//---------------------------------------------------------------------
// <copyright file="MetadataCollection.cs" company="Microsoft">
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
//
// @owner       Microsoft
// @backupOwner Microsoft
//---------------------------------------------------------------------

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Data.Common;
using System.Reflection;
using System.Text;
using System.Diagnostics;
using System.Threading;

namespace System.Data.Metadata.Edm
{
    /// <summary>
    /// Class representing an actual implementaton of a collection of metadata objects
    /// </summary>
    /// <typeparam name="T">The type of items in this collection</typeparam>
    internal class MetadataCollection<T> : IList<T> where T : MetadataItem
    {
        // The way the collection supports both case sensitive and insensitive search is that it maintains two lists: one list
        // for keep tracking of the order (the ordered list) and another list sorted case sensitively (the sorted list) by the
        // identity of the item.  When a look up on ordinal is requested, the ordered list is used.  When a look up on the name
        // is requested, the sorted list is used.  The two list must be kept in sync for all update operations.  For case
        // sensitive name lookup, the sorted list is searched.  For case insensitive name lookup, a binary search is used on the
        // sorted list to find the match.

        // Note: Care must be taken when modifying logic in this class to call virtual methods in this class.  Since virtual methods
        // can be override by a derived class, the possible results must be thought through.  If needed, add an internal method and
        // have the public virtual method delegates to it.

        #region Constructors
        /// <summary>
        /// Default constructor for constructing an empty collection
        /// </summary>
        internal MetadataCollection()
            : this(null)
        {
        }

        /// <summary>
        /// The constructor for constructing the collection with the given items
        /// </summary>
        /// <param name="items">The items to populate the collection</param>
        internal MetadataCollection(IEnumerable<T> items)
        {
            _collectionData = new CollectionData();
            if (items != null)
            {
                foreach (T item in items)
                {
                    if (item == null)
                    {
                        throw EntityUtil.CollectionParameterElementIsNull("items");
                    }

                    Debug.Assert(!String.IsNullOrEmpty(item.Identity), "Identity of the item must never be null or empty");
                    AddInternal(item);
                }
            }

        }
        #endregion

        #region Fields

        /// <summary>structure to contain the indexes of items whose identity match by OrdinalIgnoreCase</summary>
        private struct OrderedIndex {
            /// <summary>the index of the item whose identity was used to create the initial dictionary entry</summary>
            internal readonly int ExactIndex;

            /// <summary>the continuation of indexes whose item identities match by OrdinalIgnoreCase</summary>
            internal readonly int[] InexactIndexes;

            internal OrderedIndex(int exactIndex, int[] inexactIndexes)
            {
                ExactIndex = exactIndex;
                InexactIndexes = inexactIndexes;
            }
        }

        private CollectionData _collectionData;
        private bool _readOnly;
        
#endregion

        #region Properties
        /// <summary>
        /// Gets whether the collection is a readonly collection
        /// </summary>
        public bool IsReadOnly
        {
            get
            {
                return _readOnly;
            }
        }

        /// <summary>
        /// Returns the collection as a readonly collection
        /// </summary>
        public virtual System.Collections.ObjectModel.ReadOnlyCollection<T> AsReadOnly
        {
            get
            {
                return _collectionData.OrderedList.AsReadOnly();
            }
        }


        /// <summary>
        /// Returns the collection as a read-only metadata collection.
        /// </summary>
        public virtual ReadOnlyMetadataCollection<T> AsReadOnlyMetadataCollection()
        {
            return new ReadOnlyMetadataCollection<T>(this);
        }

        /// <summary>
        /// Gets the count on the number of items in the collection
        /// </summary>
        public virtual int Count
        {
            get
            {
                return _collectionData.OrderedList.Count;
            }
        }

        /// <summary>
        /// Gets an item from the collection with the given index
        /// </summary>
        /// <param name="index">The index to search for</param>
        /// <returns>An item from the collection</returns>
        /// <exception cref="System.ArgumentOutOfRangeException">Thrown if the index is out of the range for the Collection</exception>
        /// <exception cref="System.InvalidOperationException">Always thrown on setter</exception>
        public virtual T this[int index]
        {
            get
            {
                return _collectionData.OrderedList[index];
            }
            set
            {
                throw EntityUtil.OperationOnReadOnlyCollection();
            }
        }

