// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
namespace System.Windows.Forms;
 
public sealed partial class ImageList
{
    /// <summary>
    ///  This class is for classes that want to support both an ImageIndex
    ///  and ImageKey. We want to toggle between using keys or indexes.
    ///  Default is to use the integer index.
    /// </summary>
    internal class Indexer
    {
        // Used by TreeViewImageIndexConverter to show "(none)"
        internal const int NoneIndex = -2;
 
        // Used by generally across the board to indicate unset image
        internal const string DefaultKey = "";
        internal const int DefaultIndex = -1;
 
        private string _key = DefaultKey;
        private int _index = DefaultIndex;
        private bool _useIntegerIndex = true;
 
        public virtual ImageList? ImageList { get; set; }
 
        [AllowNull]
        public virtual string Key
        {
            get => _key;
            set
            {
                _index = DefaultIndex;
                _key = value ?? DefaultKey;
                _useIntegerIndex = false;
            }
        }
 
        public virtual int Index
        {
            get => _index;
            set
            {
                _key = DefaultKey;
                _index = value;
                _useIntegerIndex = true;
            }
        }
 
        public virtual int ActualIndex
        {
            get
            {
                if (_useIntegerIndex)
                {
                    return Index;
                }
 
                if (ImageList is not null)
                {
                    return ImageList.Images.IndexOfKey(Key);
                }
 
                return DefaultIndex;
            }
        }
    }
}