using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Web;

namespace Umbraco.Core.ObjectResolution
{
    /// <summary>
    /// The base class for all lazy many-objects resolvers.
    /// </summary>
    /// <typeparam name="TResolver">The type of the concrete resolver class.</typeparam>
    /// <typeparam name="TResolved">The type of the resolved objects.</typeparam>
    /// <remarks>
    /// <para>This is a special case resolver for when types get lazily resolved in order to resolve the actual types. This is useful
    /// for when there is some processing overhead (i.e. Type finding in assemblies) to return the Types used to instantiate the instances. 
    /// In some these cases we don't want to have to type-find during application startup, only when we need to resolve the instances.</para>
	/// <para>Important notes about this resolver: it does not support Insert or Remove and therefore does not support any ordering unless 
    /// the types are marked with the WeightedPluginAttribute.</para>
	/// </remarks>
	internal abstract class LazyManyObjectsResolverBase<TResolver, TResolved> : ManyObjectsResolverBase<TResolver, TResolved>
		where TResolved : class
		where TResolver : class
	{
		#region Constructors
		
        /// <summary>
        /// Initializes a new instance of the <see cref="LazyManyObjectsResolverBase{TResolver, TResolved}"/> class with an empty list of objects,
        /// with creation of objects based on an HttpRequest lifetime scope.
        /// </summary>
        /// <param name="scope">The lifetime scope of instantiated objects, default is per Application.</param>
        /// <remarks>If <paramref name="scope"/> is per HttpRequest then there must be a current HttpContext.</remarks>
        /// <exception cref="InvalidOperationException"><paramref name="scope"/> is per HttpRequest but the current HttpContext is null.</exception>
		protected LazyManyObjectsResolverBase(ObjectLifetimeScope scope = ObjectLifetimeScope.Application)
			: base(scope)
		{ }

        /// <summary>
        /// Initializes a new instance of the <see cref="LazyManyObjectsResolverBase{TResolver, TResolved}"/> class with an empty list of objects,
        /// with creation of objects based on an HttpRequest lifetime scope.
        /// </summary>
        /// <param name="httpContext">The HttpContextBase corresponding to the HttpRequest.</param>
        /// <exception cref="ArgumentNullException"><paramref name="httpContext"/> is <c>null</c>.</exception>
		protected LazyManyObjectsResolverBase(HttpContextBase httpContext)
			: base(httpContext)
		{ }

        /// <summary>
        /// Initializes a new instance of the <see cref="LazyManyObjectsResolverBase{TResolver, TResolved}"/> class with an initial list
        /// <remarks>If <paramref name="scope"/> is per HttpRequest then there must be a current HttpContext.</remarks>
        /// <exception cref="InvalidOperationException"><paramref name="scope"/> is per HttpRequest but the current HttpContext is null.</exception>
        protected LazyManyObjectsResolverBase(IEnumerable<Lazy<Type>> lazyTypeList, ObjectLifetimeScope scope = ObjectLifetimeScope.Application)
			: this(scope)
		{			
			AddTypes(lazyTypeList);
		}

        /// <summary>
        /// Initializes a new instance of the <see cref="LazyManyObjectsResolverBase{TResolver, TResolved}"/> class with an initial list
        /// of functions producing types, and an optional lifetime scope.
        /// </summary>
        /// <param name="typeListProducerList">The list of functions producing types.</param>
        /// <param name="scope">The lifetime scope of instantiated objects, default is per Application.</param>
        /// <remarks>If <paramref name="scope"/> is per HttpRequest then there must be a current HttpContext.</remarks>
        /// <exception cref="InvalidOperationException"><paramref name="scope"/> is per HttpRequest but the current HttpContext is null.</exception>
        protected LazyManyObjectsResolverBase(Func<IEnumerable<Type>> typeListProducerList, ObjectLifetimeScope scope = ObjectLifetimeScope.Application)
			: this(scope)
		{
			_typeListProducerList.Add(typeListProducerList);
		}

        /// <summary>
        /// Initializes a new instance of the <see cref="LazyManyObjectsResolverBase{TResolver, TResolved}"/> class with an initial list of
        /// lazy object types, with creation of objects based on an HttpRequest lifetime scope.
        /// </summary>
        /// <param name="httpContext">The HttpContextBase corresponding to the HttpRequest.</param>
        /// <param name="lazyTypeList">The list of lazy object types.</param>
        /// <exception cref="ArgumentNullException"><paramref name="httpContext"/> is <c>null</c>.</exception>
		protected LazyManyObjectsResolverBase(HttpContextBase httpContext, IEnumerable<Lazy<Type>> lazyTypeList)
			: this(httpContext)
		{
			AddTypes(lazyTypeList);
		}

