GSS2Rework/GSS2.UI.Core/ViewModels/AsyncImageViewModel.cs

using Avalonia.Media;
using Avalonia.Media.Imaging;
using Avalonia.Threading;

using CommunityToolkit.Mvvm.ComponentModel;

namespace GSS2.UI.Core.ViewModels;

public partial class AsyncImageRecordViewModel : ViewModelBase
{
    private static readonly SemaphoreSlim _semaphore = new(1, 1);

    [ObservableProperty] public partial string? Data { get; set; }
    [ObservableProperty] public partial IImage? Image { get; set; }
    [ObservableProperty] public partial bool IsLoading { get; set; } = false;

    public AsyncImageRecordViewModel(string? data = null)
    {
        Data = data;
    }

    partial void OnDataChanged(string? value) => _ = LoadAsync();

    private async Task LoadAsync()
    {
        await _semaphore.WaitAsync();

        try
        {
            if (Data is not null)
            {
                IsLoading = true;
                byte[] imageBytes = Convert.FromBase64String(Data);
                Bitmap bitmap;
                using (var stream = new MemoryStream(imageBytes))
                {
                    bitmap = await Task.Run(() => new Bitmap(stream));
                }

                await Dispatcher.UIThread.InvokeAsync(() =>
                {
                    Image = bitmap;
                    IsLoading = false;
                });
            }
            else
            {
                Image = new WriteableBitmap(new Avalonia.PixelSize(1, 1), new Avalonia.Vector(96, 96), Avalonia.Platform.PixelFormat.Bgra8888, Avalonia.Platform.AlphaFormat.Premul);
            }
        }
        catch
        {
            await Dispatcher.UIThread.InvokeAsync(() => IsLoading = false);
        }
        finally
        {
            _semaphore.Release();
        }
    }
}