# L-13 MCS 260 Wed 10 Feb 2010 : simuwait.py

# simulate processing of jobs to compute waiting times

def form(L):
   """
   Given in L a list of floats, returns a string
   that contains the floats in %.2f format.
   """
   s = "[ " + '%.2f' % L[0]
   for i in range(1,len(L)):
      s += ', ' + '%.2f' % L[i]
   return s + ' ]'

def ask():
   """
   Prompts the user for the parameters of the simulation:
     n : the number of jobs,
     T : the length of time,
     mu : the average time per job,
     sg : the deviation in procesing times.
   Returns the tuple (n,T,mu,sg).
   """
   n = input('number of jobs : ')
   T = input('length of time : ')
   mu = input(' mean time/job : ')
   sg = input(' deviation/job : ')
   return (n,T,mu,sg)

def make_jobs(n,T,mu,sg):
   """
   Given the parameters of the simulation,
   returns tuple of two lists with arrival
   and process times for each job.
   """
   A = [] # arrival times of jobs
   P = [] # time to process each job
   import random
   for i in range(0,n):
      A.append(random.uniform(0,T))
      P.append(random.gauss(mu,sg))
   A.sort()
   return (A,P)

def simulate(A,P):
   """
   Given a list of arrivals and process times,
   returns a list of wait times for each job.
   """
   W = [0]  # no wait for first job
   b = P[0] # time busy for job
   for i in range(1,len(A)):
      t = A[i] - A[i-1] # elapsed time
      if t >= b:        # idle printer
         b = 0          # no wait
      else:             # busy printer
         b = b - t      # wait 
      W.append(b)       # store wait
      b = b + P[i]      # update busy
   return W

def avgdev(W):
   """
   Returns a tuple with the average and 
   standard deviation of the numbers in W.
   """
   import math
   avg = sum(W)/len(W)
   dev = 0
   for i in range(0,len(W)):
      dev += (W[i] - avg)**2
   dev = math.sqrt(dev)
   return (avg,dev)

def main():
   (n,T,mu,sg) = ask()
   (A,P) = make_jobs(n,T,mu,sg)
   print ' arrivals : ' + form(A)
   print 'job times : ' + form(P)
   W = simulate(A,P)
   print 'wait times : ' + form(W)
   (a,d) = avgdev(W)
   print 'average wait : %.2f' % a
   print '   deviation : %.2f' % d

main()