Nuclex.Support/Source/Tracking/Internal/WeightedTransactionWrapperCollection.cs

#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2010 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;

using Nuclex.Support.Collections;

namespace Nuclex.Support.Tracking {

  /// <summary>Collection of transactions with a weighting value</summary>
  /// <typeparam name="TransactionType">Type of transactions to manage</typeparam>
  /// <remarks>
  ///   <para>
  ///     This collection is exposed as a read-only collection to the user that
  ///     stores WeightedTransactions. Internally, it merely wraps a collection of
  ///     an internal type used to keep track of the individual transaction's
  ///     progress in the TransactionGroup and OperationQueue classes.
  ///   </para>
  ///   <para>
  ///     It is read-only because the design requires a transaction to only ever finish
  ///     once. If it was possible eg. to add items after a TransactionGroup had signalled
  ///     itself as being finished, it would be moved into an unfinished state again.
  ///     Also, an empty TransactionGroup is, by definition, finished (simply because
  ///     there is no work to do) - unless the contents of the group are passed to the
  ///     TransactionGroup's constructor and never modified at all, the design would be
  ///     violated as soon as an instance of the TransactionGroup or OperationQueue
  ///     classes was created.
  ///   </para>
  /// </remarks>
  internal class WeightedTransactionWrapperCollection<TransactionType> :
    TransformingReadOnlyCollection<
      ObservedWeightedTransaction<TransactionType>, WeightedTransaction<TransactionType>
    >
    where TransactionType : Transaction {

    /// <summary>Initializes a new weighted transaction collection wrapper</summary>
    /// <param name="items">Items to be exposed as weighted transactions</param>
    internal WeightedTransactionWrapperCollection(
      IList<ObservedWeightedTransaction<TransactionType>> items
    )
      : base(items) { }

    /// <summary>Transforms an item into the exposed type</summary>
    /// <param name="item">Item to be transformed</param>
    /// <returns>The transformed item</returns>
    /// <remarks>
    ///   This method is used to transform an item in the wrapped collection into
    ///   the exposed item type whenever the user accesses an item. Expect it to
    ///   be called frequently, because the TransformingReadOnlyCollection does
    ///   not cache otherwise store the transformed items.
    /// </remarks>
    protected override WeightedTransaction<TransactionType> Transform(
      ObservedWeightedTransaction<TransactionType> item
    ) {
      return item.WeightedTransaction;
    }

  }

} // namespace Nuclex.Support.Tracking