// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
//
// Description: The root node of a TextBlock splay tree.
//
 
using MS.Internal;
 
namespace System.Windows.Documents
{
    // The root node of a TextBlock splay tree.
    internal class TextTreeRootTextBlock : SplayTreeNode
    {
        //------------------------------------------------------
        //
        //  Constructors
        //
        //------------------------------------------------------
 
        #region Constructors
 
        // Creates a TextTreeRootTextBlock instance.
        internal TextTreeRootTextBlock()
        {
            TextTreeTextBlock block;
 
            // Allocate an initial block with just two characters -- one for
            // each edge of the root node.  The block will grow when/if
            // additional content is added.
            block = new TextTreeTextBlock(2);
            block.InsertAtNode(this, ElementEdge.AfterStart);
        }
 
        #endregion Constructors
 
        //------------------------------------------------------
        //
        //  Public Methods
        //
        //------------------------------------------------------
 
        #region Public Methods
 
#if DEBUG
        // Debug-only ToString override.
        public override string ToString()
        {
            return ("RootTextBlock Id=" + this.DebugId);
        }
#endif // DEBUG
 
        #endregion Public Methods
 
        //------------------------------------------------------
        //
        //  Internal Properties
        //
        //------------------------------------------------------
 
        #region Internal Properties
 
        // The root node never has a parent node.
        internal override SplayTreeNode ParentNode
        {
            get
            {
                return null;
            }
            
            set
            {
                Invariant.Assert(false, "Can't set ParentNode on TextBlock root!");
            }
        }
 
        // Root node of a contained tree, if any.
        internal override SplayTreeNode ContainedNode
        {
            get
            {
                return _containedNode;
            }
            
            set
            {
                _containedNode = (TextTreeTextBlock)value;
            }
        }
 
        // The root node never has sibling nodes, so the LeftSymbolCount is a
        // constant zero.
        internal override int LeftSymbolCount
        {
            get
            {
                return 0;
            }
 
            set
            {
                Invariant.Assert(false, "TextContainer root is never a sibling!");
            }
        }
 
        // Count of unicode chars of all siblings preceding this node.
        // This property is only used by TextTreeNodes.
        internal override int LeftCharCount
        {
            get
            {
                return 0;
            }
 
            set
            {
                Invariant.Assert(value == 0);
            }
        }
 
        // The root node never has siblings, so it never has child nodes.
        internal override SplayTreeNode LeftChildNode
        {
            get
            {
                return null;
            }
            
            set
            {
                Invariant.Assert(false, "TextBlock root never has sibling nodes!");
            }
        }
 
        // The root node never has siblings, so it never has child nodes.
        internal override SplayTreeNode RightChildNode
        {
            get
            {
                return null;
            }
            
            set
            {
                Invariant.Assert(false, "TextBlock root never has sibling nodes!");
            }
        }
 
        // The tree generation.  Not used for TextTreeRootTextBlock.
        internal override uint Generation
        {
            get
            {
                return 0;
            }
            
            set
            {
                Invariant.Assert(false, "TextTreeRootTextBlock does not track Generation!");
            }
        }
 
        // Cached symbol offset.  The root node is always at offset zero.
        internal override int SymbolOffsetCache
        {
            get
            {
                return 0;
            }
            
            set
            {
                Invariant.Assert(false, "TextTreeRootTextBlock does not track SymbolOffsetCache!");
            }
        }
 
        // Not used for TextTreeRootTextBlock.
        internal override int SymbolCount
        {
            get
            {
                return -1;
            }
            
            set
            {
                Invariant.Assert(false, "TextTreeRootTextBlock does not track symbol count!");
            }
        }
 
        // Count of unicode chars covered by this node and any contained nodes.
        // This property is only used by TextTreeNodes.
        internal override int IMECharCount
        {
            get
            {
                return 0;
            }
 
            set
            {
                Invariant.Assert(value == 0);
            }
        }
 
        #endregion Internal Properties
 
        //------------------------------------------------------
        //
        //  Private Fields
        //
        //------------------------------------------------------
 
        #region Private Fields
 
        // Root node of a contained tree, if any.
        private TextTreeTextBlock _containedNode;
 
        #endregion Private Fields
    }
}