        /// <summary>
        /// Gets an item from the collection with the given identity
        /// </summary>
        /// <param name="identity">The identity of the item to search for</param>
        /// <returns>An item from the collection</returns>
        /// <exception cref="System.ArgumentNullException">Thrown if identity argument passed in is null</exception>
        /// <exception cref="System.ArgumentException">Thrown if the Collection does not have an item with the given identity</exception>
        /// <exception cref="System.InvalidOperationException">Always thrown on setter</exception>
        public virtual T this[string identity]
        {
            get
            {
                return GetValue(identity, false);
            }
            set
            {
                throw EntityUtil.OperationOnReadOnlyCollection();
            }
        }
        #endregion

        #region Methods
        /// <summary>
        /// Gets an item from the collection with the given identity
        /// </summary>
        /// <param name="identity">The identity of the item to search for</param>
        /// <param name="ignoreCase">Whether case is ignore in the search</param>
        /// <returns>An item from the collection</returns>
        /// <exception cref="System.ArgumentNullException">Thrown if identity argument passed in is null</exception>
        /// <exception cref="System.ArgumentException">Thrown if the Collection does not have an item with the given identity</exception>
        public virtual T GetValue(string identity, bool ignoreCase)
        {
            T item = InternalTryGetValue(identity, ignoreCase);
            if (null == item)
            {
                throw EntityUtil.ItemInvalidIdentity(identity, "identity");
            }
            return item;
        }

        /// <summary>
        /// Adds an item to the collection
        /// </summary>
        /// <param name="item">The item to add to the list</param>
        /// <exception cref="System.ArgumentNullException">Thrown if item argument is null</exception>
        /// <exception cref="System.InvalidOperationException">Thrown if the item passed in or the collection itself instance is in ReadOnly state</exception>
        /// <exception cref="System.ArgumentException">Thrown if the MetadataCollection already contains an item with the same identity</exception>
        /// <exception cref="System.ArgumentException">Thrown if the item passed into Setter has null or String.Empty identity</exception>
        public virtual void Add(T item)
        {
            AddInternal(item);
        }

        /// <summary>Adds an item to the identityDictionary</summary>
        /// <param name="collectionData">The collection data to add to</param>
        /// <param name="identity">The identity to add</param>
        /// <param name="index">The identity's index in collection</param>
        /// <param name="updateIfFound">Whether the item should be updated if a matching item is found.</param>
        /// <returns>
        /// Index of the added entity, possibly different from the index 
        /// parameter if updateIfFound is true.
        /// </returns>
        private static int AddToDictionary(CollectionData collectionData, string identity, int index, bool updateIfFound)
        {
            Debug.Assert(collectionData != null && collectionData.IdentityDictionary != null, "the identity dictionary is null");
            Debug.Assert(!String.IsNullOrEmpty(identity), "empty identity");
            int[] inexact = null;
            OrderedIndex orderIndex;
            int exactIndex = index;

            // find the item(s) by OrdinalIgnoreCase
            if (collectionData.IdentityDictionary.TryGetValue(identity, out orderIndex))
            {
                // identity was already tracking an item, verify its not a duplicate by exact name
                if (EqualIdentity(collectionData.OrderedList, orderIndex.ExactIndex, identity))
                {
                    // If the item is already here and we are updating, there is no more work to be done.
                    if (updateIfFound)
                    {
                        return orderIndex.ExactIndex;
                    }
                    throw EntityUtil.ItemDuplicateIdentity(identity, "item", null);
                }
                else if (null != orderIndex.InexactIndexes)
                {
                    // search against the ExactIndex and all InexactIndexes
                    // identity was already tracking multiple items, verify its not a duplicate by exact name
                    for(int i = 0; i < orderIndex.InexactIndexes.Length; ++i)
                    {
                        if (EqualIdentity(collectionData.OrderedList, orderIndex.InexactIndexes[i], identity))
                        {
                            // If the item is already here and we are updating, there is no more work to be done.
                            if (updateIfFound)
                            {
                                return orderIndex.InexactIndexes[i];
                            }
                            throw EntityUtil.ItemDuplicateIdentity(identity, "item", null);
                        }
                    }
                    // add another item for existing identity that already was tracking multiple items
                    inexact = new int[orderIndex.InexactIndexes.Length + 1];
                    orderIndex.InexactIndexes.CopyTo(inexact, 0);
                    inexact[inexact.Length-1] = index;
                }
                else
                {
                    // turn the previously unique identity by ignore case into a multiple item for identity by ignore case
                    inexact = new int[1] { index };
                }
                // the index of the item whose identity was used to create the initial dictionary entry
                exactIndex = orderIndex.ExactIndex;
            }
            // else this is a new identity

            collectionData.IdentityDictionary[identity] = new OrderedIndex(exactIndex, inexact);
            return index;
        }

