// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
//
// Description: Rtf format stack.
//
 
using System.Collections;
using MS.Internal; // Invariant
 
namespace System.Windows.Documents
{
    /// <summary>
    /// RtfFormatStack
    /// </summary>
    internal class RtfFormatStack : ArrayList
    {
        //------------------------------------------------------
        //
        //  Constructors
        //
        //------------------------------------------------------
 
        #region Constructors
 
        internal RtfFormatStack() : base(20)
        {
        }
 
        #endregion Constructors
 
        //------------------------------------------------------
        //
        //  Internal Methods
        //
        //------------------------------------------------------
 
        #region Internal Methods
 
        internal void Push()
        {
            FormatState previousFormatState = Top();
            FormatState formatState;
 
            formatState = previousFormatState != null ? new FormatState(previousFormatState) : new FormatState();
 
            Add(formatState);
        }
 
        internal void Pop()
        {
            Invariant.Assert(Count != 0);
 
            if (Count > 0)
            {
                RemoveAt(Count - 1);
            }
        }
 
        internal FormatState Top()
        {
            return Count > 0 ? EntryAt(Count - 1) : null;
        }
 
        internal FormatState PrevTop(int fromTop)
        {
            int index = Count - 1 - fromTop;
 
            if (index < 0 || index >= Count)
            {
                return null;
            }
 
            return EntryAt(index);
        }
 
        internal FormatState EntryAt(int index)
        {
            return (FormatState)this[index];
        }
 
        #endregion Internal Methods
    }
}