patbond-flutter/lib/features/post/post_detail_page.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:patbond_flutter/core/network/api_exception.dart';
import 'package:patbond_flutter/core/theme/app_theme.dart';
import 'package:patbond_flutter/core/widgets/comment_tile.dart';
import 'package:patbond_flutter/core/widgets/inline_error_banner.dart';
import 'package:patbond_flutter/core/widgets/like_button.dart';
import 'package:patbond_flutter/core/widgets/pet_avatar.dart';
import 'package:patbond_flutter/core/widgets/post_media_grid.dart';
import 'package:patbond_flutter/features/community/community_controller.dart';
import 'package:patbond_flutter/features/community/community_display.dart';
import 'package:patbond_flutter/features/community/community_exceptions.dart';
import 'package:patbond_flutter/features/community/community_interaction_analytics.dart';
import 'package:patbond_flutter/features/community/community_models.dart';
import 'package:patbond_flutter/widgets/common.dart';

/// 帖子详情页（T3-15 整页替换，demo 数据层退役）：媒体全量渲染
/// （真九宫格 + 大图预览）+ 作者卡（关注双态）+ 正文 + 操作行
/// （ToggleSync 接线，Feed 卡片与详情共享同一 [CommunityController]
/// 实例，互动状态跨页一致）+ 评论区（游标列表 / 输入框创建 /
/// 仅本人评论可删）。
///
/// 形态取舍：
/// - 多图媒体区按本单裁定走**真九宫格**（[PostMediaGrid] 全量形态，
///   05 号 D11 的轮播方案弃用）；点格进全屏大图浏览
///   （03 号拍板 E：内置 InteractiveViewer，体验不达再升级 photo_view）。
/// - 40403（不存在/已删/防枚举合并）→ SnackBar 提示后返回 Feed 并
///   触发刷新（列表剔除失效帖）。
/// - 评论 @ 回复的**发起** UI 留待（数据层 replyToUserId 已支持），
///   响应中的 replyToUser 照常呈现。
class PostDetailPage extends StatefulWidget {
  const PostDetailPage({
    required this.controller,
    required this.postId,
    super.key,
    this.currentUserId,
    this.analytics,
    this.now,
  });

  /// Tab 级单例（app.dart 装配）；详情副本与 Feed 卡片互动字段同源。
  final CommunityController controller;

  final String postId;

  /// 当前登录用户 id（评论删除入口与关注钮自见性的 UI 判定；
  /// 服务端仍是权限的唯一裁决者）。
  final String? currentUserId;

  /// 互动域埋点（评论成败对 + 关注对；点赞/收藏对经 controller 上报）。
  final CommunityInteractionAnalytics? analytics;

  /// 相对时间的参考时钟（测试注入；缺省取当前时间）。
  final DateTime? now;

  @override
  State<PostDetailPage> createState() => _PostDetailPageState();
}

enum _DetailPhase { loading, error, ready }

class _PostDetailPageState extends State<PostDetailPage> {
  final _commentController = TextEditingController();
  final _commentFocus = FocusNode();

  _DetailPhase _phase = _DetailPhase.loading;
  ApiException? _loadError;

  /// 评论列表（页面级状态按页自建，03 号评估 §2 纪律；DESC 新评在前）。
  _DetailPhase _commentsPhase = _DetailPhase.loading;
  ApiException? _commentsError;
  List<PostComment> _comments = const [];
  String? _commentsCursor;
  bool _commentsHasMore = false;
  LoadMorePhase _commentsLoadMore = LoadMorePhase.idle;

  bool _sending = false;
  final Set<String> _deletingIds = {};

  /// 输入会话起点（首个字符输入时记；comment_create_succeeded 的
  /// durationMs 口径，评论不设 started 事件）。
  DateTime? _composeStartedAt;

  /// 本次输入会话内的提交序号（comment_create_failed.attemptSeq，
  /// 从 1 起；成功或清空输入后重置）。
  int _attemptSeq = 0;

  /// 关注状态（页面级；作者为本人或加载失败时不渲染关注钮）。
  FollowStats? _followStats;
  bool _following = false;

  /// 40403 返回 Feed 的单次守卫（详情与评论路径都可能触发）。
  bool _leaving = false;

  CommunityController get _controller => widget.controller;

