C# Attribute Helper

// Copyright 2004-2012 Castle Project - http://www.castleproject.org/
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

namespace Castle.Core.Internal
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Linq;
    using System.Reflection;

    /// <summary>
    /// Helper class for retrieving attributes.
    /// </summary>
    public static class AttributesUtil
    {
        /// <summary>
        /// Gets the attribute.
        /// </summary>
        /// <param name="type">The type.</param>
        /// <returns>The type attribute.</returns>
        public static T GetAttribute<T>(this Type type) where T : Attribute
        {
            return GetAttributes<T>(type).FirstOrDefault();
        }

        /// <summary>
        /// Gets the attributes. Does not consider inherited attributes!
        /// </summary>
        /// <param name="type">The type.</param>
        /// <returns>The type attributes.</returns>
        public static IEnumerable<T> GetAttributes<T>(this Type type) where T : Attribute
        {
            foreach (T a in type.GetTypeInfo().GetCustomAttributes(typeof(T), false))
            {
                yield return a;
            }
        }

        /// <summary>
        /// Gets the attribute.
        /// </summary>
        /// <param name="member">The member.</param>
        /// <returns>The member attribute.</returns>
        public static T GetAttribute<T>(this MemberInfo member) where T : Attribute
        {
            return GetAttributes<T>(member).FirstOrDefault();
        }

        /// <summary>
        /// Gets the attributes. Does not consider inherited attributes!
        /// </summary>
        /// <param name="member">The member.</param>
        /// <returns>The member attributes.</returns>
        public static IEnumerable<T> GetAttributes<T>(this MemberInfo member) where T : Attribute
        {
            foreach (T a in member.GetCustomAttributes(typeof(T), false))
            {
                yield return a;
            }
        }

        /// <summary>
        ///   Gets the type attribute.
        /// </summary>
        /// <param name = "type">The type.</param>
        /// <returns>The type attribute.</returns>
        public static T GetTypeAttribute<T>(this Type type) where T : Attribute
        {
            var attribute = GetAttribute<T>(type);
            if (attribute == null)
            {
                foreach (var baseInterface in type.GetInterfaces())
                {
                    attribute = GetTypeAttribute<T>(baseInterface);
                    if (attribute != null)
                    {
                        break;
                    }
                }
            }

            return attribute;
        }

        /// <summary>
        ///   Gets the type attributes.
        /// </summary>
        /// <param name = "type">The type.</param>
        /// <returns>The type attributes.</returns>
        public static T[] GetTypeAttributes<T>(Type type) where T : Attribute
        {
            var attributes = GetAttributes<T>(type).ToArray();
            if (attributes.Length == 0)
            {
                foreach (var baseInterface in type.GetInterfaces())
                {
                    attributes = GetTypeAttributes<T>(baseInterface);
                    if (attributes.Length > 0)
                    {
                        break;
                    }
                }
            }

            return attributes;
        }

        public static AttributeUsageAttribute GetAttributeUsage(this Type attributeType)
        {
            var attributes = attributeType.GetTypeInfo().GetCustomAttributes<AttributeUsageAttribute>(true).ToArray();
            return attributes.Length != 0 ? attributes[0] : DefaultAttributeUsage;
        }

        private static readonly AttributeUsageAttribute DefaultAttributeUsage = new AttributeUsageAttribute(AttributeTargets.All);

        /// <summary>
        /// Gets the type converter.
        /// </summary>
        /// <param name="member">The member.</param>
        public static Type GetTypeConverter(MemberInfo member)
        {
            var attrib = GetAttribute<TypeConverterAttribute>(member);

            if (attrib != null)
            {
                return Type.GetType(attrib.ConverterTypeName);
            }

            return null;
        }
    }
}