from SimPy.Simulation import *
import random
from math import sqrt

AISLES = 6         # Number of open aisles
ITEMTIME = 0.1     # Time to ring up one item
AVGITEMS = 20      # Average number of items purchased
CLOSING = 60*12    # Minutes from store open to store close
AVGCUST = 1500     # Average number of daily customers
RUNS = 8           # Number of times to run the simulation
SEED = 111333555   # seed value for random numbers

class Customer(Process):
    def __init__(self):
        Process.__init__(self)
        # Randomly pick how many items this customer is buying
        self.items = 1 + int(random.expovariate(1.0/AVGITEMS))
    def checkout(self):
        start = now()           # Customer decides to check out
        yield request, self, checkout_aisle
        at_checkout = now()     # Customer gets to front of line
        waittime.tally(at_checkout-start)
        yield hold, self, self.items*ITEMTIME
        leaving = now()         # Customer completes purchase
        checkouttime.tally(leaving-at_checkout)
        yield release, self, checkout_aisle

class Customer_Factory(Process):
    def run(self):
        while 1:
            c = Customer()
            activate(c, c.checkout())
            arrival = random.expovariate(float(AVGCUST)/CLOSING)
            yield hold, self, arrival

class Monitor2(Monitor):
    def __init__(self):
        Monitor.__init__(self)
        self.min, self.max = (int(2**31-1),0)
    def tally(self, x):
        self.observe(x)
        self.min = min(self.min, x)
        self.max = max(self.max, x)

random.seed(SEED)
print 'Market'
for run in range(RUNS):
    waittime = Monitor2()
    checkouttime = Monitor2()
    checkout_aisle = Resource(AISLES)
    initialize()
    cf = Customer_Factory()
    activate(cf, cf.run(), 0.0)
    simulate(until=CLOSING)

    print "Waiting time average: %.1f" % waittime.mean(), \
          "(std dev %.1f, maximum %.1f)" % (sqrt(waittime.var()),waittime.max)

print 'AISLES:', AISLES, '  ITEM TIME:', ITEMTIME
