using System.Collections.Generic;
using System.Formats.Cbor;
using System.Text;
using System.Text.Json;

namespace StellaOps.Scanner.WebService.Serialization;

internal static class DeterministicCborSerializer
{
    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
    {
        WriteIndented = false
    };

    public static byte[] Serialize<T>(T value)
    {
        using var document = JsonSerializer.SerializeToDocument(value, JsonOptions);
        var writer = new CborWriter(CborConformanceMode.Canonical);

        WriteElement(writer, document.RootElement);
        return writer.Encode();
    }

    private static void WriteElement(CborWriter writer, JsonElement element)
    {
        switch (element.ValueKind)
        {
            case JsonValueKind.Object:
                WriteObject(writer, element);
                return;
            case JsonValueKind.Array:
                writer.WriteStartArray(element.GetArrayLength());
                foreach (var item in element.EnumerateArray())
                {
                    WriteElement(writer, item);
                }
                writer.WriteEndArray();
                return;
            case JsonValueKind.String:
                writer.WriteTextString(element.GetString() ?? string.Empty);
                return;
            case JsonValueKind.Number:
                if (element.TryGetInt64(out var int64))
                {
                    writer.WriteInt64(int64);
                    return;
                }

                writer.WriteDouble(element.GetDouble());
                return;
            case JsonValueKind.True:
                writer.WriteBoolean(true);
                return;
            case JsonValueKind.False:
                writer.WriteBoolean(false);
                return;
            case JsonValueKind.Null:
            case JsonValueKind.Undefined:
                writer.WriteNull();
                return;
            default:
                writer.WriteNull();
                return;
        }
    }

    private static void WriteObject(CborWriter writer, JsonElement element)
    {
        var properties = new List<(byte[] KeyBytes, string Key, JsonElement Value)>();

        foreach (var property in element.EnumerateObject())
        {
            var keyBytes = Encoding.UTF8.GetBytes(property.Name);
            properties.Add((keyBytes, property.Name, property.Value));
        }

        properties.Sort(static (left, right) =>
        {
            var lengthCompare = left.KeyBytes.Length.CompareTo(right.KeyBytes.Length);
            if (lengthCompare != 0)
            {
                return lengthCompare;
            }

            for (var i = 0; i < left.KeyBytes.Length; i++)
            {
                var byteCompare = left.KeyBytes[i].CompareTo(right.KeyBytes[i]);
                if (byteCompare != 0)
                {
                    return byteCompare;
                }
            }

            return 0;
        });

        writer.WriteStartMap(properties.Count);

        foreach (var (_, key, value) in properties)
        {
            writer.WriteTextString(key);
            WriteElement(writer, value);
        }

        writer.WriteEndMap();
    }
}