/Source/Bifrost/Commands/CommandHandlerInvoker.cs

#region License

//

// Copyright (c) 2008-2012, DoLittle Studios and Komplett ASA

//

// Licensed under the Microsoft Permissive License (Ms-PL), Version 1.1 (the "License")

// With one exception :

//   Commercial libraries that is based partly or fully on Bifrost and is sold commercially, 

//   must obtain a commercial license.

//

// You may not use this file except in compliance with the License.

// You may obtain a copy of the license at 

//

//   http://bifrost.codeplex.com/license

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

//

#endregion

using System;

using System.Linq;

using System.Collections.Generic;

using Bifrost.Execution;

using Microsoft.Practices.ServiceLocation;

using System.Reflection;



namespace Bifrost.Commands

{

	/// <summary>

	/// Represents a <see cref="ICommandHandlerInvoker">ICommandHandlerInvoker</see> for handling

	/// command handlers that have methods called Handle() and takes specific <see cref="ICommand">commands</see>

	/// in as parameters

	/// </summary>

	[Singleton]

	public class CommandHandlerInvoker : ICommandHandlerInvoker

	{

        const string HandleMethodName = "Handle";



		readonly ITypeDiscoverer _discoverer;

	    readonly IServiceLocator _serviceLocator;

        readonly Dictionary<Type, MethodInfo> _commandHandlers = new Dictionary<Type, MethodInfo>();

	    bool _initialized;



	    /// <summary>

	    /// Initializes a new instance of <see cref="CommandHandlerInvoker">CommandHandlerInvoker</see>

	    /// </summary>

	    /// <param name="discoverer">A <see cref="ITypeDiscoverer"/> to use for discovering <see cref="ICommandHandler">command handlers</see></param>

	    /// <param name="serviceLocator">A <see cref="IServiceLocator"/> to use for getting instances of objects</param>

	    public CommandHandlerInvoker(ITypeDiscoverer discoverer, IServiceLocator serviceLocator)

		{

			_discoverer = discoverer;

		    _serviceLocator = serviceLocator;

	        _initialized = false;

		}



		private void Initialize()

		{

		    var handlers = _discoverer.FindMultiple<ICommandHandler>();

			Array.ForEach(handlers, Register);

		    _initialized = true;

		}



		/// <summary>

		/// Register a command handler explicitly 

		/// </summary>

		/// <param name="handlerType"></param>

		/// <remarks>

		/// The registration process will look into the handler and find methods that 

		/// are called Handle() and takes a command as parameter

		/// </remarks>

		public void Register(Type handlerType)

		{

            var allMethods = handlerType.GetMethods(BindingFlags.Public | BindingFlags.Instance);



            var query = from m in allMethods

                        where m.Name.Equals(HandleMethodName) &&

                              m.GetParameters().Length == 1 &&

                              typeof(ICommand).IsAssignableFrom(m.GetParameters()[0].ParameterType)

                        select m;



            foreach (var method in query)

                _commandHandlers[method.GetParameters()[0].ParameterType] = method;

		}



#pragma warning disable 1591 // Xml Comments

		public bool TryHandle(ICommand command)

		{

            if( !_initialized)

                Initialize();



            var commandType = command.GetType();

            if (_commandHandlers.ContainsKey(commandType))

            {

                var commandHandlerType = _commandHandlers[commandType].DeclaringType;

                var commandHandler = _serviceLocator.GetInstance(commandHandlerType);

                var method = _commandHandlers[commandType];

                method.Invoke(commandHandler, new[] { command });

                return true;

            }



		    return false;

		}

#pragma warning restore 1591 // Xml Comments

	}

}