"""
A craps simulation,
along the lines of the material
in Zelle's textook, chapter 9.

Jim Mahoney and the Python programming class
Oct 16 2008
GPL
"""

debugPrint = False

def d6(n):  
  """ Roll n 6-sided dice and return the sum. """  
  from random import randrange 
  sum = 0
  for i in range(n):
    sum = sum + randrange(1,7)
  return sum
  
def test_die_roll(die, low, high, dice_count=1):
  """ Return true if rolls of die(1) are between low and high.
      >>> test_die_roll(d6, 1, 6)
      True
      >>> test_die_roll(d6, 2, 12, 2)
      True
  """
  number_of_rolls = (high - low + 1) * 100
  for i in range(number_of_rolls):
    roll = die(dice_count)
    if roll < low:
      return False
    if roll > high:
      return False
  return True

def craps():
  """ Simulate one game of craps.  Return True for a win, False for a loss. """
  first_roll = d6(2)
  if debugPrint: print "first roll : ", first_roll
  if first_roll in [7, 11]:
    return True
  elif first_roll in [2, 3, 12]:
    return False
  else:
    while True:
      next_roll = d6(2)
      if debugPrint: print "next roll : ", next_roll
      if next_roll == first_roll:
        return True
      elif next_roll == 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 minmax_series(n_series, n_games):
  """ Return min and max found from count_wins(n_games) done n_series times. """
  highest = 0
  lowest = 2*n_games
  for i in range(n_series):
    n_wins = count_wins(n_games)
    if n_wins > highest:
      highest = n_wins
    if n_wins < lowest:
      lowest = n_wins
  return (lowest, highest)

def main():
  print "--- Estimated odds of winning at craps ---"
  n_games = input("How many games would you 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 "Estimated odds of winning: %.2f" % (float(n_wins)/n_games)
  print
  print "--- Estimated error ---"
  n_series = input("How many times would you like to repeat that series of %i games? " % n_games)
  (lowest, highest) = minmax_series(n_series, n_games)
  low_odds = (float(lowest)/n_games)
  hi_odds = (float(highest)/n_games)
  print "Lowest estimated odds: %.2f" % low_odds
  print "Highest estimated odds: %.2f" % hi_odds
  print "Error range = (high - low) = %.4f " % (hi_odds - low_odds)

if __name__ == "__main__":
  import doctest
  doctest.testmod()

main()