Composite Application Reloaded

//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation.  All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious.  No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Xml.Linq;
using StockTraderRI.Infrastructure.Interfaces;
using StockTraderRI.Infrastructure.Models;
using StockTraderRI.Modules.Market.Properties;
using System.ComponentModel.Composition;

namespace StockTraderRI.Modules.Market.Services
{
	[Export(typeof(IMarketHistoryService))]
	public class MarketHistoryService : IMarketHistoryService
	{
		private Dictionary<string, MarketHistoryCollection> _marketHistory;

		public MarketHistoryService()
		{
			InitializeMarketHistory();
		}

		private void InitializeMarketHistory()
		{
			XDocument document = XDocument.Parse(Resources.MarketHistory);

			_marketHistory = document.Descendants("MarketHistoryItem")
				.GroupBy(x => x.Attribute("TickerSymbol").Value,
						 x => new MarketHistoryItem
								  {
									  DateTimeMarker = DateTime.Parse(x.Attribute("Date").Value, CultureInfo.InvariantCulture),
									  Value = Decimal.Parse(x.Value, NumberStyles.Float, CultureInfo.InvariantCulture)
								  })
				.ToDictionary(group => group.Key, group => new MarketHistoryCollection(group));
		}

		public MarketHistoryCollection GetPriceHistory(string tickerSymbol)
		{
			MarketHistoryCollection items = _marketHistory[tickerSymbol];
			return items;
		}
	}
}