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public RegistrationSubItemParameterMap()
        {
            ToTable("RegistrationSubItemParameters");

            Property(_ => _.Name).IsRequired().HasMaxLength(120);
            Property(_ => _.Value).IsRequired().HasMaxLength(255);
            HasRequired(_ => _.RegistrationSubItem).WithMany(_ => _.Parameters).Map(_ => _.MapKey("RegistrationSubItemId"));
        }

public RegistrationSubItemMap()
        {
            ToTable("RegistrationSubItems");

            HasKey(_ => _.Id);
            HasRequired(_ => _.RegistrationItem).WithMany(_ => _.SubItems).Map(_ => _.MapKey("RegistrationItemId"));
            Property(_ => _.Duration).IsOptional();
            Property(_ => _.ItemId).IsRequired();
            Property(_ => _.Status).IsRequired();
            HasMany(_ => _.Parameters).WithRequired(_ => _.RegistrationSubItem);
        }

public class RegistrationSubItem : Entity<RegistrationSubItem>, ILoggable
    {
        #region Private Members
        ICollection<RegistrationSubItemParameter> _parameters = new List<RegistrationSubItemParameter>();
        #endregion

        #region Properties
        public RegistrationItem RegistrationItem { get; protected set; }
        public int ItemId { get; protected set; }
        public RegistrationStatus Status { get; protected set; }
        public int? Duration { get; protected set; }
        public virtual ICollection<RegistrationSubItemParameter> Parameters => _parameters;
    }

public class RegistrationMap : EntityMap<Registration>
    {
        public RegistrationMap()
        {
            ToTable("Registrations");

            HasKey(_ => _.Id);
            HasRequired(_ => _.Student).WithMany().Map(_ => _.MapKey("UserId"));
            HasRequired(_ => _.Group).WithMany().Map(_ => _.MapKey("GroupId"));
            Property(_ => _.RegisteredAt).IsRequired();
            Property(_ => _.FinishedAt).IsOptional();
            HasMany(_ => _.Items).WithRequired(_ => _.Registration);
            Property(_ => _.IsFrozen);
            
            Ignore(_ => _.State);
            Ignore(_ => _.EntityName);
            Ignore(_ => _.ModuleName);
        }
    }

public RegistrationItemMap()
        {
            ToTable("RegistrationItems");

            HasKey(_ => _.Id);
            HasRequired(_ => _.Registration).WithMany(_ => _.Items).Map(_ => _.MapKey("RegistrationId"));
            HasRequired(_ => _.Content).WithMany().Map(_ => _.MapKey("ContentId"));
            HasRequired(_ => _.Class).WithMany().Map(_ => _.MapKey("ClassId"));
            HasMany(_ => _.SubItems).WithRequired(_ => _.RegistrationItem);
            Property(_ => _.FinishedAt).IsOptional();
            
            Ignore(_ => _.State);
            Ignore(_ => _.EntityName);
            Ignore(_ => _.ModuleName);
        }

public class RegistrationItem : Entity<RegistrationItem>, ILoggable
    {
        #region Private Members
        private ICollection<RegistrationSubItem> _subItems = new Collection<RegistrationSubItem>();
        private RegistrationStatus CurrentStatus { get; set; }
        #endregion

        #region Properties
        public virtual ICollection<RegistrationSubItem> SubItems => _subItems;
        public Registration Registration { get; protected set; }
        public Content Content { get; protected set; }
        public Class Class { get; protected set; }
        public DateTime? FinishedAt { get; protected set; }
        public RegistrationItemState State
        {
            get { return RegistrationItemState.FromValue(CurrentStatus); }
            protected set { CurrentStatus = value.Status; }
        }
    }

public class RegistrationFactory
    {
        private readonly IContentRepository _contentRepository;

        public RegistrationFactory(IContentRepository contentRepository)
        {
            _contentRepository = contentRepository;
        }

        public Registration CreateRegistration(Student student, Group group)
        {
            if (student.IsNull()) throw new ArgumentNullException("student");
            if (group.IsNull()) throw new ArgumentNullException("group");

            var registration = new Registration(student, group);

            var items = group
                .GetActiveCourseContent()
                .Select(classContent => RegistrationItem.Create(registration, classContent, _ => CreateSubItems(_, classContent.Content)));

            registration.AddItems(items);
            registration.Freeze();

            return registration;
        }

        private IEnumerable<RegistrationSubItem> CreateSubItems(RegistrationItem item, Content content)
        {
            if (content.Type == ContentType.Scorm)
                return GetSharableContentItems(item, content);

            if (content.Type == ContentType.Page)
                return new[] { new RegistrationSubItem(item, content.Id) };

            if (content.Type == ContentType.Form)
                return new[] { new RegistrationSubItem(item, content.Id) };

