[Core] Add custom expression autocomplete support

2 files changed, 181 insertions, 0 deletions

diff --git a/Xamarin.PropertyEditing.Tests/PropertyViewModelTests.cs b/Xamarin.PropertyEditing.Tests/PropertyViewModelTests.cs
index 00d7e3b..c207b4f 100644
--- a/Xamarin.PropertyEditing.Tests/PropertyViewModelTests.cs
+++ b/Xamarin.PropertyEditing.Tests/PropertyViewModelTests.cs
@@ -1085,6 +1085,96 @@ namespace Xamarin.PropertyEditing.Tests
 			Assert.That (requested, Is.True, "CreateResourceRequested did not fire");
 		}
 
+		[TestCase (true, true, true)]
+		[TestCase (false, true, false)]
+		[TestCase (true, false, false)]
+		public void AutocompleteEnabled (bool customExpressions, bool hasInterface, bool expected)
+		{
+			var target = new object ();
+			var property = GetPropertyMock ();
+			var editor = new Mock<IObjectEditor> ();
+			editor.SetupGet (e => e.Target).Returns (target);
+			SetupPropertySetAndGet (editor, property.Object);
+
+			if (hasInterface) {
+				string[] results = { "Foo", "Bar", "Baz" };
+				var complete = editor.As<ICompleteValues> ();
+				complete.Setup (c => c.GetCompletionsAsync (property.Object, It.IsAny<string> (), It.IsAny<CancellationToken> ()))
+					.ReturnsAsync (results);
+			}
+
+			var mockProvider = new MockEditorProvider (editor.Object);
+			var resources = new MockResourceProvider ();
+			var platform = new TargetPlatform (mockProvider, resources) {
+				SupportsCustomExpressions = customExpressions
+			};
+
+			var vm = GetViewModel (platform, property.Object, new[] { editor.Object });
+			Assert.That (vm.SupportsAutocomplete, Is.EqualTo (expected));
+		}
+
+		[Test]
+		public void AutocompleteResults ()
+		{
+			var target = new object ();
+			var property = GetPropertyMock ();
+			var editor = new Mock<IObjectEditor> ();
+			editor.SetupGet (e => e.Target).Returns (target);
+			SetupPropertySetAndGet (editor, property.Object);
+
+			string[] results = new[] { "Foo", "Bar", "Baz" };
+			var complete = editor.As<ICompleteValues> ();
+			complete.Setup (c => c.GetCompletionsAsync (property.Object, It.IsAny<string> (), It.IsAny<CancellationToken> ())).ReturnsAsync (results);
+
+			var mockProvider = new MockEditorProvider (editor.Object);
+			var resources = new MockResourceProvider();
+			var platform = new TargetPlatform (mockProvider, resources) {
+				SupportsCustomExpressions = true
+			};
+
+			var vm = GetViewModel (platform, property.Object, new[] { editor.Object });
+			Assume.That (vm.SupportsAutocomplete, Is.True);
+			vm.PreviewCustomExpression = "preview";
+
+			CollectionAssert.AreEqual (vm.AutocompleteItems, results);
+			complete.Verify (c => c.GetCompletionsAsync (property.Object, "preview", It.IsAny<CancellationToken> ()));
+		}
+
+		[Test]
+		public void AutocompleteCancels ()
+		{
+			var target = new object ();
+			var property = GetPropertyMock ();
+			var editor = new Mock<IObjectEditor> ();
+			editor.SetupGet (e => e.Target).Returns (target);
+			SetupPropertySetAndGet (editor, property.Object);
+
+			string[] results = new[] { "Foo", "Bar", "Baz" };
+			var tcs = new TaskCompletionSource<IReadOnlyList<string>> ();
+
+			var complete = editor.As<ICompleteValues> ();
+			complete.Setup (c => c.GetCompletionsAsync (property.Object, It.IsAny<string> (), It.IsAny<CancellationToken> ()))
+				.Returns<IPropertyInfo,string,CancellationToken> ((a,b,c) => {
+					c.Register (() => {
+						tcs.TrySetCanceled ();
+					});
+					return tcs.Task;
+				});
+
+			var mockProvider = new MockEditorProvider (editor.Object);
+			var resources = new MockResourceProvider ();
+			var platform = new TargetPlatform (mockProvider, resources) {
+				SupportsCustomExpressions = true
+			};
+
+			var vm = GetViewModel (platform, property.Object, new[] { editor.Object });
+			Assume.That (vm.SupportsAutocomplete, Is.True);
+			vm.PreviewCustomExpression = "preview";
+
+			vm.PreviewCustomExpression = "attempt2";
+			Assert.That (tcs.Task.IsCanceled, Is.True);
+		}
+
 		protected TViewModel GetViewModel (IPropertyInfo property, IObjectEditor editor)
 		{
 			return GetViewModel (property, new[] { editor });
diff --git a/Xamarin.PropertyEditing/ViewModels/PropertyViewModel.cs b/Xamarin.PropertyEditing/ViewModels/PropertyViewModel.cs
index 4e353c8..605b8c5 100644
--- a/Xamarin.PropertyEditing/ViewModels/PropertyViewModel.cs
+++ b/Xamarin.PropertyEditing/ViewModels/PropertyViewModel.cs
@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using System.Windows.Input;
 
