using System.IO.Compression;
using System.Text;

namespace MeWeb.Core.Knowledge;

public class NetworkInfo
{
  public uint Number { get; set; }
  public string Organisation { get; set; }
  public List<uint> Upstreams { get; set; } = [];
}

public sealed class NetworkTable
{
  const uint Magic = 0x324B574D;

  readonly Dictionary<uint, NetworkInfo> networks = [];

  public DateTimeOffset BuiltAt { get; private set; }

  public int Count => networks.Count;

  public NetworkInfo Find(uint number) => networks.GetValueOrDefault(number);

  public static NetworkTable Read(Stream compressed)
  {
    using var brotli = new BrotliStream(compressed, CompressionMode.Decompress);
    using var reader = new BinaryReader(brotli, Encoding.UTF8);
    if (reader.ReadUInt32() != Magic) throw new InvalidDataException("not a me-web? network table");
    var table = new NetworkTable { BuiltAt = DateTimeOffset.FromUnixTimeSeconds(reader.ReadInt64()) };
    var count = reader.Read7BitEncodedInt();
    var previous = 0u;
    for (var i = 0; i < count; i++)
    {
      previous += (uint)reader.Read7BitEncodedInt64();
      var info = new NetworkInfo { Number = previous, Organisation = reader.ReadString() };
      var upstreams = reader.Read7BitEncodedInt();
      for (var u = 0; u < upstreams; u++) info.Upstreams.Add((uint)reader.Read7BitEncodedInt64());
      if (info.Organisation.Length == 0) info.Organisation = null;
      table.networks[info.Number] = info;
    }
    return table;
  }

  public static void Write(Stream output, DateTimeOffset builtAt, IEnumerable<NetworkInfo> networks)
  {
    var list = networks.Where(n => n.Number != 0).OrderBy(n => n.Number).ToList();
    using var brotli = new BrotliStream(output, CompressionLevel.SmallestSize, leaveOpen: true);
    using var writer = new BinaryWriter(brotli, Encoding.UTF8);
    writer.Write(Magic);
    writer.Write(builtAt.ToUnixTimeSeconds());
    writer.Write7BitEncodedInt(list.Count);
    var previous = 0u;
    foreach (var info in list)
    {
      writer.Write7BitEncodedInt64(info.Number - previous);
      writer.Write(info.Organisation ?? "");
      writer.Write7BitEncodedInt(info.Upstreams.Count);
      foreach (var upstream in info.Upstreams) writer.Write7BitEncodedInt64(upstream);
      previous = info.Number;
    }
  }
}