () => _submitting ? null : _pickDateTime(isStart: isStart),
        borderRadius: BorderRadius.circular(8),
        child: InputDecorator(
          decoration: InputDecoration(
            labelText: isStart ? l10n.albumStartAt : l10n.albumEndAtOptional,
            suffixIcon: value == null
                ? const Icon(Icons.edit_calendar_outlined)
                : Row(
                    mainAxisSize: MainAxisSize.min,
                    children: [
                      const Icon(Icons.edit_calendar_outlined),
                      if (!isStart)
                        IconButton(
                          tooltip: l10n.clearEndAt,
                          icon: const Icon(Icons.clear),
                          onPressed: _submitting
                              ? null
                              : () => setState(() => _endAt = null),
                        ),
                    ],
                  ),
          ),
          child: Text(
            formatted ?? (isStart ? l10n.formStartAtRequired : l10n.notSet),
            style: formatted == null
                ? theme.textTheme.bodyMedium?.copyWith(
                    color: theme.colorScheme.onSurfaceVariant,
                  )
                : theme.textTheme.bodyMedium,
          ),
        ),
      ),
    );
  }

  String _errorText(AppLocalizations l10n, AlbumFormError error) {
    switch (error) {
      case AlbumFormError.defaultLocaleMissing:
        return l10n.formDefaultLocaleMissing;
      case AlbumFormError.titleRequiredWithFields:
        return l10n.formTitleRequiredWithFields;
      case AlbumFormError.startAtRequired:
        return l10n.formStartAtRequired;
      case AlbumFormError.endAtNotAfterStartAt:
        return l10n.formEndAtNotAfterStartAt;
      case AlbumFormError.timezoneInvalid:
        return l10n.albumTimezoneInvalid;
    }
  }
}