using System.Security.Cryptography;
using System.Text;

namespace StellaOps.Scanner.ReachabilityDrift;

internal static class DeterministicIds
{
    internal static readonly Guid CodeChangeNamespace = new("a420df67-6c4b-4f80-9870-0d070a845b4b");
    internal static readonly Guid DriftResultNamespace = new("c60e2a63-9bc4-4ff0-9f8c-2a7c11c2f8c4");
    internal static readonly Guid DriftedSinkNamespace = new("9b8ed5d2-4b6f-4f6f-9e3b-3a81e9f85a25");

    public static Guid Create(Guid namespaceId, params string[] segments)
    {
        var normalized = string.Join(
            '|',
            segments.Select(static s => (s ?? string.Empty).Trim()));
        return Create(namespaceId, Encoding.UTF8.GetBytes(normalized));
    }

    public static Guid Create(Guid namespaceId, ReadOnlySpan<byte> nameBytes)
    {
        Span<byte> namespaceBytes = stackalloc byte[16];
        namespaceId.TryWriteBytes(namespaceBytes);

        Span<byte> buffer = stackalloc byte[namespaceBytes.Length + nameBytes.Length];
        namespaceBytes.CopyTo(buffer);
        nameBytes.CopyTo(buffer[namespaceBytes.Length..]);

        Span<byte> hash = stackalloc byte[32];
        SHA256.TryHashData(buffer, hash, out _);

        Span<byte> guidBytes = stackalloc byte[16];
        hash[..16].CopyTo(guidBytes);

        guidBytes[6] = (byte)((guidBytes[6] & 0x0F) | 0x50);
        guidBytes[8] = (byte)((guidBytes[8] & 0x3F) | 0x80);

        return new Guid(guidBytes);
    }
}