        /// <summary>
        /// Adds an item to the collection
        /// </summary>
        /// <remarks>This method only exists to allow ctor to avoid virtual method call</remarks>
        /// <param name="item">The item to add to the list</param>
        /// <exception cref="System.ArgumentNullException">Thrown if item argument is null</exception>
        /// <exception cref="System.InvalidOperationException">Thrown if the item passed in or the collection itself instance is in ReadOnly state</exception>
        /// <exception cref="System.ArgumentException">Thrown if the MetadataCollection already contains an item with the same identity</exception>
        /// <exception cref="System.ArgumentException">Thrown if the item passed into Setter has null or String.Empty identity</exception>
        private void AddInternal(T item)
        {
            Util.AssertItemHasIdentity(item, "item");
            ThrowIfReadOnly();

            AddInternalHelper(item, _collectionData, false);
        }


        // This magic number was determined by the performance test cases in SQLBU 489927.
        // It compared Dictionary (hashtable), SortedList (binary search) and linear searching.
        // Its the approximate (x86) point at which doing a OrdinalCaseInsenstive linear search on _orderedItems.
        // becomes slower than doing a OrdinalCaseInsenstive Dictionary lookup in identityDictionary.
        // On x64, the crossover point is lower - but we desire to keep a smaller overal memory footprint.
        // We expect the ItemCollections to be large, but individual Member/Facet collections to be small.
        private const int UseSortedListCrossover = 25;

        /// <summary>
        /// Adds an item to the collection represented by a list and a dictionary
        /// </summary>
        /// <param name="item">The item to add to the list</param>
        /// <param name="collectionData">The collection data where the item will be added</param>
        /// <param name="updateIfFound">Whether the item should be updated if a matching item is found.</param>
        /// <exception cref="System.ArgumentNullException">Thrown if item argument is null</exception>
        /// <exception cref="System.InvalidOperationException">Thrown if the item passed in or the collection itself instance is in ReadOnly state</exception>
        /// <exception cref="System.ArgumentException">Thrown if the MetadataCollection already contains an item with the same identity</exception>
        /// <exception cref="System.ArgumentException">Thrown if the item passed into Setter has null or String.Empty identity</exception>
        /// <remarks>
        /// If updateIfFound is true, then an update is done in-place instead of
        /// having an exception thrown. The in-place aspect is required to avoid
        /// disrupting the indices generated for indexed items, and to enable
        /// foreach loops to be able to modify the enumerated facets as if it
        /// were a property update rather than an instance replacement.
        /// </remarks>
        private static void AddInternalHelper(T item, CollectionData collectionData, bool updateIfFound)
        {
            Util.AssertItemHasIdentity(item, "item");
            
            int index;
            int listCount = collectionData.OrderedList.Count;
            if (null != collectionData.IdentityDictionary)
            {
                index = AddToDictionary(collectionData, item.Identity, listCount, updateIfFound);
            }
            else
            {
                // We only have to take care of the ordered list.
                index = IndexOf(collectionData, item.Identity, false);
                if (0 <= index)
                {
                    // The item is found in the linear ordered list. Unless
                    // we're updating, it's an error.
                    if (!updateIfFound)
                    {
                        throw EntityUtil.ItemDuplicateIdentity(item.Identity, "item", null);
                    }
                }
                else
                {
                    // This is a new item to be inserted. Grow if we must before adding to ordered list.
                    if (UseSortedListCrossover <= listCount)
                    {
                        collectionData.IdentityDictionary = new Dictionary<string, OrderedIndex>(collectionData.OrderedList.Count + 1, StringComparer.OrdinalIgnoreCase);
                        for (int i = 0; i < collectionData.OrderedList.Count; ++i)
                        {
                            AddToDictionary(collectionData, collectionData.OrderedList[i].Identity, i, false);
                        }
                        AddToDictionary(collectionData, item.Identity, listCount, false);
                    }
                }
            }

            // Index will be listCount when AddToDictionary doesn't find
            // an existing match, and -1 if IndexOf doesn't find in ordered list.
            if (0 <= index && index < listCount)
            {
                collectionData.OrderedList[index] = item;
            }
            else
            {
                System.Diagnostics.Debug.Assert(index == -1 || index == listCount);
                collectionData.OrderedList.Add(item);
            }
        }

