StabilityMatrix/StabilityMatrix.Avalonia/Controls/CodeCompletion/CompletionListBox.cs

// Copyright (c) 2014 AlphaSierraPapa for the SharpDevelop Team
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

using System;
using Avalonia.Controls;
using Avalonia.Controls.Primitives;
using AvaloniaEdit.Utils;

namespace StabilityMatrix.Avalonia.Controls.CodeCompletion;

/// <summary>
/// The list box used inside the CompletionList.
/// </summary>
public class CompletionListBox : ListBox
{
    internal ScrollViewer? ScrollViewer;

    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
    {
        base.OnApplyTemplate(e);
        ScrollViewer = e.NameScope.Find("PART_ScrollViewer") as ScrollViewer;
    }

    /// <summary>
    /// Gets the number of the first visible item.
    /// </summary>
    public int FirstVisibleItem
    {
        get
        {
            if (ScrollViewer == null || ScrollViewer.Extent.Height == 0)
            {
                return 0;
            }

            return (int)(ItemCount * ScrollViewer.Offset.Y / ScrollViewer.Extent.Height);
        }
        set
        {
            value = value.CoerceValue(0, ItemCount - VisibleItemCount);
            if (ScrollViewer != null)
            {
                ScrollViewer.Offset = ScrollViewer.Offset.WithY(
                    (double)value / ItemCount * ScrollViewer.Extent.Height
                );
            }
        }
    }

    /// <summary>
    /// Gets the number of visible items.
    /// </summary>
    public int VisibleItemCount
    {
        get
        {
            if (ScrollViewer == null || ScrollViewer.Extent.Height == 0)
            {
                return 10;
            }
            return Math.Max(
                3,
                (int)
                    Math.Ceiling(
                        ItemCount * ScrollViewer.Viewport.Height / ScrollViewer.Extent.Height
                    )
            );
        }
    }

    /// <summary>
    /// Removes the selection.
    /// </summary>
    public void ClearSelection()
    {
        SelectedIndex = -1;
    }

    /// <summary>
    /// Selects the item with the specified index and scrolls it into view.
    /// </summary>
    public void SelectIndex(int index)
    {
        if (index >= ItemCount)
            index = ItemCount - 1;
        if (index < 0)
            index = 0;
        SelectedIndex = index;
        if (SelectedItem is { } item)
        {
            ScrollIntoView(item);
        }
    }

    /// <summary>
    /// Centers the view on the item with the specified index.
    /// </summary>
    public void CenterViewOn(int index)
    {
        FirstVisibleItem = index - VisibleItemCount / 2;
    }
}