@@ -77,6 +78,32 @@ namespace Xamarin.PropertyEditing.ViewModels
 			}
 		}
 
+		public bool SupportsAutocomplete
+		{
+			get { return this.supportsAutocomplete; }
+			private set
+			{
+				if (this.supportsAutocomplete == value)
+					return;
+
+				this.supportsAutocomplete = value;
+				OnPropertyChanged();
+
+				if (!value) {
+					this.autocomplete = null;
+					this.autocompleteCancel?.Cancel();
+					this.autocompleteCancel = null;
+				}
+			}
+		}
+
+		public IReadOnlyList<string> AutocompleteItems => this.autocomplete;
+
+		public string PreviewCustomExpression
+		{
+			set { UpdateAutocomplete (value); }
+		}
+
 		public string CustomExpression
 		{
 			get { return this.value?.CustomExpression; }
@@ -228,6 +255,23 @@ namespace Xamarin.PropertyEditing.ViewModels
 			}
 		}
 
+		protected override void OnEditorsChanged (object sender, NotifyCollectionChangedEventArgs e)
+		{
+			base.OnEditorsChanged (sender, e);
+
+			if (e.Action == NotifyCollectionChangedAction.Add && SupportsAutocomplete)
+				return;
+
+			if (TargetPlatform.SupportsCustomExpressions) {
+				foreach (IObjectEditor editor in Editors) {
+					if (editor is ICompleteValues) {
+						SupportsAutocomplete = true;
+						break;
+					}
+				}
+			}
+		}
+
 		private readonly ICoerce<TValue> coerce;
 		private readonly IValidator<TValue> validator;
 		private readonly ICanNavigateToSource valueNavigator;
@@ -235,6 +279,10 @@ namespace Xamarin.PropertyEditing.ViewModels
 		private bool isNullable;
 		private ValueInfo<TValue> value;
 
+		private bool supportsAutocomplete;
+		private ObservableCollectionEx<string> autocomplete;
+		private CancellationTokenSource autocompleteCancel;
+
 		private void SignalValueChange ()
 		{
 			OnPropertyChanged (nameof (Value));
@@ -359,6 +407,49 @@ namespace Xamarin.PropertyEditing.ViewModels
 			});
 		}
 
+		private async void UpdateAutocomplete (string value)
+		{
+			if (!SupportsAutocomplete)
+				return;
+
+			if (this.autocomplete == null) {
+				this.autocomplete = new ObservableCollectionEx<string> ();
+				OnPropertyChanged (nameof(AutocompleteItems));
+			} else {
+				this.autocompleteCancel.Cancel();
+			}
+
+			this.autocompleteCancel = new CancellationTokenSource ();
+			CancellationToken cancel = this.autocompleteCancel.Token;
+
+			try {
+				HashSet<string> common = null;
+				List<Task<IReadOnlyList<string>>> tasks = new List<Task<IReadOnlyList<string>>> ();
+
+				foreach (IObjectEditor editor in Editors) {
+					if (!(editor is ICompleteValues complete))
+						continue;
+
+					tasks.Add (complete.GetCompletionsAsync (Property, value, cancel));
+				}
+
+				IReadOnlyList<string> list = null;
+				do {
+					Task<IReadOnlyList<string>> results = await Task.WhenAny (tasks);
+					tasks.Remove (results);
+
+					if (list == null) {
+						list = results.Result;
+						common = new HashSet<string> (list);
+					} else
+						common.IntersectWith (results.Result);
+				} while (tasks.Count > 0 && !cancel.IsCancellationRequested);
+
+				this.autocomplete.Reset (list.Where (common.Contains));
+			} catch (OperationCanceledException) {
+			}
+		}
+
 		private static TValue DefaultValue;
 	}