class Array

# File lib/to_xls-rails.rb, line 5
def to_xls(options = {}, &block)

  return '' if self.empty? && options[:prepend].blank?

  columns = []
  options.reverse_merge!(:header => true)

  xls_report = StringIO.new

  Spreadsheet.client_encoding = options[:client_encoding] || "UTF-8"

  book = Spreadsheet::Workbook.new
  sheet = book.create_worksheet

  if options[:only]
    columns = Array(options[:only]).map(&:to_sym)
  elsif !self.empty?
    if self.first.is_a? Hash
      columns = self.first.keys.map(&:to_sym) - Array(options[:except]).map(&:to_sym)
    else
      columns = self.first.attributes.keys.map(&:to_sym) - Array(options[:except]).map(&:to_sym)
    end
  end

  return '' if columns.empty? && options[:prepend].blank?

  sheet_index = 0

  unless options[:prepend].blank?
    options[:prepend].each do |array|
      sheet.row(sheet_index).concat(array)
      sheet_index += 1
    end
  end

  if options[:header]
    sheet.row(sheet_index).concat(options[:header_columns].blank? ? columns.map(&:to_s).map(&:humanize) : options[:header_columns])
    sheet_index += 1
  end

  if options[:column_width]
    options[:column_width].each_index {|index| sheet.column(index).width = options[:column_width][index]}
  end

  self.each_with_index do |obj, index|
    if block
      sheet.row(sheet_index).replace(columns.map { |column| block.call(column, obj.is_a?(Hash) ? obj[column] : obj.send(column), index) })
    else
      sheet.row(sheet_index).replace(columns.map { |column| obj.is_a?(Hash) ? obj[column] : obj.send(column) })
    end
    sheet_index += 1
  end

  unless options[:append].blank?
    options[:append].each do |array|
      sheet.row(sheet_index).concat(array)
      sheet_index += 1
    end
  end

  book.write(xls_report)

  xls_report.string
end