Simple simulation for my blog post

simulation.rb

SIMULATION_LENGTH=24 * 60 * 60 # one day
ARRIVAL_RATE="random"
ARRIVAL_NUMBER= 240
OVERALL_WIP=8

class Simulation

  class Car
		attr_accessor :enter_time
		attr_accessor :leave_time

		def initialize(enter_time)
			@enter_time = enter_time
		end

		def to_s
			"car_#{@enter_time}"
		end
	end

  def initialize(simulation_length, arrival_rate, arrival_number, overall_wip)
		@order_queue = []
		@order_station = {:time => 20}
		@pay_queue = []
		@pay_station = {:time => 30}
		@collect_queue = []
		@collect_station = {:time => 40}
		@done = []

		@simulation_length = simulation_length
		@arrival_rate = arrival_rate
		@arrival_number = arrival_number
		@overall_wip = overall_wip
	end

	def start
		(0..@simulation_length).each do |second|

			if @arrival_rate.eql?("random")
				new_car_should_arrive = (rand(@arrival_number) == 0)
			else
				new_car_should_arrive = (second % @arrival_number == 0)
			end

			if new_car_should_arrive
				car = Car.new(second)
				@order_queue << car
		  end

			if @order_station[:car]
				@order_station[:time] += 1
				if @order_station[:time] == 20
					# puts "#{second} order done with order: #{@order_station[:car]}"
					@pay_queue << @order_station[:car]
					@order_station[:car] = nil
				end
			end

			if @order_station[:car] == nil && wip_allows_it?
				if !@order_queue.empty?
					@order_station[:car] = @order_queue.shift
					@order_station[:time] = 0
				end
			end

			if @pay_station[:car]
				@pay_station[:time] += 1
				if @pay_station[:time] == 30
					# puts "#{second} pay done with order: #{@pay_station[:car]}"
					@collect_queue << @pay_station[:car]
					@pay_station[:car] = nil
				end
			end

			if @pay_station[:car] == nil
				if !@pay_queue.empty?
					@pay_station[:car] = @pay_queue.shift
					@pay_station[:time] = 0
				end
			end

			if @collect_station[:car]
				@collect_station[:time] += 1
				if @collect_station[:time] == 40
					# puts "#{second} collect done with order: #{@collect_station[:car]}"
					@collect_station[:car].leave_time = second
					@done << @collect_station[:car]
					@collect_station[:car] = nil

					# -- duplication
					if @order_station[:car] == nil && wip_allows_it?
						if !@order_queue.empty?
							@order_station[:car] = @order_queue.shift
							@order_station[:time] = 0
						end
					end
					# -- duplication
				end
			end

			if @collect_station[:car] == nil
				if !@collect_queue.empty?
					@collect_station[:car] = @collect_queue.shift
					@collect_station[:time] = 0
				end
			end
		end

		#print_done_content
		print_lead_time_distribution
		print_throughput
	end

	private
	def wip_allows_it?
		# order queue is not part of the wip (it is ~infinite)
		current_wip = @pay_queue.size
		current_wip += @collect_queue.size
		current_wip += 1 if @order_station[:car]
		current_wip += 1 if @pay_station[:car]
		current_wip += 1 if @collect_station[:car]

		current_wip < @overall_wip
	end

	def print_done_content
		@done.each do |car|
			puts "#{car.enter_time} -> #{car.leave_time - car.enter_time}"
		end
	end

	def print_lead_time_distribution
		distribution = {}
		@done.each do |car|
			lead_time = car.leave_time - car.enter_time
			if distribution[lead_time]
				distribution[lead_time] += 1
			else
				distribution[lead_time] = 1
			end
		end

		distribution.sort_by {|k| k[0].to_i }.each do |key,value|
			puts "#{key},#{value}"
		end

		# puts "longest lead time: #{distribution.sort_by {|k| k[0].to_i }.last[0]}"
	end

	def print_throughput
		throughtput_all = @done.size
		puts "throughtput: #{throughtput_all}"
		throughtput_per_minute = ((@simulation_length / 60.0) / throughtput_all)
		puts "throughtput per minute: #{throughtput_per_minute}"
	end
end

# main
Simulation.new(SIMULATION_LENGTH, ARRIVAL_RATE, ARRIVAL_NUMBER, OVERALL_WIP).start