import 'package:flutter/material.dart';
import 'package:patbond_flutter/core/theme/app_theme.dart';
import 'package:patbond_flutter/widgets/common.dart';

/// 图片九宫格展示态（05 号规范 §3.2）。
///
/// - 列数规则：2、4 图 → 2 列；3、5–9 图 → 3 列；全部 1:1 cover、
///   格间距 4、单格圆角 `sm`(12)，`RemoteImage` 复用（loading tint 块 /
///   失败图标兜底，缓存 key 已剥签名）。
/// - 超出折叠：最多显 9 格，[totalCount] 超过显示数时末格叠
///   `ink` 80% scrim + 白字「+N」20/w800（合成最亮白图 7.10:1；60% 档
///   3.88:1 不达标弃用，§5.1 精算）。
/// - 单图折叠形态：Feed 卡片契约只带封面 + mediaCount（FeedCard 裁剪），
///   [urls] 单元素而 [totalCount] > 1 时渲染 4:3 单格 + 右下「+N」角标
///   胶囊（同 80% scrim 精算）。
///
/// 编辑态（「＋」格 / 删除角标）随发布页工单（T3-17）扩展。
class PostMediaGrid extends StatelessWidget {
  const PostMediaGrid({
    required this.urls,
    super.key,
    this.totalCount,
    this.onCellTap,
  }) : assert(urls.length > 0, 'PostMediaGrid 至少一张图');

  /// 可展示的图片 URL（Feed 卡片仅封面一张；详情页全量）。
  final List<String> urls;

  /// 实际总张数（缺省 = urls.length）；大于可展示数时渲染「+N」。
  final int? totalCount;

  /// 格子点按（全屏浏览入口，T3-15 详情页接线）。
  final ValueChanged<int>? onCellTap;

  static const _maxCells = 9;
  static const _spacing = 4.0;

  int get _effectiveTotal => totalCount ?? urls.length;

  /// 列数规则（§3.2）：2、4 → 2 列；其余 → 3 列（1 图不走网格）。
  static int columnsFor(int cellCount) =>
      (cellCount == 2 || cellCount == 4) ? 2 : 3;

  @override
  Widget build(BuildContext context) {
    if (urls.length == 1) {
      return _CollapsedCover(
        url: urls.first,
        hiddenCount: _effectiveTotal - 1,
        onTap: onCellTap == null ? null : () => onCellTap!(0),
      );
    }

    final cellCount = urls.length > _maxCells ? _maxCells : urls.length;
    final overflow = _effectiveTotal - cellCount;
    final columns = columnsFor(cellCount);
    return GridView.builder(
      shrinkWrap: true,
      physics: const NeverScrollableScrollPhysics(),
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: columns,
        mainAxisSpacing: _spacing,
        crossAxisSpacing: _spacing,
      ),
      itemCount: cellCount,
      itemBuilder: (context, index) {
        final isOverflowCell = overflow > 0 && index == cellCount - 1;
        Widget cell = RemoteImage(
          url: urls[index],
          borderRadius: BorderRadius.circular(AppRadius.sm),
        );
        if (isOverflowCell) {
          cell = Stack(
            fit: StackFit.expand,
            children: [
              cell,
              DecoratedBox(
                decoration: BoxDecoration(
                  color: AppColors.ink.withAlpha(204),
                  borderRadius: BorderRadius.circular(AppRadius.sm),
                ),
                child: Center(
                  child: Text(
                    '+$overflow',
                    style: const TextStyle(
                      color: Colors.white,
                      fontSize: 20,
                      fontWeight: FontWeight.w800,
                    ),
                  ),
                ),
              ),
            ],
          );
        }
        if (onCellTap != null) {
          cell = InkWell(
            onTap: () => onCellTap!(index),
            borderRadius: BorderRadius.circular(AppRadius.sm),
            child: cell,
          );
        }
        return cell;
      },
    );
  }
}

/// 单图折叠形态：4:3 圆角封面 + 右下「+N」胶囊角标。
class _CollapsedCover extends StatelessWidget {
  const _CollapsedCover({
    required this.url,
    required this.hiddenCount,
    this.onTap,
  });

  final String url;
  final int hiddenCount;
  final VoidCallback? onTap;

  @override
  Widget build(BuildContext context) {
    Widget cover = AspectRatio(
      aspectRatio: 4 / 3,
      child: Stack(
        fit: StackFit.expand,
        children: [
          RemoteImage(
            url: url,
            borderRadius: BorderRadius.circular(AppRadius.sm),
          ),
          if (hiddenCount > 0)
            Positioned(
              right: 8,
              bottom: 8,
              child: Container(
                padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 3),
                decoration: BoxDecoration(
                  color: AppColors.ink.withAlpha(204),
                  borderRadius: BorderRadius.circular(AppRadius.pill),
                ),
                child: Text(
                  '+$hiddenCount',
                  style: const TextStyle(
                    color: Colors.white,
                    fontSize: 12,
                    fontWeight: FontWeight.w700,
                  ),
                ),
              ),
            ),
        ],
      ),
    );
    if (onTap != null) {
      cover = InkWell(
        onTap: onTap,
        borderRadius: BorderRadius.circular(AppRadius.sm),
        child: cover,
      );
    }
    return cover;
  }
}