ReelShort/lib/core/widgets/empty_state.dart

// Author: fruit.com.cn

import 'package:flutter/material.dart';

import '../theme/app_colors.dart';
import '../theme/app_dimens.dart';

const double _regularIconSize = 48;
const double _compactIconSize = 32;
const double _maxContentWidth = 260;
const double _regularHorizontal = 24;
const double _regularVertical = 28;
const double _compactPad = 16;
const double _regularGap = 20;
const double _compactGap = 12;
const double _actionMinHeight = 44;

/// 统一空列表占位：一枚图标、标题、可选说明与操作。
class EmptyState extends StatelessWidget {
  const EmptyState({
    super.key,
    required this.icon,
    required this.title,
    this.subtitle,
    this.actionLabel,
    this.actionKey,
    this.onAction,
    this.footer,
    this.compact = false,
  });

  final IconData icon;
  final String title;
  final String? subtitle;
  final String? actionLabel;
  final Key? actionKey;
  final VoidCallback? onAction;
  final Widget? footer;
  final bool compact;

  @override
  Widget build(BuildContext context) {
    final hasAction = actionLabel != null && onAction != null;
    return Center(
      child: ConstrainedBox(
        key: const Key('empty-state-content'),
        constraints: const BoxConstraints(maxWidth: _maxContentWidth),
        child: Padding(
          key: const Key('empty-state-padding'),
          padding: EdgeInsets.symmetric(
            horizontal: compact ? _compactPad : _regularHorizontal,
            vertical: compact ? _compactPad : _regularVertical,
          ),
          child: Semantics(
            container: true,
            label: title,
            child: Column(
              mainAxisSize: MainAxisSize.min,
              children: [
                ExcludeSemantics(
                  child: _EmptyMark(icon: icon, compact: compact),
                ),
                SizedBox(height: compact ? _compactGap : _regularGap),
                _EmptyCopy(
                  title: title,
                  subtitle: subtitle,
                  actionLabel: hasAction ? actionLabel : null,
                  actionKey: actionKey,
                  onAction: hasAction ? onAction : null,
                  footer: footer,
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

/// 空状态只留一枚图标，不加水印底和描边。
class _EmptyMark extends StatelessWidget {
  const _EmptyMark({required this.icon, required this.compact});

  final IconData icon;
  final bool compact;

  @override
  Widget build(BuildContext context) {
    final dark = Theme.of(context).brightness == Brightness.dark;
    return Icon(
      icon,
      key: const Key('empty-state-icon'),
      size: compact ? _compactIconSize : _regularIconSize,
      color: dark ? AppColors.gold : AppColors.blue,
    );
  }
}

class _EmptyCopy extends StatelessWidget {
  const _EmptyCopy({
    required this.title,
    required this.subtitle,
    required this.actionLabel,
    required this.actionKey,
    required this.onAction,
    required this.footer,
  });

  final String title;
  final String? subtitle;
  final String? actionLabel;
  final Key? actionKey;
  final VoidCallback? onAction;
  final Widget? footer;

  @override
  Widget build(BuildContext context) {
    final scheme = Theme.of(context).colorScheme;
    return Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        ExcludeSemantics(
          child: Text(
            title,
            key: const Key('empty-state-title'),
            maxLines: 2,
            overflow: TextOverflow.ellipsis,
            textAlign: TextAlign.center,
            style: TextStyle(
              color: scheme.onSurface,
              fontSize: 15,
              fontWeight: FontWeight.w600,
              height: 1.35,
            ),
          ),
        ),
        if (subtitle != null) ...[
          const SizedBox(height: 6),
          ExcludeSemantics(
            child: Text(
              subtitle!,
              maxLines: 2,
              overflow: TextOverflow.ellipsis,
              textAlign: TextAlign.center,
              style: const TextStyle(
                color: AppColors.muted,
                fontSize: AppDimens.emptyStateSubtitle,
                height: 1.45,
              ),
            ),
          ),
        ],
        if (actionLabel != null && onAction != null) ...[
          const SizedBox(height: 8),
          TextButton(
            key: actionKey ?? const Key('empty-state-action'),
            onPressed: onAction,
            style: TextButton.styleFrom(
              foregroundColor: AppColors.blueSoft,
              minimumSize: const Size(44, _actionMinHeight),
              padding: const EdgeInsets.symmetric(horizontal: 14),
            ),
            child: Text(
              actionLabel!,
              style: const TextStyle(fontSize: AppDimens.emptyStateAction),
            ),
          ),
        ],
        if (footer != null) ...[const SizedBox(height: 12), footer!],
      ],
    );
  }
}