inabox/InABox.Avalonia/Components/Accordion/Accordion.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Controls.Metadata;
using Avalonia.Controls.Primitives;
using Avalonia.LogicalTree;
using Avalonia.Media;
using Avalonia.Metadata;
using CommunityToolkit.Mvvm.Input;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace InABox.Avalonia.Components;

[TemplatePart(Name = "PART_Grid")]
public partial class Accordion : TemplatedControl
{
    public static readonly StyledProperty<ObservableCollection<AccordionItem>> ItemsProperty =
        AvaloniaProperty.Register<Accordion, ObservableCollection<AccordionItem>>(nameof(Items));
    
    public static readonly StyledProperty<object?> SelectedItemProperty = 
        AvaloniaProperty.Register<Accordion, object?>(nameof(SelectedItem));

    public static readonly DirectProperty<Accordion, int> SelectedIndexProperty =
        AvaloniaProperty.RegisterDirect<Accordion, int>(nameof(SelectedIndex), x => x.SelectedIndex, (x, v) => x.SelectedIndex = v);

    [Content]
    public ObservableCollection<AccordionItem> Items
    {
        get => GetValue(ItemsProperty);
        set => SetValue(ItemsProperty, value);
    }

    private AccordionItem? SelectedButton
    {
        get => Items.FirstOrDefault(x => x.Selected);
        set
        {
            var i = 0;
            var index = -1;
            foreach(var item in Items)
            {
                item.Selected = item == value;
                if(item == value)
                {
                    index = i;
                }
                if(Grid is not null)
                {
                    Grid.RowDefinitions[i].Height = item == value ? GridLength.Star : GridLength.Auto;
                }
                ++i;
            }
            SelectedItem = value?.Tag;
        }
    }

    public object? SelectedItem
    {
        get => GetValue(SelectedItemProperty);
        private set => SetValue(SelectedItemProperty, value);
    }

    public int SelectedIndex
    {
        get => SelectedButton != null && Items.Contains(SelectedButton) ? Items.IndexOf(SelectedButton) : -1;
        set => SelectedButton = value > -1 && value < Items.Count ? Items[value] : null;
    }

    public event EventHandler? SelectionChanged;

    private Grid? Grid;

    static Accordion()
    {
        ItemsProperty.Changed.AddClassHandler<Accordion>(Items_Changed);
    }

    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
    {
        base.OnApplyTemplate(e);
        
        Grid = e.NameScope.Get<Grid>("PART_Grid");
        if(Grid is not null)
        {
            foreach(var item in Items)
            {
                Grid.SetRow(item, Grid.RowDefinitions.Count);
                Grid.RowDefinitions.Add(new(item.Selected ? GridLength.Star : GridLength.Auto));
                Grid.Children.Add(item);
            }
        }
    }

    private static void Items_Changed(Accordion strip, AvaloniaPropertyChangedEventArgs args)
    {
        strip.LogicalChildren.Clear();
        strip.Grid?.Children.Clear();

        if (strip.Items is not null)
        {
            strip.SelectedButton = strip.Items.FirstOrDefault();

            strip.LogicalChildren.AddRange(strip.Items);
            foreach(var item in strip.Items)
            {
                item.Command = strip.ItemSelectedCommand;
                if(strip.Grid is not null)
                {
                    Grid.SetRow(item, strip.Grid.RowDefinitions.Count);
                    strip.Grid.RowDefinitions.Add(new(item.Selected ? GridLength.Star : GridLength.Auto));
                    strip.Grid.Children.Add(item);
                }
            }
        }
    }

    public Accordion()
    {
        Items = new();
        Items.CollectionChanged += Items_CollectionChanged;
    }

    private void Items_CollectionChanged(object? sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        SelectedButton ??= Items.FirstOrDefault();
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                AddControlItemsToLogicalChildren(e.NewItems);
                break;
            case NotifyCollectionChangedAction.Remove:
                RemoveControlItemsFromLogicalChildren(e.OldItems);
                break;
        }
        foreach(var item in Items)
        {
            item.Command = ItemSelectedCommand;
        }
    }

    private void AddControlItemsToLogicalChildren(IEnumerable? items)
    {
        if (items is null) return;

        List<Control>? toAdd = null;
        foreach(var i in items)
        {
            if(i is Control control && !LogicalChildren.Contains(control))
            {
                toAdd ??= new();
                toAdd.Add(control);
            }
        }
        if(toAdd is not null)
        {
            LogicalChildren.AddRange(toAdd);
            if(Grid is not null)
            {
                foreach(var item in toAdd)
                {
                    Grid.SetRow(item, Grid.RowDefinitions.Count);
                    Grid.RowDefinitions.Add(new(item is AccordionItem aItem && aItem.Selected ? GridLength.Star : GridLength.Auto));
                    Grid.Children.Add(item);
                }
            }
        }
    }
    private void RemoveControlItemsFromLogicalChildren(IEnumerable? items)
    {
        if (items is null) return;

        List<Control>? toRemove = null;
        foreach(var i in items)
        {
            if(i is Control control)
            {
                toRemove ??= new();
                toRemove.Add(control);
            }
        }
        if(toRemove is not null)
        {
            foreach(var item in toRemove)
            {
                var index = LogicalChildren.IndexOf(item);
                if(index != -1)
                {
                    Grid?.RowDefinitions.RemoveAt(index);
                    Grid?.Children.Remove(item);
                }
            }
            LogicalChildren.RemoveAll(toRemove);
            if(Grid is not null)
            {
                var i = 0;
                foreach(var item in LogicalChildren)
                {
                    if(item is Control control)
                    {
                        Grid.SetRow(control, i);
                        ++i;
                    }
                }
            }
        }
    }

    [RelayCommand]
    private void ItemSelected(AccordionItem item)
    {
        var children = this.GetLogicalChildren().ToArray();
        SelectedButton = item;
        SelectionChanged?.Invoke(this, new());
    }
}

[PseudoClasses(":selected")]
public class AccordionItem : TemplatedControl
{
    public static readonly StyledProperty<string> TextProperty = AvaloniaProperty.Register<AccordionItem, string>(nameof(Text));
    public static readonly StyledProperty<object?> ContentProperty = AvaloniaProperty.Register<AccordionItem, object?>(nameof(Content));
    public static readonly StyledProperty<bool> SelectedProperty = AvaloniaProperty.Register<AccordionItem, bool>(nameof(Selected));
    public static readonly StyledProperty<int> IndexProperty = AvaloniaProperty.Register<AccordionItem, int>(nameof(Index));
    public static readonly StyledProperty<ICommand> CommandProperty = AvaloniaProperty.Register<AccordionItem, ICommand>(nameof(Command));

    public string Text
    {
        get => GetValue(TextProperty);
        set => SetValue(TextProperty, value);
    }
    [Content]
    public object? Content
    {
        get => GetValue(ContentProperty);
        set => SetValue(ContentProperty, value);
    }
    public bool Selected
    {
        get => GetValue(SelectedProperty);
        set => SetValue(SelectedProperty, value);
    }
    public int Index
    {
        get => GetValue(IndexProperty);
        set => SetValue(IndexProperty, value);
    }
    public ICommand Command
    {
        get => GetValue(CommandProperty);
        set => SetValue(CommandProperty, value);
    }

    static AccordionItem()
    {
        SelectedProperty.Changed.AddClassHandler<AccordionItem>(Selected_Changed);
    }

    private static void Selected_Changed(AccordionItem item, AvaloniaPropertyChangedEventArgs args)
    {
        item.PseudoClasses.Set(":selected", item.Selected);
    }
}