  Post? get _post => _controller.cachedPost(widget.postId);

  @override
  void initState() {
    super.initState();
    _commentController.addListener(_onComposeChanged);
    if (_post != null) {
      _phase = _DetailPhase.ready;
      _ensureFollowStats(_post!);
    }
    unawaited(_loadPost());
    unawaited(_loadComments());
  }

  @override
  void dispose() {
    _commentController.dispose();
    _commentFocus.dispose();
    super.dispose();
  }

  // ---- 详情加载 ----

  Future<void> _loadPost() async {
    if (_post == null && _phase != _DetailPhase.loading) {
      setState(() {
        _phase = _DetailPhase.loading;
        _loadError = null;
      });
    }
    try {
      final post = await _controller.getPost(widget.postId);
      if (!mounted) return;
      setState(() => _phase = _DetailPhase.ready);
      _ensureFollowStats(post);
    } on PostNotFoundException {
      _handleGone();
    } on ApiException catch (error) {
      if (!mounted) return;
      // 有内存副本则保留展示（后台刷新失败不打断阅读）；无副本收敛 error 态。
      if (_post == null) {
        setState(() {
          _phase = _DetailPhase.error;
          _loadError = error;
        });
      }
    }
  }

  /// 40403：帖子不存在/已删/不可见——提示后返回 Feed 并刷新
  /// （整体替换剔除失效帖）。
  void _handleGone() {
    if (_leaving || !mounted) return;
    _leaving = true;
    ScaffoldMessenger.of(
      context,
    ).showSnackBar(const SnackBar(content: Text('帖子不存在或已被删除')));
    unawaited(_controller.refresh());
    Navigator.of(context).pop();
  }

  // ---- 评论列表 ----

  Future<void> _loadComments() async {
    setState(() {
      _commentsPhase = _DetailPhase.loading;
      _commentsError = null;
    });
    try {
      final page = await _controller.repository.listComments(widget.postId);
      if (!mounted) return;
      setState(() {
        _comments = page.items;
        _commentsCursor = page.nextCursor;
        _commentsHasMore = page.hasMore;
        _commentsPhase = _DetailPhase.ready;
        _commentsLoadMore = LoadMorePhase.idle;
      });
    } on PostNotFoundException {
      _handleGone();
    } on ApiException catch (error) {
      if (!mounted) return;
      setState(() {
        _commentsPhase = _DetailPhase.error;
        _commentsError = error;
      });
    }
  }

  Future<void> _loadMoreComments() async {
    if (_commentsPhase != _DetailPhase.ready ||
        !_commentsHasMore ||
        _commentsLoadMore == LoadMorePhase.loading) {
      return;
    }
    setState(() => _commentsLoadMore = LoadMorePhase.loading);
    try {
      final page = await _controller.repository.listComments(
        widget.postId,
        cursor: _commentsCursor,
      );
      if (!mounted) return;
      setState(() {
        _comments = [..._comments, ...page.items];
        _commentsCursor = page.nextCursor;
        _commentsHasMore = page.hasMore;
        _commentsLoadMore = LoadMorePhase.idle;
      });
    } on ApiException {
      if (!mounted) return;
      setState(() => _commentsLoadMore = LoadMorePhase.error);
    }
  }

  bool _onScrollNotification(ScrollNotification notification) {
    if (notification is ScrollUpdateNotification ||
        notification is ScrollEndNotification) {
      // 触底翻页（余量 400 提前预取）；失败态只走显式重试（Feed 同款守卫）。
      if (notification.metrics.extentAfter < 400 &&
          _commentsLoadMore == LoadMorePhase.idle) {
        unawaited(_loadMoreComments());
      }
    }
    return false;
  }

  // ---- 评论创建 / 删除 ----

  void _onComposeChanged() {
    final text = _commentController.text;
    if (text.isEmpty) {
      // 清空 = 输入会话结束（durationMs 起点与 attemptSeq 一并重置）。
      _composeStartedAt = null;
      _attemptSeq = 0;
    } else {
      _composeStartedAt ??= DateTime.now();
    }
    setState(() {}); // 发送钮可用态跟随文本。
  }

