// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

namespace System.Data.Entity.Core.Metadata.Edm
{
    using System.Collections.Generic;
    using System.Data.Entity.Core.Common.Utils;
    using System.Data.Entity.Utilities;
    using System.Linq;
    using System.Reflection;

    // <summary>
    // Metadata collection class supporting delay-loading of system item attributes and
    // extended attributes.
    // </summary>
    internal sealed class MetadataPropertyCollection : MetadataCollection<MetadataProperty>
    {
        // <summary>
        // Constructor taking item.
        // </summary>
        // <param name="item"> Item with which the collection is associated. </param>
        internal MetadataPropertyCollection(MetadataItem item)
            : base(GetSystemMetadataProperties(item))
        {
        }

        private static readonly Memoizer<Type, ItemTypeInformation> _itemTypeMemoizer =
            new Memoizer<Type, ItemTypeInformation>(clrType => new ItemTypeInformation(clrType), null);

        // Given an item, returns all system type attributes for the item.
        private static IEnumerable<MetadataProperty> GetSystemMetadataProperties(MetadataItem item)
        {
            DebugCheck.NotNull(item);

            var type = item.GetType();
            var itemTypeInformation = GetItemTypeInformation(type);
            return itemTypeInformation.GetItemAttributes(item);
        }

        // Retrieves metadata for type.
        private static ItemTypeInformation GetItemTypeInformation(Type clrType)
        {
            return _itemTypeMemoizer.Evaluate(clrType);
        }

        // <summary>
        // Encapsulates information about system item attributes for a particular item type.
        // </summary>
        private class ItemTypeInformation
        {
            // <summary>
            // Retrieves system attribute information for the given type.
            // Requires: type must derive from MetadataItem
            // </summary>
            // <param name="clrType"> Type </param>
            internal ItemTypeInformation(Type clrType)
            {
                DebugCheck.NotNull(clrType);

                _itemProperties = GetItemProperties(clrType);
            }

            private readonly List<ItemPropertyInfo> _itemProperties;

            // Returns system item attributes for the given item.
            internal IEnumerable<MetadataProperty> GetItemAttributes(MetadataItem item)
            {
                foreach (var propertyInfo in _itemProperties)
                {
                    yield return propertyInfo.GetMetadataProperty(item);
                }
            }

            // Gets type information for item with the given type. Uses cached information where 
            // available.
            private static List<ItemPropertyInfo> GetItemProperties(Type clrType)
            {
                var result = new List<ItemPropertyInfo>();
                foreach (var propertyInfo in clrType.GetInstanceProperties())
                {
                    foreach (var attribute in propertyInfo.GetCustomAttributes<MetadataPropertyAttribute>(inherit: false))
                    {
                        result.Add(new ItemPropertyInfo(propertyInfo, attribute));
                    }
                }
                return result;
            }
        }

        // <summary>
        // Encapsulates information about a CLR property of an item class.
        // </summary>
        private class ItemPropertyInfo
        {
            // <summary>
            // Initialize information.
            // Requires: attribute must belong to the given property.
            // </summary>
            // <param name="propertyInfo"> Property referenced. </param>
            // <param name="attribute"> Attribute for the property. </param>
            internal ItemPropertyInfo(PropertyInfo propertyInfo, MetadataPropertyAttribute attribute)
            {
                DebugCheck.NotNull(propertyInfo);
                DebugCheck.NotNull(attribute);

                _propertyInfo = propertyInfo;
                _attribute = attribute;
            }

            private readonly MetadataPropertyAttribute _attribute;
            private readonly PropertyInfo _propertyInfo;

            // <summary>
            // Given an item, returns an instance of the item attribute described by this class.
            // </summary>
            // <param name="item"> Item from which to retrieve attribute. </param>
            // <returns> Item attribute. </returns>
            internal MetadataProperty GetMetadataProperty(MetadataItem item)
            {
                return new MetadataProperty(
                    _propertyInfo.Name, _attribute.Type, _attribute.IsCollectionType,
                    new MetadataPropertyValue(_propertyInfo, item));
            }
        }
    }
}
