import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import '../../../../core/theme/app_colors.dart';
import '../providers/chat_providers.dart';

/// Session summary returned from the backend.
class SessionSummary {
  final String id;
  final String title;
  final String status;
  final DateTime createdAt;
  final DateTime updatedAt;

  const SessionSummary({
    required this.id,
    required this.title,
    required this.status,
    required this.createdAt,
    required this.updatedAt,
  });

  factory SessionSummary.fromJson(Map<String, dynamic> json) {
    return SessionSummary(
      id: json['id'] as String,
      // NOTE: Never use systemPrompt as title — it's an internal engine instruction
      // (voice sessions set systemPrompt to the voice-mode rules string, which caused
      // every voice conversation to appear as "你正在通过语音与用户实时对话。请…").
      // Always derive the display title from metadata or the session creation time.
      title: _generateTitle(json),
      status: json['status'] as String? ?? 'active',
      createdAt: DateTime.tryParse(json['createdAt'] as String? ?? '') ?? DateTime.now(),
      updatedAt: DateTime.tryParse(json['updatedAt'] as String? ?? '') ?? DateTime.now(),
    );
  }

  static String _generateTitle(Map<String, dynamic> json) {
    final meta = json['metadata'] as Map<String, dynamic>?;

    // 1. Use the explicit title stored by the backend on first task (text sessions)
    final storedTitle = meta?['title'] as String?;
    if (storedTitle != null && storedTitle.isNotEmpty) return storedTitle;

    final createdAt = DateTime.tryParse(json['createdAt'] as String? ?? '');

    // 2. Voice sessions: prefix with 🎙 and show time
    final isVoice = meta?['voiceMode'] as bool? ?? false;
    if (isVoice && createdAt != null) {
      return '语音对话 ${createdAt.month}/${createdAt.day} ${createdAt.hour}:${createdAt.minute.toString().padLeft(2, '0')}';
    }

    // 3. Fallback: date-based title
    if (createdAt != null) {
      return '对话 ${createdAt.month}/${createdAt.day} ${createdAt.hour}:${createdAt.minute.toString().padLeft(2, '0')}';
    }
    return '新对话';
  }
}

/// Groups sessions by date category.
enum DateGroup { today, yesterday, previous7Days, previous30Days, older }

/// Left drawer showing conversation history list.
/// Pattern: ChatGPT / Claude / Gemini style side drawer.
class ConversationDrawer extends ConsumerWidget {
  const ConversationDrawer({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final sessions = ref.watch(sessionListProvider);
    final currentSessionId = ref.watch(currentSessionIdProvider);

    return Drawer(
      backgroundColor: AppColors.background,
      child: SafeArea(
        child: Column(
          children: [
            // Header: New Chat button
            Padding(
              padding: const EdgeInsets.fromLTRB(16, 12, 16, 8),
              child: SizedBox(
                width: double.infinity,
                child: OutlinedButton.icon(
                  onPressed: () {
                    ref.read(chatProvider.notifier).startNewChat();
                    Navigator.of(context).pop();
                  },
                  icon: const Icon(Icons.add, size: 18),
                  label: const Text('新对话'),
                  style: OutlinedButton.styleFrom(
                    foregroundColor: AppColors.textPrimary,
                    side: BorderSide(color: AppColors.surfaceLight.withOpacity(0.6)),
                    padding: const EdgeInsets.symmetric(vertical: 12),
                    shape: RoundedRectangleBorder(
                      borderRadius: BorderRadius.circular(10),
                    ),
                  ),
                ),
              ),
            ),

            const Divider(color: AppColors.surfaceLight, height: 1),

            // Session list
            Expanded(
              child: sessions.when(
                data: (list) {
                  if (list.isEmpty) {
                    return Center(
                      child: Column(
                        mainAxisSize: MainAxisSize.min,
                        children: [
                          Icon(Icons.chat_bubble_outline, size: 48, color: AppColors.textMuted),
                          const SizedBox(height: 12),
                          Text('暂无对话历史', style: TextStyle(color: AppColors.textMuted, fontSize: 14)),
                        ],
                      ),
                    );
                  }

                  final grouped = _groupByDate(list);
                  return ListView(
                    padding: const EdgeInsets.symmetric(vertical: 8),
                    children: grouped.entries.expand((entry) {
                      return [
                        // Date group header
                        Padding(
                          padding: const EdgeInsets.fromLTRB(16, 12, 16, 4),
                          child: Text(
                            _dateGroupLabel(entry.key),
                            style: TextStyle(
                              color: AppColors.textMuted,
                              fontSize: 11,
                              fontWeight: FontWeight.w600,
                              letterSpacing: 0.5,
                            ),
                          ),
                        ),
                        // Sessions in this group
                        ...entry.value.map((session) => _SessionTile(
                          session: session,
                          isActive: session.id == currentSessionId,
                          onTap: () {
                            ref.read(chatProvider.notifier).switchSession(session.id);
                            Navigator.of(context).pop();
                          },
                          onDelete: () {
                            _confirmDelete(context, ref, session);
                          },
                        )),
                      ];
                    }).toList(),
                  );
                },
                loading: () => const Center(child: CircularProgressIndicator()),
                error: (err, _) => Center(
                  child: Column(
                    mainAxisSize: MainAxisSize.min,
                    children: [
                      Icon(Icons.error_outline, color: AppColors.error),
                      const SizedBox(height: 8),
                      Text('加载失败', style: TextStyle(color: AppColors.error)),
                      TextButton(
                        onPressed: () => ref.invalidate(sessionListProvider),
                        child: const Text('重试'),
                      ),
                    ],
                  ),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }

