#!/usr/bin/python

## Copyright (C) 2004 Crutcher Dunnavant <crutcher@gmail.com>

## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.

## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.

## You should have received a copy of the GNU General Public License
## along with this program; if not, write to the Free Software
## Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

#!-- ================================================================== --#

# Pattern: a(b){3,4}c
# Key:
#    (X) := 'if (X)'
#    [X] := 'do (X)'
# Graph:
#                    +--(c0<4)--+
#                    |          |
#                    v          |
#                               |
# s0 -('a')-> s1 -> s2 -('b')-> s3 -(c0>=2)-> s4 -('c')-> s5
#           [c0=0]            [s0++]

NORMAL=0
LOOP_INIT=1
LOOP_SENTRY=2

regex = {
	'accept-states': [5],

	'counters' : 1,

	'states': [
		# State 0
		{ 'type': NORMAL, 'accept': 0,
		  'epsilon-transitions': [],
		  'test-transitions': [ ('a', 1), ] },

		# State 1
		{ 'type': LOOP_INIT, 'counter': 0,
		  'next-state': 2 },
		
		# State 2
		{ 'type': NORMAL, 'accept': 0,
		  'epsilon-transitions': [],
		  'test-transitions': [('b', 3)] },

		# State 3
		{ 'type': LOOP_SENTRY, 'counter': 0,
		  'min': 3, 'max': 4,
		  'loop-next': 2,
		  'loop-break': 4 },
		
		# State 4
		{ 'type': NORMAL, 'accept': 0,
		  'epsilon-transitions': [],
		  'test-transitions': [('c', 5)] },

		# State 5
		{ 'type': NORMAL, 'accept': 1,
		  'epsilon-transitions': [],
		  'test-transitions': [] },
	],
}

#!-- ================================================================== --#

class StateTable:
	def __init__(self):
		self.table = []

	def addState(self, i, state):
		if len(self.table) > i:
			step_table = self.table[i]
		elif len(self.table) == i:
			step_table = []
			self.table.append(step_table)
		else:
			raise ValueException, "Invalid step %d" % i

		if state not in step_table:
			print "\t\tadding state (%d, %s)" % (i, state)
			step_table.append(state)
		else:
			print "\t\tstate (%d, %d) already present" \
				% (i, state)

	def __str__(self):
		s = ""
		for i in range(len(self.table)):
			s = s + ("State %d: %s\n" \
				 % (i, str(self.table[i])))
		return s

#!-- ================================================================== --#

def process_regex(regex, input):
	print "Processing Regex on input \"%s\"" % input
	st = StateTable()

	# i == the number of characters of input consumed so far
	i = 0

	init_counters = map(lambda x: 0, range(regex['counters']))

	# We start at state 0, with no characters consumed.
	st.addState(i, (0, init_counters))

	match = None

	while i < len(input) and len(st.table) > i:
		next_char = input[i]
		print "step %d, next_char = '%s'" % (i, next_char)

		for (j, counters) in st.table[i]:
			print "\tvisiting", (i, (j, counters))

			state = regex['states'][j]

			if state['type'] == NORMAL:
				if state['accept']:
					match = input[:i]

				for k in state['epsilon-transitions']:
					st.addState(i, (k, counters))
				for (t, k) in state['test-transitions']:
					if next_char == t:
						st.addState \
							(i + 1, (k, counters))

			elif state['type'] == LOOP_INIT:
				l = counters[:]
				l[state['counter']] = 0

				st.addState \
					(i, (state['next-state'], l))

			elif state['type'] == LOOP_SENTRY:
				l = counters[:]
				c = l[state['counter']]
				c += 1
				l[state['counter']] = c

				if state['min'] < 0 or c >= state['min']:
					st.addState \
						(i, (state['loop-break'], l))

				if state['max'] < 0 or c < state['max']:
					st.addState \
						(i, (state['loop-next'], l))

		i = i + 1

	# If we ate all the input, scan the last state set for accepters.
	if i == len(input) and len(st.table) > i:
		for (j, counters) in st.table[i]:
			state = regex['states'][j]

			if state['type'] == NORMAL:
				if state['accept']:
					match = input[:i]

	print
	print "State Table Dump:"
	print st

	return match
			

#!-- ================================================================== --#

import sys

def main():
	if len(sys.argv) > 1:
		input = sys.argv[1]
	else:
		input = "abbbc monkey"

	match = process_regex(regex, input)
	if match:
		print "matched \"%s\"" % match
	else:
		print "no match"

if __name__ == "__main__":
	main()