using System;
using System.Linq;
using System.Net;
#if NET8_0_OR_GREATER
using IPNetwork = System.Net.IPNetwork;
#else
using Microsoft.AspNetCore.HttpOverrides;
using IPNetwork = Microsoft.AspNetCore.HttpOverrides.IPNetwork;
#endif

namespace MessagePack.Formatters
{
	/// <summary>
	/// Serialization of an <see cref="IPNetwork"/> to and from <see cref="MessagePack"/>.
	/// </summary>
	[System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
	public class IPNetworkFormatter : IMessagePackFormatter<IPNetwork>
	{
		/// <inheritdoc/>
		public IPNetwork Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
		{
			if (reader.IsNil)
				return default;

			byte[] bytes = options.Resolver.GetFormatterWithVerify<byte[]>().Deserialize(ref reader, options);
			return DeserializeInternal(bytes);
		}

		/// <inheritdoc/>
		public void Serialize(ref MessagePackWriter writer, IPNetwork value, MessagePackSerializerOptions options)
		{
			if (value == default)
			{
				writer.WriteNil();
				return;
			}

			byte[] bytes = SerializeInternal(value);
			options.Resolver.GetFormatterWithVerify<byte[]>().Serialize(ref writer, bytes, options);
		}

		internal static byte[] SerializeInternal(IPNetwork network)
		{
			// IP network prefix has a maximum of 128 bit - therefore the length can be covered with a byte.
			byte prefixLength = (byte)network.PrefixLength;
#if NET8_0_OR_GREATER
			byte[] prefixBytes = network.BaseAddress.GetAddressBytes();
#else
			byte[] prefixBytes = network.Prefix.GetAddressBytes();
#endif

			byte[] bytes = new byte[prefixBytes.Length + 1];
			bytes[0] = prefixLength;
			Array.Copy(prefixBytes, 0, bytes, 1, prefixBytes.Length);

			return bytes;
		}

		internal static IPNetwork DeserializeInternal(byte[] bytes)
		{
			byte prefixLength = bytes[0];
			byte[] prefixBytes = bytes.Skip(1).ToArray();

			var prefix = new IPAddress(prefixBytes);
			return new IPNetwork(prefix, prefixLength);
		}
	}
}