ContextStack.cs

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using System.Collections;
 
namespace System.ComponentModel.Design.Serialization;
 
public sealed class ContextStack
{
    private ArrayList _contextStack;
 
    public object? Current
    {
        get
        {
            if (_contextStack != null && _contextStack.Count > 0)
            {
                return _contextStack[_contextStack.Count - 1];
            }
            return null;
        }
    }
 
    public object? this[int level]
    {
        get
        {
            if (level < 0)
            {
                throw new ArgumentOutOfRangeException("level");
            }
            if (_contextStack != null && level < _contextStack.Count)
            {
                return _contextStack[_contextStack.Count - 1 - level];
            }
            return null;
        }
    }
 
    public object? this[Type type]
    {
        get
        {
            if (type == null)
            {
                throw new ArgumentNullException("type");
            }
            if (_contextStack != null)
            {
                int num = _contextStack.Count;
                while (num > 0)
                {
                    object obj = _contextStack[--num];
                    if (type.IsInstanceOfType(obj))
                    {
                        return obj;
                    }
                }
            }
            return null;
        }
    }
 
    public void Append(object context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("context");
        }
        if (_contextStack == null)
        {
            _contextStack = new ArrayList();
        }
        _contextStack.Insert(0, context);
    }
 
    public object? Pop()
    {
        object result = null;
        if (_contextStack != null && _contextStack.Count > 0)
        {
            int index = _contextStack.Count - 1;
            result = _contextStack[index];
            _contextStack.RemoveAt(index);
        }
        return result;
    }
 
    public void Push(object context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("context");
        }
        if (_contextStack == null)
        {
            _contextStack = new ArrayList();
        }
        _contextStack.Add(context);
    }
}