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

import '../../api/ai_api.dart';
import '../../core/network/api_env.dart';
import '../../models/ai.dart';
import '../../providers/ai_provider.dart';
import '../../providers/ai_config_provider.dart';
import '../../providers/ai_persona_provider.dart';
import '../../providers/auth_provider.dart';
import 'ai_config_page.dart';
import '../../utils/toast.dart';
import '../../widgets/avatar.dart';
import '../../widgets/state_views.dart';
import '../../widgets/cute_icon.dart';

/// 助手：和 AI 对话，问账单、问笔记。
///
/// 既是底部 Tab，也能从首页那个输入框 push 进来 —— 所以顶部自己画了
/// 返回箭头（canPop 时才画）。
class AssistantPage extends ConsumerStatefulWidget {
  const AssistantPage({super.key});

  @override
  ConsumerState<AssistantPage> createState() => _AssistantPageState();
}

class _AssistantPageState extends ConsumerState<AssistantPage> {
  final _input = TextEditingController();
  final _scroll = ScrollController();

  /// 空状态下的引导问题 —— 让用户知道能问什么，比一句「你好」有用
  static const _suggestions = [
    '这个月花了多少钱？',
    '上个月的支出分类排行',
    '我的笔记里有哪些关于 MySQL 的？',
  ];

  @override
  void initState() {
    super.initState();
    // 打开就把上一次的对话展开，而不是每次都从空白开始。
    // 放进 postFrameCallback：initState 里改 provider 状态会撞上「构建期间改状态」。
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (!mounted) return;
      ref.read(assistantProvider.notifier).restoreLastSessionIfNeeded();
    });
  }

  @override
  void dispose() {
    _input.dispose();
    _scroll.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final state = ref.watch(assistantProvider);
    _scheduleScroll();

    return Scaffold(
      body: Container(
        width: double.infinity,
        height: double.infinity,
        decoration: const BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment.topLeft,
            end: Alignment.bottomRight,
            colors: [Color(0xFFFFE5CC), Color(0xFFFFD4A8), Color(0xFFFFC08A)],
          ),
        ),
        child: SafeArea(
          child: Column(
            children: [
              _header(context),
              Expanded(child: _body(context, state)),
              if (state.error != null) _errorBar(state.error!),
              _inputBar(state),
            ],
          ),
        ),
      ),
    );
  }

  // ---------------------------------------------------------------- 顶部

  Widget _header(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.fromLTRB(10, 6, 8, 6),
      child: Row(
        children: [
          if (Navigator.of(context).canPop())
            _iconButton(
              icon: Icons.arrow_back,
              tooltip: '返回',
              onTap: () => Navigator.of(context).pop(),
            ),
          const Padding(
            padding: EdgeInsets.only(left: 6),
            child: Text(
              '助手',
              style: TextStyle(
                fontSize: 20,
                fontWeight: FontWeight.bold,
                color: Color(0xFF5D4037),
              ),
            ),
          ),
          const SizedBox(width: 8),
          // 当前用的哪个模型 —— 点一下就能换。
          // 放在标题旁边而不是藏进菜单里，是因为「刚才那句话怎么答得怪怪的」
          // 十有八九就是切错了模型，得让它随时可见。
          Flexible(child: _configChip(context)),
          const Spacer(),
          _iconButton(
            icon: Icons.history,
            tooltip: '历史对话',
            onTap: () => _showSessions(context),
          ),
          _iconButton(
            icon: Icons.add_comment_outlined,
            tooltip: '新对话',
            // 新对话要先选人设 —— 选了之后这一轮就锁定它，中途不会换
            onTap: () => _startNewChat(context),
          ),
        ],
      ),
    );
  }

