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

import '../../core/constants.dart';
import '../../core/exceptions.dart';
import '../../providers/chat_provider.dart';
import 'chat_screen.dart';

class ConversationsListScreen extends ConsumerStatefulWidget {
  const ConversationsListScreen({super.key});

  @override
  ConsumerState<ConversationsListScreen> createState() =>
      _ConversationsListScreenState();
}

class _ConversationsListScreenState
    extends ConsumerState<ConversationsListScreen> {
  int? _selectedConvId;

  Future<void> _newConversation(bool isWide) async {
    try {
      final conv = await ref.read(conversationsProvider.notifier).create('');
      if (!mounted) return;
      if (isWide) {
        setState(() => _selectedConvId = conv.id);
      } else {
        context.push(Routes.chat.replaceFirst(':id', '${conv.id}'));
      }
    } on AppException catch (e) {
      if (mounted) {
        ScaffoldMessenger.of(context)
            .showSnackBar(SnackBar(content: Text(e.message)));
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    final convsAsync = ref.watch(conversationsProvider);
    final isWide = MediaQuery.of(context).size.width >= 600;

    // Clear stale selection when switching to narrow mode.
    if (!isWide && _selectedConvId != null) {
      _selectedConvId = null;
    }

    return Scaffold(
      body: isWide
          ? Row(
              children: [
                SizedBox(
                  width: 300,
                  child: Column(
                    children: [
                      Expanded(child: _buildListPane(convsAsync, isWide)),
                      const Divider(height: 1),
                      ListTile(
                        leading: const Icon(Icons.add),
                        title: const Text('New conversation'),
                        onTap: () => _newConversation(isWide),
                      ),
                    ],
                  ),
                ),
                const VerticalDivider(width: 1),
                Expanded(child: _buildDetailPane()),
              ],
            )
          : _buildListPane(convsAsync, isWide),
      floatingActionButton: isWide
          ? null
          : FloatingActionButton(
              heroTag: 'chat_fab',
              onPressed: () => _newConversation(isWide),
              child: const Icon(Icons.add),
            ),
    );
  }

  Widget _buildDetailPane() {
    if (_selectedConvId == null) {
      return const Center(child: Text('Select a conversation to open it.'));
    }
    return ChatScreen(
      key: ValueKey(_selectedConvId),
      conversationId: _selectedConvId!,
    );
  }

  Widget _buildListPane(AsyncValue convsAsync, bool isWide) {
    return convsAsync.when(
      loading: () => const Center(child: CircularProgressIndicator()),
      error: (_, _) => Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            const Icon(Icons.cloud_off, size: 48),
            const SizedBox(height: 12),
            const Text('Could not load conversations.'),
            const SizedBox(height: 4),
            TextButton(
              onPressed: () => ref.invalidate(conversationsProvider),
              child: const Text('Retry'),
            ),
          ],
        ),
      ),
      data: (convs) {
        if (convs.isEmpty) {
          return const Center(
              child: Text('No conversations yet. Tap + to start one.'));
        }
        return RefreshIndicator(
          onRefresh: () => ref.refresh(conversationsProvider.future),
          child: ListView.separated(
            itemCount: convs.length,
            separatorBuilder: (_, _) => const Divider(height: 1),
            itemBuilder: (context, i) {
              final conv = convs[i];
              return ListTile(
                leading: const Icon(Icons.chat_bubble_outline),
                title: Text(
                  conv.title.isNotEmpty ? conv.title : 'New conversation',
                ),
                subtitle: Text(
                  conv.updatedAt.toLocal().toString().substring(0, 16),
                  style: Theme.of(context).textTheme.bodySmall?.copyWith(
                        color: Theme.of(context).colorScheme.onSurfaceVariant,
                      ),
                ),
                selected: isWide && _selectedConvId == conv.id,
                selectedTileColor:
                    Theme.of(context).colorScheme.secondaryContainer,
                onTap: () {
                  if (isWide) {
                    setState(() => _selectedConvId = conv.id);
                  } else {
                    context.push(
                      Routes.chat.replaceFirst(':id', '${conv.id}'),
                    );
                  }
                },
                onLongPress: () async {
                  final confirm = await showDialog<bool>(
                    context: context,
                    builder: (dialogContext) => AlertDialog(
                      title: const Text('Delete conversation?'),
                      content: Text(
                        conv.title.isNotEmpty
                            ? conv.title
                            : 'New conversation',
                      ),
                      actions: [
                        TextButton(
                          onPressed: () =>
                              Navigator.pop(dialogContext, false),
                          child: const Text('Cancel'),
                        ),
                        TextButton(
                          onPressed: () =>
                              Navigator.pop(dialogContext, true),
                          child: const Text('Delete'),
                        ),
                      ],
                    ),
                  );
                  if (confirm == true) {
                    await ref
                        .read(conversationsProvider.notifier)
                        .delete(conv.id);
                    if (mounted && _selectedConvId == conv.id) {
                      setState(() => _selectedConvId = null);
                    }
                  }
                },
              );
            },
          ),
        );
      },
    );
  }
}