//------------------------------------------------------------------------------
//  Microsoft Avalon
//  Copyright (c) Microsoft Corporation, 2001
//                                             
//  File:       GenericEnumerator.cs
//------------------------------------------------------------------------------
 
using System;
using System.Collections;
using System.Diagnostics;
using System.Windows;
using MS.Utility;
 
#if PRESENTATION_CORE
using SR=MS.Internal.PresentationCore.SR;
using SRID=MS.Internal.PresentationCore.SRID;
#else
using SR=System.Windows.SR;
using SRID=System.Windows.SRID;
#endif
 
namespace MS.Internal
{
    /// <summary>
    /// GenericEnumerator
    /// </summary>
    internal class GenericEnumerator : IEnumerator
    {
        #region Delegates
 
        internal delegate int GetGenerationIDDelegate();
 
        #endregion
 
        #region Constructors
 
        private GenericEnumerator()
        {
        }
 
        internal GenericEnumerator(IList array, GetGenerationIDDelegate getGenerationID)
        {
            _array     = array;
            _count     = _array.Count;
            _position  = -1;
            _getGenerationID = getGenerationID;
            _originalGenerationID = _getGenerationID();
        }
 
        #endregion
 
        #region Private
 
        private void VerifyCurrent()
        {
            if (   (-1 == _position)
                || (_position >= _count))
            {
                throw new InvalidOperationException(SR.Get(SRID.Enumerator_VerifyContext));
            }
        }
 
        #endregion
 
        #region IEnumerator
 
        /// <summary>
        /// Returns the object at the current location of the key times list.
        /// Use the strongly typed version instead.
        /// </summary>
        object
            IEnumerator.Current
        {
            get
            {
                VerifyCurrent();
 
                return _current;
            }
        }
 
        /// <summary>
        /// Move to the next value in the key times list
        /// </summary>
        /// <returns>true if succeeded, false if at the end of the list</returns>
        public bool MoveNext()
        {
            if (_getGenerationID() != _originalGenerationID)
            {
                throw new InvalidOperationException(SR.Get(SRID.Enumerator_CollectionChanged));
            }
 
            _position++;
 
            if (_position >= _count)
            {
                _position = _count;
 
                return false;
            }
            else
            {
                Debug.Assert(_position >= 0);
 
                _current = _array[_position];
 
                return true;
            }
        }
 
        /// <summary>
        /// Move to the position before the first value in the list.
        /// </summary>
        public void Reset()
        {
            if (_getGenerationID() != _originalGenerationID)
            {
                throw new InvalidOperationException(SR.Get(SRID.Enumerator_CollectionChanged));
            }
            else
            {
                _position = -1;
            }
        }
 
        #endregion
        
        #region Data
 
        private IList   _array;
        private object  _current;
        private int     _count;
        private int     _position;
        private int     _originalGenerationID;
 
        private GetGenerationIDDelegate _getGenerationID;
 
        #endregion
    }
}