  /// 顶栏上的「当前模型」小胶囊
  Widget _configChip(BuildContext context) {
    final active = ref.watch(activeAiConfigProvider);
    final label = active?.name ?? '--';

    return GestureDetector(
      onTap: () => openAiConfigPage(context),
      child: Container(
        padding: const EdgeInsets.symmetric(horizontal: 9, vertical: 4),
        decoration: BoxDecoration(
          color: const Color(0xFFFFF3E6),
          borderRadius: BorderRadius.circular(10),
        ),
        child: Row(
          mainAxisSize: MainAxisSize.min,
          children: [
            const Icon(Icons.memory, size: 12, color: Color(0xFFC8956E)),
            const SizedBox(width: 4),
            Flexible(
              child: Text(
                label,
                maxLines: 1,
                overflow: TextOverflow.ellipsis,
                style: const TextStyle(fontSize: 11.5, color: Color(0xFF8D6E63)),
              ),
            ),
            const Icon(Icons.expand_more, size: 13, color: Color(0xFFBCAAA4)),
          ],
        ),
      ),
    );
  }

  Widget _iconButton({
    required IconData icon,
    required String tooltip,
    required VoidCallback onTap,
  }) {
    return Tooltip(
      message: tooltip,
      child: InkWell(
        onTap: onTap,
        borderRadius: BorderRadius.circular(20),
        child: Padding(
          padding: const EdgeInsets.all(7),
          child: Icon(icon, size: 21, color: const Color(0xFF5D4037)),
        ),
      ),
    );
  }

  // ---------------------------------------------------------------- 主体

  Widget _body(BuildContext context, AssistantState state) {
    if (state.loadingHistory) {
      return const LoadingView(tip: '正在加载对话…');
    }
    if (state.isEmpty) {
      return _welcome(context);
    }

    final showTool = state.streaming && state.bubbles.isNotEmpty;
    return ListView.builder(
      controller: _scroll,
      physics: const AlwaysScrollableScrollPhysics(),
      padding: const EdgeInsets.fromLTRB(14, 8, 14, 12),
      itemCount: state.bubbles.length + (showTool ? 1 : 0),
      itemBuilder: (context, index) {
        if (index >= state.bubbles.length) {
          return _toolIndicator(state.activeTool);
        }
        return _bubble(context, state.bubbles[index]);
      },
    );
  }

  Widget _welcome(BuildContext context) {
    return ListView(
      padding: const EdgeInsets.fromLTRB(24, 40, 24, 0),
      children: [
        const Center(child: CuteIcon('assistant', size: 48)),
        const SizedBox(height: 14),
        const Center(
          child: Text(
            '问我点什么',
            style: TextStyle(
              fontSize: 17,
              fontWeight: FontWeight.w600,
              color: Color(0xFF5D4037),
            ),
          ),
        ),
        const SizedBox(height: 6),
        const Center(
          child: Text(
            '我能查你的账单统计和笔记',
            style: TextStyle(fontSize: 12.5, color: Color(0xFF8D6E63)),
          ),
        ),
        const SizedBox(height: 26),
        for (final s in _suggestions) ...[
          _suggestionChip(s),
          const SizedBox(height: 10),
        ],
      ],
    );
  }

  Widget _suggestionChip(String text) {
    return GestureDetector(
      onTap: () => _send(text),
      child: Container(
        padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 13),
        decoration: BoxDecoration(
          color: Colors.white.withValues(alpha: 0.9),
          borderRadius: BorderRadius.circular(14),
          border: Border.all(color: const Color(0xFFE8D9C5)),
        ),
        child: Row(
          children: [
            Expanded(
              child: Text(
                text,
                style: const TextStyle(fontSize: 13.5, color: Color(0xFF5D4037)),
              ),
            ),
            const Icon(Icons.north_east, size: 15, color: Color(0xFFBCAAA4)),
          ],
        ),
      ),
    );
  }

