MyAvaloniaDemo/AuroraDesk.Presentation/ViewModels/Pages/ImageGalleryPageViewModel.cs

using AuroraDesk.Presentation.ViewModels.Base;
using AuroraDesk.Presentation.Services;
using Microsoft.Extensions.Logging;
using ReactiveUI;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Reactive;
using System.Threading;
using System.Threading.Channels;
using System.Threading.Tasks;
using Avalonia.Controls;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Media.Imaging;
using Avalonia.Platform.Storage;
using Avalonia.Threading;

namespace AuroraDesk.Presentation.ViewModels.Pages;

/// <summary>
/// 图片浏览页面 ViewModel
/// 参考 IconsPageViewModel 实现真正的按需加载
/// 
/// 核心改进：
/// 1. 初始仅加载前 30 个 ImageMetadata
/// 2. 滚动接近底部时再加载下一批（每次 50 个）
/// 3. 只创建当前需要显示的元数据对象
/// 4. 对 10 万张图片，内存占用显著降低
/// </summary>
public class ImageGalleryPageViewModel : RoutableViewModel
{
    private string _selectedDirectory = string.Empty;
    private ObservableCollection<ImageMetadata> _images = new();
    private ImageMetadata? _selectedImage;
    private bool _isLoading;
    private int _totalImageCount;
    private string _statusMessage = "请选择一个包含图片的目录";
    private CancellationTokenSource? _loadingCancellationTokenSource;
    private bool _isLoadingMore; // 是否正在加载更多
    
    private readonly ILogger<ImageGalleryPageViewModel>? _logger;
    
    // 数据层：只保存文件路径列表（List<string>），不加载实际图片对象
    private List<string> _allFilePaths = new();
    
    // 已加载的元数据数量（跟踪已加载数量）
    private int _loadedMetadataCount = 0;
    
    // 支持的图片格式
    private static readonly string[] SupportedImageExtensions = 
    {
        ".jpg", ".jpeg", ".png", ".gif", ".bmp", ".webp", ".ico"
    };
    
    // 初始加载数量
    private const int InitialBatchSize = 30;
    
    // 每次加载更多时的批次大小
    private const int IncrementalBatchSize = 50;
    
    public ObservableCollection<ImageMetadata> Images
    {
        get => _images;
        set => this.RaiseAndSetIfChanged(ref _images, value);
    }
    
    public ImageMetadata? SelectedImage
    {
        get => _selectedImage;
        set => this.RaiseAndSetIfChanged(ref _selectedImage, value);
    }
    
    public bool IsLoading
    {
        get => _isLoading;
        set => this.RaiseAndSetIfChanged(ref _isLoading, value);
    }
    
    public string SelectedDirectory
    {
        get => _selectedDirectory;
        set => this.RaiseAndSetIfChanged(ref _selectedDirectory, value);
    }
    
    public int TotalImageCount
    {
        get => _totalImageCount;
        set => this.RaiseAndSetIfChanged(ref _totalImageCount, value);
    }
    
    public string StatusMessage
    {
        get => _statusMessage;
        set => this.RaiseAndSetIfChanged(ref _statusMessage, value);
    }
    
    // 命令
    public ReactiveCommand<Unit, Unit> SelectDirectoryCommand { get; }
    public ReactiveCommand<ImageMetadata, Unit> SelectImageCommand { get; }
    
    /// <summary>
    /// 构造函数
    /// </summary>
    public ImageGalleryPageViewModel(
        IScreen hostScreen,
        ILogger<ImageGalleryPageViewModel>? logger = null) 
        : base(hostScreen, "ImageGallery")
    {
        _logger = logger;
        
        // 创建命令
        SelectDirectoryCommand = ReactiveCommand.CreateFromTask(SelectDirectoryAsync);
        SelectImageCommand = ReactiveCommand.Create<ImageMetadata>(SelectImage);
    }
    
