import math
import itertools
import argparse
from abc import abstractmethod
from collections import deque
from typing import Iterator, Optional


class ParsingError(Exception):
	pass


class Token:
	"""Abstract base class representing a single item of a regular expressions."""
	# is the Token mandatory, or can it be omitted
	is_skippable = False

	@abstractmethod
	def list_first(self) -> Iterator[int]:
		"""List all possible string positions the token can start with."""
		pass

	@abstractmethod
	def list_last(self) -> Iterator[int]:
		"""List all possible string positions the token can end with."""
		pass

	@abstractmethod
	def list_neighbours(self) -> Iterator[tuple[int, int]]:
		"""List positions of all possibly neighbouring subtokens."""
		pass


class Lambda(Token):
	"""An empty string, useful as an `Alternative`."""
	is_skippable = True

	def list_first(self):
		yield from []

	def list_last(self):
		yield from []

	def list_neighbours(self):
		yield from []


class Symbol(Token):
	"""A regular letter or any other symbol without a special function."""
	def __init__(self, position: int, value: str):
		self.position = position
		self.value = value

	def list_first(self):
		yield self.position

	def list_last(self):
		yield self.position

	def list_neighbours(self):
		yield from []

	def __str__(self):
		return self.value


class Asterisk(Token):
	"""A unary operator specifying its content to occur zero or more times."""
	is_skippable = True

	def __init__(self, content: Token):
		self.content = content

	def list_first(self):
		yield from self.content.list_first()

	def list_last(self):
		yield from self.content.list_last()

	def list_neighbours(self):
		yield from self.content.list_neighbours()
		for x in self.list_last():
			for y in self.list_first():
				yield (x, y)

	def __str__(self):
		return str(self.content) + "*"


class Alternative(Token):
	"""An operator with a variable number of arguments, specifying exchangeable alternatives."""
	def __init__(self, content: list[Token]):
		""":raises ParsingError: raised on an empty variant. That is an AlternativeSeparator surrounded by no other Tokens."""
		self.variants = []
		subsequence = []

		for token in content:
			if isinstance(token, AlternativeSeparator):
				if not subsequence:
					raise ParsingError("Found an empty Alternative variant.")
				self.variants.append(Chain(subsequence))
				subsequence = []
			else:
				subsequence.append(token)
		
		if not subsequence:
				raise ParsingError("Found an empty Alternative variant.")
		self.variants.append(Chain(subsequence))
		

	def list_first(self):
		for x in self.variants:
			yield from x.list_first()

	def list_last(self):
		for x in self.variants:
			yield from x.list_last()
	
	def list_neighbours(self):
		for x in self.variants:
			yield from x.list_neighbours()

	@property
	def is_skippable(self):
		return any(x.is_skippable for x in self.variants)

class AlternativeSeparator:
	"""A special token to temporarily separate Alternative variants. Removed in the Alternative constructor."""
	pass

class Chain(Token):
	"""An operator expressing a concatenation of its content Tokens."""
	def __init__(self, content: list[Token]):
		self.content = content

	def list_first(self):
		for token in self.content:
			yield from token.list_first()
			if not token.is_skippable:
				break

	def list_last(self):
		for token in reversed(self.content):
			yield from token.list_last()
			if not token.is_skippable:
				break

	def list_neighbours(self):
		previous = []
		for token in self.content:
			for t in previous:
				for x in t.list_last():
					for y in token.list_first():
						yield (x, y)
			yield from token.list_neighbours()

			if token.is_skippable:
				previous.append(token)
			else:
				previous = [token]

	@property
	def is_skippable(self):
		return all(x.is_skippable for x in self.content)

	def __str__(self):
		return "(" + "".join(str(x) for x in self.content) + ")"


def find_closing_parenthesis(pattern: str, pos: int) -> int:
	"""Given an opening parenthesis, find the closing one.
	
	:param pattern: the regexp pattern
	:param pos: the opening parenthesis position
	:return: a position of the matching closing parenthesis
	:raises AssertionError: on an incorrect call, if there is not an opening parenthesis at `pos`
	:raises ParsingError: on a malformed pattern with no matching parenthesis"""
	assert pattern[pos] == "("
	counter = 0

	for (i, c) in enumerate(pattern[pos:]):
		if c == "(":
			counter += 1
		elif c == ")":
			counter -= 1
		if counter == 0:
			return pos+i

	raise ParsingError(f'A closing parenthesis not found. Pattern: "{pattern}", position: {pos}')


def parse(pattern: str, offset: int=0) -> Token:
	"""Recursively parse the pattern into a Token tree.