        /// <summary>
        /// Adds a collection of items to the collection 
        /// </summary>
        /// <param name="items">The items to add to the list</param>
        /// <exception cref="System.ArgumentNullException">Thrown if item argument is null</exception>
        /// <exception cref="System.InvalidOperationException">Thrown if the item passed in or the collection itself instance is in ReadOnly state</exception>
        /// <exception cref="System.ArgumentException">Thrown if the item that is being added already belongs to another ItemCollection</exception>
        /// <exception cref="System.ArgumentException">Thrown if the ItemCollection already contains an item with the same identity</exception>
        /// <returns>Whether the add was successful</returns>
        internal bool AtomicAddRange(List<T> items)
        {
            CollectionData originalData = _collectionData;
            CollectionData newData = new CollectionData(originalData, items.Count);

            // Add the new items, this will also perform duplication check
            foreach (T item in items)
            {
                AddInternalHelper(item, newData, false);
            }

            CollectionData swappedOutData = Interlocked.CompareExchange<CollectionData>(ref _collectionData, newData, originalData);

            // Check if the exchange was done, if not, then someone must have changed the data in the meantime, so
            // return false
            if (swappedOutData != originalData)
            {
                return false;
            }

            return true;
        }

        /// <summary>Does Item at index have the same identity</summary>
        private static bool EqualIdentity(List<T> orderedList, int index, string identity)
        {
            return ((string)orderedList[index].Identity == (string)identity);
        }
        
        /// <summary>
        /// Not supported, the collection is treated as read-only.
        /// </summary>
        /// <param name="index">The index where to insert the given item</param>
        /// <param name="item">The item to be inserted</param>
        /// <exception cref="System.InvalidOperationException">Thrown if the item passed in or the collection itself instance is in ReadOnly state</exception>
        void IList<T>.Insert(int index, T item)
        {
            throw EntityUtil.OperationOnReadOnlyCollection();
        }

        /// <summary>
        /// Not supported, the collection is treated as read-only.
        /// </summary>
        /// <param name="item">The item to be removed</param>
        /// <returns>True if the item is actually removed, false if the item is not in the list</returns>
        /// <exception cref="System.InvalidOperationException">Always thrown</exception>
        bool ICollection<T>.Remove(T item)
        {
            throw EntityUtil.OperationOnReadOnlyCollection();
        }

        /// <summary>
        /// Not supported, the collection is treated as read-only.
        /// </summary>
        /// <param name="index">The index at which the item is removed</param>
        /// <exception cref="System.InvalidOperationException">Always thrown</exception>
        void IList<T>.RemoveAt(int index)
        {
            throw EntityUtil.OperationOnReadOnlyCollection();
        }

        /// <summary>
        /// Not supported, the collection is treated as read-only.
        /// </summary>
        /// <exception cref="System.InvalidOperationException">Always thrown</exception>
        void ICollection<T>.Clear()
        {
            throw EntityUtil.OperationOnReadOnlyCollection();
        }

        /// <summary>
        /// Determines if this collection contains the given item
        /// </summary>
        /// <param name="item">The item to check for</param>
        /// <returns>True if the collection contains the item</returns>
        /// <exception cref="System.ArgumentNullException">Thrown if item argument passed in is null</exception>
        /// <exception cref="System.ArgumentException">Thrown if the item passed in has null or String.Empty identity</exception>
        public bool Contains(T item)
        {
            Util.AssertItemHasIdentity(item, "item");
            return (-1 != IndexOf(item));
        }

        /// <summary>
        /// Determines if this collection contains an item of the given identity
        /// </summary>
        /// <param name="identity">The identity of the item to check for</param>
        /// <returns>True if the collection contains the item with the given identity</returns>
        /// <exception cref="System.ArgumentNullException">Thrown if identity argument passed in is null</exception>
        /// <exception cref="System.ArgumentException">Thrown if identity argument passed in is empty string</exception>
        public virtual bool ContainsIdentity(string identity)
        {
            EntityUtil.CheckStringArgument(identity, "identity");
            return (0 <= IndexOf(_collectionData, identity, false));
        }

