#app/admin/posts.rb
ActiveAdmin.register Post do
  config.xlsx_builder.i18n_scope = [:active_record, :models, :posts]
end

#app/admin/posts.rb
ActiveAdmin.register Post do
  config.xlsx_builder.column('author_name') do |resource|
    resource.author.name
  end
end

#app/admin/posts.rb
ActiveAdmin.register Post do
  config.xlsx_builder.header_style = { :bg_color => 'FF0000',
                                       :fg_color => 'FF' }
end

#app/admin/posts.rb
ActiveAdmin.register Post do
  config.xlsx_builder.delete_columns :id, :created_at, :updated_at
end

ActiveAdmin.register Post do

  # i18n_scope and header style are set via options
  xlsx(:i18n_scope => [:active_admin, :axlsx, :post],
       :header_style => {:bg_color => 'FF0000', :fg_color => 'FF' }) do

    # Specify that you want to white list column output.
    # whitelist

    # Do not serialize the header, only output data.
    # skip_header

    # deleting columns from the report
    delete_columns :id, :created_at, :updated_at

    # adding a column to the report
    column(:author) { |resource| "#{resource.author.first_name} #{resource.author.last_name}" }

    # creating a chart and inserting additional data with after_filter
    after_filter { |sheet|
      sheet.add_row []
      sheet.add_row ['Author Name', 'Number of Posts']
      data = []
      labels = []
      User.all.each do |user|
        data << user.posts.size
        labels << "#{user.first_name} #{user.last_name}"
        sheet.add_row [labels.last, data.last]
      end
      chart_color =  %w(88F700 279CAC B2A200 FD66A3 F20062 C8BA2B 67E6F8 DFFDB9 FFE800 B6F0F8)
      sheet.add_chart(::Axlsx::Pie3DChart, :title => "post by author") do |chart|
        chart.add_series :data => data, :labels => labels, :colors => chart_color
        chart.start_at 4, 0
        chart.end_at 7, 20
      end
    }

    # iserting data with before_filter
    before_filter do |sheet|
      sheet.add_row ['Created', Time.zone.now]
      sheet.add_row []
    end
  end
end