using System.IO;
using GemBox.Spreadsheet;

public sealed class CsvFileReader : TextReader
{
    private const int MaxRow = 1048576;
    private readonly TextReader reader;

    private int currentRow;
    private bool isCompleted;

    public static ExcelFile Read(string path, CsvLoadOptions options)
    {
        var workbook = new ExcelFile();
        int sheetIndex = 0;

        using (var reader = new CsvFileReader(path))
            while (reader.CanReadNextSheet())
            {
                ++sheetIndex;
                workbook.Worksheets.AddCopy(
                    string.Format("Sheet {0}", sheetIndex),
                    ExcelFile.Load(reader, options).Worksheets.ActiveWorksheet);
            }

        return workbook;
    }

    private CsvFileReader(string path)
    {
        this.reader = File.OpenText(path);
    }

    private bool CanReadNextSheet()
    {
        if (this.isCompleted)
            return false;

        this.currentRow = 0;
        return true;
    }

    public override string ReadLine()
    {
        if (this.currentRow < MaxRow)
        {
            ++this.currentRow;
            string line = this.reader.ReadLine();

            if (line == null)
                this.isCompleted = true;

            return line;
        }

        return null;
    }
    
    protected override void Dispose(bool disposing)
    {
        this.reader.Dispose();
    }
}