  Future<void> _submitComment() async {
    final text = _commentController.text.trim();
    if (text.isEmpty || _sending) return;
    final startedAt = _composeStartedAt ?? DateTime.now();
    _attemptSeq += 1;
    setState(() => _sending = true);
    try {
      final comment = await _controller.repository.createComment(
        widget.postId,
        CreateCommentRequest(content: text),
      );
      if (!mounted) return;
      widget.analytics?.commentCreateSucceeded(
        durationMs: DateTime.now().difference(startedAt).inMilliseconds,
        isReply: false,
        textLength: text.length,
      );
      setState(() {
        _comments = [comment, ..._comments];
        _sending = false;
      });
      _controller.adjustCommentCount(widget.postId, 1);
      _commentController.clear();
      _commentFocus.unfocus();
    } on ApiException catch (error) {
      if (!mounted) return;
      final reason = commentCreateFailureReasonOf(error);
      if (reason != null) {
        widget.analytics?.commentCreateFailed(
          reason: reason,
          attemptSeq: _attemptSeq,
          errorCode: error is ApiBusinessException ? error.code : null,
        );
      }
      setState(() => _sending = false);
      if (error is PostNotFoundException) {
        _handleGone();
        return;
      }
      ScaffoldMessenger.of(
        context,
      ).showSnackBar(SnackBar(content: Text(_commentErrorMessage(error))));
    }
  }

  String _commentErrorMessage(ApiException error) => switch (error) {
    ApiNetworkException _ => '网络异常，请检查网络后重试',
    ApiRateLimitException _ => '请求过于频繁，请稍后再试',
    ApiBusinessException(code: ApiCodes.paramError) => '评论内容不合规，请修改后重试',
    _ => '评论发送失败，请稍后重试',
  };

  Future<void> _deleteComment(PostComment comment) async {
    final confirmed = await showDialog<bool>(
      context: context,
      builder: (context) => AlertDialog(
        title: const Text('删除这条评论？'),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context, false),
            child: const Text('取消'),
          ),
          FilledButton(
            onPressed: () => Navigator.pop(context, true),
            child: const Text('删除'),
          ),
        ],
      ),
    );
    if (confirmed != true || !mounted) return;
    setState(() => _deletingIds.add(comment.id));
    try {
      await _controller.repository.deleteComment(comment.id);
      if (!mounted) return;
      _removeCommentLocally(comment.id);
    } on CommentNotFoundException {
      // 已在别处删除：本地同步剔除（终态一致，下次 getPost 对齐权威计数）。
      if (!mounted) return;
      _removeCommentLocally(comment.id);
    } on ApiException catch (error) {
      if (!mounted) return;
      setState(() => _deletingIds.remove(comment.id));
      final message = switch (error) {
        PostAccessDeniedException _ => '没有权限删除这条评论',
        ApiNetworkException _ => '网络异常，请检查网络后重试',
        _ => '删除失败，请稍后重试',
      };
      ScaffoldMessenger.of(
        context,
      ).showSnackBar(SnackBar(content: Text(message)));
    }
  }

  void _removeCommentLocally(String commentId) {
    setState(() {
      _deletingIds.remove(commentId);
      _comments = _comments.where((c) => c.id != commentId).toList();
    });
    _controller.adjustCommentCount(widget.postId, -1);
  }

  // ---- 关注 ----

  void _ensureFollowStats(Post post) {
    if (_followStats != null) return;
    final authorId = post.author.userId;
    if (authorId == widget.currentUserId) return; // 本人帖不渲染关注钮。
    unawaited(() async {
      try {
        final stats = await _controller.repository.getFollowStats(authorId);
        if (!mounted) return;
        setState(() {
          _followStats = stats;
          _following = stats.followedByMe;
        });
      } on ApiException {
        // 关注状态拉取失败：不渲染关注钮（不阻塞正文阅读）。
      }
    }());
  }

