using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using System.IO;

namespace MyService.Helpers
{
    /// <summary>
    /// Helps discovering all the abstract BaseDtoEntity derived classes.
    /// Used like this:     [ServiceKnownType("GetKnownTypes", typeof(ServiceKnownTypesDiscovery))]
    /// on service contract interface
    /// </summary>
    class ServiceKnownTypesDiscovery
    {
        private static List<Type> _cachedTypes = null;

        /// <summary>
        /// Extracts known entity types from entities library
        /// </summary>
        /// <param name="provider">Passed in by WCF</param>
        /// <returns>List of BaseDtoEntity derived entity types</returns>
        public static IEnumerable<Type> GetKnownTypes(ICustomAttributeProvider provider)
        {
            // lazy init on first demand
            if (_cachedTypes == null)
            {
                _cachedTypes = new List<Type>();
                var baseType = typeof(BaseDtoEntity);

                foreach (var asmFile in Directory.GetFiles(AppDomain.CurrentDomain.RelativeSearchPath ??
                    AppDomain.CurrentDomain.BaseDirectory, "*.Entities.dll")) // project specific name of the library where entities are stored
                {
                    Assembly asm = Assembly.LoadFrom(asmFile);

                    // BaseDtoEntity is abstract, therefore we excluded it
                    _cachedTypes.AddRange(asm.GetTypes().Where(p => p != baseType &&
                                                            baseType.IsAssignableFrom(p)));
                }
            }

            return _cachedTypes;
        }
    }
}