    /// <summary>
    /// 选择目录（用户交互层）
    /// </summary>
    private async Task SelectDirectoryAsync()
    {
        try
        {
            var app = Avalonia.Application.Current;
            TopLevel? topLevel = null;
            
            if (app?.ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
            {
                topLevel = desktop.MainWindow;
            }
            
            if (topLevel?.StorageProvider == null)
            {
                _logger?.LogWarning("无法获取 StorageProvider");
                StatusMessage = "无法打开文件对话框";
                return;
            }
            
            // 打开文件夹选择对话框
            var folders = await topLevel.StorageProvider.OpenFolderPickerAsync(
                new FolderPickerOpenOptions
                {
                    Title = "选择包含图片的文件夹",
                    AllowMultiple = false
                });
            
            if (folders.Count > 0 && folders[0].TryGetLocalPath() is { } path)
            {
                SelectedDirectory = path;
                await LoadImagesFromDirectoryAsync(path);
            }
        }
        catch (Exception ex)
        {
            _logger?.LogError(ex, "选择目录时发生错误");
            StatusMessage = $"选择目录失败: {ex.Message}";
        }
    }
    
    /// <summary>
    /// 从目录加载图片（数据加载层）
    /// 1. 扫描所有图片文件路径
    /// 2. 初始仅加载前 30 个 ImageMetadata
    /// 3. 后续通过 LoadMoreImagesAsync 按需加载
    /// </summary>
    private async Task LoadImagesFromDirectoryAsync(string directoryPath)
    {
        // 取消之前的加载任务
        _loadingCancellationTokenSource?.Cancel();
        _loadingCancellationTokenSource?.Dispose();
        _loadingCancellationTokenSource = new CancellationTokenSource();
        var cancellationToken = _loadingCancellationTokenSource.Token;
        
        try
        {
            IsLoading = true;
            StatusMessage = "正在扫描图片文件...";
            Images.Clear();
            SelectedImage = null;
            _allFilePaths.Clear();
            _loadedMetadataCount = 0;
            TotalImageCount = 0;
            
            _logger?.LogInformation("开始从目录加载图片: {Directory}", directoryPath);
            
            if (!Directory.Exists(directoryPath))
            {
                StatusMessage = "目录不存在";
                IsLoading = false;
                return;
            }
            
            // 第一步：异步扫描目录，收集所有图片路径
            await Task.Run(async () =>
            {
                try
                {
                    await foreach (var filePath in EnumerateImageFilesAsync(directoryPath, cancellationToken))
                    {
                        if (cancellationToken.IsCancellationRequested)
                            break;
                        
                        _allFilePaths.Add(filePath);
                        
                        // 每找到1000个文件就更新一次UI
                        if (_allFilePaths.Count % 1000 == 0)
                        {
                            await UpdateStatusAsync($"已找到 {_allFilePaths.Count} 个图片文件...", _allFilePaths.Count);
                            await Task.Yield();
                        }
                    }
                }
                catch (OperationCanceledException)
                {
                    _logger?.LogInformation("文件扫描已取消");
                    return;
                }
            }, cancellationToken);
            
            if (cancellationToken.IsCancellationRequested)
            {
                return;
            }
            
            // 对文件路径按文件名排序（自然排序）
            _allFilePaths.Sort(NaturalStringComparer.Instance);
            
            TotalImageCount = _allFilePaths.Count;
            _logger?.LogInformation("找到 {Count} 张图片", TotalImageCount);
            
            if (TotalImageCount == 0)
            {
                await UpdateStatusAsync("未找到图片文件", isLoading: false);
                return;
            }
            
            // 第二步：初始仅加载前 30 个 ImageMetadata（真正的按需加载）
            await LoadMoreImagesAsync(InitialBatchSize);
            
            _logger?.LogInformation("图片加载完成，初始加载: {Count} 张，总数: {Total}", _loadedMetadataCount, TotalImageCount);
            
