Refactor attempt following SRP

checking.rb

def do_bulk_creation # Controller action called from request
  prize = Prize.find_by_id(params[:code][:prize_id])
  codes = params[:code][:codes].split("\r\n").each{ |c| c.strip } 
  if bulk_creation_valid?(prize, codes)
    perform_bulk_creation(prize, codes) 
  else
    set_bulk_creation_error(prize, codes)
    @bulk = Code.new(params[:code])
    render :action => :bulk_create
  end
end

private

def bulk_creation_valid?(prize, codes)
  !prize.nil? && prize.digital && codes.size > 1
end

def perform_bulk_creation(prize, codes)
  codes.each do |code|
    prize.codes.create(code: code)
  end
  flash[:notice] = "Created #{codes.size} codes for prize #{prize.description}"
  redirect_to :action => :index
end

def set_bulk_creation_error(prize, codes)
  flash[:error] = if prize.nil?
                    "You must select a prize"
                  elsif !prize.digital
                    "You can only add codes for digital prizes"
                  elsif codes.size < 1
                    "You must enter some codes"
                  end
end

def bulk_creation_valid?(prize, codes)
  if prize.nil?
    flash[:error] = "You must select a prize"
  elsif !prize.digital
    flash[:error] = "You can only add codes for digital prizes"
  elsif codes.size < 1
    flash[:error] = "You must enter some codes"
  end
  flash[:error].nil?
end