﻿// adapted from sample code at http://linqinaction.net/files/folders/linqinaction/entry1952.aspx

// The code in this file comes from Matt Warren's series of blog posts on how to build a LINQ provider
// http://blogs.msdn.com/mattwar/archive/2007/08/09/linq-building-an-iqueryable-provider-part-i.aspx

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;

namespace Divan.Linq
{
    internal static class TypeSystem
    {
        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 != null && 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;
        }

        internal static Type GetSequenceType(Type elementType)
        {
            return typeof(IEnumerable<>).MakeGenericType(elementType);
        }

        internal static Type GetElementType(Type seqType)
        {
            Type ienum = FindIEnumerable(seqType);
            if (ienum == null)
                return seqType;
            return ienum.GetGenericArguments()[0];
        }

        internal static bool IsNullableType(Type type)
        {
            return type != null && type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>);
        }

        internal static bool IsNullAssignable(Type type)
        {
            return !type.IsValueType || IsNullableType(type);
        }

        internal static Type GetNonNullableType(Type type)
        {
            if (IsNullableType(type))
                return type.GetGenericArguments()[0];
            return type;
        }

        internal static Type GetMemberType(MemberInfo mi)
        {
            FieldInfo fi = mi as FieldInfo;
            if (fi != null)
                return fi.FieldType;
            PropertyInfo pi = mi as PropertyInfo;
            if (pi != null)
                return pi.PropertyType;
            EventInfo ei = mi as EventInfo;
            if (ei != null)
                return ei.EventHandlerType;
            return null;
        }
    }
}