Chain of Responsibility

chain_of_responsibility.rb

# frozen_string_literal: true

class Handler
  attr_accessor :next_handler

  def initialize(next_handler = nil)
    @next_handler = next_handler
  end

  def handle(package)
    if do_handle package
      puts "Handled by #{self.class}"
    else
      return @next_handler.handle package if @next_handler
      puts 'No handlers available'
    end
  end
end

class SmallDomesticHandler < Handler
  def do_handle(package)
    return false unless package[:type] == :domestic
    return false if package[:weight] > 2
    return false if package[:length] > 30
    return false if package[:width] > 30
    return false if package[:height] > 15

    package[:price] = 4.25
    # @stamp_chain.handle package

    true
  end
end
class LargeDomesticHandler < Handler
  def do_handle(package)
    return false unless package[:type] == :domestic
    return false if package[:weight] > 5
    return false if package[:length] > 60
    return false if package[:width] > 30
    return false if package[:height] > 15

    package[:price] = 6.75

    true
  end
end
class EuropeanUnionHandler < Handler
  def do_handle(package)
    return false unless package[:type] == :european_union
    return false if package[:weight] > 10
    return false if package[:length] > 80
    return false if package[:width] > 60
    return false if package[:height] > 100

    package[:price] = 10.25

    true
  end
end
class InternationalHandler < Handler
  def do_handle(package)
    return false unless package[:type] == :international
    return false if package[:weight] > 70
    return false if package[:length] > 150
    return false if package[:width] > 60
    return false if package[:height] > 70

    package[:price] = 30

    true
  end
end
class SmallStampHandler < Handler
  def do_handle(package)
    loop do
      return false if package[:price] < 0.25
      package[:price] -= 0.25
      package[:stamps] ||= { 0.25 => 0, 0.5 => 0, 1 => 0 }
      package[:stamps][0.25] += 1
    end
    return false
  end
end
class MediumStampHandler < Handler
  def do_handle(package)
    loop do
      return false if package[:price] < 0.5
      package[:price] -= 0.5
      package[:stamps] ||= { 0.25 => 0, 0.5 => 0, 1 => 0 }
      package[:stamps][0.5] += 1
    end
    return false
  end
end
class LargeStampHandler < Handler
  def do_handle(package)
    loop do
      return false if package[:price] < 1
      package[:price] -= 1
      package[:stamps] ||= { 0.25 => 0, 0.5 => 0, 1 => 0 }
      package[:stamps][1] += 1
    end
    return false
  end
end


##
# Client
#

chain = SmallDomesticHandler.new(LargeDomesticHandler.new(EuropeanUnionHandler.new InternationalHandler.new))
stamp_chain = LargeStampHandler.new(MediumStampHandler.new SmallStampHandler.new)

package = {
  :weight => 1.5,
  :length => 26,
  :width => 30,
  :height => 15,
  :type => :domestic
}

puts package

chain.handle package
stamp_chain.handle package

puts "Stamped with #{package[:stamps].sort.collect { |k,v| "#{v} x €#{k}" unless v == 0 }.compact.join ', '}"