	:param pattern: the regexp string
	:param offset: where the `pattern` starts in the original pattern, to record correct global token positions in the subcalls
	:return: a token sequence, wrapped in a Chain or an Alternative"""
	res = []
	is_alternative = False

	i = 0
	while i < len(pattern):
		c = pattern[i]
		if c == "(":
			j = find_closing_parenthesis(pattern, i)
			inner_content = parse(pattern[i+1:j], offset+i+1)
			res.append(inner_content)
			i = j+1
		elif c == "*":
			try:
				token = res.pop()
			except IndexError as e:
				raise ParsingError(f'The asterisk operator is missing an argument. Pattern: "{pattern}", position {i}')
			res.append(Asterisk(token))
			i += 1
		elif c == ")":
			raise ParsingError(f'An opening parenthesis not found. Pattern: "{pattern}", position: {i}')
		elif c == "|" or c == "+":
			is_alternative = True
			res.append(AlternativeSeparator())
			i += 1
		elif c == "_":
			res.append(Lambda())
			i += 1
		else:
			res.append(Symbol(i+offset, c))
			i += 1

	if is_alternative:
		return Alternative(res)
	else:
		return Chain(res)


def print_dfa(dfa: "RegexpDFA", label: str=""):
	"""Utility function for printing automatons in a readable format."""
	n = len(dfa.alphabet_index)
	print(label)
	for i in range(0, len(dfa.rules), n):
		print(i//n, dfa.rules[i:i+n])
	print(dfa.end_states)


class Regexp:
	def __init__(self, pattern: str):
		"""Parse a pattern string into a sequence of Tokens and build a non-deterministic finite automaton from them."""
		r = parse(pattern)
		# (state, symbol): {state1, ...}
		rules = dict()
		alphabet = set()

		# record possible starting symbols
		for i in r.list_first():
			c = pattern[i]
			alphabet.add(c)
			key = (-1, c)
			if key not in rules:
				rules[key] = set()
			rules[key].add(i)

		# record all pairs of symbols that can immediately follow each other
		for (i, j) in r.list_neighbours():
			c = pattern[j]
			alphabet.add(c)
			key = (i, c)
			if key not in rules:
				rules[key] = set()
			rules[key].add(j)

		# record possible last symbols and mark them as accepting states
		end_states = set(r.list_last())
		if r.is_skippable:
			end_states.add(-1)

		self.rules = rules
		self.end_states = end_states
		self.alphabet = alphabet

	def match(self, s: str) -> bool:
		"""Decide if a string matches the regexp.
		
		:param s: an input string"""
		current = {-1}

		for c in s:
			new_state = set()
			for st in current:
				key = (st, c)
				if key in self.rules:
					new_state.update(self.rules[key])
			current = new_state

		return any(st in self.end_states for st in current)

	def determinize(self) -> "RegexpDFA":
		"""Convert the non-deterministic finite automaton into a deterministic one."""
		alphabet_index = {c: i for (i, c) in enumerate(sorted(self.alphabet))}
		n = len(alphabet_index)
		compact_rules = [-1] * n
		end_states = {0} if -1 in self.end_states else set()

		index = {(-1,): 0}
		stack = [(-1,)]
		# explore all possible state sets the NFA can visit
		while stack:
			multistate = stack.pop()
			new_rules = dict()
			
			# collect possible target states
			for ((st, c), target) in filter(lambda item: item[0][0] in multistate, self.rules.items()):
				if c not in new_rules:
					new_rules[c] = set()
				new_rules[c].update(target)
			
			# map the state sets to integer labels and record them in a single dimensional rules list
			for (c, target_set) in new_rules.items():
				target_tup = tuple(sorted(target_set))
				if target_tup not in index:
					new_target = len(index)
					index[target_tup] = new_target
					compact_rules.extend([-1] * n)
					stack.append(target_tup)
				compact_rules[index[multistate]*n + alphabet_index[c]] = index[target_tup]
				if any(st in self.end_states for st in target_set):
					end_states.add(index[target_tup])

		# create an additional fail state
		# and redirect all undefined transition rules to it
		fail = len(index)
		compact_rules = [(st if st >= 0 else fail) for st in compact_rules]
		compact_rules.extend([fail] * n)
		
		return RegexpDFA(compact_rules, end_states, alphabet_index)


class RegexpDFA:
	def __init__(self, rules: list[int], end_states: set[int], alphabet_index: dict[str, int]):
		"""A deterministic finite automaton constructor.

		If the `rules` or the `alphabet_index` are empty, then instead of an empty automaton we create a trivial automaton failing on any input (accepting empty strings).

		:param rules: transition rules, where (i*n+j)th item defines the transition for i-th state on j-th alphabet symbol
		:param end_states: accepting states
		:param alphabet_index: mapping from alphabet symbols to rule columns"""
		self.rules = rules or [1, 1]
		self.end_states = end_states
		self.alphabet_index = alphabet_index or {"": 0}

	@staticmethod
	def create(pattern: str) -> "RegexpDFA":
		"""Create a `Regexp` and determinize it."""
		r = Regexp(pattern)
		return r.determinize()

	def match(self, s: str):
		"""Decide if a string matches the regexp.
		
