How to extend a WPF Textbox to Custom Picker

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:extToolkit="http://schemas.microsoft.com/winfx/2006/xaml/presentation/toolkit/extended"
                    xmlns:Converter="clr-namespace:CustomPicker.Utility">

    <Converter:DoubleStringConverter x:Key="doubleStringConverter" />
    
    <ControlTemplate x:Key="IconButton" TargetType="{x:Type ToggleButton}">
        <Border>
            <ContentPresenter />
        </Border>
    </ControlTemplate>

    <Style x:Key="tbCalculatorStyle" TargetType="{x:Type TextBox}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TextBox}">
                    <Grid>
                        <Border BorderThickness="1" BorderBrush="DarkGray">
                            <ScrollViewer x:Name="PART_ContentHost" />
                        </Border>
                        <ToggleButton Template="{StaticResource IconButton}"
                              MaxHeight="21" 
                              Margin="-1,0,0,0" 
                              Name="PopUpImageButton" 
                              Focusable="False"
                              IsChecked="False">
                            <Image Source="Images\Calculator_Icon.png" Stretch="Uniform" Visibility="Hidden" HorizontalAlignment="Right" Name="imgPicker" >
                            </Image>
                        </ToggleButton>
                        <Popup IsOpen="{Binding Path=IsChecked, ElementName=PopUpImageButton, Mode=TwoWay}" x:Name="CustomPopup" Margin="0,-1,0,0" PopupAnimation="Fade" StaysOpen="False">
                            <extToolkit:Calculator Margin="0,0,0,0" x:Name="CalDisplay" 
                                      DisplayText="{Binding RelativeSource={RelativeSource Mode=TemplatedParent}, Path=Text, Mode=TwoWay, Converter={StaticResource doubleStringConverter}}" 
                                      Focusable="False"                                       
                                      Precision="2">
                                <Control.Triggers>
                                    <EventTrigger RoutedEvent="extToolkit:Calculator.LostFocus">
                                        <BeginStoryboard>
                                            <Storyboard>
                                                <BooleanAnimationUsingKeyFrames Storyboard.TargetName="PopUpImageButton" Storyboard.TargetProperty="IsChecked">
                                                    <DiscreteBooleanKeyFrame KeyTime="00:00:00" Value="False"></DiscreteBooleanKeyFrame>
                                                </BooleanAnimationUsingKeyFrames>
                                            </Storyboard>
                                        </BeginStoryboard>
                                    </EventTrigger>
                                    <EventTrigger RoutedEvent="extToolkit:Calculator.MouseLeave">
                                        <BeginStoryboard>
                                            <Storyboard>
                                                <BooleanAnimationUsingKeyFrames Storyboard.TargetName="PopUpImageButton" Storyboard.TargetProperty="IsChecked">
                                                    <DiscreteBooleanKeyFrame KeyTime="00:00:00" Value="False"></DiscreteBooleanKeyFrame>
                                                </BooleanAnimationUsingKeyFrames>
                                            </Storyboard>
                                        </BeginStoryboard>
                                    </EventTrigger>
                                </Control.Triggers>
                            </extToolkit:Calculator>
                        </Popup>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsMouseOver" Value="true">
                            <Setter Property="Visibility" TargetName="imgPicker" Value="Visible" />
                        </Trigger>
                        <Trigger Property="IsFocused" Value="true">
                            <Setter Property="Visibility" TargetName="imgPicker" Value="Visible" />
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>