        /// <summary>Find the index of an item identitified by identity</summary>
        /// <param name="collectionData">The collection data to search in</param>
        /// <param name="identity">The identity whose index is to be returned</param>
        /// <param name="ignoreCase">Should OrdinalIgnoreCase be used?</param>
        /// <returns>The index of the found item, -1 if not found</returns>
        /// <exception cref="System.ArgumentException">Thrown if ignoreCase and an exact match does not exist, but has multiple inexact matches</exception>
        private static int IndexOf(CollectionData collectionData, string identity, bool ignoreCase)
        {
            Debug.Assert(null != identity, "null identity");

            int index = -1;
            if (null != collectionData.IdentityDictionary)
            {   // OrdinalIgnoreCase dictionary lookup
                OrderedIndex orderIndex;
                if (collectionData.IdentityDictionary.TryGetValue(identity, out orderIndex))
                {
                    if (ignoreCase)
                    {
                        index = orderIndex.ExactIndex;
                    }
                    //return this, only in case when ignore case is false
                    else if (EqualIdentity(collectionData.OrderedList, orderIndex.ExactIndex, identity))
                    {   // fast return if exact match
                        return orderIndex.ExactIndex;
                    }

                    // search against the ExactIndex and all InexactIndexes
                    if (null != orderIndex.InexactIndexes)
                    {
                        if (ignoreCase)
                        {   // the ignoreCase will throw,
                            throw EntityUtil.MoreThanOneItemMatchesIdentity(identity);
                        }
                        // search for the exact match or throw if ignoreCase
                        for (int i = 0; i < orderIndex.InexactIndexes.Length; ++i)
                        {
                            if (EqualIdentity(collectionData.OrderedList, orderIndex.InexactIndexes[i], identity))
                            {
                                return orderIndex.InexactIndexes[i];
                            }
                        }
                    }
                    Debug.Assert(ignoreCase == (0 <= index), "indexof verification");
                }
            }
            else if (ignoreCase)
            {   // OrdinalIgnoreCase linear search
                for(int i = 0; i < collectionData.OrderedList.Count; ++i)
                {
                    if (String.Equals(collectionData.OrderedList[i].Identity, identity, StringComparison.OrdinalIgnoreCase))
                    {
                        if (0 <= index)
                        {
                            throw EntityUtil.MoreThanOneItemMatchesIdentity(identity);
                        }
                        index = i;
                    }
                }
            }
            else
            {   // Ordinal linear search
                for (int i = 0; i < collectionData.OrderedList.Count; ++i)
                {
                    if (EqualIdentity(collectionData.OrderedList, i, identity))
                    {
                        return i;
                    }
                }
            }
            return index;
        }

        /// <summary>
        /// Find the index of an item
        /// </summary>
        /// <param name="item">The item whose index is to be looked for</param>
        /// <returns>The index of the found item, -1 if not found</returns>
        /// <exception cref="System.ArgumentNullException">Thrown if item argument passed in is null</exception>
        /// <exception cref="System.ArgumentException">Thrown if the item passed in has null or String.Empty identity</exception>
        public virtual int IndexOf(T item)
        {
            Util.AssertItemHasIdentity(item, "item");
            int index = IndexOf(_collectionData, item.Identity, false);

            if (index != -1 && _collectionData.OrderedList[index] == item)
            {
                return index;
            }

            return -1;
        }

        /// <summary>
        /// Copies the items in this collection to an array
        /// </summary>
        /// <param name="array">The array to copy to</param>
        /// <param name="arrayIndex">The index in the array at which to start the copy</param>
        /// <exception cref="System.ArgumentNullException">Thrown if array argument is null</exception>
        /// <exception cref="System.ArgumentOutOfRangeException">Thrown if the arrayIndex is less than zero</exception>
        /// <exception cref="System.ArgumentException">Thrown if the array argument passed in with respect to the arrayIndex passed in not big enough to hold the MetadataCollection being copied</exception>
        public virtual void CopyTo(T[] array, int arrayIndex)
        {
            EntityUtil.GenericCheckArgumentNull(array, "array");

            if (arrayIndex < 0)
            {
                throw EntityUtil.ArgumentOutOfRange("arrayIndex");
            }

            if (_collectionData.OrderedList.Count > array.Length - arrayIndex)
            {
                throw EntityUtil.ArrayTooSmall("arrayIndex");
            }

            _collectionData.OrderedList.CopyTo(array, arrayIndex);
        }

        /// <summary>
        /// Gets the enumerator over this collection
        /// </summary>
        /// <returns></returns>
        public ReadOnlyMetadataCollection<T>.Enumerator GetEnumerator()
        {
            return new ReadOnlyMetadataCollection<T>.Enumerator(this);
        }

