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csvparse.cs

using System;
using System.Buffers;
using System.ComponentModel.Design;
using System.IO;
using System.IO.Pipelines;
using System.Text;
using System.Threading.Tasks;
using iot.project.domain.entities;

namespace iot.project.service.Util
{
    public abstract class CsvParseUtil<T> where T : class, ICsvParseUtil<T>
    {
        private readonly byte[] _header;
        private readonly byte _separator = (byte)',';
        
        public virtual async Task<T[]> Parse(string filePath)
        {
            var csvPool = ArrayPool<T>.Shared;
            var csv = csvPool.Rent(500);
            int position = 0;

            await using (var fileStream = File.Open(filePath, FileMode.Open, FileAccess.Read))
            {
                var reader = PipeReader.Create(fileStream);

                while (true)
                {
                    var data = await reader.ReadAsync();
                    var dataBuffer = data.Buffer;

                    var actualPosition = ParseLine(dataBuffer, position, csv);
                    reader.AdvanceTo(actualPosition, dataBuffer.End);

                    if (data.IsCompleted)
                        break;
                }

                await reader.CompleteAsync();
            }

            csvPool.Return(csv);
            return csv;
        }

        public virtual SequencePosition ParseLine(ReadOnlySequence<byte> dataBuffer, int position, T[] csvs)
        {
            var reader = new SequenceReader<byte>(dataBuffer);
            
            while(reader.TryReadTo(out ReadOnlySpan<byte> line, (byte) '\n'))
            {
                T csv = GetDataFromCsv(line);
                if (csv != null)
                {
                    csvs[position] = csv;
                    position++;
                }
            }

            return reader.Position;
        }

        private T GetDataFromCsv(ReadOnlySpan<byte> line)
        {
             if (line.IndexOf(_header) >= 0)
                return null;

            var record = new <typed object>();

            for (int i = 0; i < 1; i++)
            {
                var index = line.IndexOf(_separator);
                if (index < 0)
                {
                    index = line.Length;
                }

                switch (i)
                {
                    case 0:
                        record.Region = Encoding.UTF8.GetString(line.Slice(0, index));
                        break;

                    case 1:
                        record.Country = Encoding.UTF8.GetString(line.Slice(0, index));
                        break;
                        
                line = line.Slice(index + 1);
            }

            return record;
        }
    }
}