            // 初始加载完成后，延迟检查是否需要继续加载更多
            // 等待UI布局完成后再检查，确保有足够内容填满视口
            _ = Task.Run(async () =>
            {
                await Task.Delay(500);
                if (_loadedMetadataCount < _allFilePaths.Count && !_isLoadingMore)
                {
                    // 再次检查并加载更多，确保有足够内容填满视口
                    await LoadMoreImagesAsync(IncrementalBatchSize);
                }
            });
        }
        catch (OperationCanceledException)
        {
            _logger?.LogInformation("图片加载已取消");
            await UpdateStatusAsync("加载已取消", isLoading: false);
        }
        catch (Exception ex)
        {
            _logger?.LogError(ex, "加载图片时发生错误");
            await UpdateStatusAsync($"加载图片失败: {ex.Message}", isLoading: false);
        }
    }
    
    /// <summary>
    /// 加载更多图片（按需加载）
    /// 参考 IconsPageViewModel 的流式加载策略
    /// </summary>
    public async Task LoadMoreImagesAsync(int count = IncrementalBatchSize)
    {
        if (_isLoadingMore || _loadedMetadataCount >= _allFilePaths.Count)
            return;
        
        _isLoadingMore = true;
        
        try
        {
            // 计算需要加载的文件路径范围
            var startIndex = _loadedMetadataCount;
            var endIndex = Math.Min(_loadedMetadataCount + count, _allFilePaths.Count);
            var filePathsToLoad = _allFilePaths.Skip(startIndex).Take(endIndex - startIndex).ToList();
            
            if (filePathsToLoad.Count == 0)
                return;
            
            _logger?.LogInformation("开始加载更多图片: {Start} - {End} (共 {Count} 张)", 
                startIndex, endIndex, filePathsToLoad.Count);
            
            // 在后台线程创建元数据
            var metadataList = await CreateImageMetadataAsync(filePathsToLoad, CancellationToken.None);
            
            // 在 UI 线程批量添加
            await Dispatcher.UIThread.InvokeAsync(() =>
            {
                var wasEmpty = _images.Count == 0;
                
                foreach (var metadata in metadataList)
                {
                    _images.Add(metadata);
                    // 触发缩略图加载（按需加载）
                    metadata.EnsureThumbnailLoaded();
                }
                
                // 只在第一次加载时触发 PropertyChanged
                if (wasEmpty)
                {
                    this.RaisePropertyChanged(nameof(Images));
                }
                
                _loadedMetadataCount = _images.Count;
                IsLoading = false;
                StatusMessage = $"已加载 {_loadedMetadataCount} / {TotalImageCount} 张图片";
            }, DispatcherPriority.Background);
            
            _logger?.LogInformation("加载更多图片完成: 已加载 {Loaded} / {Total}", _loadedMetadataCount, TotalImageCount);
        }
        catch (Exception ex)
        {
            _logger?.LogError(ex, "加载更多图片时发生错误");
        }
        finally
        {
            _isLoadingMore = false;
        }
    }
    
    /// <summary>
    /// 异步枚举图片文件（流式处理）
    /// </summary>
    private async IAsyncEnumerable<string> EnumerateImageFilesAsync(
        string directoryPath, 
        [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
    {
        var channel = Channel.CreateUnbounded<string>();
        var writer = channel.Writer;
        
        _ = Task.Run(async () =>
        {
            try
            {
                var dirQueue = new Queue<string>();
                dirQueue.Enqueue(directoryPath);
                
                while (dirQueue.Count > 0 && !cancellationToken.IsCancellationRequested)
                {
                    var currentDir = dirQueue.Dequeue();
                    
                    try
                    {
                        // 枚举当前目录的文件
                        foreach (var file in Directory.EnumerateFiles(currentDir, "*.*", SearchOption.TopDirectoryOnly))
                        {
                            if (cancellationToken.IsCancellationRequested)
                                return;
                            
                            var ext = Path.GetExtension(file).ToLowerInvariant();
                            if (SupportedImageExtensions.Contains(ext))
                            {
                                await writer.WriteAsync(file, cancellationToken);
                            }
                        }
                        
                        // 枚举子目录（递归）
                        foreach (var subDir in Directory.EnumerateDirectories(currentDir, "*", SearchOption.TopDirectoryOnly))
                        {
                            if (cancellationToken.IsCancellationRequested)
                                return;
                            