            return Enumerable.Empty<RegistrationSubItem>();
        }

        private IEnumerable<RegistrationSubItem> GetSharableContentItems(RegistrationItem registrationItem, Content content)
        {
            var contendId = content.Id;
            var sharableContent = _contentRepository
                .GetSharableContents()
                .Eager(_ => _.Organization)
                .Eager(_ => _.Organization.Activities)
                .First(_ => _.Content.Id == contendId);

            return sharableContent
                .Organization
                .Activities
                .Flatten(_ => _.Children)
                .Distinct()
                .Select(_ => (new RegistrationSubItem(registrationItem, _.Id)).Tap(trackintItem => AddDefaultParameters(trackintItem, _)));
        }

        private void AddDefaultParameters(RegistrationSubItem registrationSubItem, Activity activity)
        {
            registrationSubItem.AddOrUpdateParameter("cmi.core.credit", "credit");
            registrationSubItem.AddOrUpdateParameter("cmi.core.lesson_status", "not attempted");
            registrationSubItem.AddOrUpdateParameter("cmi.core.entry", "ab-initio");
            registrationSubItem.AddOrUpdateParameter("cmi.core.lesson_mode", "normal");
            registrationSubItem.AddOrUpdateParameter("cmi.core.exit", "suspend");
            registrationSubItem.AddOrUpdateParameter("cmi.student_data.time_limit_action", "continue,no message");

            if (activity.Parameters.MasteryScore.HasValue)
                registrationSubItem.AddOrUpdateParameter("adlcp:masteryscore", activity.Parameters.MasteryScore.ToString());
            if (activity.Parameters.MaxTimeAllowed.IsNotEmpty())
                registrationSubItem.AddOrUpdateParameter("adlcp:maxtimeallowed", activity.Parameters.MaxTimeAllowed);
        }
    }

public class Registration : Entity<Registration>, ILoggable, IFreezable,  IAggregateRoot
    {
        #region Private Members
        private ICollection<RegistrationItem> _items = new List<RegistrationItem>();
        private RegistrationStatus CurrentStatus { get; set; }
        #endregion

        #region Properties
        public bool IsFrozen { get; private set; }
        public Student Student { get; protected set; }
        public Group Group { get; protected set; }
        public RegistrationState State
        {
            get { return RegistrationState.FromValue(CurrentStatus); }
            protected set { CurrentStatus = value.Status; }
        }
        public DateTime RegisteredAt { get; protected set; }
        public DateTime? FinishedAt { get; protected set; }
        public virtual ICollection<RegistrationItem> Items => _items;
    }

public void Save<T>(T entity) where T : class, IEntity<T>, IAggregateRoot
        {
            var context = GetContext<T>();
            //var e = context.Entry(entity);
            //if (e.State == EntityState.Detached)
            //{
            //    context.Set<T>().Attach(entity);
            //    return;
            //}

            if (entity.IsPersisted()) {
                context.Entry(entity).State = EntityState.Modified;
            } else {
                context.Set<T>().Add(entity);
            }
        }

public ICommandResult Handle(CreateRegistrationCommand command)
        {
            using (var scope = new TransactionScope(TransactionScopeOption.Required, new TransactionOptions{ IsolationLevel = IsolationLevel.ReadCommitted }))
            {
                var course = _courseRepository
                    .GetCourses()
                    .Published()
                    .Eager(_ => _.Groups)
                    .Eager(_ => _.Groups.Select(g => g.Course))
                    .ById(command.CourseId);

                if (course.IsNull())
                    return CommandResult.BadRequest(ErrorCode.COURSE_NOT_FOUND);

                var student = _studentRepository.GetStudents().ById(command.UserId);
                if (student.IsNull())
                    return CommandResult.BadRequest(ErrorCode.STUDENT_NOT_FOUND);

                var availableGroup = course.GetAvailableGroup(command.GroupId);
                if (availableGroup.IsNull())
                    return CommandResult.BadRequest(ErrorCode.GROUP_NOT_FOUND);

                var registration = _registrationFactory.CreateRegistration(student, availableGroup);
                if (registration.Items.IsEmpty())
                    return CommandResult.BadRequest(ErrorCode.REGISTRATION_INCONSISTENT);

                _registrationRepository.Save(registration);

                _unitOfWork.SaveChanges();

                scope.Complete();

                return CommandResult.Created((new { Id = registration.Id, CourseId = course.Id }).ToDynamic());
            }
        }

public abstract class BaseContext<TContext> : DbContext, IDataContext, IQueryDataContext, IUnitOfWork
        where TContext : DbContext
    {
        public override int SaveChanges()
        {
            return Save(() =>
            {
                var affectedRows = base.SaveChanges();
                return Task.FromResult(affectedRows);
            }).Result;
        }
    }