Generate CSV data

csv_generator.rb

class CsvGenerator
  def initialize(file_name, collection)
    @file_name = file_name
    @collection = collection
    @columns = []
  end

  def register_column(column_header, &block)
    columns << Column.new(column_header, block)
  end

  def to_csv
    CSV.open(file_name, 'w') do |csv|
      csv << build_header
      collection.each { |record| csv << build_row(record) }
    end
  end

  private

  attr_reader :file_name, :collection
  attr_accessor :columns

  def build_header
    columns.map(&:header)
  end

  def build_row(record)
    columns.map { |column| record.instance_exec(&column.block) }
  end

  class Column < Struct.new(:header, :block); end
end

invite_codes_report.rb

require 'csv'

class InviteCodesReport
  def to_csv(file_name)
    CsvGenerator.new("#{file_name}.csv", invite_codes).tap do |generator|
      generator.register_column("Invite Code") { code }
      generator.register_column("Invite Code Created At") { created_at }
      generator.register_column("Care Provider Name") { care_provider.name }
      generator.register_column("Care Provider ID") { care_provider.id }
    end.to_csv
  end

  private

  def invite_codes
    InviteCode.where(id: invite_code_ids).includes(care_provider: :address)
  end
end