Calcium: A modular application toolset leveraging PRISM – Part 1

#region File and License Information
/*
<File>
	<Copyright>Copyright © 2007, Daniel Vaughan. All rights reserved.</Copyright>
	<License>
		Redistribution and use in source and binary forms, with or without
		modification, are permitted provided that the following conditions are met:
			* Redistributions of source code must retain the above copyright
			  notice, this list of conditions and the following disclaimer.
			* Redistributions in binary form must reproduce the above copyright
			  notice, this list of conditions and the following disclaimer in the
			  documentation and/or other materials provided with the distribution.
			* Neither the name of the <organization> nor the
			  names of its contributors may be used to endorse or promote products
			  derived from this software without specific prior written permission.

		THIS SOFTWARE IS PROVIDED BY <copyright holder> ''AS IS'' AND ANY
		EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
		WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
		DISCLAIMED. IN NO EVENT SHALL <copyright holder> BE LIABLE FOR ANY
		DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
		(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
		LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
		ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
		(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
		SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	</License>
	<Owner Name="Daniel Vaughan" Email="dbvaughan@gmail.com"/>
	<CreationDate>2009-05-17 19:13:39Z</CreationDate>
</File>
*/
#endregion

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Windows;

using DanielVaughan.Calcium.Client.Gui;

using Microsoft.Practices.Composite.Events;
using Microsoft.Practices.Composite.Presentation.Events;

namespace DanielVaughan.Calcium.Client.Services.ViewService
{
	/// <summary>
	/// Default implementation of <see cref="IViewService"/>.
	/// Uses the <see cref="SelectedWorkspaceViewChangedEvent"/> for active view tracking.
	/// </summary>
	public class ViewService : IViewService
	{
		class UIElementVisibility
		{
			public IUIElement UIElement { get; set; }
			public Visibility HiddenVisibility { get; set; }

			public override int GetHashCode() /* We use the UIElement as the collection key. */
			{
				return UIElement != null ? UIElement.GetHashCode() : base.GetHashCode();
			}
		}

		readonly Dictionary<Type, List<UIElementVisibility>> uiElementDictionary = new Dictionary<Type, List<UIElementVisibility>>();
		readonly ReaderWriterLockSlim uiElementDictionaryLock = new ReaderWriterLockSlim();

		bool initialized;

		[MethodImpl(MethodImplOptions.Synchronized)]
		void EnsureInitialized()
		{
			if (initialized)
			{
				return;
			}

			var eventAggregator = UnitySingleton.Container.Resolve<IEventAggregator>();
			var viewChangedEvent = eventAggregator.GetEvent<SelectedWorkspaceViewChangedEvent>();
			viewChangedEvent.Subscribe(AssignVisibilitiesToUIElements, ThreadOption.UIThread, false);
			initialized = true;
		}

		/// <summary>
		/// Updates the ui elements by hiding those that do not have an associated <code>Type</code>
		/// that is implemented by the specified view.
		/// </summary>
		/// <param name="view">The view.</param>
		void AssignVisibilitiesToUIElements(IView view)
		{
			IEnumerable<UIElementVisibility> elements;
			uiElementDictionaryLock.EnterReadLock();
			try
			{
				elements = (from list in uiElementDictionary.Values
							from element in list
							select element).ToList();
			}
			finally
			{
				uiElementDictionaryLock.ExitReadLock();
			}

			if (view == null)
			{
				foreach (var element in elements)
				{
					element.UIElement.Visibility = element.HiddenVisibility;
				}
				return;
			}

			IEnumerable<UIElementVisibility> elementsToMakeVisible;

			uiElementDictionaryLock.EnterReadLock();
			try
			{
				elementsToMakeVisible = (from pair in uiElementDictionary
										 where pair.Key.IsAssignableFrom(view.GetType())
										 from element in pair.Value
										 select element).ToList();
			}
			finally
			{
				uiElementDictionaryLock.ExitReadLock();
			}

			/* elements to hide = all elements / elementsToMakeVisible. */
			var elementsToHide = elements.Except(elementsToMakeVisible);

			foreach (var element in elementsToHide)
			{
				element.UIElement.Visibility = element.HiddenVisibility;
			}

			foreach (var element in elementsToMakeVisible)
			{
				element.UIElement.Visibility = Visibility.Visible;
			}
		}

		public void AssociateVisibility(Type workspaceContentType, IUIElement uiElement,
			Visibility hiddenVisibility)
		{
			ArgumentValidator.AssertNotNull(workspaceContentType, "workspaceContentType");
			ArgumentValidator.AssertNotNull(uiElement, "uiElement");

			EnsureInitialized(); /* This call is synchronized to ensure that it is only performed once. */

			var uiElementVisibility = new UIElementVisibility { UIElement = uiElement, HiddenVisibility = hiddenVisibility };

			uiElementDictionaryLock.EnterWriteLock(); /* We avoid the complexity of upgrading a read lock here. */
			try
			{
				List<UIElementVisibility> uiElements;
				if (!uiElementDictionary.TryGetValue(workspaceContentType, out uiElements))
				{
					uiElements = new List<UIElementVisibility>();
					uiElementDictionary.Add(workspaceContentType, uiElements);
				}
				if (uiElements.Contains(uiElementVisibility))
				{
					return;
				}
				uiElements.Add(uiElementVisibility);
			}
			finally
			{
				uiElementDictionaryLock.ExitWriteLock();
			}
		}

	}
}