  Future<void> _toggleFollow(String authorId) async {
    final target = !_following;
    if (!target) {
      final confirmed = await showDialog<bool>(
        context: context,
        builder: (context) => AlertDialog(
          title: const Text('不再关注 TA？'),
          actions: [
            TextButton(
              onPressed: () => Navigator.pop(context, false),
              child: const Text('取消'),
            ),
            FilledButton(
              onPressed: () => Navigator.pop(context, true),
              child: const Text('不再关注'),
            ),
          ],
        ),
      );
      if (confirmed != true || !mounted) return;
    }
    setState(() => _following = target); // 乐观翻转（§4.5）。
    try {
      final state = target
          ? await _controller.repository.followUser(authorId)
          : await _controller.repository.unfollowUser(authorId);
      if (!mounted) return;
      target
          ? widget.analytics?.userFollowed(source: InteractionSource.postDetail)
          : widget.analytics?.userUnfollowed(
              source: InteractionSource.postDetail,
            );
      setState(() => _following = state.following); // 权威终态对账。
    } on ApiException {
      if (!mounted) return;
      // 回滚直接跳变 + SnackBar（§4.5，无过渡动画）。
      setState(() => _following = !target);
      ScaffoldMessenger.of(
        context,
      ).showSnackBar(const SnackBar(content: Text('操作失败，请重试')));
    }
  }

  // ---- 大图浏览 ----

  void _openGallery(List<PostMediaItem> media, int initialIndex) {
    Navigator.of(context).push(
      MaterialPageRoute<void>(
        fullscreenDialog: true,
        builder: (context) => _MediaGalleryPage(
          urls: [for (final item in media) item.url],
          initialIndex: initialIndex,
        ),
      ),
    );
  }

  // ---- 渲染 ----

  @override
  Widget build(BuildContext context) {
    return ListenableBuilder(
      listenable: _controller,
      builder: (context, _) {
        // 点赞/收藏对账失败的一次性 SnackBar（§3.5 回滚提示）。
        if (_controller.toggleError != null) {
          _controller.clearToggleError();
          WidgetsBinding.instance.addPostFrameCallback((_) {
            if (!mounted) return;
            ScaffoldMessenger.of(
              context,
            ).showSnackBar(const SnackBar(content: Text('操作失败，请重试')));
          });
        }
        final post = _post;
        return Scaffold(
          appBar: AppBar(
            title: const Text(
              '社区动态',
              style: TextStyle(fontSize: 16, fontWeight: FontWeight.w800),
            ),
            centerTitle: true,
            actions: [
              IconButton(
                tooltip: '分享',
                onPressed: () => ScaffoldMessenger.of(
                  context,
                ).showSnackBar(const SnackBar(content: Text('分享功能即将上线'))),
                icon: const Icon(Icons.ios_share_outlined),
              ),
            ],
          ),
          body: post != null ? _content(post) : _placeholder(),
          bottomSheet: post != null ? _commentInputBar() : null,
        );
      },
    );
  }

  /// 无内存副本时的 loading / error 态。
  Widget _placeholder() {
    if (_phase == _DetailPhase.error) {
      return Padding(
        padding: const EdgeInsets.all(24),
        child: Column(
          children: [
            InlineErrorBanner(message: feedLoadErrorMessage(_loadError)),
            const SizedBox(height: 16),
            FilledButton(onPressed: _loadPost, child: const Text('重试')),
          ],
        ),
      );
    }
    return const Center(child: CircularProgressIndicator());
  }

  Widget _content(Post post) {
    return NotificationListener<ScrollNotification>(
      onNotification: _onScrollNotification,
      child: ListView(
        padding: const EdgeInsets.only(bottom: 100),
        children: [
          _mediaSection(post),
          Padding(
            padding: const EdgeInsets.all(16),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                _authorCard(post),
                const SizedBox(height: 14),
                _bodyCard(post),
                const SizedBox(height: 14),
                _actionRow(post),
                const SizedBox(height: 22),
                Text(
                  '评论 (${post.commentCount})',
                  style: Theme.of(context).textTheme.titleLarge,
                ),
                const SizedBox(height: 12),
                ..._commentsSection(),
              ],
            ),
          ),
        ],
      ),
    );
  }

