csv_builder.rb

# c = CSVBuilder.new ['column 1 name', 'column 2 name', 'column 3 name']
# rowdata.each do |r|
#   special_column = r.boolean ? 'YES' : 'NO'
#   c.add_row [special_column, r.name, r.date]
# end
# c.export('optional_filename.csv')

class CSVBuilder
  def initialize(head)
    if head.is_a?(Array)
      @tempfile = Tempfile.new('csvbuilder', Rails.root.join('tmp'))
      @tempfile << CSV.generate_line(head)
    else
      raise 'Headers MUST be provided as an array'
    end
  end

  def add_row(row)
    if row.is_a?(Array)
      @tempfile << CSV.generate_line(row)
    else
      raise 'Row MUST be provided as an array'
    end
  end

  def export(filename='export.csv')
    @tempfile.fsync
    @tempfile.close
    @tempfile.rewind(@tempfile.path, Rails.root.join(filename))
  end
end