  // ---------------------------------------------------------------- 新对话

  /// 「新对话」：先让用户挑个人设，再开始。
  ///
  /// 挑完就锁定在这一轮对话上（存进 AssistantState.personaId），
  /// 之后不管用户在设置页怎么换人设，这轮都不会变 —— 这是刻意的，
  /// 见 `AssistantState.personaId` 的注释。
  ///
  /// 列表里第一项是「默认人设」，也就是什么都不选的状态。用户直接关掉弹层
  /// （返回 null）时也按默认处理，不强迫他做选择。
  Future<void> _startNewChat(BuildContext context) async {
    final picked = await showModalBottomSheet<_PersonaChoice>(
      context: context,
      backgroundColor: Colors.white,
      isScrollControlled: true,
      shape: const RoundedRectangleBorder(
        borderRadius: BorderRadius.vertical(top: Radius.circular(20)),
      ),
      builder: (_) => const _PersonaPickerSheet(),
    );
    if (!mounted) return;

    // 关掉弹层 = 取消，不开新对话。
    // 不自动用默认人设开始：误触一下就把用户正在看的对话顶掉太亏了。
    // 想用默认人设就点列表里第一项「默认人设」，一样是一下
    if (picked == null) return;

    // 记住这次选的，下次新对话默认预选它。
    // 这是**唯一**写这个偏好的地方 —— 设置页不提供「选说话的人」这个动作
    ref.read(preferredPersonaProvider.notifier).remember(picked.personaId);

    ref.read(assistantProvider.notifier).newChat(personaId: picked.personaId);
  }

  // ---------------------------------------------------------------- 气泡
  //
  // 微信风格：左右两侧都带头像，气泡紧贴头像那一侧。
  //   · 对方（AI）头像在左，用**当前会话绑的人设头像**；没设过就是默认小人
  //   · 自己（用户）头像在右，用账号头像；没设过是默认小人
  //
  // 头像只给 36px —— 太大反而抢戏，微信也就这个量级。

  Widget _bubble(BuildContext context, ChatBubble bubble) {
    final user = ref.watch(authProvider).user;

    if (bubble.isUser) {
      return _row(
        avatar: Avatar(
          assetPath: user?.avatar,
          size: 36,
          fallbackIcon: 'user',
        ),
        bubble: Container(
          margin: const EdgeInsets.only(left: 40),
          padding: const EdgeInsets.symmetric(horizontal: 14, vertical: 10),
          decoration: BoxDecoration(
            gradient: const LinearGradient(
              colors: [Color(0xFFC8956E), Color(0xFFD9A87C)],
            ),
            borderRadius: const BorderRadius.only(
              topLeft: Radius.circular(16),
              topRight: Radius.circular(16),
              bottomLeft: Radius.circular(16),
              bottomRight: Radius.circular(4),
            ),
          ),
          child: SelectableText(
            bubble.content,
            style: const TextStyle(
              fontSize: 14.5,
              height: 1.5,
              color: Colors.white,
            ),
          ),
        ),
        isUser: true,
      );
    }

    return _row(
      avatar: Avatar(
        // 会话锁定了哪个人设，气泡上就显示谁 —— 和这段回答实际用的 prompt 同一个人。
        // 不能用「新对话预选的那条」：用户之后新对话选了别人，
        // 这条旧会话的历史消息不该跟着换头像
        assetPath: _sessionPersonaAvatar(),
        size: 36,
        fallbackIcon: 'assistant',
      ),
      bubble: Container(
        margin: const EdgeInsets.only(right: 40),
        padding: const EdgeInsets.fromLTRB(14, 10, 14, 10),
        decoration: BoxDecoration(
          color: Colors.white,
          borderRadius: const BorderRadius.only(
            topLeft: Radius.circular(16),
            topRight: Radius.circular(16),
            bottomLeft: Radius.circular(4),
            bottomRight: Radius.circular(16),
          ),
          boxShadow: [
            BoxShadow(
              color: const Color(0xFF5D4037).withValues(alpha: 0.06),
              blurRadius: 8,
              offset: const Offset(0, 2),
            ),
          ],
        ),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            if (bubble.content.isEmpty)
              const _TypingDots()
            else
              MarkdownBody(
                data: bubble.content,
                selectable: true,
                styleSheet: _markdownStyle(context),
                onTapLink: (text, href, title) {
                  if (href == null || href.isEmpty) return;
                  Clipboard.setData(ClipboardData(text: href));
                  showToast(context, '链接已复制');
                },
                imageBuilder: (uri, title, alt) => Padding(
                  padding: const EdgeInsets.symmetric(vertical: 6),
                  child: ClipRRect(
                    borderRadius: BorderRadius.circular(8),
                    child: Image.network(resolveAssetUrl(uri.toString())),
                  ),
                ),
              ),
            if (bubble.streaming && bubble.content.isNotEmpty) ...[
              const SizedBox(height: 6),
              const _TypingDots(),
            ],
          ],
        ),
      ),
      isUser: false,
    );
  }

