MultiTerm/MultiTerm.Wpf.CustomControl/MultiFormatTextBox/MultiFormatTextBox.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;

namespace MultiTerm.Wpf.CustomControl;

/// <summary>
/// Follow steps 1a or 1b and then 2 to use this custom control in a XAML file.
///
/// Step 1a) Using this custom control in a XAML file that exists in the current project.
/// Add this XmlNamespace attribute to the root element of the markup file where it is 
/// to be used:
///
///     xmlns:MyNamespace="clr-namespace:MultiTerm.Wpf.CustomControl"
///
///
/// Step 1b) Using this custom control in a XAML file that exists in a different project.
/// Add this XmlNamespace attribute to the root element of the markup file where it is 
/// to be used:
///
///     xmlns:MyNamespace="clr-namespace:MultiTerm.Wpf.CustomControl.MultiFormatTextBox;assembly=MultiTerm.Wpf.CustomControl.MultiFormatTextBox"
///
/// You will also need to add a project reference from the project where the XAML file lives
/// to this project and Rebuild to avoid compilation errors:
///
///     Right click on the target project in the Solution Explorer and
///     "Add Reference"->"Projects"->[Browse to and select this project]
///
///
/// Step 2)
/// Go ahead and use your control in the XAML file.
///
///     <MyNamespace:MultiFormatTextBox/>
///
/// </summary>
internal class Format
{
    public string Name { get; set; }
    public Brush BackgroundBrush { get; set; }
    public Predicate<Key> IsKeyValid { get; set; }
    public Format(string name, Brush backgroundBrush, Predicate<Key> keyValidator)
    {
        this.Name = name;
        this.BackgroundBrush = backgroundBrush;
        this.IsKeyValid = keyValidator;
    }
    public Format(string name, string backgroundBrushColorHexCode, Predicate<Key> keyValidator)
    {
        this.Name = name;
        var brushObj = new BrushConverter().ConvertFrom(backgroundBrushColorHexCode);
        if(brushObj == null) throw new ArgumentException(nameof(backgroundBrushColorHexCode));
        this.BackgroundBrush = (SolidColorBrush)brushObj;
        this.IsKeyValid = keyValidator;
    }
    public static List<string> GetListOfNames(IEnumerable<Format> formats)
    {
        return formats.Select(item => item.Name).ToList();
    }
}

public class MultiFormatTextBox : Control
{
    private static readonly Brush defaultBackgroundBrush = Brushes.White;
    private static readonly List<Format> formats = new()
    {
        // character input, accepts all keys except space
        new Format("CHAR", Brushes.LightSkyBlue, delegate(Key k) { return (k != Key.Space); }),
        //new Format("CHAR", "B4EBEB", delegate(Key k) { return (k != Key.Space); }),
        // hex input, ignores all keys that are not inbetween 0 and F
        new Format("HEX", Brushes.LightGreen, delegate(Key k) { return (k >= Key.D0 && k <= Key.F); }),
        //new Format("HEX", "C8C8FF", delegate(Key k) { return (k >= Key.D0 && k <= Key.F); }),
        // binary input, ignores all keys except 0 and 1
        new Format("BIN", Brushes.LightPink, delegate(Key k) { return (k == Key.D0 || k == Key.D1); })
        //new Format("BIN", "C8FFC8", delegate(Key k) { return (k == Key.D0 || k == Key.D1); })
    };

    private ComboBox comboBox;
    private RichTextBox richTextBox;
    private Format currentlySelectedFormat = formats.First();
    private int offsetContentStartToFormatStart;

    static MultiFormatTextBox()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(MultiFormatTextBox), new FrameworkPropertyMetadata(typeof(MultiFormatTextBox)));
    }

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();

        // get comboBox from template
        var comboBox = GetTemplateChild("comboBox") as ComboBox;
        if (comboBox != null)
        {
            this.comboBox = comboBox;
            this.comboBox.ItemsSource = Format.GetListOfNames(formats);
            this.comboBox.SelectedItem = currentlySelectedFormat.Name;
            this.comboBox.SelectionChanged += ComboBox_SelectionChanged;
        }

        // get richTextBox from template
        var richTextBox = GetTemplateChild("richTextBox") as RichTextBox;
        if (richTextBox != null)
        {
            this.richTextBox = richTextBox;
            this.richTextBox.KeyDown += RichTextBox_KeyDown;
            this.richTextBox.TextChanged += RichTextBox_TextChanged;
            this.offsetContentStartToFormatStart = 0;
        }

    }


    private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        // match all formats with the name selected in the combobox
        var matchingFormats = formats.Where(format => format.Name == (string)this.comboBox!.SelectedItem);
        // check if exactly one format was matched
        if(matchingFormats.Count() != 1)
        {
            throw new Exception($"{nameof(ComboBox_SelectionChanged)} could not match a correct amount of formats");
        }
        // set currently selected format, reset offset counter
        this.currentlySelectedFormat = matchingFormats.First();

        // insert space to separate formats
        this.InsertSeparation();

        // set new start position
        this.offsetContentStartToFormatStart = this.richTextBox.CaretPosition.GetOffsetToPosition(this.richTextBox.Document.ContentStart);

        // focus textbox
        this.richTextBox.Focus();
    }

    private void InsertSeparation()
    {
        // disable event handler
        this.richTextBox.TextChanged -= RichTextBox_TextChanged;

        // store caret position before
        this.offsetContentStartToFormatStart = this.richTextBox.CaretPosition.GetOffsetToPosition(this.richTextBox.Document.ContentStart);

        // insert
        this.richTextBox.AppendText(" ");

        // change background
        RtbChangeTextBackground(this.richTextBox,
           start: this.richTextBox.Document.ContentStart.GetPositionAtOffset(-this.offsetContentStartToFormatStart),
           end: this.richTextBox.Document.ContentEnd,
           color: defaultBackgroundBrush);

        // store new caret position after
        this.offsetContentStartToFormatStart = this.richTextBox.CaretPosition.GetOffsetToPosition(this.richTextBox.Document.ContentStart);

        // reenable
        this.richTextBox.TextChanged += RichTextBox_TextChanged;
    }

    private void RichTextBox_KeyDown(object sender, KeyEventArgs e)
    {
        // guard combobox null
        if (this.comboBox == null) throw new Exception($"{nameof(this.comboBox)} cannot be null");

        // if key is invalid for this format => ignore it (handled = true)
        if(this.currentlySelectedFormat.IsKeyValid(e.Key) == false)
        {
            e.Handled = true;
        }
    }

    private void RichTextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        if(e.Changes.Count > 1) { return; }

        RtbChangeTextBackground(this.richTextBox,
            start: this.richTextBox.Document.ContentStart.GetPositionAtOffset(-this.offsetContentStartToFormatStart),
            end: this.richTextBox.Document.ContentEnd,
            color: this.currentlySelectedFormat.BackgroundBrush);
    }

    private static void RtbChangeTextBackground(RichTextBox rtb, TextPointer start, TextPointer end, Brush color)
    {
        // Get text selection
        TextSelection textRange = rtb.Selection;
        textRange.Select(start, end);

        // Apply property to the selection:
        textRange.ApplyPropertyValue(TextElement.BackgroundProperty, color);

        // deselect
        rtb.Selection.Select(rtb.Document.ContentEnd, rtb.Document.ContentEnd);
    }

}