import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:go_router/go_router.dart';
import 'package:worldhopper/config/constants.dart';
import 'package:worldhopper/providers/reading_progress_provider.dart';
import 'package:worldhopper/providers/server_provider.dart';
import 'package:worldhopper/widgets/worldhopper_app_bar.dart';
import 'package:worldhopper/widgets/recently_read_card.dart';

/// Screen displaying the user's reading history and library
class LibraryScreen extends ConsumerWidget {
  const LibraryScreen({super.key});

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

    return Scaffold(
      appBar: const WorldhopperAppBar(
        title: Text('Library'),
      ),
      body: RefreshIndicator(
        onRefresh: () async {
          ref.invalidate(recentlyReadProvider);
        },
        child: recentlyReadAsync.when(
          data: (recentlyRead) {
            if (recentlyRead.isEmpty) {
              return _buildEmptyState(context, ref);
            }

            return CustomScrollView(
              slivers: [
                // Recently read section header
                const SliverToBoxAdapter(
                  child: Padding(
                    padding: EdgeInsets.fromLTRB(16.0, 8.0, 16.0, 8.0),
                    child: Text(
                      'Recently Read',
                      style: TextStyle(
                        fontSize: 20,
                        fontWeight: FontWeight.bold,
                      ),
                    ),
                  ),
                ),

                // Recently read grid
                SliverPadding(
                  padding: const EdgeInsets.symmetric(horizontal: 16.0),
                  sliver: SliverGrid(
                    gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
                      crossAxisCount: 2,
                      childAspectRatio: 0.7,
                      crossAxisSpacing: 16,
                      mainAxisSpacing: 16,
                    ),
                    delegate: SliverChildBuilderDelegate(
                      (context, index) {
                        final progress = recentlyRead[index];
                        return RecentlyReadCard(progress: progress);
                      },
                      childCount: recentlyRead.length,
                    ),
                  ),
                ),

                const SliverToBoxAdapter(
                  child: SizedBox(height: 16),
                ),
              ],
            );
          },
          loading: () => const Center(child: CircularProgressIndicator()),
          error: (error, stack) => _buildErrorState(context, error),
        ),
      ),
    );
  }

  Widget _buildEmptyState(BuildContext context, WidgetRef ref) {
    final serversAsync = ref.watch(serverListProvider);

    return serversAsync.when(
      data: (servers) {
        // Case 1: No servers configured
        if (servers.isEmpty) {
          return _buildNoServersState(context);
        }

        // Case 2: Servers exist but no reading history
        return _buildNoHistoryState(context);
      },
      loading: () => const Center(child: CircularProgressIndicator()),
      error: (_, __) => _buildNoHistoryState(context), // Fallback
    );
  }

  Widget _buildNoServersState(BuildContext context) {
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(32.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Icon(
              Icons.dns_outlined,
              size: 80,
              color: Theme.of(context).colorScheme.outline,
            ),
            const SizedBox(height: 24),
            Text(
              'No Servers Configured',
              style: Theme.of(context).textTheme.headlineSmall,
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: 12),
            Text(
              'Add an OPDS server to start reading books',
              style: Theme.of(context).textTheme.bodyMedium?.copyWith(
                    color: Theme.of(context).colorScheme.onSurface.withOpacity(0.6),
                  ),
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: 24),
            FilledButton.icon(
              onPressed: () => context.go(AppConstants.routeServerList),
              icon: const Icon(Icons.add),
              label: const Text('Add Server'),
            ),
          ],
        ),
      ),
    );
  }

  Widget _buildNoHistoryState(BuildContext context) {
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(32.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Icon(
              Icons.auto_stories_outlined,
              size: 80,
              color: Theme.of(context).colorScheme.outline,
            ),
            const SizedBox(height: 24),
            Text(
              'No Reading History',
              style: Theme.of(context).textTheme.headlineSmall,
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: 12),
            Text(
              'Start reading a book to see it here',
              style: Theme.of(context).textTheme.bodyMedium?.copyWith(
                    color: Theme.of(context).colorScheme.onSurface.withOpacity(0.6),
                  ),
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: 24),
            FilledButton.icon(
              onPressed: () => context.go(AppConstants.routeServerList),
              icon: const Icon(Icons.dns),
              label: const Text('Browse Servers'),
            ),
          ],
        ),
      ),
    );
  }

  Widget _buildErrorState(BuildContext context, Object error) {
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(32.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Icon(
              Icons.error_outline,
              size: 80,
              color: Theme.of(context).colorScheme.error,
            ),
            const SizedBox(height: 24),
            Text(
              'Error Loading Library',
              style: Theme.of(context).textTheme.headlineSmall,
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: 12),
            Text(
              error.toString(),
              style: Theme.of(context).textTheme.bodyMedium,
              textAlign: TextAlign.center,
            ),
          ],
        ),
      ),
    );
  }

}