  /// 当前会话绑定的人设头像。null = 没设过（或人设被删了），显示默认图标。
  ///
  /// 关键在「按会话存的那个 id 去找」而不是读全局偏好 —— 见
  /// [personaByIdProvider] 的说明。
  String? _sessionPersonaAvatar() {
    final personaId = ref.watch(assistantProvider.select((s) => s.personaId));
    return ref.watch(personaByIdProvider(personaId))?.avatar;
  }

  /// 一行 = 头像 + 气泡。用户侧左右镜像。
  ///
  /// 头像用 [CrossAxisAlignment.start]（贴顶）而不是居中 —— 回答很长时
  /// 头像跟着垂直居中会飘到中间，微信也是贴顶的。
  Widget _row({
    required Widget avatar,
    required Widget bubble,
    required bool isUser,
  }) {
    return Padding(
      padding: const EdgeInsets.only(top: 10),
      child: Row(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: isUser
            ? [
                Expanded(child: Align(alignment: Alignment.centerRight, child: bubble)),
                const SizedBox(width: 8),
                avatar,
              ]
            : [
                avatar,
                const SizedBox(width: 8),
                Expanded(child: Align(alignment: Alignment.centerLeft, child: bubble)),
              ],
      ),
    );
  }

  MarkdownStyleSheet _markdownStyle(BuildContext context) {
    final base = MarkdownStyleSheet.fromTheme(Theme.of(context));
    return base.copyWith(
      p: const TextStyle(fontSize: 14.5, height: 1.6, color: Color(0xFF3E2723)),
      h1: const TextStyle(fontSize: 18, fontWeight: FontWeight.bold, height: 1.4, color: Color(0xFF3E2723)),
      h2: const TextStyle(fontSize: 16.5, fontWeight: FontWeight.bold, height: 1.4, color: Color(0xFF3E2723)),
      h3: const TextStyle(fontSize: 15.5, fontWeight: FontWeight.w600, height: 1.4, color: Color(0xFF3E2723)),
      listBullet: const TextStyle(fontSize: 14.5, height: 1.6, color: Color(0xFF3E2723)),
      code: const TextStyle(
        fontSize: 13,
        backgroundColor: Color(0xFFF5EFE6),
        color: Color(0xFF8D4B2A),
      ),
      codeblockDecoration: BoxDecoration(
        color: const Color(0xFFF5EFE6),
        borderRadius: BorderRadius.circular(8),
      ),
      blockquoteDecoration: BoxDecoration(
        color: const Color(0xFFFBF6EF),
        borderRadius: BorderRadius.circular(6),
        border: const Border(left: BorderSide(color: Color(0xFFC8956E), width: 3)),
      ),
      tableBorder: TableBorder.all(color: const Color(0xFFE8D9C5)),
      tableCellsPadding: const EdgeInsets.symmetric(horizontal: 8, vertical: 5),
    );
  }

  /// 工具调用提示：「正在查账单…」
  Widget _toolIndicator(String? tool) {
    return Padding(
      padding: const EdgeInsets.only(top: 10, left: 4),
      child: Row(
        children: [
          const SizedBox(
            width: 12,
            height: 12,
            child: CircularProgressIndicator(strokeWidth: 1.6, color: Color(0xFFC8956E)),
          ),
          const SizedBox(width: 8),
          Text(
            _toolLabel(tool),
            style: const TextStyle(fontSize: 12.5, color: Color(0xFF8D6E63)),
          ),
        ],
      ),
    );
  }

