app/APP/Utility/SaveBoy.cs

using System.Text.Json;
using APP.DTO;

namespace APP.Utility;

internal static class SaveBoy
{
    private static readonly string AuthFile = ".." + Path.DirectorySeparatorChar + "reg.json";

    internal static async Task<Auth?> ReadAuth()
    {
        if (File.Exists(AuthFile))
        {
            return await ReadFromFile<Auth>(AuthFile);
        }

        return null;
    }

    internal static void DeleteAuth()
    {
        if (File.Exists(AuthFile))
        {
            File.Delete(AuthFile);
        }
    }

    internal static async Task SaveAuth(Auth auth)
    {
        await WriteToFile(AuthFile, auth);
    }

    private static async Task WriteToFile<T>(string filePath, T objectToWrite)
    {
        try
        {
            await using var sw = new StreamWriter(filePath, false);
            try
            {
                var res = JsonSerializer.Serialize(objectToWrite);
                await sw.WriteAsync(res);
            }
            finally
            {
                sw.Close();
            }
        }
        catch (Exception ex)
        {
            await Console.Error.WriteLineAsync(ex.Message);
        }
    }

    private static async Task<T?> ReadFromFile<T>(string filePath)
    {
        try
        {
            using var sr = new StreamReader(filePath);
            try
            {
                var text = await sr.ReadToEndAsync();
                var res = JsonSerializer.Deserialize<T>(text);
                return res;
            }
            finally
            {
                sr.Close();
            }
        }
        catch (Exception ex)
        {
            await Console.Error.WriteLineAsync(ex.Message);
        }

        return default;
    }
}