using System.Collections.Generic;
using System.Net;

namespace AMWD.Common.Comparer
{
	/// <summary>
	/// Defines a method to compare two IP addresses.
	/// </summary>
	public class IPAddressComparer : IComparer<IPAddress>
	{
		/// <summary>
		/// Compares two IP addresses and returns a value indicating whether one is less than,
		/// equal to, or greater than the other.
		/// </summary>
		/// <param name="x">The first IP address.</param>
		/// <param name="y">The second IP address.</param>
		/// <returns>
		/// A signed integer that indicates the relative values of x and y, as shown in the following table.
		/// <list type="table">
		///   <listheader>
		///     <term>Value</term>
		///     <description>Meaning</description>
		///   </listheader>
		///   <item>
		///     <term>Less than zero</term>
		///     <description>x is less than y.</description>
		///   </item>
		///   <item>
		///     <term>Zero</term>
		///     <description>x equals y.</description>
		///   </item>
		///   <item>
		///     <term>Greater than zero</term>
		///     <description>x is greater than y.</description>
		///   </item>
		/// </list>
		/// </returns>
		public int Compare(IPAddress x, IPAddress y)
		{
			if (x == null && y == null)
				return 0;

			if (x == null)
				return -1;

			if (y == null)
				return 1;

			byte[] xBytes = x.GetAddressBytes();
			byte[] yBytes = y.GetAddressBytes();

			// Make IPv4 and IPv6 comparable
			byte[] left = xBytes.Length == 16
				? xBytes
				: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, xBytes[0], xBytes[1], xBytes[2], xBytes[3]];
			byte[] right = yBytes.Length == 16
				? yBytes
				: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, yBytes[0], yBytes[1], yBytes[2], yBytes[3]];

			// Compare byte for byte
			for (int i = 0; i < left.Length; i++)
			{
				int result = left[i].CompareTo(right[i]);
				if (result != 0)
					return result;
			}

			return 0;
		}
	}
}