  String _toolLabel(String? name) => switch (name) {
        'query_bills' => '正在查账单…',
        'query_notes' => '正在搜笔记…',
        'get_note' => '正在读笔记…',
        _ => '正在查询…',
      };

  // ---------------------------------------------------------------- 错误与输入

  Widget _errorBar(String message) {
    return Container(
      width: double.infinity,
      margin: const EdgeInsets.fromLTRB(14, 0, 14, 6),
      padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 9),
      decoration: BoxDecoration(
        color: const Color(0xFFFFEBEE),
        borderRadius: BorderRadius.circular(10),
      ),
      child: Row(
        children: [
          const Icon(Icons.error_outline, size: 16, color: Color(0xFFD32F2F)),
          const SizedBox(width: 8),
          Expanded(
            child: Text(
              message,
              style: const TextStyle(fontSize: 12.5, color: Color(0xFFB71C1C)),
            ),
          ),
          GestureDetector(
            onTap: () => ref.read(assistantProvider.notifier).clearError(),
            child: const Icon(Icons.close, size: 15, color: Color(0xFFB71C1C)),
          ),
        ],
      ),
    );
  }

  Widget _inputBar(AssistantState state) {
    return Container(
      padding: const EdgeInsets.fromLTRB(14, 8, 14, 10),
      child: Row(
        crossAxisAlignment: CrossAxisAlignment.end,
        children: [
          Expanded(
            child: Container(
              decoration: BoxDecoration(
                color: Colors.white,
                borderRadius: BorderRadius.circular(22),
                border: Border.all(color: const Color(0xFFE8D9C5)),
              ),
              padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 2),
              child: TextField(
                controller: _input,
                enabled: !state.streaming,
                minLines: 1,
                maxLines: 4,
                textInputAction: TextInputAction.send,
                onSubmitted: _send,
                decoration: const InputDecoration(
                  border: InputBorder.none,
                  isDense: true,
                  contentPadding: EdgeInsets.symmetric(vertical: 12),
                  hintText: '问点什么…',
                  hintStyle: TextStyle(fontSize: 14, color: Color(0xFFBCAAA4)),
                ),
                style: const TextStyle(fontSize: 14.5, color: Color(0xFF5D4037)),
              ),
            ),
          ),
          const SizedBox(width: 8),
          _sendButton(state),
        ],
      ),
    );
  }

  Widget _sendButton(AssistantState state) {
    final disabled = state.streaming;
    return GestureDetector(
      onTap: disabled ? null : () => _send(_input.text),
      child: Container(
        width: 42,
        height: 42,
        decoration: BoxDecoration(
          shape: BoxShape.circle,
          gradient: disabled
              ? null
              : const LinearGradient(colors: [Color(0xFFC8956E), Color(0xFFF5D59E)]),
          color: disabled ? const Color(0xFFE8D9C5) : null,
        ),
        child: Icon(
          disabled ? Icons.hourglass_empty : Icons.arrow_upward,
          size: 20,
          color: disabled ? const Color(0xFFBCAAA4) : const Color(0xFF5D4037),
        ),
      ),
    );
  }

  void _send(String text) {
    final trimmed = text.trim();
    if (trimmed.isEmpty) return;
    _input.clear();
    ref.read(assistantProvider.notifier).send(trimmed);
  }

  // ---------------------------------------------------------------- 历史会话

  Future<void> _showSessions(BuildContext context) async {
    final selected = await showModalBottomSheet<ChatSessionItem>(
      context: context,
      backgroundColor: Colors.white,
      isScrollControlled: true,
      shape: const RoundedRectangleBorder(
        borderRadius: BorderRadius.vertical(top: Radius.circular(20)),
      ),
      builder: (_) => const _SessionSheet(),
    );
    if (selected == null || !mounted) return;
    // 把人设一并带进去 —— 历史对话要用它当时绑的那个，
    // 不能因为你现在换了默认人设就跟着变
    ref
        .read(assistantProvider.notifier)
        .openSession(selected.id, personaId: selected.personaId);
  }

