checkout-ch-2.rb

class CheckoutMachine
  PRODUCT_LIST = {
    123 => { product: :chips,      price: 200  },
    456 => { product: :salsa,      price: 100  },
    789 => { product: :wine,       price: 1000 },
    111 => { product: :cigarettes, price: 550  },
    000 => { product: :bonus_card, price: nil  }
  }

  def initialize
    @balance ||= Balance.new
    @counter ||= Counter.new
  end

  def scan(sku)
    price = Scanner.scan(sku)

    balance.add(price)
    counter.increment(sku)
    Discounter.apply_any_discounts(
      sku:     sku,
      counter: counter,
      balance: balance
    )
  end

  def total
    balance.total
  end

  private

  attr_reader :balance, :counter, :discounter
end

# Scans items and returns item price from PriceList
class Scanner
  def self.scan(sku)
    CheckoutMachine::PRODUCT_LIST[sku][:price]
  end
end

# Keeps track of what has been scanned
class Counter
  def increment(sku)
    products_and_counts[sku_to_product(sku)] += 1
  end

  def product_count(product)
    @products_and_counts[product]
  end

  private

  def products_and_counts
    @products_and_counts ||= CheckoutMachine::PRODUCT_LIST
      .each_with_object({}) { |product, memo| memo[product[1][:product]] = 0 }
  end

  def sku_to_product(sku)
    CheckoutMachine::PRODUCT_LIST[sku][:product]
  end
end

# Maintains state of total
class Balance
  attr_accessor :total

  def initialize
    @total = 0
  end

  def add(amount)
    self.total += amount.to_i
  end

  def subtract(amount)
    self.total -= amount.to_i
  end
end

class Discounter
  def self.apply_any_discounts(sku:, counter:, balance:)
    @@sku, @@counter, @@balance = sku, counter, balance

    apply_bonus_card_discounts if bonus_card_scanned?
  end

  private

  def self.apply_bonus_card_discounts
    @@balance.subtract(salsa_discount)
    @@balance.subtract(chips_discount)
  end

  def self.salsa_discount
    50 * @@counter.product_count(:salsa)
  end

  def self.chips_discount
    200 * (@@counter.product_count(:chips)/3).floor
  end

  def self.bonus_card_scanned?
    CheckoutMachine::PRODUCT_LIST[@@sku][:product] == :bonus_card
  end
end