using System;
using System.Collections.Generic;
using System.Linq;

namespace Chernobyl.Reflection
{
    /// <summary>
    /// Extension methods for use with .NET reflection.
    /// </summary>
    public static class Extensions
    {
        /// <summary>
        /// Gets the common base type of a <see cref="IEnumerable{Type}"/> 
        /// collection.
        /// 
        /// References: this method was taken and modified from 
        /// http://stackoverflow.com/questions/353430/easiest-way-to-get-a-common-base-class-from-a-collection-of-types
        /// </summary>
        /// <param name="types">The collection of types to get the common base 
        /// class of.</param>
        /// <returns>The base type that is common for each of the types passed 
        /// in. If the array passed in has a zero length, then typeof(object) 
        /// is returned.</returns>
        public static Type GetCommonBaseType(this IEnumerable<Type> types)
        {
            Type result = types.FirstOrDefault();

            if (result != null)
            {
                result = types.First();

                foreach (Type type in types)
                {
                    if (type.IsAssignableFrom(result))
                        result = type;
                    else
                    {
                        // This will always terminate when return == typeof(object) 
                        while (!result.IsAssignableFrom(type))
                            result = result.BaseType;
                    }
                }
            }
            else
                result = typeof(object);

            return result;
        }
    }
}