  // ---------------------------------------------------------------- 滚动

  /// 只在用户本来就贴着底部时才自动滚动 —— 生成过程中用户往上翻看历史时别抢
  void _scheduleScroll() {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (!mounted || !_scroll.hasClients) return;
      final pos = _scroll.position;
      if (pos.maxScrollExtent - pos.pixels > 140) return;
      _scroll.jumpTo(pos.maxScrollExtent);
    });
  }
}

/// 生成中的三个点
class _TypingDots extends StatelessWidget {
  const _TypingDots();

  @override
  Widget build(BuildContext context) {
    return const Text(
      '●●●',
      style: TextStyle(fontSize: 7, letterSpacing: 2, color: Color(0xFFC8956E)),
    );
  }
}

/// 新对话时选人设的结果
class _PersonaChoice {
  const _PersonaChoice(this.personaId);

  /// null = 内置默认人设
  final int? personaId;
}

/// 新对话的人设选择面板。
///
/// 为什么新对话要先选人设：人设一旦定了，这轮对话就不再变（换了会前后不一致）。
/// 所以在「开始一段对话」这个时刻选是最自然的 —— 而不是聊着聊着去设置页改。
class _PersonaPickerSheet extends ConsumerWidget {
  const _PersonaPickerSheet();

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final personasAsync = ref.watch(aiPersonasProvider);
    // 预选上次用的那套，省得每次重选。注意这只是「预选」——
    // 真正生效的人设是新建会话时定下的那个
    final preferred = ref.watch(preferredPersonaProvider);

    return SafeArea(
      child: Padding(
        padding: const EdgeInsets.fromLTRB(16, 16, 16, 12),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            const Text(
              '这次想找谁聊？',
              style: TextStyle(
                fontSize: 15,
                fontWeight: FontWeight.w600,
                color: Color(0xFF5D4037),
              ),
            ),
            const SizedBox(height: 4),
            const Text(
              '选定后整段对话都是这个人，中途不会换',
              style: TextStyle(fontSize: 11.5, color: Color(0xFFBCAAA4)),
            ),
            const SizedBox(height: 12),
            Flexible(
              child: personasAsync.when(
                loading: () => const LoadingView(tip: '加载中…'),
                error: (e, _) => ErrorView(
                  message: '人设加载失败',
                  onRetry: () => ref.invalidate(aiPersonasProvider),
                ),
                data: (list) {
                  if (list.isEmpty) {
                    // 极端情况：后端一个人设都没有。不该卡住用户，
                    // 直接给一个「用默认」的出口
                    return ListTile(
                      contentPadding: const EdgeInsets.symmetric(horizontal: 4),
                      leading: const Avatar(size: 38, fallbackIcon: 'assistant'),
                      title: const Text('默认人设', style: TextStyle(fontSize: 14.5)),
                      onTap: () => Navigator.pop(context, const _PersonaChoice(null)),
                    );
                  }
                  return ListView.builder(
                    shrinkWrap: true,
                    itemCount: list.length,
                    itemBuilder: (context, index) {
                      final p = list[index];
                      final active = p.selectionKey == (preferred ?? -1);
                      return ListTile(
                        contentPadding: const EdgeInsets.symmetric(horizontal: 4),
                        leading: Avatar(
                          assetPath: p.avatar,
                          size: 42,
                          fallbackIcon: 'assistant',
                        ),
                        title: Text(
                          p.name,
                          maxLines: 1,
                          overflow: TextOverflow.ellipsis,
                          style: TextStyle(
                            fontSize: 14.5,
                            fontWeight: active ? FontWeight.w600 : FontWeight.normal,
                            color: const Color(0xFF5D4037),
                          ),
                        ),
                        subtitle: Text(
                          p.isDefault ? '代码内置的那套' : p.preview,
                          maxLines: 1,
                          overflow: TextOverflow.ellipsis,
                          style: const TextStyle(fontSize: 11.5, color: Color(0xFFBCAAA4)),
                        ),
                        trailing: active
                            ? const Icon(Icons.check_circle,
                                size: 19, color: Color(0xFFC8956E))
                            : null,
                        onTap: () => Navigator.pop(context, _PersonaChoice(p.id)),
                      );
                    },
                  );
                },
              ),
            ),
          ],
        ),
      ),
    );
  }
}

