using System.IO.Compression;

using Microsoft.EntityFrameworkCore.Storage.ValueConversion;

using Newtonsoft.Json;

/// <summary>
/// Компрессор для больших списков чисел с плавающей точкой
/// </summary>
public class CompressedFloatListConverter : ValueConverter<List<float>, string>
{
    public CompressedFloatListConverter()
    : base(
        v => Compress(v),
        v => Decompress(v)
    )
    { }

    private static string Compress(List<float> list)
    {
        if (list is null || list.Count == 0)
            return "";

        byte[] floatBytes = new byte[list.Count * sizeof(float)];
        Buffer.BlockCopy(list.ToArray(), 0, floatBytes, 0, floatBytes.Length);

        using var outputStream = new MemoryStream();
        using (var compressionStream = new BrotliStream(outputStream, CompressionLevel.Optimal))
            compressionStream.Write(floatBytes, 0, floatBytes.Length);

        return Convert.ToBase64String(outputStream.ToArray());
    }

    private static List<float> Decompress(string base64String)
    {
        if (string.IsNullOrEmpty(base64String))
            return new List<float>();

        byte[] compressedBytes;
        float[]? floatArray;
        
        try
        {
            compressedBytes = Convert.FromBase64String(base64String);
        }
        catch (FormatException)
        {
            floatArray = JsonConvert.DeserializeObject<float[]>(base64String);
            if (floatArray is null)
                throw;
            return new List<float>(floatArray);
        }

        using var inputStream = new MemoryStream(compressedBytes);
        using var decompressionStream = new BrotliStream(inputStream, CompressionMode.Decompress);
        using var outputStream = new MemoryStream();
        decompressionStream.CopyTo(outputStream);

        byte[] decompressedBytes = outputStream.ToArray();
        floatArray = new float[decompressedBytes.Length / sizeof(float)];
        Buffer.BlockCopy(decompressedBytes, 0, floatArray, 0, decompressedBytes.Length);

        return new List<float>(floatArray);
    }
}