        /// <summary>
        /// Gets the enumerator over this collection
        /// </summary>
        /// <returns></returns>
        IEnumerator<T> IEnumerable<T>.GetEnumerator()
        {
            return this.GetEnumerator();
        }

        /// <summary>
        /// Gets the enumerator over this collection
        /// </summary>
        /// <returns></returns>
        IEnumerator IEnumerable.GetEnumerator()
        {
            return this.GetEnumerator();
        }

        /// <summary>
        /// Set this collection as readonly so no more changes can be made on it
        /// </summary>
        public MetadataCollection<T> SetReadOnly()
        {
            for (int i = 0; i < _collectionData.OrderedList.Count; i++)
            {
                _collectionData.OrderedList[i].SetReadOnly();
            }
            _collectionData.OrderedList.TrimExcess();
            _readOnly = true;
            return this;
        }

        /// <summary>
        /// Gets an item from the collection with the given identity
        /// </summary>
        /// <param name="identity">The identity of the item to search for</param>
        /// <param name="ignoreCase">Whether case is ignore in the search</param>
        /// <param name="item">An item from the collection, null if the item is not found</param>
        /// <returns>True an item is retrieved</returns>
        /// <exception cref="System.ArgumentNullException">Thrown if the identity argument is null </exception>
        public virtual bool TryGetValue(string identity, bool ignoreCase, out T item)
        {
            item = InternalTryGetValue(identity, ignoreCase);
            return (null != item);
        }

        /// <summary>
        /// Gets an item from the collection with the given identity
        /// </summary>
        /// <param name="identity">The identity of the item to search for</param>
        /// <param name="ignoreCase">Whether case is ignore in the search</param>
        /// <returns>item else null</returns>
        private T InternalTryGetValue(string identity, bool ignoreCase)
        {
            int index = IndexOf(_collectionData, EntityUtil.GenericCheckArgumentNull(identity, "identity"), ignoreCase);
            Debug.Assert((index < 0) ||
                        (ignoreCase && String.Equals(_collectionData.OrderedList[index].Identity, identity, StringComparison.OrdinalIgnoreCase)) ||
                        EqualIdentity(_collectionData.OrderedList, index, identity), "different exact identity");
            return (0 <= index) ? _collectionData.OrderedList[index] : null;
        }

        /// <summary>
        /// Throws an appropriate exception if the given item is a readonly, used when an attempt is made to change
        /// the collection
        /// </summary>
        internal void ThrowIfReadOnly()
        {
            if (IsReadOnly)
            {
                throw EntityUtil.OperationOnReadOnlyCollection();
            }
        }

        #endregion

        #region InnerClasses

        /// <summary>
        /// The data structures for this collection, which contains a list and a dictionary
        /// </summary>
        private class CollectionData
        {
            /// <summary>
            /// The IdentityDictionary is a case-insensitive dictionary
            /// used after a certain # of elements have been added to the OrderedList.
            /// It aids in fast lookup by T.Identity by mapping a string value to
            /// an OrderedIndex structure with other case-insensitive matches for the
            /// entry.  See additional comments in AddInternal.
            /// </summary>
            internal Dictionary<string, OrderedIndex> IdentityDictionary;
            internal List<T> OrderedList;

            internal CollectionData()
            {
                OrderedList = new List<T>();
            }

            internal CollectionData(CollectionData original, int additionalCapacity)
            {
                this.OrderedList = new List<T>(original.OrderedList.Count + additionalCapacity);
                foreach (T item in original.OrderedList)
                {   // using AddRange results in a temporary memory allocation
                    this.OrderedList.Add(item);
                }

                if (UseSortedListCrossover <= this.OrderedList.Capacity)
                {
                    this.IdentityDictionary = new Dictionary<string, OrderedIndex>(this.OrderedList.Capacity, StringComparer.OrdinalIgnoreCase);

                    if (null != original.IdentityDictionary)
                    {
                        foreach (KeyValuePair<string, OrderedIndex> pair in original.IdentityDictionary)
                        {
                            this.IdentityDictionary.Add(pair.Key, pair.Value);
                        }
                    }
                    else
                    {
                        for (int i = 0; i < this.OrderedList.Count; ++i)
                        {
                            AddToDictionary(this, this.OrderedList[i].Identity, i, false);
                        }
                    }
                }
            }
        }

        #endregion 
    }
}