                            dirQueue.Enqueue(subDir);
                        }
                    }
                    catch (UnauthorizedAccessException)
                    {
                        _logger?.LogWarning("无权限访问目录: {Directory}", currentDir);
                    }
                    catch (DirectoryNotFoundException)
                    {
                        // 跳过不存在的目录
                    }
                    catch (Exception ex)
                    {
                        _logger?.LogWarning(ex, "处理目录时出错: {Directory}", currentDir);
                    }
                }
            }
            finally
            {
                writer.Complete();
            }
        }, cancellationToken);
        
        // 流式返回找到的文件
        await foreach (var filePath in channel.Reader.ReadAllAsync(cancellationToken))
        {
            yield return filePath;
        }
    }
    
    /// <summary>
    /// 创建图片元数据（轻量数据结构）
    /// </summary>
    private async Task<List<ImageMetadata>> CreateImageMetadataAsync(
        IEnumerable<string> filePaths, 
        CancellationToken cancellationToken)
    {
        var filePathsList = filePaths.ToList();
        var metadataList = new List<ImageMetadata>(filePathsList.Count);
        
        await Task.Run(() =>
        {
            foreach (var filePath in filePathsList)
            {
                if (cancellationToken.IsCancellationRequested)
                    break;
                
                try
                {
                    var fileInfo = new FileInfo(filePath);
                    if (fileInfo.Exists)
                    {
                        var metadata = new ImageMetadata
                        {
                            FilePath = filePath,
                            FileName = Path.GetFileName(filePath),
                            FileSize = fileInfo.Length,
                            LastModified = fileInfo.LastWriteTime
                        };
                        metadataList.Add(metadata);
                    }
                }
                catch
                {
                    // 忽略文件信息获取失败
                }
            }
        }, cancellationToken);
        
        return metadataList;
    }
    
    private void SelectImage(ImageMetadata image)
    {
        if (image == null) return;
        
        SelectedImage = image;
        _logger?.LogInformation("选择图片: {FileName}", image.FileName);
    }
    
    /// <summary>
    /// 清理资源（取消正在进行的加载任务）
    /// </summary>
    public void CancelLoading()
    {
        _loadingCancellationTokenSource?.Cancel();
        _loadingCancellationTokenSource?.Dispose();
        _loadingCancellationTokenSource = null;
    }
    
    /// <summary>
    /// 更新状态消息（UI 线程安全）
    /// </summary>
    private async Task UpdateStatusAsync(
        string message, 
        int? totalCount = null, 
        bool? isLoading = null)
    {
        await Dispatcher.UIThread.InvokeAsync(() =>
        {
            StatusMessage = message;
            if (totalCount.HasValue)
                TotalImageCount = totalCount.Value;
            if (isLoading.HasValue)
                IsLoading = isLoading.Value;
        }, DispatcherPriority.Background);
    }
}

/// <summary>
/// 图片元数据（轻量数据结构）
/// 按照 images.md：只包含文件名、大小、修改时间
/// </summary>
public class ImageMetadata : ReactiveObject
{
    private string _filePath = string.Empty;
    private string _fileName = string.Empty;
    private long _fileSize;
    private DateTime _lastModified;
    private Bitmap? _thumbnailSource;
    private bool _isLoadingThumbnail;
    
    // 缩略图缓存服务（单例）
    private static readonly ThumbnailCacheService _thumbnailCache = ThumbnailCacheService.Instance;
    
    public string FilePath
    {
        get => _filePath;
        set => this.RaiseAndSetIfChanged(ref _filePath, value);
    }
    
    public string FileName
    {
        get => _fileName;
        set => this.RaiseAndSetIfChanged(ref _fileName, value);
    }
    
    public long FileSize
    {
        get => _fileSize;
        set => this.RaiseAndSetIfChanged(ref _fileSize, value);
    }
    
    public DateTime LastModified
    {
        get => _lastModified;
        set => this.RaiseAndSetIfChanged(ref _lastModified, value);
    }
    
