Minics/Universal/ExcelReader.cs

using NPOI.SS.UserModel;
using NPOI.XSSF.UserModel;

namespace Universal;

public class ExcelReader
{
    public static Dictionary<string, Dictionary<int, Dictionary<int, string>>> Read(string filePath, int startRow)
    {
        Dictionary<string, Dictionary<int, Dictionary<int, string>>> sheets = [];
        
        using FileStream file = new(filePath, FileMode.Open, FileAccess.Read);

        for (int i = 0; ; i++)
        {
            ISheet sheet;
            try
            {
                sheet = new XSSFWorkbook(file).GetSheetAt(i);
                if (sheet is null)
                    break;
            }
            catch
            {
                break;
            }
            Dictionary<int, Dictionary<int, string>> contents = [];
            sheets[sheet.SheetName] = contents;

            for (int row = startRow; row <= sheet.LastRowNum; row++)
            {
                if (sheet.GetRow(row) is not IRow currentRow)
                    continue;
                contents[row] = [];
                for (int colum = 0; colum < currentRow.LastCellNum; colum++)
                {
                    ICell cell = currentRow.GetCell(colum);
                    contents[row][colum] = cell?.ToString() ?? string.Empty;
                }
            }
        }
        return sheets;
    }
}