class Roo::Excel

def read_cells(sheet = default_sheet)
  validate_sheet!(sheet)
  return if @cells_read[sheet]
  worksheet = @workbook.worksheet(sheet_no(sheet))
  row_index = 1
  worksheet.each(0) do |row|
    (0..row.size).each do |cell_index|
      cell = row.at(cell_index)
      next if cell.nil?  # skip empty cells
      next if cell.class == ::Spreadsheet::Formula && cell.value.nil? # skip empty formula cells
      value_type, v =
        if date_or_time?(row, cell_index)
          read_cell_date_or_time(row, cell_index)
        else
          read_cell(row, cell_index)
        end
      formula = tr = nil # TODO:???
      col_index = cell_index + 1
      font = row.format(cell_index).font
      font.extend(ExcelFontExtensions)
      set_cell_values(sheet, row_index, col_index, 0, v, value_type, formula, tr, font)
    end # row
    row_index += 1
  end # worksheet
  @cells_read[sheet] = true
end