using System;
using System.Linq;
using System.Web;
using System.Web.Hosting;
using System.Web.Mvc;
using StackExchange.Profiling;
using Umbraco.Core.Configuration;
using Umbraco.Core.LightInject;
using Umbraco.Core.Logging;
using Umbraco.Core.ObjectResolution;
using Umbraco.Core.Logging;

namespace Umbraco.Core
{

    /// <summary>
    /// The abstract class for the Umbraco HttpApplication
    /// </summary>
    /// <remarks>
    /// This is exposed in the core so that we can have the IApplicationEventHandler in the core project so that 
    /// IApplicationEventHandler's can fire/execute outside of the web contenxt (i.e. in console applications)
    /// </remarks>
    public abstract class UmbracoApplicationBase : System.Web.HttpApplication
    {

        /// <summary>
        /// Umbraco application's IoC container
        /// </summary>
        internal ServiceContainer Container { get; private set; }

        private ILogger _logger;

        /// <summary>
        /// Constructor
        /// </summary>
        protected UmbracoApplicationBase()
        {
            //create the container for the application, the boot managers are responsible for registrations
            Container = new ServiceContainer();         
        }

        public event EventHandler ApplicationStarting;
        public event EventHandler ApplicationStarted;

        /// <summary>
        /// Called when the HttpApplication.Init() is fired, allows developers to subscribe to the HttpApplication events
        /// </summary>
        /// <remarks>
        /// Needs to be static otherwise null refs occur - though I don't know why
        /// </remarks>
        public static event EventHandler ApplicationInit;
        public static event EventHandler ApplicationError;
        public static event EventHandler ApplicationEnd;
        

        /// <summary>
        /// Boots up the Umbraco application
        /// </summary>
        internal void StartApplication(object sender, EventArgs e)
        {
            //boot up the application
            GetBootManager()
                .Initialize()
                .Startup(appContext => OnApplicationStarting(sender, e))
                .Complete(appContext => OnApplicationStarted(sender, e));
        }

        /// <summary>
        /// Initializes the Umbraco application
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Application_Start(object sender, EventArgs e)
        {
            StartApplication(sender, e);
        }

        /// <summary>
        /// Override init and raise the event
        /// </summary>
        public override void Init()
        {
            base.Init();
            OnApplicationInit(this, new EventArgs());
        }

        /// <summary>
        /// Developers can override this method to modify objects on startup
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected virtual void OnApplicationStarting(object sender, EventArgs e)
        {
            if (ApplicationStarting != null)
                ApplicationStarting(sender, e);
        }

        /// <summary>
        /// Developers can override this method to do anything they need to do once the application startup routine is completed.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected virtual void OnApplicationStarted(object sender, EventArgs e)
        {
            if (ApplicationStarted != null)
                ApplicationStarted(sender, e);
        }

        /// <summary>
        /// Called to raise the ApplicationInit event
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void OnApplicationInit(object sender, EventArgs e)
        {
            if (ApplicationInit != null)
                ApplicationInit(sender, e);
        }

        /// <summary>
        /// A method that can be overridden to invoke code when the application has an error.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected virtual void OnApplicationError(object sender, EventArgs e)
        {
            var handler = ApplicationError;
            if (handler != null) handler(this, EventArgs.Empty);
        }

        protected void Application_Error(object sender, EventArgs e)
        {
            // Code that runs when an unhandled error occurs

            // Get the exception object.
            var exc = Server.GetLastError();

            // Ignore HTTP errors
            if (exc.GetType() == typeof(HttpException))
            {
                return;
            }
            
            Logger.Error<UmbracoApplicationBase>("An unhandled exception occurred", exc);

            OnApplicationError(sender, e);
        }

        /// <summary>
        /// A method that can be overridden to invoke code when the application shuts down.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected virtual void OnApplicationEnd(object sender, EventArgs e)
        {
            var handler = ApplicationEnd;
            if (handler != null) handler(this, EventArgs.Empty);
        }

        protected void Application_End(object sender, EventArgs e)
        {
            if (SystemUtilities.GetCurrentTrustLevel() == AspNetHostingPermissionLevel.Unrestricted)
            {
                Logger.Info<UmbracoApplicationBase>("Application shutdown. Reason: " + HostingEnvironment.ShutdownReason);
            }
            OnApplicationEnd(sender, e);
        }

        protected abstract IBootManager GetBootManager();

        /// <summary>
        /// Returns the logger instance for the application - this will be used throughout the entire app
        /// </summary>
        public virtual ILogger Logger
        {
            get { return _logger ?? (_logger = Logging.Logger.CreateWithDefaultLog4NetConfiguration()); }
        }

    }
}