using System.Globalization;
using System.Runtime.InteropServices;

namespace System.Collections
{
	[Serializable]
	[ComVisible(true)]
	public sealed class Comparer : IComparer
	{
		public static readonly Comparer Default = new Comparer();

		public static readonly Comparer DefaultInvariant = new Comparer(CultureInfo.InvariantCulture);

		private CompareInfo m_compareInfo;

		private Comparer()
		{
		}

		public Comparer(CultureInfo culture)
		{
			if (culture == null)
			{
				throw new ArgumentNullException("culture");
			}
			m_compareInfo = culture.CompareInfo;
		}

		public int Compare(object a, object b)
		{
			if (a == b)
			{
				return 0;
			}
			if (a == null)
			{
				return -1;
			}
			if (b == null)
			{
				return 1;
			}
			if (m_compareInfo != null)
			{
				string sa = a as string;
				string sb = b as string;
				if (sa != null && sb != null)
				{
					return m_compareInfo.Compare(sa, sb);
				}
			}
			if (a is IComparable)
			{
				return (a as IComparable).CompareTo(b);
			}
			if (b is IComparable)
			{
				return -(b as IComparable).CompareTo(a);
			}
			throw new ArgumentException("Neither 'a' nor 'b' implements IComparable.");
		}
	}
}