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

#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2008 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 waitables with a weighting value</summary>
  /// <typeparam name="WaitableType">Type of waitables to manage</typeparam>
  /// <remarks>
  ///   <para>
  ///     This collection is exposed as a read-only collection to the user that
  ///     stores WeightedWaitables. Internally, it merely wraps a collection of
  ///     an internal type used to keep track of the individual waitable's
  ///     progress in the WaitableSet and OperationQueue classes.
  ///   </para>
  ///   <para>
  ///     It is read-only because the design requires a waitable to only ever
  ///     finish once. If it was possible eg. to add items after a WaitableSet
  ///     had signalled itself as being finished, it would be moved into an
  ///     unfinished state again. Also, an empty WaitableSet is, by definition,
  ///     finished (simply because there is no work to do) - unless the contents
  ///     of set are passed to the WaitableSet's constructor and never modified
  ///     at all, the design would be violated as soon as ab instance of the
  ///     WaitableSet or OperationQueue classes was created.
  ///   </para>
  /// </remarks>
  internal class WeightedWaitableWrapperCollection<WaitableType> :
    TransformingReadOnlyCollection<
      ObservedWeightedWaitable<WaitableType>, WeightedWaitable<WaitableType>
    >
    where WaitableType : Waitable {

    /// <summary>Initializes a new weighted waitable collection wrapper</summary>
    /// <param name="items">Items to be exposed as weighted waitables</param>
    internal WeightedWaitableWrapperCollection(
      IList<ObservedWeightedWaitable<WaitableType>> 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 WeightedWaitable<WaitableType> Transform(
      ObservedWeightedWaitable<WaitableType> item
    ) {
      return item.WeightedWaitable;
    }

  }

} // namespace Nuclex.Support.Tracking