using System;

using System.Collections.Generic;

using System.Globalization;

using System.Linq;

using System.Reactive;

using System.Reactive.Concurrency;

using System.Reactive.Linq;

using System.Text;

using System.Windows;

using System.Windows.Controls;

using System.Windows.Data;

using System.Windows.Documents;

using System.Windows.Input;

using System.Windows.Media;

using System.Windows.Media.Imaging;

using System.Windows.Navigation;

using System.Windows.Shapes;

 

namespace WpfApplication2

    /// <summary>

    /// Interaction logic for MainWindow.xaml

    /// </summary>

    public partial class MainWindow : Window

    {

        public MainWindow()

        {

            InitializeComponent();

            Observable.FromEventPattern(textBox, "TextChanged").Throttle(TimeSpan.FromMilliseconds(500)).ObserveOnDispatcher().Subscribe(OnTextChanged);

        }

 

        public void OnTextChanged(EventPattern<EventArgs> eventPatternArgs)

        {

            var textBox = eventPatternArgs.Sender as TextBox;

            if(textBox != null)

            {

               var adornerLayer = AdornerLayer.GetAdornerLayer(textBox);

 

                textBoxHintAdorner = new TextBoxHintAdorner(textBox);

                adornerLayer.Add(textBoxHintAdorner);

            }

 

            disposable = Observable.FromEventPattern(textBox, "TextChanged").ObserveOnDispatcher().Subscribe(OnRemoveAdorner);

        }

 

        public void OnRemoveAdorner(EventPattern<EventArgs> eventPatternArgs)

        {

            var textBox = eventPatternArgs.Sender as TextBox;

            if (textBox != null)

            {

                var adornerLayer = AdornerLayer.GetAdornerLayer(textBox);

 

                if (textBoxHintAdorner != null)

                    adornerLayer.Remove(textBoxHintAdorner);

            }

 

            disposable.Dispose();

        }

 

        private IDisposable disposable;

        private TextBoxHintAdorner textBoxHintAdorner;

    }

 

    public class TextBoxHintAdorner : Adorner

    {

        public TextBoxHintAdorner(UIElement adornedElement) : base(adornedElement)

        {

           

        }

 

        protected override void OnRender(DrawingContext drawingContext)

        {

            var textBox = AdornedElement as TextBox;

            if(textBox == null)

                return;

           

            String hintText = TextHint.GetHint(textBox.Text);

 

            var formattedText = new FormattedText(hintText, CultureInfo.GetCultureInfo("en-us"), FlowDirection.LeftToRight, new Typeface("Verdana"), 10, Brushes.Black);

 

            Rect rect = textBox.GetRectFromCharacterIndex(textBox.Text.Length);

 

            drawingContext.DrawRectangle(Brushes.Yellow, null, new Rect(rect.TopRight.X + 10, rect.TopRight.Y, formattedText.Width, formattedText.Height));

            drawingContext.DrawText(formattedText, new Point(rect.BottomRight.X + 10, 0));

        }

    }

 

    public class TextHint

    {

        public static String GetHint(String text)

        {

            int words = text.Split(new char[] {' '}).Count();

            if(words == 1)

                return "circle|polygon";

            if (words == 2)

                return "<n> sides";

            if (words == 4)

                return "<x> colour";

 

            return string.Empty;

        }

    }