// Author: fruit.com.cn

import 'dart:async';

import 'package:flutter/material.dart';

import '../../core/theme/app_colors.dart';
import '../../core/theme/app_dimens.dart';
import '../../core/widgets/app_pull_to_refresh.dart';
import '../../core/widgets/empty_state.dart';
import '../../core/widgets/paged_list_footer.dart';
import '../../l10n/app_localizations.dart';

class FollowingPagedGrid extends StatelessWidget {
  const FollowingPagedGrid({
    super.key,
    required this.scrollController,
    required this.loading,
    required this.loadingMore,
    required this.hasMore,
    required this.hasItems,
    required this.itemCount,
    required this.itemBuilder,
    required this.empty,
    required this.onRefresh,
    required this.onLoadMore,
    this.showInitialLoading = true,
    this.singleColumn = false,
    this.errorMessage,
    this.loadMoreError,
    this.topSlivers = const [],
  });

  static const double _loadMoreThreshold = 240;

  final ScrollController scrollController;
  final bool loading;
  final bool loadingMore;
  final bool hasMore;
  final bool hasItems;
  final int itemCount;
  final IndexedWidgetBuilder itemBuilder;
  final Widget empty;
  final String? errorMessage;
  final String? loadMoreError;
  final bool showInitialLoading;
  final bool singleColumn;

  /// 列表顶部的非分页内容（继续观看横幅、区块标题等）。
  /// 必须是 sliver；空列表时也会保留，因此可携带空态上方的固定区块。
  final List<Widget> topSlivers;
  final Future<void> Function() onRefresh;
  final Future<void> Function() onLoadMore;

  @override
  Widget build(BuildContext context) {
    if (showInitialLoading && loading && !hasItems) {
      return const Center(child: CircularProgressIndicator());
    }
    return LayoutBuilder(
      builder: (context, constraints) {
        final gridWidth =
            constraints.maxWidth - AppDimens.feedPageHorizontal * 2;
        final itemWidth = (gridWidth - AppDimens.followingGridGap * 2) / 3;
        final itemExtent =
            itemWidth / AppDimens.cardCoverAspectRatio +
            AppDimens.followingCardTextExtent;
        final gridDelegate = singleColumn
            ? const SliverGridDelegateWithFixedCrossAxisCount(
                crossAxisCount: 1,
                mainAxisSpacing: AppDimens.followingHistoryRowGap,
                mainAxisExtent: AppDimens.followingHistoryCoverHeight,
              )
            : SliverGridDelegateWithFixedCrossAxisCount(
                crossAxisCount: 3,
                crossAxisSpacing: AppDimens.followingGridGap,
                mainAxisSpacing: AppDimens.followingGridRowGap,
                mainAxisExtent: itemExtent,
              );
        return NotificationListener<ScrollNotification>(
          onNotification: _onScroll,
          child: AppPullToRefresh(
            onRefresh: onRefresh,
            child: CustomScrollView(
              key: ValueKey<String>('following-scroll-$runtimeType'),
              controller: scrollController,
              physics: AppPullToRefresh.physics,
              slivers: [
                ...topSlivers,
                if (itemCount == 0)
                  SliverFillRemaining(
                    hasScrollBody: false,
                    child: errorMessage == null
                        ? empty
                        : EmptyState(
                            icon: Icons.cloud_off_rounded,
                            title: errorMessage!,
                            actionLabel: AppLocalizations.of(context)!.retry,
                            onAction: () => unawaited(onRefresh()),
                          ),
                  )
                else ...[
                  if (errorMessage != null)
                    SliverToBoxAdapter(
                      child: Padding(
                        padding: const EdgeInsets.fromLTRB(
                          AppDimens.feedPageHorizontal,
                          AppDimens.spaceSm,
                          AppDimens.feedPageHorizontal,
                          0,
                        ),
                        child: Text(
                          errorMessage!,
                          style: const TextStyle(
                            color: AppColors.textTertiary,
                            fontSize: AppDimens.followingSubtitleFont,
                          ),
                        ),
                      ),
                    ),
                  SliverPadding(
                    padding: const EdgeInsets.fromLTRB(
                      AppDimens.feedPageHorizontal,
                      0,
                      AppDimens.feedPageHorizontal,
                      AppDimens.spaceSm,
                    ),
                    sliver: SliverGrid(
                      gridDelegate: gridDelegate,
                      delegate: SliverChildBuilderDelegate(
                        itemBuilder,
                        childCount: itemCount,
                      ),
                    ),
                  ),
                  SliverToBoxAdapter(
                    child: PagedListFooter(
                      loading: loadingMore,
                      hasMore: hasMore,
                      hasItems: hasItems,
                      errorMessage: loadMoreError,
                      onRetry: onLoadMore,
                    ),
                  ),
                  const SliverToBoxAdapter(
                    child: SizedBox(height: AppDimens.spaceXl),
                  ),
                ],
              ],
            ),
          ),
        );
      },
    );
  }

  bool _onScroll(ScrollNotification notification) {
    if (notification.depth != 0) return false;
    if (notification.metrics.extentAfter > _loadMoreThreshold) return false;
    if (notification is ScrollUpdateNotification ||
        notification is ScrollEndNotification ||
        notification is OverscrollNotification) {
      unawaited(onLoadMore());
    }
    return false;
  }
}