  Map<DateGroup, List<SessionSummary>> _groupByDate(List<SessionSummary> sessions) {
    final now = DateTime.now();
    final today = DateTime(now.year, now.month, now.day);
    final yesterday = today.subtract(const Duration(days: 1));
    final week = today.subtract(const Duration(days: 7));
    final month = today.subtract(const Duration(days: 30));

    final grouped = <DateGroup, List<SessionSummary>>{};

    for (final session in sessions) {
      final date = DateTime(session.updatedAt.year, session.updatedAt.month, session.updatedAt.day);
      DateGroup group;
      if (!date.isBefore(today)) {
        group = DateGroup.today;
      } else if (!date.isBefore(yesterday)) {
        group = DateGroup.yesterday;
      } else if (!date.isBefore(week)) {
        group = DateGroup.previous7Days;
      } else if (!date.isBefore(month)) {
        group = DateGroup.previous30Days;
      } else {
        group = DateGroup.older;
      }
      grouped.putIfAbsent(group, () => []).add(session);
    }

    return grouped;
  }

  String _dateGroupLabel(DateGroup group) {
    switch (group) {
      case DateGroup.today:
        return '今天';
      case DateGroup.yesterday:
        return '昨天';
      case DateGroup.previous7Days:
        return '最近7天';
      case DateGroup.previous30Days:
        return '最近30天';
      case DateGroup.older:
        return '更早';
    }
  }

  void _confirmDelete(BuildContext context, WidgetRef ref, SessionSummary session) {
    showDialog(
      context: context,
      builder: (ctx) => AlertDialog(
        backgroundColor: AppColors.surface,
        title: const Text('删除对话', style: TextStyle(color: AppColors.textPrimary)),
        content: Text(
          '确定要删除「${session.title}」吗？此操作不可恢复。',
          style: const TextStyle(color: AppColors.textSecondary),
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.of(ctx).pop(),
            child: const Text('取消'),
          ),
          TextButton(
            onPressed: () {
              Navigator.of(ctx).pop();
              ref.read(chatProvider.notifier).deleteSession(session.id);
              ref.invalidate(sessionListProvider);
            },
            style: TextButton.styleFrom(foregroundColor: AppColors.error),
            child: const Text('删除'),
          ),
        ],
      ),
    );
  }
}

/// Individual session list tile with long-press menu.
class _SessionTile extends StatelessWidget {
  final SessionSummary session;
  final bool isActive;
  final VoidCallback onTap;
  final VoidCallback onDelete;

  const _SessionTile({
    required this.session,
    required this.isActive,
    required this.onTap,
    required this.onDelete,
  });

  @override
  Widget build(BuildContext context) {
    return ListTile(
      dense: true,
      selected: isActive,
      selectedTileColor: AppColors.surfaceLight.withOpacity(0.4),
      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(8)),
      contentPadding: const EdgeInsets.symmetric(horizontal: 16, vertical: 2),
      leading: Icon(
        Icons.chat_bubble_outline,
        size: 18,
        color: isActive ? AppColors.primary : AppColors.textMuted,
      ),
      title: Text(
        session.title,
        maxLines: 1,
        overflow: TextOverflow.ellipsis,
        style: TextStyle(
          color: isActive ? AppColors.textPrimary : AppColors.textSecondary,
          fontSize: 13,
          fontWeight: isActive ? FontWeight.w600 : FontWeight.normal,
        ),
      ),
      onTap: onTap,
      onLongPress: () {
        showModalBottomSheet(
          context: context,
          backgroundColor: AppColors.surface,
          shape: const RoundedRectangleBorder(
            borderRadius: BorderRadius.vertical(top: Radius.circular(16)),
          ),
          builder: (ctx) => SafeArea(
            child: Column(
              mainAxisSize: MainAxisSize.min,
              children: [
                ListTile(
                  leading: const Icon(Icons.delete_outline, color: AppColors.error),
                  title: const Text('删除对话', style: TextStyle(color: AppColors.error)),
                  onTap: () {
                    Navigator.of(ctx).pop();
                    onDelete();
                  },
                ),
              ],
            ),
          ),
        );
      },
    );
  }
}