  /// 媒体全量：单图原比例（高度钳制 [0.75w, 1.33w]）；多图真九宫格
  ///（PostMediaGrid 全量形态，列数 2/4→2 列、3/5–9→3 列 + 超 9 折叠）。
  Widget _mediaSection(Post post) {
    final media = [...post.media]
      ..sort((a, b) => a.position.compareTo(b.position));
    if (media.isEmpty) return const SizedBox.shrink();
    if (media.length == 1) {
      final item = media.first;
      var ratio = 4 / 3;
      final width = item.widthPx;
      final height = item.heightPx;
      if (width != null && height != null && width > 0 && height > 0) {
        // 高度钳制 [宽×0.75, 宽×1.33]（05 §2.2）→ 宽高比落 [1/1.33, 1/0.75]。
        ratio = (width / height).clamp(1 / 1.33, 1 / 0.75);
      }
      return GestureDetector(
        onTap: () => _openGallery(media, 0),
        child: AspectRatio(
          aspectRatio: ratio,
          child: RemoteImage(url: item.url),
        ),
      );
    }
    return Padding(
      padding: const EdgeInsets.fromLTRB(16, 4, 16, 0),
      child: PostMediaGrid(
        urls: [for (final item in media) item.url],
        onCellTap: (index) => _openGallery(media, index),
      ),
    );
  }

  Widget _authorCard(Post post) {
    final author = post.author;
    final isSelf = author.userId == widget.currentUserId;
    return SectionCard(
      child: Row(
        children: [
          PetAvatar(size: PetAvatarSize.md, url: author.avatarUrl),
          const SizedBox(width: 12),
          Expanded(
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                Text(
                  authorDisplayName(author),
                  maxLines: 1,
                  overflow: TextOverflow.ellipsis,
                  style: Theme.of(context).textTheme.titleMedium,
                ),
                const SizedBox(height: 2),
                Text(
                  feedRelativeTime(
                    post.publishedAt ?? post.createdAt,
                    now: widget.now,
                  ),
                  style: const TextStyle(
                    color: AppColors.inkSoft,
                    fontSize: 12,
                  ),
                ),
              ],
            ),
          ),
          if (!isSelf && _followStats != null) _followButton(author.userId),
        ],
      ),
    );
  }

  /// 关注双态（05 §2.2）：未关注 tonal「＋ 关注」；已关注 Outlined
  /// 「已关注」+ 取关确认。
  Widget _followButton(String authorId) {
    if (_following) {
      return OutlinedButton(
        onPressed: () => _toggleFollow(authorId),
        style: OutlinedButton.styleFrom(
          foregroundColor: AppColors.inkSoft,
          side: const BorderSide(color: AppColors.border),
        ),
        child: const Text('已关注'),
      );
    }
    return FilledButton.tonal(
      onPressed: () => _toggleFollow(authorId),
      child: const Text('＋ 关注'),
    );
  }

  Widget _bodyCard(Post post) {
    return SectionCard(
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          if (post.title != null) ...[
            Text(post.title!, style: Theme.of(context).textTheme.titleMedium),
            const SizedBox(height: 8),
          ],
          if (post.category == PostCategory.help) ...[
            const TagPill('求助', color: AppColors.accent),
            const SizedBox(height: 8),
          ],
          Text(
            post.content,
            style: const TextStyle(
              color: AppColors.ink,
              fontSize: 14,
              height: 1.6,
            ),
          ),
          const SizedBox(height: 12),
          Text(
            '发布于 ${feedRelativeTime(post.publishedAt ?? post.createdAt, now: widget.now)}',
            style: const TextStyle(color: AppColors.inkSoft, fontSize: 12),
          ),
        ],
      ),
    );
  }

  /// 操作行：与 Feed 卡片同一套组件、同一 ToggleSync 实例（卡片外裸排，
  /// demo 的 FilledButton.tonalIcon 形态弃用）。
  Widget _actionRow(Post post) {
    return Row(
      children: [
        LikeButton(
          variant: LikeButtonVariant.like,
          active: post.likedByMe,
          count: post.likeCount,
          onPressed: () => _controller.toggleLike(
            widget.postId,
            source: InteractionSource.postDetail,
          ),
          semanticLabel: '点赞',
        ),
        const SizedBox(width: 4),
        // 评论锚点：聚焦底部输入框（唤起键盘直接开写）。
        Semantics(
          label: '评论',
          button: true,
          child: InkWell(
            onTap: _commentFocus.requestFocus,
            borderRadius: BorderRadius.circular(AppRadius.pill),
            child: ConstrainedBox(
              constraints: const BoxConstraints(minWidth: 44, minHeight: 44),
              child: Padding(
                padding: const EdgeInsets.symmetric(horizontal: 8),
                child: Row(
                  mainAxisSize: MainAxisSize.min,
                  children: [
                    const Icon(
                      Icons.chat_bubble_outline,
                      size: 20,
                      color: AppColors.inkSoft,
                    ),
                    const SizedBox(width: 4),
                    Text(
                      '${post.commentCount}',
                      style: const TextStyle(
                        color: AppColors.inkSoft,
                        fontSize: 13,
                        fontWeight: FontWeight.w600,
                      ),
                    ),
                  ],
                ),
              ),
            ),
          ),
        ),
        const SizedBox(width: 4),
        LikeButton(
          variant: LikeButtonVariant.bookmark,
          active: post.bookmarkedByMe,
          count: post.bookmarkCount,
          onPressed: () => _controller.toggleBookmark(
            widget.postId,
            source: InteractionSource.postDetail,
          ),
          semanticLabel: '收藏',
        ),
      ],
    );
  }

