You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: placement_export_csv_service.rb
    path of file: ./repos/casa/app/services
    
    the code of the file until where you have to start completion: require "csv"

class PlacementExportCsvService
  
    
  def perform
    placements = fetch_placements

    CSV.generate(headers: true) do |csv|
      csv << full_data.keys.map(&:to_s).map(&:titleize)
      placements.decorate.each do |placement|
        csv << full_data(placement).values
      end
    end
  end