#!/bin/python

################################################################################
#
#	ContextFreeGrammar- 3.23.09 - Joe Mariglio <www.joemariglio.com>
#
#===============================================================================
#
#	produces cfg's using a grammar file with the format
#	'rule' -> 'expansion_0' | 'expansion_1' ... | 'expansion_n'
#	currently prints to stdout but this could change...
#
################################################################################

import sys, string, os.path, random, array, re

contextRules = {}

def addRule(rule, expansion):
	if rule in contextRules.keys():
		contextRules[rule].append(expansion)
	else:
		contextRules[rule] = [expansion]
def dump(rule):
	return rule + " -> " + str(contextRules[rule])
def iter_expand(current):
	if current not in contextRules.keys():
		yield current
	else:
		toExpand = random.choice(contextRules[current]).split(" ")
		for item in toExpand:
			yield expand(item)
def expand(current):
	return [i for i in iter_expand(current)]
def iter_flatten(iterable):
	it = iter(iterable)
	for e in it:
		if isinstance(e, (list, tuple)):
			for f in iter_flatten(e):
			        yield f
		else:
			yield e
def flatten(signal):
	return [i for i in iter_flatten(signal)]
def renderExpansion(expansion):
	out = ""
	expansion = flatten(expansion)
	for item in expansion:
		out += item + " "
	return out
def parseFile(path):
	comment = re.compile(r'#.*$')
	rule = re.compile(r'(\w+) *-> *(.*)')
	exps = re.compile(r'\s*\|\s*')
	infile = open(path, "r")
	lines = infile.readlines()
	infile.close()
	for line in lines:
		line = comment.sub("", line)
		m = rule.search(line)
		if m:
			key = m.group(1)
			value = m.group(2)
			values = exps.split(m.group(2))
			for value in values:
				addRule(key, value)
def main(argv):
	if len(sys.argv) == 2:
		path = sys.argv[1]
		parseFile(path)
		print(renderExpansion(expand("S")))
	else:
		print("wha?")
if __name__ == '__main__':
	import sys, string, os.path, random, array, re
	main(sys.argv[1:])