tboss_oa_module/lib/features/expense_apply/widgets/attachment_preview_page.dart

import 'dart:typed_data';
import 'package:flutter/material.dart';

/// 图片预览弹窗，支持捏合缩放。
///
/// 以半透明蒙版覆盖在当前页面上方，内部自动加载图片，
/// 加载期间显示 loading 动画，加载失败显示错误提示。
///
/// 使用方式：
/// ```dart
/// AttachmentPreview.show(context,
///   loader: api.downloadAttachment(id),
///   fileName: 'photo.jpg',
///   loadingText: '加载中…',
/// );
/// ```
class AttachmentPreview {
  AttachmentPreview._();

  /// 显示图片预览弹窗。
  static Future<void> show(
    BuildContext context, {
    required Future<Uint8List?> loader,
    required String fileName,
    required String loadingText,
  }) {
    return showGeneralDialog(
      context: context,
      barrierDismissible: true,
      barrierLabel: 'Close',
      barrierColor: Colors.black87,
      transitionDuration: const Duration(milliseconds: 250),
      pageBuilder: (context, animation, secondaryAnimation) {
        return FadeTransition(
          opacity: animation,
          child: Material(
            type: MaterialType.transparency,
            child: _PreviewContent(
              loader: loader,
              fileName: fileName,
              loadingText: loadingText,
            ),
          ),
        );
      },
    );
  }
}

class _PreviewContent extends StatefulWidget {
  final Future<Uint8List?> loader;
  final String fileName;
  final String loadingText;

  const _PreviewContent({
    required this.loader,
    required this.fileName,
    required this.loadingText,
  });

  @override
  State<_PreviewContent> createState() => _PreviewContentState();
}

class _PreviewContentState extends State<_PreviewContent> {
  Uint8List? _bytes;
  bool _loading = true;
  String? _error;

  @override
  void initState() {
    super.initState();
    _load();
  }

  Future<void> _load() async {
    try {
      final bytes = await widget.loader;
      if (!mounted) return;
      if (bytes == null) {
        setState(() { _error = 'Download failed'; _loading = false; });
        return;
      }
      setState(() { _bytes = bytes; _loading = false; });
    } catch (_) {
      if (!mounted) return;
      setState(() { _error = 'Open failed'; _loading = false; });
    }
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Stack(
        children: [
          Center(child: _buildBody()),
          Positioned(
            top: 8,
            right: 8,
            child: IconButton(
              icon: const Icon(Icons.close, color: Colors.white70, size: 28),
              onPressed: () => Navigator.of(context).pop(),
            ),
          ),
          Positioned(
            top: 16,
            left: 16,
            right: 56,
            child: Text(
              widget.fileName,
              style: const TextStyle(color: Colors.white, fontSize: 15),
              overflow: TextOverflow.ellipsis,
            ),
          ),
        ],
      ),
    );
  }

  Widget _buildBody() {
    if (_loading) {
      return Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          const CircularProgressIndicator(color: Colors.white),
          const SizedBox(height: 16),
          Text(widget.loadingText,
              style: const TextStyle(color: Colors.white70, fontSize: 14)),
        ],
      );
    }
    if (_error != null || _bytes == null) {
      return Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          const Icon(Icons.broken_image_outlined, color: Colors.white54, size: 48),
          const SizedBox(height: 12),
          Text(_error ?? 'Unknown error',
              style: const TextStyle(color: Colors.white70, fontSize: 14)),
        ],
      );
    }
    return InteractiveViewer(
      minScale: 0.5,
      maxScale: 4.0,
      child: Image.memory(_bytes!),
    );
  }
}