Avalonia/src/OSX/Avalonia.MonoMac/DragSource.cs

using System;
using System.Collections.Generic;
using System.Data;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Reactive.Linq;
using System.Reactive.Subjects;
using System.Runtime.InteropServices;
using System.Runtime.Serialization.Formatters.Binary;
using System.Threading.Tasks;
using Avalonia.Controls;
using Avalonia.Input;
using Avalonia.Input.Platform;
using Avalonia.Input.Raw;
using MonoMac;
using MonoMac.AppKit;
using MonoMac.CoreGraphics;
using MonoMac.Foundation;
using MonoMac.OpenGL;

namespace Avalonia.MonoMac
{
    public class DragSource : NSDraggingSource, IPlatformDragSource
    {
        private const string NSPasteboardTypeString = "public.utf8-plain-text";
        private const string NSPasteboardTypeFileUrl = "public.file-url";
        
        private readonly Subject<DragDropEffects> _result = new Subject<DragDropEffects>();
        private readonly IInputManager _inputManager;
        private DragDropEffects _allowedEffects;
        
        public override bool IgnoreModifierKeysWhileDragging => false;
      
        public DragSource()
        {
            _inputManager = AvaloniaLocator.Current.GetService<IInputManager>();
        }

        private string DataFormatToUTI(string s)
        {
            if (s == DataFormats.FileNames)
                return NSPasteboardTypeFileUrl;
            if (s == DataFormats.Text)
                return NSPasteboardTypeString;
            return s;
        }
        
        private NSDraggingItem CreateDraggingItem(string format, object data)
        {
            var pasteboardItem = new NSPasteboardItem();
            NSData nsData;
            if (data is string s)
            {
                if (format == DataFormats.FileNames)
                    s = new Uri(s).AbsoluteUri; // Ensure file uris...
                nsData = NSData.FromString(s);
            }
            else if (data is Stream strm)
                nsData = NSData.FromStream(strm);
            else if (data is byte[] bytes)
                nsData = NSData.FromArray(bytes);
            else
            {
                BinaryFormatter bf = new BinaryFormatter();
                using (var ms = new MemoryStream())
                {
                    bf.Serialize(ms, data);
                    ms.Position = 0;
                    nsData = NSData.FromStream(ms);
                }
            }
            pasteboardItem.SetDataForType(nsData, DataFormatToUTI(format));

            NSPasteboardWriting writing = new NSPasteboardWriting(pasteboardItem.Handle);
  
            return new NSDraggingItem(writing);
        }

        public IEnumerable<NSDraggingItem> CreateDraggingItems(string format, object data)
        {
            if (format == DataFormats.FileNames && data is IEnumerable<string> files)
            {
                foreach (var file in files)
                    yield return CreateDraggingItem(format, file);

                yield break;
            }

            yield return CreateDraggingItem(format, data);
        }
        
        
        public async Task<DragDropEffects> DoDragDrop(IDataObject data, DragDropEffects allowedEffects)
        {
            // We need the TopLevelImpl + a mouse location so we just wait for the next event.
            var mouseEv = await _inputManager.PreProcess.OfType<RawMouseEventArgs>().FirstAsync();
            var view = ((mouseEv.Root as TopLevel)?.PlatformImpl as TopLevelImpl)?.View;
            if (view == null)
                return DragDropEffects.None;

            // Prepare the source event:
            var pt = view.TranslateLocalPoint(mouseEv.Position).ToMonoMacPoint();    
            var ev = NSEvent.MouseEvent(NSEventType.LeftMouseDown, pt, 0, 0, 0, null, 0, 0, 0);

            _allowedEffects = allowedEffects;
            var items = data.GetDataFormats().SelectMany(fmt => CreateDraggingItems(fmt, data.Get(fmt))).ToArray();
            view.BeginDraggingSession(items ,ev, this);

            return await _result;
        }
        
        public override NSDragOperation DraggingSourceOperationMaskForLocal(bool flag)
        {
            return DraggingInfo.ConvertDragOperation(_allowedEffects);
        }
            
        public override void DraggedImageEndedAtOperation(NSImage image, CGPoint screenPoint, NSDragOperation operation)
        {
            _result.OnNext(DraggingInfo.ConvertDragOperation(operation));
            _result.OnCompleted();
        }
    }
}