using System;
using System.IO;
using System.Collections;
using System.Text;
using System.Xml;

using System.Reflection;

using NHibernate;
using NHibernate.Cache;

using System.Web;

using log4net;
using log4net.Config;

namespace SV01.Library.AUM
{
    /// <summary>
    /// Handles creation and management of sessions and transactions.  It is a singleton because 
    /// building the initial session factory is very expensive. Inspiration for this class came 
    /// from Chapter 8 of Hibernate in Action by Bauer and King.  Although it is a sealed singleton
    /// you can use TypeMock (http://www.typemock.com) for more flexible testing.
    /// </summary>
    internal sealed class NHibernateSessionManager
    {
        #region Thread-safe, lazy Singleton

        /// <summary>
        /// This is a thread-safe, lazy singleton.  See http://www.yoda.arachsys.com/csharp/singleton.html
        /// for more details about its implementation.
        /// </summary>
        public static NHibernateSessionManager Instance {
            get {
                return Nested.nHibernateSessionManager;
            }
        }

        /// <summary>
        /// Initializes the NHibernate session factory upon instantiation.
        /// </summary>
        private NHibernateSessionManager() {
            InitSessionFactory();
        }

        /// <summary>
        /// Assists with ensuring thread-safe, lazy singleton
        /// </summary>
        private class Nested
        {
            static Nested() { }
            internal static readonly NHibernateSessionManager nHibernateSessionManager = new NHibernateSessionManager();
        }

        #endregion

        private void InitSessionFactory() {
			LoggingManager.Instance.Debug("start init NHibernate session factory");

			NHibernate.Cfg.Configuration cfg = new NHibernate.Cfg.Configuration();

			Stream stream = null;
			try
			{
				stream = Assembly.GetExecutingAssembly().GetManifestResourceStream(this.GetType(), "hibernate.cfg.xml");
				if (stream == null) throw new ApplicationException("NHibernate configuration not found!");					
				cfg.Configure(new XmlTextReader(stream));

				sessionFactory = cfg.BuildSessionFactory();
			}
			finally
			{
				if (stream != null) stream.Close();
			}

			LoggingManager.Instance.Debug("end init NHibernate session factory");
        }

        public ISession CreateSession() {
            return CreateSession(null);
        }

        /// <summary>
        /// Gets a session with or without an interceptor.  This method is not called directly; instead,
        /// it gets invoked from other public methods.
        /// </summary>
        private ISession CreateSession(IInterceptor interceptor) {
            ISession session;

            if (interceptor != null) {
				session = sessionFactory.OpenSession(interceptor);
            }
            else {
				session = sessionFactory.OpenSession();
            }

			return session;
        }

        public void CloseSession(ISession session) {
            if (session != null && session.IsOpen) {
                session.Close();
            }
        }

        private ISessionFactory sessionFactory;
    }
}