    /// <summary>
    /// 缩略图源（异步加载）
    /// 按照 images.md：后台线程池按需生成缩略图
    /// </summary>
    public Bitmap? ThumbnailSource
    {
        get => _thumbnailSource;
        private set => this.RaiseAndSetIfChanged(ref _thumbnailSource, value);
    }
    
    /// <summary>
    /// 是否正在加载缩略图
    /// </summary>
    public bool IsLoadingThumbnail
    {
        get => _isLoadingThumbnail;
        private set => this.RaiseAndSetIfChanged(ref _isLoadingThumbnail, value);
    }
    
    /// <summary>
    /// 确保缩略图已加载（按需加载）
    /// 按照 images.md：优先渲染可见项的缩略图
    /// </summary>
    public void EnsureThumbnailLoaded()
    {
        if (_thumbnailSource != null || _isLoadingThumbnail || string.IsNullOrEmpty(_filePath))
            return;
        
        _ = LoadThumbnailAsync();
    }
    
    /// <summary>
    /// 异步加载缩略图（使用 ThumbnailCacheService）
    /// 按照 images.md：支持内存LRU缓存和磁盘缓存
    /// </summary>
    private async Task LoadThumbnailAsync()
    {
        if (string.IsNullOrEmpty(_filePath) || !File.Exists(_filePath))
        {
            ThumbnailSource = null;
            return;
        }
        
        IsLoadingThumbnail = true;
        
        try
        {
            // 使用 ThumbnailCacheService 加载缩略图（自动处理内存+磁盘缓存）
            var thumbnail = await _thumbnailCache.GetThumbnailAsync(_filePath);
            
            // 在UI线程更新
            await Dispatcher.UIThread.InvokeAsync(() =>
            {
                ThumbnailSource = thumbnail;
                IsLoadingThumbnail = false;
            });
        }
        catch
        {
            await Dispatcher.UIThread.InvokeAsync(() =>
            {
                ThumbnailSource = null;
                IsLoadingThumbnail = false;
            });
        }
    }
    
    /// <summary>
    /// 格式化文件大小
    /// </summary>
    public string FormattedFileSize
    {
        get
        {
            if (_fileSize < 1024) return $"{_fileSize} B";
            if (_fileSize < 1024 * 1024) return $"{_fileSize / 1024.0:F2} KB";
            return $"{_fileSize / (1024.0 * 1024.0):F2} MB";
        }
    }
}

/// <summary>
/// 自然字符串比较器（支持数字文件名排序）
/// </summary>
internal class NaturalStringComparer : IComparer<string>
{
    public static readonly NaturalStringComparer Instance = new();
    
    public int Compare(string? x, string? y)
    {
        if (x == null && y == null) return 0;
        if (x == null) return -1;
        if (y == null) return 1;
        
        var fileNameX = Path.GetFileName(x);
        var fileNameY = Path.GetFileName(y);
        
        var fileNameCompare = CompareNatural(fileNameX, fileNameY);
        if (fileNameCompare != 0)
            return fileNameCompare;
        
        return string.Compare(x, y, StringComparison.OrdinalIgnoreCase);
    }
    
    private static int CompareNatural(string? x, string? y)
    {
        if (x == null && y == null) return 0;
        if (x == null) return -1;
        if (y == null) return 1;
        
        int i = 0, j = 0;
        
        while (i < x.Length && j < y.Length)
        {
            if (char.IsDigit(x[i]) && char.IsDigit(y[j]))
            {
                int numX = 0, numY = 0;
                
                while (i < x.Length && char.IsDigit(x[i]))
                {
                    numX = numX * 10 + (x[i] - '0');
                    i++;
                }
                
                while (j < y.Length && char.IsDigit(y[j]))
                {
                    numY = numY * 10 + (y[j] - '0');
                    j++;
                }
                
                if (numX != numY)
                    return numX.CompareTo(numY);
            }
            else
            {
                int charCompare = char.ToLowerInvariant(x[i]).CompareTo(char.ToLowerInvariant(y[j]));
                if (charCompare != 0)
                    return charCompare;
                
                i++;
                j++;
            }
        }
        
        return x.Length.CompareTo(y.Length);
    }
}