using System;
using ln.objects.catalog;

namespace ln.types.odb.ng.mappings
{
    public class ReferenceMapping<T> : IODBMapping where T:class
	{
		public Type ReferencedType { get; private set; }
		public String ReferencedCollectionName { get; set; }

		public ReferenceMapping()
		{
			ReferencedType = typeof(T);
			ReferencedCollectionName = ReferencedType.FullName;
		}

		public ODBValue MapValue(ODBMapper mapper, object value)
		{
			if (value == null)
			{
				return ODBNull.Instance;
			}
			else
			{
				ClassMapping classMapping = mapper.GetMapping(ReferencedType) as ClassMapping;
				if (classMapping == null)
					throw new NullReferenceException(String.Format("classMapping not found for Type {0}",ReferencedType));

				object referenceID = classMapping.getID(value);
				return mapper.MapValue(referenceID);
			}
		}

		public object UnmapValue(ODBMapper mapper, ODBValue oval)
		{
			ClassMapping classMapping = mapper.GetMapping(ReferencedType) as ClassMapping;
			if (classMapping == null)
				throw new NullReferenceException(String.Format("classMapping not found for Type {0}", ReferencedType));

			object referenceID = mapper.UnmapValue(classMapping.IDType, oval);
			T referenced = mapper.GetCollection<T>(ReferencedCollectionName).Select(referenceID);
			return referenced;
		}
	}
}