        /// <summary>
        /// Initializes a new instance of the <see cref="LazyManyObjectsResolverBase{TResolver, TResolved}"/> class with an initial list of
        /// functions producing types, with creation of objects based on an HttpRequest lifetime scope.
        /// </summary>
        /// <param name="httpContext">The HttpContextBase corresponding to the HttpRequest.</param>
        /// <param name="typeListProducerList">The list of functions producing types.</param>
        /// <exception cref="ArgumentNullException"><paramref name="httpContext"/> is <c>null</c>.</exception>
        protected LazyManyObjectsResolverBase(HttpContextBase httpContext, Func<IEnumerable<Type>> typeListProducerList)
			: this(httpContext)
		{
			_typeListProducerList.Add(typeListProducerList);
		} 

		#endregion	

		private readonly List<Lazy<Type>> _lazyTypeList = new List<Lazy<Type>>();
		private readonly List<Func<IEnumerable<Type>>> _typeListProducerList = new List<Func<IEnumerable<Type>>>();

		private List<Type> _resolvedTypes = null;
		private readonly ReaderWriterLockSlim _resolvedTypesLock = new ReaderWriterLockSlim();
		
		/// <summary>
		/// Gets a value indicating whether the resolver has resolved types to create instances from.
		/// </summary>
        /// <remarks>To be used in unit tests.</remarks>
		internal bool HasResolvedTypes
		{
			get
            {
                using (new ReadLock(_resolvedTypesLock))
                {
                    return _resolvedTypes != null;
                }
            }
		}

        /// <summary>
        /// Gets the list of types to create instances from.
        /// </summary>
        /// <remarks>When called, will get the types from the lazy list.</remarks>
        protected override IEnumerable<Type> InstanceTypes
		{
			get
			{
				using (var lck = new UpgradeableReadLock(_resolvedTypesLock))
				{
					if (_resolvedTypes == null)
					{
                        // get the types by evaluating the lazy & producers
                        var types = new List<Type>();
                        types.AddRange(_lazyTypeList.Select(x => x.Value));
                        types.AddRange(_typeListProducerList.SelectMany(x => x()));
                        
                        lck.UpgradeToWriteLock();

						_resolvedTypes = new List<Type>();

                        // we need to validate each resolved type now since we could
                        // not do it before evaluating the lazy & producers
                        foreach (var type in types)
							AddValidAndNoDuplicate(_resolvedTypes, type);
					}

					return _resolvedTypes;	
				}				
			}
		}

        // ensures that type is valid and not a duplicate
        // then appends the type to the end of the list
        private void AddValidAndNoDuplicate(List<Type> list, Type type)
		{
            EnsureCorrectType(type);
            if (list.Contains(type))
			{
                throw new InvalidOperationException(string.Format(
                    "Type {0} is already in the collection of types.", type.FullName));
            }
            list.Add(type);
		}

        #region Types collection manipulation

        /// <summary>
        /// Lazily adds types from lazy types.
		/// </summary>
        /// <param name="types">The lazy types, to add.</param>
		protected void AddTypes(IEnumerable<Lazy<Type>> types)
		{
			EnsureSupportsAdd();

            using (Resolution.Configuration)
            using (GetWriteLock())
			{
				foreach (var t in types)
				{				
					_lazyTypeList.Add(t);
				}
			}
		}

		/// <summary>
        /// Lazily adds types from a function producing types.
		/// </summary>
        /// <param name="typeListProducer">The functions producing types, to add.</param>
        public void AddTypeListDelegate(Func<IEnumerable<Type>> typeListProducer)
		{
            EnsureSupportsAdd();

            using (Resolution.Configuration)
            using (GetWriteLock())
			{
                _typeListProducerList.Add(typeListProducer);
			}
		}

		/// <summary>
        /// Lazily adds a type from a lazy type.
		/// </summary>
        /// <param name="value">The lazy type, to add.</param>
		public void AddType(Lazy<Type> value)
		{
            EnsureSupportsAdd();

            using (Resolution.Configuration)
            using (GetWriteLock())
			{				
				_lazyTypeList.Add(value);
			}
		}

		/// <summary>
        /// Lazily adds a type from an actual type.
		/// </summary>
        /// <param name="types">The actual type, to add.</param>
        /// <remarks>The type is converted to a lazy type.</remarks>
		public override void AddType(Type value)
		{
			AddType(new Lazy<Type>(() => value));
		}

		/// <summary>
		/// Clears all lazy types
		/// </summary>
		public override void Clear()
		{
			EnsureSupportsClear();

            using (Resolution.Configuration)
            using (GetWriteLock())
			{
				_lazyTypeList.Clear();
			}
		}

        #endregion

        #region Types collection manipulation support

        /// <summary>
        /// Gets a <c>false</c> value indicating that the resolver does NOT support removing types.
		/// </summary>
		protected override bool SupportsRemove
		{
			get { return false; }
		}

		/// <summary>
        /// Gets a <c>false</c> value indicating that the resolver does NOT support inserting types.
		/// </summary>
		protected override bool SupportsInsert
		{
			get { return false; }
        }

        #endregion
    }
}