poppin_bottles.rb

#!/usr/bin/env ruby

class PoppinBottles

  def self.run
    loop do
      print "\nNumber of dollars to invest: $"
      input = gets.chomp
      begin
        dollars = Float(input)
      rescue
        puts "Error: '#{input}' is not a valid number"
        next
      end
      begin
        print_redemption_summary RedeemingCusomer.new dollars
      rescue => err
        puts "Error: #{err.message}"
      end
    end
  end

  private

  def self.print_redemption_summary(customer)
    puts "For their investment of $#{'%.02f' % customer.dollars_invested} the customer got a total of #{customer.total_bottles} #{customer.total_bottles == 1 ? 'bottle' : 'bottles'} of pop."
    puts "#{customer.bottles_purchased} #{customer.bottles_purchased == 1 ? 'bottle was' : 'bottles were'} purchased."
    puts "#{customer.bottles_from_bottle_redemption} #{customer.bottles_from_bottle_redemption == 1 ? 'bottle was' : 'bottles were'} gained through bottle recycling."
    puts "#{customer.bottles_from_cap_redemption} #{customer.bottles_from_cap_redemption == 1 ? 'bottle was' : 'bottles were'} gained through cap recycling."
    puts "The customer has #{customer.bottles} #{customer.bottles == 1 ? 'bottle' : 'bottles'} left over."
    puts "The customer has #{customer.caps} #{customer.caps == 1 ? 'cap' : 'caps'} left over."
    puts "The customer has $#{'%.02f' % customer.dollars} left over."
  end

end

class RedeemingStore

  @@bottle_purchase_price = 2.0

  @@redemption_rates = {
      bottles: 2,
      caps: 4
  }

  def self.bottle_purchase_price
    @@bottle_purchase_price
  end

  def self.redemption_rate(item)
    @@redemption_rates[item]
  end

end

class RedeemingCusomer

  attr_reader :dollars_invested, :bottles_purchased, :dollars

  def initialize(dollars)
    @dollars_invested = dollars.round(2)
    unless @dollars_invested > 0.0
      raise 'dollars must be greater than 0.00'
    end
    @bottles_purchased = (@dollars_invested / RedeemingStore::bottle_purchase_price).floor
    @dollars = @dollars_invested - @bottles_purchased * RedeemingStore::bottle_purchase_price
    @inventory = {
        bottles: @bottles_purchased,
        caps: @bottles_purchased
    }
    @bottles_from_redemption = {
        bottles: 0,
        caps: 0
    }
    redeem if can_redeem?
  end

  def total_bottles
    @bottles_purchased + @bottles_from_redemption[:bottles] + @bottles_from_redemption[:caps]
  end

  def bottles
    @inventory[:bottles]
  end

  def caps
    @inventory[:caps]
  end

  def bottles_from_bottle_redemption
    @bottles_from_redemption[:bottles]
  end

  def bottles_from_cap_redemption
    @bottles_from_redemption[:caps]
  end

  private

  def redeem
    redeem_items :bottles
    redeem_items :caps
    redeem if can_redeem?
  end

  def redeem_items(item)
    new_bottles = @inventory[item] / RedeemingStore::redemption_rate(item)
    @inventory[item] -= new_bottles * RedeemingStore::redemption_rate(item)
    @inventory[:bottles] += new_bottles
    @inventory[:caps] += new_bottles
    @bottles_from_redemption[item] += new_bottles
  end

  def can_redeem?
    @inventory[:bottles] >= RedeemingStore::redemption_rate(:bottles) || @inventory[:caps] >= RedeemingStore::redemption_rate(:caps)
  end

end

if __FILE__ == $PROGRAM_NAME
  PoppinBottles.run
end