MultiTerm/MultiTerm.Wpf.CustomControl/MultiFormatDataView/MultiFormatDataView.cs

using MultiTerm.Core.ViewModel;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;

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.MultiFormatDataView"
///
///
/// 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.MultiFormatDataView;assembly=MultiTerm.Wpf.CustomControl.MultiFormatDataView"
///
/// 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:MultiFormatDataView/>
///
/// </summary>

public class MultiFormatDataView : Control
{
    private static readonly Dictionary<StackPanel, MultiFormatDataView> itemParentPairs = new();
    private const string itemsControlTemplateName = "itemsControl";
    private ListBox? itemsControl;
    private List<DataViewModel> currentSelectedItems = new();

    #region Dependency Properties
    public static readonly DependencyProperty DataSourceProperty =
        DependencyProperty.Register("DataSource",
        typeof(IEnumerable), typeof(MultiFormatDataView),
        new PropertyMetadata(null, OnDataSourcePropertyChanged));

    public static readonly DependencyProperty SelectedItemsProperty =
        DependencyProperty.Register("SelectedItems",
        typeof(IList), typeof(MultiFormatDataView),
        new FrameworkPropertyMetadata(OnSelectedItemsPropertyChanged)
        {
            BindsTwoWayByDefault = false
        });

    public static readonly DependencyProperty RealizedItemsCountProperty =
        DependencyProperty.Register("RealizedItemsCount",
        typeof(uint), typeof(MultiFormatDataView),
        new PropertyMetadata((uint)0, OnRealizedItemsCountChanged));

    public static readonly DependencyProperty ItemLoadedProperty =
        DependencyProperty.RegisterAttached("ItemLoaded",
        typeof(bool),
        typeof(MultiFormatDataView),
        new UIPropertyMetadata(false, OnItemLoaded));

    public static readonly DependencyProperty ItemUnloadedProperty =
        DependencyProperty.RegisterAttached("ItemUnloaded",
        typeof(bool),
        typeof(MultiFormatDataView),
        new UIPropertyMetadata(false, OnItemUnloaded));

    /// <summary>
    /// .NET Property for DataSource.
    /// </summary>
    [Bindable(true)]
    public IEnumerable DataSource
    {
        get { return (IEnumerable)GetValue(DataSourceProperty); }
        set { SetValue(DataSourceProperty, value); }
    }

    /// <summary>
    /// .NET Property for SelectedItems.
    /// </summary>
    [Bindable(true)]
    public IList SelectedItems
    {
        get { return (IList)GetValue(SelectedItemsProperty); }
        set { SetValue(SelectedItemsProperty, value); }
    }

    /// <summary>
    /// .NET Property for RealizedItemsCount.
    /// </summary>
    [Bindable(true)]
    public uint RealizedItemsCount
    {
        get { return (uint)GetValue(RealizedItemsCountProperty); }
        set { SetValue(RealizedItemsCountProperty, value); }
    }

    /// <summary>
    /// .NET Property for ItemLoaded.
    /// </summary>
    public bool ItemLoaded
    {
        get { return (bool)GetValue(ItemLoadedProperty); }
        set { SetValue(ItemLoadedProperty, value); }
    }

    /// <summary>
    /// .NET Property for ItemUnloaded.
    /// </summary>
    public bool ItemUnloaded
    {
        get { return (bool)GetValue(ItemUnloadedProperty); }
        set { SetValue(ItemUnloadedProperty, value); }
    }
    #endregion

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

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();
        this.SelectedItems = new List<DataViewModel>();

        // get itemsControl from template
        if (GetTemplateChild(itemsControlTemplateName) is ListBox listBox)
        {
            this.itemsControl = listBox;
            this.itemsControl.SelectionChanged += ItemsControl_SelectionChanged;
        }
        else
        {
            throw new Exception($"Implementation fault, {itemsControlTemplateName} not found in template.");
        }
    }

    private void ItemsControl_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if(this.currentSelectedItems == null) 
        { this.currentSelectedItems = new List<DataViewModel>(); }

        // if there are no changes => return
        if (e.AddedItems.Count <= 0 && e.RemovedItems.Count <= 0) { return; }

        // otherwise update internal list
        foreach (DataViewModel item in e.RemovedItems)
        {
            this.SelectedItems.Remove(item);
        }
        foreach (DataViewModel item in e.AddedItems)
        {
            this.SelectedItems.Add(item);
        }
    }

    private static void OnSelectedItemsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        // NOP
    }


    private static void OnDataSourcePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        // extract instance and guard null
        if (d is not MultiFormatDataView mfdv) { return; }
        // extract instance of new Value and guard null
        if (e.NewValue is not IEnumerable enumerable) { return; }

        // check if enumerable items are all of correct type
        foreach (var item in enumerable)
        {
            if (item is not DataViewModel) 
            { throw new ArgumentException($"{nameof(DataSourceProperty)} must be of type {nameof(DataViewModel)}"); }
        }

        // add group property
        CollectionView view = (CollectionView)CollectionViewSource.GetDefaultView(e.NewValue);
        PropertyGroupDescription groupDescription = new(nameof(DataViewModel.LineIdentifier));
        view.GroupDescriptions.Add(groupDescription);
    }


    private static void OnRealizedItemsCountChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        // NOP
    }

    private static void OnItemLoaded(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        // extract instance and guard null
        if (d is not StackPanel stackPanel) { return; }

        // check if value was set to true
        if (e.NewValue is bool boolean && boolean == true)
        {
            // find visual parent of correct type, throw exception if not found
            var parentMFDV = UIHelper.FindVisualParent<MultiFormatDataView>(stackPanel) ?? 
                throw new NullReferenceException($"Could not find parent of type " +
                    $"{nameof(MultiFormatDataView)} in {nameof(stackPanel)}");

            // add to static dictionary
            itemParentPairs.Add(stackPanel, parentMFDV);
            // increment counter
            parentMFDV.RealizedItemsCount++;
        }
    }

    private static void OnItemUnloaded(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        // extract instance and guard null
        if (d is not StackPanel stackPanel) { return; }

        // check if value was set to true
        if (e.NewValue is bool boolean && boolean == true)
        {
            // get parent from static dictionary
            var parentMFDV = itemParentPairs[stackPanel];
            // remove the element from the dictionary
            itemParentPairs.Remove(stackPanel);
            // decrement counter
            parentMFDV.RealizedItemsCount--;
        }
    }
}