// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.InteropServices;

internal static partial class Interop
{
    internal static partial class Sys
    {
        internal const int IPv4AddressBytes = 4;
        internal const int IPv6AddressBytes = 16;

        internal const int MAX_IP_ADDRESS_BYTES = 16;

        internal const int INET_ADDRSTRLEN = 22;
        internal const int INET6_ADDRSTRLEN = 65;

        // NOTE: `_isIPv6` cannot be of type `bool` because `bool` is not a blittable type and this struct is
        //       embedded in other structs for interop purposes.
        [StructLayout(LayoutKind.Sequential)]
        internal unsafe struct IPAddress : IEquatable<IPAddress>
        {
            public bool IsIPv6
            {
                get { return _isIPv6 != 0; }
                set { _isIPv6 = value ? 1u : 0u; }
            }

            internal fixed byte Address[MAX_IP_ADDRESS_BYTES]; // Buffer to fit an IPv4 or IPv6 address
            private  uint _isIPv6;                             // Non-zero if this is an IPv6 address; zero for IPv4.
            internal uint ScopeId;                             // Scope ID (IPv6 only)

            public override int GetHashCode()
            {
                HashCode h = default;
                h.AddBytes(MemoryMarshal.CreateReadOnlySpan(ref Address[0], IsIPv6 ? IPv6AddressBytes : IPv4AddressBytes));
                return h.ToHashCode();
            }

            public override bool Equals([NotNullWhen(true)] object? obj) =>
                obj is IPAddress other && Equals(other);

            public bool Equals(IPAddress other)
            {
                int addressByteCount;
                if (IsIPv6)
                {
                    if (!other.IsIPv6)
                    {
                        return false;
                    }
                    if (ScopeId != other.ScopeId)
                    {
                        return false;
                    }

                    addressByteCount = IPv6AddressBytes;
                }
                else
                {
                    if (other.IsIPv6)
                    {
                        return false;
                    }

                    addressByteCount = IPv4AddressBytes;
                }

                return MemoryMarshal.CreateReadOnlySpan(ref Address[0], addressByteCount).SequenceEqual(
                       new ReadOnlySpan<byte>(other.Address, addressByteCount));
            }
        }
    }
}