using System;
using System.Collections.Generic;
using System.Linq;

namespace Kreta.Framework.Entities.Associations
{
    public static class AssociationHandlerManager
    {
        private static Dictionary<string, Type> associationHandlers = null;

        private static void Initialize()
        {
            if (associationHandlers == null)
            {
                associationHandlers = new Dictionary<string, Type>();
                var handlers = from assembly in AppDomain.CurrentDomain.GetAssemblies()
                               where SDAServer.Instance.IsAssemblyAllowed(assembly)
                               from type in assembly.GetTypes()
                               where type.IsDefined(typeof(AssociationAttribute), false)
                               select new
                               {
                                   AssociationName = ((AssociationAttribute)type.GetCustomAttributes(typeof(AssociationAttribute), false)[0]).AssociationName.ToLower(),
                                   HandlerType = type,
                               };
                foreach (var handler in handlers)
                {
                    associationHandlers.Add(handler.AssociationName, handler.HandlerType);
                }
            }
        }

        public static AssociationHandler<LeftEntity, RightEntity> Create<LeftEntity, RightEntity>(string associationName)
            where LeftEntity : Entity
            where RightEntity : Entity
        {
            Initialize();

            return associationHandlers.TryGetValue(associationName.ToLower(), out Type type)
                ? (AssociationHandler<LeftEntity, RightEntity>)Activator.CreateInstance(type, true)
                : new AssociationHandler<LeftEntity, RightEntity>();
        }
    }
}