"""
 craps_2010.py

 Craps simulation, worked out in class Oct 14 2010
 Jim Mahoney, GPL
"""

debugPrint = False

def d6(n):
  """ Return total from rolling n 6 sided dice. """
  from random import randrange
  total = 0
  for i in range(n):
    total = total + randrange(1,7)
  return total

def test_dice(n_dice, number_of_times):
  """ Make sure d6() is doing what it should.
      >>> test_dice(2, 100)
      True
  """
  low = n_dice
  high = 6 * n_dice
  for i in range(number_of_times):
    roll = d6(n_dice)
    if roll < low:
      return False
    if roll > high:
      return False
  return True

def craps():
  """ Simulate one round of craps.  Return True for win. """
  roll1 = d6(2)
  if debugPrint: print " debug: roll1 = ", roll1
  if roll1 == 7 or roll1 == 11:
    return True
  elif roll1 == 2 or roll1 == 3 or roll1 == 12:
    return False
  else:
    while True:
      rolln = d6(2)
      if debugPrint: print " debug: rolln = ", rolln
      if rolln == roll1:
        return True
      elif rolln == 7:
        return False

def count_wins(n_games):
  """ Return number of wins when playing n_games of craps. """
  wins = 0
  for i in range(n_games):
    if craps():
      wins = wins + 1
  return wins

def simulate_series(n_games, n_times):
  """ Return (high, low) probability of wins in n_games over n_times. """
  highest = -1
  lowest = 1.1
  for i in range(n_times):
    n_wins = count_wins(n_games)
    prob = float(n_wins)/n_games
    if prob > highest:
      highest = prob
    if prob < lowest:
      lowest = prob
  return (highest, lowest)

def main():
  """ Simulate craps, and report odds. """
  print "--- Estimated odds of winning at craps ---"
  n_games = input("How many games would you like to simulate? ")
  print "Simulating %i games ..." % n_games
  n_wins = count_wins(n_games)
  print "done."
  print "Number of simulated wins : %i" % n_wins
  print "Odds of winning : %.3f" % (float(n_wins) / n_games)
  #
  print "--- Estimated error ---"
  n_times = input("How many times would you like to repeat that series of %i games? " % n_games)
  print "Simulating %i series of %i games ..." % (n_times, n_games)
  (high_prob, low_prob) = simulate_series(n_games, n_times)
  print "done."
  print "Lowest estimated odds = %.3f" % low_prob
  print "Highest estimated odds = %.3f" % high_prob
  print "Error range = (high-low) = %.3f" % (high_prob - low_prob)

if __name__ == "__main__":
  from doctest import testmod
  testmod()
  main()