/*
 * LargeArray.Enumerator.cs
 * 
 * Copyright © 2009
 * Diversified Technical Systems, Inc.
 * All Rights Reserved
 */

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Runtime.ConstrainedExecution;
using System.Runtime.InteropServices;
using System.Text;
using DTS.Common.Utilities;
using DTS.Common.Utilities.DotNetProgrammingConstructs;

namespace DTS.Common.Utilities.IO.MemoryMap
{
    // *** see LargeArray.cs ***
    public partial class LargeArray<T>
    {
        /// <summary>
        /// An enumerator class for <see cref="T:LargeArray"/>.
        /// </summary>
        public class Enumerator : Exceptional, IEnumerator
        {
            /// <summary>
            /// Initialize an instance of the <see cref="T:LargeArray.Enumerator"/> class.
            /// </summary>
            /// 
            /// <param name="enumeratee">
            /// The <see cref="T:LargeArray"/> object to be operated upon by this instance.
            /// </param>
            /// 
            public Enumerator(LargeArray<T> enumeratee)
            {
                try
                {
                    Enumeratee = enumeratee;
                    CurrentIndex = (Enumeratee.LargeCount > 0 ? (ulong?)0 : null);
                }

                catch (System.Exception ex)
                {
                    throw new Exception("encountered problem ", ex);
                }
            }

            /// <summary>
            /// Get the <see cref="T:LargeArray"/> that his enumerator object is
            /// acting upon.
            /// </summary>
            protected LargeArray<T> Enumeratee
            {
                get => _Enumeratee.Value;
                private set => _Enumeratee.Value = value;
            }
            private Property<LargeArray<T>> _Enumeratee
                = new Property<LargeArray<T>>(
                    typeof(Enumerator).FullName + ".Enumeratee",
                    null,
                    false
                );

            /// <summary>
            /// The <see cref="ulong"/> index of the current item.
            /// </summary>
            private ulong? CurrentIndex
            {
                get;
                set;
            }

            #region IEnumerator interface
            // *********************************************************************
            // ******************** BEGIN IEnumerator Interface ********************
            // *********************************************************************

            /// <summary>
            /// Get the current element in the collection.
            /// </summary>
            ///
            /// <exception cref="System.InvalidOperationException">
            /// The enumerator is positioned before the first element of the collection or after the last element OR...
            /// The collection was modified after the enumerator was created.
            /// </exception>
            ///
            public object Current
            {
                get
                {
                    try
                    {
                        if (null == CurrentIndex)
                            throw new InvalidOperationException("the current position is outside of the collection");

                        else if ( /*EnumerateeHasBeenModified*/ true)
                            throw new InvalidOperationException("the collection has been modified since this enumerator was created");

                        //else return Enumeratee[ (ulong) CurrentIndex ]; - inaccessible code - 6/9/2010 - dtm
                    }

                    catch (InvalidOperationException)
                    {
                        throw;
                    }

                    catch (System.Exception ex)
                    {
                        throw new Exception("encountered problem getting current element in the collection", ex);
                    }
                }
            }

            /// <summary>
            /// Advances the enumerator to the next element of the collection.
            /// </summary>
            /// 
            /// <returns>
            /// <see cref="bool"/> true if the enumerator was successfully advanced to the next
            /// element; false if the enumerator has passed the end of the collection.
            /// </returns>
            /// 
            /// <exception cref="System.InvalidOperationException">
            /// The collection was modified after the enumerator was created.
            /// </exception>
            /// 
            public bool MoveNext()
            {
                //try
                //{
                throw new NotSupportedException("MemoryMapArray MoveNext not supported");
                //}
                //catch (InvalidOperationException ex) { throw ex; }
                //catch (System.Exception ex)
                //{
                //    throw new Exception("encountered problem advancing to the next element of the collection", ex);
                //}
            }

            /// <summary>
            /// Sets the enumerator to its initial position, which is before the first element
            /// in the collection.
            /// </summary>
            ///
            /// <exception cref="System.InvalidOperationException">
            /// The collection was modified after the enumerator was created.
            /// </exception>
            ///
            public void Reset()
            {
                //try
                //{
                //    // TODO: implement
                throw new NotSupportedException("MemoryMap.LargeArray Reset not supported");
                //}
                //catch (InvalidOperationException) { throw; }
                //catch (System.Exception ex)
                //{
                //    throw new Exception("encountered problem setting the enumerator to its initial position", ex);
                //}
            }

            // *******************************************************************
            // ******************** END IEnumerator Interface ********************
            // *******************************************************************
            #endregion
        }
    }
}