purchases_controller.rb

class PurchasesController < ApplicationController

  def create
    purchase_service = service_lookup[params[:purchase_type]]
    item_class = item_class_lookup[params[:purchase_type]]
    item = item_class.find_by(name: params[:item_name])

    purchase_service.new(current_student, item).purchase
    redirect_to map_path
  end

  private
  def service_lookup
    {
      trip: Purchase::Trip,
      souvenir: Purchase::Souvenir
    }.with_indifferent_access
  end

  def item_class_lookup
    {
      trip: Location,
      souvenir: Souvenir
    }.with_indifferent_access
  end
end