TypeSystem.cs

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// 
//  Copyright 2010-2015 Deveel
// 
//    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.
//

using System;
using System.Collections.Generic;

namespace Deveel.Data.Linq {
    static class TypeSystem {
        public static Type GetElementType(Type seqType) {
            Type ienum = FindIEnumerable(seqType);

            if (ienum == null)
                return seqType;

            return ienum.GetGenericArguments()[0];
        }

        private static Type FindIEnumerable(Type seqType) {
            if (seqType == null || seqType == typeof(string))
                return null;

            if (seqType.IsArray)
                return typeof(IEnumerable<>).MakeGenericType(seqType.GetElementType());

            if (seqType.IsGenericType) {
                foreach (Type arg in seqType.GetGenericArguments()) {
                    Type ienum = typeof(IEnumerable<>).MakeGenericType(arg);
                    if (ienum.IsAssignableFrom(seqType)) {
                        return ienum;
                    }
                }
            }

            Type[] ifaces = seqType.GetInterfaces();

            if (ifaces.Length > 0) {
                foreach (Type iface in ifaces) {
                    Type ienum = FindIEnumerable(iface);
                    if (ienum != null) return ienum;
                }
            }

            if (seqType.BaseType != null && seqType.BaseType != typeof(object)) {
                return FindIEnumerable(seqType.BaseType);
            }

            return null;
        }
    }
}