using System;
using System.Collections.Generic;
using System.Threading;

namespace AzureCoding.Samples.ServiceLocator
{
    /// <summary>
    /// A simple, straightforward Service Locator Implementation
    /// </summary>
    public class ServiceContainer
    {
        private readonly Dictionary<Type,Object> _Services=new Dictionary<Type, object>();
        private readonly ReaderWriterLockSlim _ServicesLock = new ReaderWriterLockSlim();

        private static readonly ServiceContainer _Container = new ServiceContainer();
        
        public static ServiceContainer Instance
        {
            get { return _Container; }
        }

        private ServiceContainer()
        {

        }
        private void AddService<TService>(TService instance)
        {
            _ServicesLock.EnterUpgradeableReadLock();
            try
            {
                if (!_Services.ContainsKey(typeof(TService)))
                {
                    _ServicesLock.EnterWriteLock();
                    try
                    {
                        _Services[typeof(TService)] = instance;
                    }
                    finally
                    {
                        _ServicesLock.ExitWriteLock();
                    }
                }
            }
            finally
            {
                _ServicesLock.ExitUpgradeableReadLock();
            }
        }

        private TService RetrieveService<TService>()
        {
            TService retVal;
            _ServicesLock.EnterReadLock();
            try
            {
                retVal = (TService)_Services[typeof(TService)];
            }
            catch (Exception)
            {
                throw new Exception(String.Format("Service Type {0} not registered with container.", typeof(TService).Name));
            }
            finally
            {
                _ServicesLock.ExitReadLock();
            }
            return retVal;
        }

        public static void RegisterService<TService>(TService instance)
        {
            _Container.AddService(instance);
        }

        public static TService GetService<TService>()
        {
            return _Container.RetrieveService<TService>();
        }

        public static void ClearServices()
        {
            _Container.Reset();
        }

        private void Reset()
        {
            _ServicesLock.EnterWriteLock();
            try
            {
                _Services.Clear();
            }
            finally
            {
                _ServicesLock.ExitWriteLock();
            }
        }
    }
}