  List<Widget> _commentsSection() {
    switch (_commentsPhase) {
      case _DetailPhase.loading:
        return const [
          _CommentSkeleton(),
          SizedBox(height: 12),
          _CommentSkeleton(),
        ];
      case _DetailPhase.error:
        return [
          Center(
            child: Column(
              children: [
                Text(
                  feedLoadErrorMessage(_commentsError),
                  style: const TextStyle(
                    color: AppColors.inkSoft,
                    fontSize: 12,
                  ),
                ),
                TextButton(
                  onPressed: _loadComments,
                  child: const Text('加载失败，点此重试'),
                ),
              ],
            ),
          ),
        ];
      case _DetailPhase.ready:
        if (_comments.isEmpty) {
          return const [
            Padding(
              padding: EdgeInsets.symmetric(vertical: 32),
              child: Column(
                children: [
                  // 纯装饰图标，muted 合法（DEBT-2 口径）。
                  Icon(
                    Icons.chat_bubble_outline,
                    size: 36,
                    color: AppColors.muted,
                  ),
                  SizedBox(height: 8),
                  Text(
                    '还没有评论，来抢沙发',
                    style: TextStyle(color: AppColors.inkSoft, fontSize: 12),
                  ),
                ],
              ),
            ),
          ];
        }
        return [
          for (final comment in _comments)
            Padding(
              padding: const EdgeInsets.only(bottom: 12),
              child: CommentTile(
                comment: comment,
                now: widget.now,
                deleting: _deletingIds.contains(comment.id),
                // 仅本人评论渲染删除入口（服务端 40301/40404 仍兜底）。
                onDelete:
                    widget.currentUserId != null &&
                        comment.author.userId == widget.currentUserId
                    ? () => _deleteComment(comment)
                    : null,
              ),
            ),
          ..._commentsTail(),
        ];
    }
  }

  List<Widget> _commentsTail() {
    switch (_commentsLoadMore) {
      case LoadMorePhase.loading:
        return const [
          Padding(
            padding: EdgeInsets.symmetric(vertical: 12),
            child: Center(
              child: SizedBox(
                width: 24,
                height: 24,
                child: CircularProgressIndicator(
                  strokeWidth: 2.5,
                  color: AppColors.primary,
                ),
              ),
            ),
          ),
        ];
      case LoadMorePhase.error:
        return [
          Center(
            child: TextButton(
              onPressed: _loadMoreComments,
              child: const Text('加载失败，点此重试'),
            ),
          ),
        ];
      case LoadMorePhase.idle:
        return const [];
    }
  }

  /// 底部固定输入条（05 §2.2）：surface 底 + 顶部 border 1px 分隔线 +
  /// isDense 输入框 + filled 发送钮（空文本禁用；发送中 18 转圈锁尺寸）。
  Widget _commentInputBar() {
    final canSend = _commentController.text.trim().isNotEmpty && !_sending;
    return Container(
      decoration: const BoxDecoration(
        color: AppColors.surface,
        border: Border(top: BorderSide(color: AppColors.border)),
      ),
      padding: const EdgeInsets.fromLTRB(12, 10, 12, 10),
      child: SafeArea(
        top: false,
        child: Row(
          children: [
            Expanded(
              child: TextField(
                controller: _commentController,
                focusNode: _commentFocus,
                textInputAction: TextInputAction.send,
                onSubmitted: (_) => _submitComment(),
                decoration: const InputDecoration(
                  hintText: '写下你的评论…',
                  isDense: true,
                ),
              ),
            ),
            const SizedBox(width: 8),
            IconButton.filled(
              tooltip: '发送评论',
              onPressed: canSend ? _submitComment : null,
              icon: _sending
                  ? const SizedBox(
                      width: 18,
                      height: 18,
                      child: CircularProgressIndicator(
                        strokeWidth: 2,
                        color: Colors.white,
                      ),
                    )
                  : const Icon(Icons.send_rounded),
            ),
          ],
        ),
      ),
    );
  }
}

