using System;
using System.Reflection;
using System.Security.Principal;
using System.Web;
using System.Web.Security;

namespace Neo.Afx.Security
{
    /// <summary>
    /// Allows for two-Level authentication with Forms Authentication and Windows Authentication in IIS 7.
    /// <remarks>
    ///     See http://mvolo.com/blogs/serverside/archive/2008/02/11/IIS-7.0-Two_2D00_Level-Authentication-with-Forms-Authentication-and-Windows-Authentication.aspx
    /// </remarks>
    /// </summary>
    public class FormsAuthModule : IHttpModule
    {
        bool _enabled;
        FormsAuthSettings _config;
        FormsAuthenticationModule _module;
        MethodInfo _onEnter;
        MethodInfo _onLeave;

        ///////////////////////////////////////////////////////////////////////////////////////////////
        // IHttpModule methods
        ///////////////////////////////////////////////////////////////////////////////////////////////

        #region Dispose

        /// <summary>
        ///     Disposes of the resources (other than memory) used by the module that implements <see cref = "T:System.Web.IHttpModule" />.
        /// </summary>
        public void Dispose()
        {
            _module.Dispose();
            _module = null;
            GC.SuppressFinalize(this);
        }

        #endregion

        #region Init

        /// <summary>
        ///     Initializes the <see cref = "FormsAuthModule" /> object.
        /// </summary>
        /// <param name = "app">The current <see cref = "HttpApplication" /> instance.</param>
        public void Init(HttpApplication app)
        {
            _module = new FormsAuthenticationModule();
            using(var application = new HttpApplication())
            {
                _module.Init(application);
            }

            var type = _module.GetType();
            _onEnter = type.GetMethod("OnEnter", BindingFlags.NonPublic | BindingFlags.Instance, null, new[]
            {
                typeof(object), typeof(EventArgs)
            }, null);
            _onLeave = type.GetMethod("OnLeave", BindingFlags.NonPublic | BindingFlags.Instance, null, new[]
            {
                typeof(object), typeof(EventArgs)
            }, null);
            if((_onEnter == null) || (_onLeave == null))
            {
                throw new Exception("Unable to get all required FormsAuthenticationModule entrypoints using reflection.");
            }
            app.AuthenticateRequest += OnAuthenticateRequest;
            app.PostAuthenticateRequest += OnPostAuthenticateRequest;
            app.EndRequest += OnEndRequest;
        }

        #endregion

        ///////////////////////////////////////////////////////////////////////////////////////////////
        // Custom event handlers methods
        ///////////////////////////////////////////////////////////////////////////////////////////////

        void OnAuthenticateRequest(object source, EventArgs e)
        {
            var application = (HttpApplication)source;
            var context = application.Context;
            _enabled = false;
            _config = FormsAuthSettings.GetSection(context);
            if(_config != null && _config.IsEnabled)
            {
                _enabled = true;
                _onEnter.Invoke(_module, new[]
                {
                    source, e
                });
            }
        }

        void OnEndRequest(object source, EventArgs e)
        {
            if(_enabled)
            {
                _onLeave.Invoke(_module, new[]
                {
                    source, e
                });
            }
        }

        void OnPostAuthenticateRequest(object source, EventArgs e)
        {
            var application = (HttpApplication)source;
            var context = application.Context;
            if(!_enabled && context.User == null)
            {
                var logonUserIdentity = context.Request.LogonUserIdentity;
                if(logonUserIdentity != null)
                {
                    context.User = logonUserIdentity.IsAnonymous
                        ? new WindowsPrincipal(WindowsIdentity.GetAnonymous())
                        : new WindowsPrincipal(logonUserIdentity);
                }
            }
        }

    }
}