Add scaffold for append autocomplete

Terminal.Gui/Core/Autocomplete/AppendAutocomplete.cs

@@ -0,0 +1,146 @@
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.IO;
+
+namespace Terminal.Gui {
+
+	/// <summary>
+	/// Autocomplete for a <see cref="TextField"/> which shows suggestions within the box.
+	/// Displayed suggestions can be completed using the tab key.
+	/// </summary>
+	public class AppendAutocomplete : IAutocomplete {
+
+		private int? currentFragment = null;
+		private string [] validFragments = new string [0];
+		private TextField textField;
+
+		public View HostControl { get => textField; set => textField = (TextField)value; }
+		public bool PopupInsideContainer { get; set; }
+		public int MaxWidth { get; set; }
+		public int MaxHeight { get; set; }
+		public bool Visible { get; set; }
+		public ReadOnlyCollection<string> Suggestions { get; set; }
+		public List<string> AllSuggestions { get; set; }
+		public int SelectedIdx { get; set; }
+		public ColorScheme ColorScheme { get; set; }
+		public Key SelectionKey { get; set; } = Key.Tab;
+		public Key CloseKey { get; set; }
+		public Key Reopen { get; set; }
+
+		public void ClearSuggestions ()
+		{
+			this.currentFragment = null;
+			this.validFragments = new string [0];
+			textField.SetNeedsDisplay ();
+		}
+
+		public void GenerateSuggestions (int columnOffset = 0)
+		{
+			validFragments = new string []{ "fish", "flipper", "fun" };
+		}
+
+		public bool MouseEvent (MouseEvent me, bool fromHost = false)
+		{
+			return false;
+		}
+
+		public bool ProcessKey (KeyEvent kb)
+		{
+			var key = kb.Key;
+			if (key == SelectionKey) {
+				return this.AcceptSelectionIfAny ();
+			} else
+			if (key == Key.CursorUp) {
+				return this.CycleSuggestion (1);
+			} else
+			if (key == Key.CursorDown) {
+				return this.CycleSuggestion (-1);
+			}
+
+			return false;
+		}
+
+		public void RenderOverlay (Point renderAt)
+		{
+			if (!this.MakingSuggestion ()) {
+				return;
+			}
+
+			// draw it like its selected even though its not
+			Application.Driver.SetAttribute (new Attribute (Color.DarkGray, Color.Black));
+			textField.Move (textField.Text.Length, 0);
+			Application.Driver.AddStr (this.validFragments [this.currentFragment.Value]);
+		}
+
+		public AppendAutocomplete (TextField textField)
+		{
+			this.textField = textField;
+		}
+
+		/// <summary>
+		/// Accepts the current autocomplete suggestion displaying in the text box.
+		/// Returns true if a valid suggestion was being rendered and acceptable or
+		/// false if no suggestion was showing.
+		/// </summary>
+		/// <returns></returns>
+		internal bool AcceptSelectionIfAny ()
+		{
+			if (this.MakingSuggestion ()) {
+				textField.Text += this.validFragments [this.currentFragment.Value];
+				this.MoveCursorToEnd ();
+
+				this.ClearSuggestions ();
+				return true;
+			}
+
+			return false;
+		}
+
+		internal void MoveCursorToEnd ()
+		{
+			textField.ClearAllSelection ();
+			textField.CursorPosition = textField.Text.Length;
+		}
+
+		internal void SetTextTo (FileSystemInfo fileSystemInfo)
+		{
+			var newText = fileSystemInfo.FullName;
+			if (fileSystemInfo is DirectoryInfo) {
+				newText += System.IO.Path.DirectorySeparatorChar;
+			}
+			textField.Text = newText;
+			this.MoveCursorToEnd ();
+		}
+
+		internal bool CursorIsAtEnd ()
+		{
+			return textField.CursorPosition == textField.Text.Length;
+		}
+
+		/// <summary>
+		/// Returns true if there is a suggestion that can be made and the control
+		/// is in a state where user would expect to see auto-complete (i.e. focused and
+		/// cursor in right place).
+		/// </summary>
+		/// <returns></returns>
+		private bool MakingSuggestion ()
+		{
+			return this.currentFragment != null && textField.HasFocus && this.CursorIsAtEnd ();
+		}
+
+		private bool CycleSuggestion (int direction)
+		{
+			if (this.currentFragment == null || this.validFragments.Length <= 1) {
+				return false;
+			}
+
+			this.currentFragment = (this.currentFragment + direction) % this.validFragments.Length;
+
+			if (this.currentFragment < 0) {
+				this.currentFragment = this.validFragments.Length - 1;
+			}
+			textField.SetNeedsDisplay ();
+			return true;
+		}
+	}
+}

Terminal.Gui/Views/TextField.cs

@@ -274,7 +274,7 @@ namespace Terminal.Gui {
 		/// Provides autocomplete context menu based on suggestions at the current cursor
 		/// position. Populate <see cref="Autocomplete.AllSuggestions"/> to enable this feature.
 		/// </summary>
-		public IAutocomplete Autocomplete { get; protected set; } = new TextFieldAutocomplete ();
+		public IAutocomplete Autocomplete { get; set; } = new TextFieldAutocomplete ();
 
 		///<inheritdoc/>
 		public override Rect Frame {

UICatalog/Scenarios/Text.cs

@@ -213,6 +213,20 @@ namespace UICatalog.Scenarios {
 			};
 
 			Win.Add (regexProviderField);
+
+			var labelAppendAutocomplete = new Label ("Append Autocomplete:") {
+				Y = Pos.Y (regexProviderField) + 2,
+				X = 1
+			};
+			var appendAutocompleteTextField = new TextField () {
+				X = Pos.Right(labelAppendAutocomplete),
+				Y = labelAppendAutocomplete.Y,
+				Width = 30
+			};
+			appendAutocompleteTextField.Autocomplete = new AppendAutocomplete (appendAutocompleteTextField);
+						
+			Win.Add (labelAppendAutocomplete);
+			Win.Add (appendAutocompleteTextField);
 		}
 
 		TimeField _timeField;