/// 评论区首载骨架（05 §3.7：32 圆 + 圆角 16 矩形块高 72，装饰性占位）。
class _CommentSkeleton extends StatelessWidget {
  const _CommentSkeleton();

  @override
  Widget build(BuildContext context) {
    return Row(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Container(
          width: 32,
          height: 32,
          decoration: const BoxDecoration(
            shape: BoxShape.circle,
            color: AppColors.surfaceTint,
          ),
        ),
        const SizedBox(width: 10),
        Expanded(
          child: Container(
            height: 72,
            decoration: BoxDecoration(
              color: AppColors.surfaceTint,
              borderRadius: BorderRadius.circular(16),
            ),
          ),
        ),
      ],
    );
  }
}

/// 全屏大图浏览（05 §2.2：黑底、双击缩放；03 号拍板 E 选内置
/// InteractiveViewer，零依赖）。横滑翻页 + 右上「n/N」ink 胶囊 + 关闭钮；
/// 下滑关闭与 InteractiveViewer 平移手势冲突，留待手势方案升级
/// （photo_view 复评条件：体验不达标）。
class _MediaGalleryPage extends StatefulWidget {
  const _MediaGalleryPage({required this.urls, required this.initialIndex});

  final List<String> urls;
  final int initialIndex;

  @override
  State<_MediaGalleryPage> createState() => _MediaGalleryPageState();
}

class _MediaGalleryPageState extends State<_MediaGalleryPage> {
  late final PageController _pageController = PageController(
    initialPage: widget.initialIndex,
  );
  late int _index = widget.initialIndex;
  final _viewerController = TransformationController();

  @override
  void dispose() {
    _pageController.dispose();
    _viewerController.dispose();
    super.dispose();
  }

  void _toggleZoom(TapDownDetails details) {
    if (_viewerController.value != Matrix4.identity()) {
      _viewerController.value = Matrix4.identity();
      return;
    }
    final position = details.localPosition;
    // 双击点为中心放大 2.5 倍。
    _viewerController.value = Matrix4.identity()
      ..translateByDouble(-position.dx * 1.5, -position.dy * 1.5, 0, 1)
      ..scaleByDouble(2.5, 2.5, 1, 1);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Stack(
        children: [
          PageView.builder(
            controller: _pageController,
            itemCount: widget.urls.length,
            onPageChanged: (index) {
              _viewerController.value = Matrix4.identity();
              setState(() => _index = index);
            },
            itemBuilder: (context, index) {
              return GestureDetector(
                onDoubleTapDown: index == _index ? _toggleZoom : null,
                onDoubleTap: () {}, // 消费事件，保留 onDoubleTapDown 的坐标。
                child: InteractiveViewer(
                  transformationController: index == _index
                      ? _viewerController
                      : null,
                  maxScale: 4,
                  child: Center(
                    child: RemoteImage(
                      url: widget.urls[index],
                      fit: BoxFit.contain,
                    ),
                  ),
                ),
              );
            },
          ),
          SafeArea(
            child: Padding(
              padding: const EdgeInsets.all(12),
              child: Row(
                children: [
                  IconButton(
                    tooltip: '关闭',
                    onPressed: () => Navigator.of(context).pop(),
                    icon: const Icon(Icons.close, color: Colors.white),
                  ),
                  const Spacer(),
                  if (widget.urls.length > 1)
                    Container(
                      padding: const EdgeInsets.symmetric(
                        horizontal: 10,
                        vertical: 4,
                      ),
                      decoration: BoxDecoration(
                        color: AppColors.ink,
                        borderRadius: BorderRadius.circular(AppRadius.pill),
                      ),
                      child: Text(
                        '${_index + 1}/${widget.urls.length}',
                        style: const TextStyle(
                          color: Colors.white,
                          fontSize: 12,
                          fontWeight: FontWeight.w700,
                        ),
                      ),
                    ),
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }
}