/// 历史会话面板
class _SessionSheet extends ConsumerWidget {
  const _SessionSheet();

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final sessionsAsync = ref.watch(chatSessionsProvider);

    return SafeArea(
      child: Padding(
        padding: const EdgeInsets.fromLTRB(16, 16, 16, 12),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            const Text(
              '历史对话',
              style: TextStyle(
                fontSize: 15,
                fontWeight: FontWeight.w600,
                color: Color(0xFF5D4037),
              ),
            ),
            const SizedBox(height: 12),
            Flexible(
              child: sessionsAsync.when(
                loading: () => const LoadingView(tip: '加载中…'),
                error: (e, _) => ErrorView(
                  message: '会话列表加载失败',
                  onRetry: () => ref.invalidate(chatSessionsProvider),
                ),
                data: (sessions) {
                  if (sessions.isEmpty) {
                    return const EmptyView(title: '还没有对话', tip: '问一句就有了');
                  }
                  return ListView.builder(
                    shrinkWrap: true,
                    itemCount: sessions.length,
                    itemBuilder: (context, index) {
                      final s = sessions[index];
                      return ListTile(
                        contentPadding: const EdgeInsets.symmetric(horizontal: 4),
                        // 会话头像 = 那条会话绑定的人设头像。
                        // 一眼看出「这段对话是谁在陪你」，不用点进去
                        leading: Avatar(
                          assetPath: s.personaAvatar,
                          size: 38,
                          fallbackIcon: 'assistant',
                        ),
                        title: Text(
                          s.title,
                          maxLines: 1,
                          overflow: TextOverflow.ellipsis,
                          style: const TextStyle(fontSize: 14.5, color: Color(0xFF5D4037)),
                        ),
                        subtitle: Text(
                          '${s.personaName} · ${s.updateTime}',
                          maxLines: 1,
                          overflow: TextOverflow.ellipsis,
                          style: const TextStyle(fontSize: 11.5, color: Color(0xFFBCAAA4)),
                        ),
                        trailing: IconButton(
                          tooltip: '删除',
                          icon: const Icon(Icons.delete_outline, size: 19),
                          color: const Color(0xFFBCAAA4),
                          onPressed: () => _confirmDelete(context, ref, s),
                        ),
                        onTap: () => Navigator.pop(context, s),
                      );
                    },
                  );
                },
              ),
            ),
          ],
        ),
      ),
    );
  }

  Future<void> _confirmDelete(BuildContext context, WidgetRef ref, ChatSessionItem session) async {
    final ok = await showDialog<bool>(
      context: context,
      builder: (dialogContext) => AlertDialog(
        title: const Text('删除对话'),
        content: Text('「${session.title}」将被删除，不能再恢复。'),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(dialogContext, false),
            child: const Text('取消'),
          ),
          TextButton(
            onPressed: () => Navigator.pop(dialogContext, true),
            child: const Text('删除', style: TextStyle(color: Color(0xFFD32F2F))),
          ),
        ],
      ),
    );
    if (ok != true) return;

    try {
      await ref.read(aiApiProvider).deleteSession(session.id);
      ref.invalidate(chatSessionsProvider);
      // 删掉的正好是当前打开的会话，就退回新对话
      final current = ref.read(assistantProvider).sessionId;
      if (current == session.id) {
        ref.read(assistantProvider.notifier).newChat();
      }
    } catch (e) {
      if (context.mounted) showToast(context, '删除失败', error: true);
    }
  }
}