using System.Numerics;
using System.Security.Cryptography;

namespace RadicadeServer.Storage;

public sealed record StudioAssetUpload(string Filename, string Hash, long Length);

public static class StudioAssetStorage
{


    public static string Filename(byte[] digest)
    {
        var value = new BigInteger(digest, isUnsigned: true, isBigEndian: false);
        const string alphabet = "0123456789abcdefghijklmnopqrstuvwxyz";
        var result = "";
        while (value > 0)
        {
            value = BigInteger.DivRem(value, 36, out var remainder);
            result = alphabet[(int)remainder] + result;
        }
        return result.PadLeft(50, '0')[..40];
    }

    public static async Task<StudioAssetUpload> Save(IFormFile file, CancellationToken cancellation)
    {
        await using var input = file.OpenReadStream();
        return await Save(input, cancellation);
    }

    public static async Task<StudioAssetUpload> Save(Stream input, CancellationToken cancellation)
    {
        Directory.CreateDirectory(DBConfig.CDNStorage);
        var temporary = Path.Combine(DBConfig.CDNStorage, Guid.NewGuid() + ".uploading");
        try
        {
            await using (var output = System.IO.File.Create(temporary))
                await input.CopyToAsync(output, cancellation);
            var length = new FileInfo(temporary).Length;
            byte[] hash;
            await using (var storedFile = System.IO.File.OpenRead(temporary))
                hash = await SHA256.HashDataAsync(storedFile, cancellation);
            var filename = Filename(hash);
            var destination = Path.Combine(DBConfig.CDNStorage, filename);
            try { System.IO.File.Move(temporary, destination); }
            catch (IOException) when (System.IO.File.Exists(destination)) { }
            return new StudioAssetUpload(filename, Convert.ToBase64String(hash), length);
        }
        finally
        {
            if (System.IO.File.Exists(temporary)) System.IO.File.Delete(temporary);
        }
    }
}