WAITING = "waiting"
IN_TRANSIT = "in transit"
ARRIVED = "arrived"

class Passenger:
	"""Passengers on an elevator.

	Instances keep track of the source and destination floor numbers
	as well as amount of time spent waiting."""

	error = "Error in Passenger class"

	count = 0
	wait = []
	transit = []

	def __init__(self, origin, destination):
		"Create passenger going from origin to destination floor."
		self.origin = origin
		self.destination = destination
		self.timeWait = 0
		self.timeTransit = 0
		self.state = WAITING
		Passenger.count += 1
		#print "Passenger", origin, destination

	def tick(self):
		"Increment wait time."
		if self.state is WAITING:
			self.timeWait += 1
		elif self.state is IN_TRANSIT:
			self.timeTransit += 1
		elif self.state is not ARRIVED:
			raise (Passenger.error,
				"unknown passenger state: %s" % str(self.state))

	def embark(self):
		"Enter an elevator."
		assert(self.state == WAITING)
		self.state = IN_TRANSIT
		#print "Boarded", self.origin, self

	def disembark(self):
		"Exit an elevator."
		self.state = ARRIVED
		Passenger.wait.append(self.timeWait)
		Passenger.transit.append(self.timeTransit)
		#print "Disembarked", self.destination, self

def waitTime():
	"""Return average and standard deviation of time spent waiting
	for an elevator to arrive."""
	import statistics
	return statistics.average(Passenger.wait)

def transitTime():
	"""Return average and standard deviation of time spent waiting
	for an elevator to go from origin to destination floor."""
	import statistics
	return statistics.average(Passenger.transit)

def count():
	"""Return number of passengers for whom we have statistics."""
	assert(len(Passenger.wait) == len(Passenger.transit))
	return len(Passenger.wait)

def totalCount():
	"""Return total number of passengers created."""
	return Passenger.count

if __name__ == "__main__":
	import random
	n = random.randrange(10, 20)
	people = []
	for i in range(n):
		people.append(Passenger(1, 10))
	while people:
		remain = []
		for p in people:
			p.tick()
			if p.state is WAITING:
				if random.randrange(10) < 2:
					p.embark()
				remain.append(p)
			elif p.state is IN_TRANSIT:
				if random.randrange(10) < 1:
					p.disembark()
				else:
					remain.append(p)
		people = remain
	print count(), "passengers"
	print "average wait time: %f (%f)" % waitTime()
	print "average transit time: %f (%f)" % transitTime()