		:param s: an input string"""
		st = 0
		n = len(self.alphabet_index)

		for c in s:
			if c not in self.alphabet_index:
				return False
			key = (st*n + self.alphabet_index[c])
			st = self.rules[key]

		return st in self.end_states

	def reduce(self) -> "RegexpDFA":
		"""Minimize the automaton by collapsing equivalent states."""
		partition = self._find_equivalent_states()
		(rules, end_states) = self._collapse_states(partition)

		return RegexpDFA(rules, end_states, self.alphabet_index)

	def normalize(self) -> "RegexpDFA":
		"""Normalize the automaton by relabeling the states in a breadth first search walkthrough order and remove unreachable states."""
		n = len(self.alphabet_index)
		index = {0: 0}
		queue = deque([0])

		rules = []

		while queue:
			si = queue.popleft()
			row = self.rules[si*n:(si+1)*n]
			for sj in row:
				if sj not in index:
					index[sj] = len(index)
					queue.append(sj)
			rules.extend(index[sj] for sj in row)
		
		end_states = {index[si] for si in self.end_states if si in index}

		return RegexpDFA(rules, end_states, self.alphabet_index)

	def find_distinguishing_string(self, r: "RegexpDFA") -> Optional[str]:
		"""Find the shortest string that is accepted by self or `r`, but not both.
		
		:param r: the other automaton
		:return: the distinguishing string, or None if the automatons are equivalent"""
		r1 = self.reduce().normalize()
		r2 = r.reduce().normalize()

		if r1.rules == r2.rules and r1.end_states == r2.end_states:
			return None

		r1 = r1._expand_alphabet(r2.alphabet_index)
		r2 = r2._expand_alphabet(r1.alphabet_index)
		product = r1._build_product_automaton(r2)

		n = len(product.alphabet_index)
		# state: symbol
		inverse_alphabet_index = {v: k for (k, v) in product.alphabet_index.items()}
		queue = deque([(0, "")])
		visited = {0}
		while queue:
			(state, acc) = queue.popleft()
			if state in product.end_states:
				return acc
			for (i, target) in enumerate(product.rules[state*n:(state+1)*n]):
				if target not in visited:
					queue.append((target, acc+inverse_alphabet_index[i]))
					visited.add(target)
		
		assert False

	def _find_equivalent_states(self) -> list[set[int]]:
		"""Partition states into their equivalence classes with Hopcroft's algorithm.
		
		:return: sets of equivalent states. Unique states get single item sets."""
		n = len(self.alphabet_index)
		m = len(self.rules) // n
		inverse_rules = [set() for i in range(m*n)]

		# a transition rules inverse. target state + alphabet symbol -> source states
		for i in range(m):
			for j in range(n):
				target = self.rules[i*n + j]
				inverse_rules[target*n + j].add(i)

		set_bag = [self.end_states, set(range(m))-self.end_states]
		res = {0, 1}
		work = {0, 1}

		while work:
			key = work.pop()
			target_set = set_bag[key]
			for j in range(n):
				source_set = set(itertools.chain.from_iterable(inverse_rules[t*n + j] for t in target_set))
				for k in res.copy():
					part = set_bag[k]
					intersection = part & source_set
					diff = part - source_set
					if not intersection or not diff:
						continue
					res.remove(k)
					ki = len(set_bag)
					set_bag.append(intersection)
					res.add(ki)
					kd = len(set_bag)
					set_bag.append(diff)
					res.add(kd)
					if k in work:
						work.remove(k)
						work.add(ki)
						work.add(kd)
					elif len(intersection) < len(diff):
						work.add(ki)
					else:
						work.add(kd)
		
		return [set_bag[k] for k in res]
	
	def _collapse_states(self, partition: list[set[int]]) -> tuple[list[int], set[int]]:
		"""Collapse equivalent states from each class into a single one.
		
		:param partition: list of equivalence classes
		:return: rules list, accepting states"""
		n = len(self.alphabet_index)
		rules = []

		# states mapping due to the equivalents collapse
		eq_mapping = dict()
		for eq_set in partition:
			states = sorted(eq_set)
			for st in states:
				eq_mapping[st] = states[0]

		# states mapping to keep the rules list compact after the equivalents collapse
		discard_mapping = dict()
		discard_count = 0

		for i in range(0, len(self.rules), n):
			si = i//n
			if eq_mapping[si] != si:
				discard_count += 1
				continue
			discard_mapping[si] = si - discard_count
			rules.extend(map(lambda st: eq_mapping[st], self.rules[i:i+n]))
		
		rules = [discard_mapping[st] for st in rules]
		end_states = {discard_mapping[eq_mapping[st]] for st in self.end_states}
		
		return (rules, end_states)

	def _expand_alphabet(self, alphabet_index: dict[str, int]) -> "RegexpDFA":
		"""Expand the automaton to accommodate union of `self.alphabet_index` and the provided `alphabet_index`.
		
		:param alphabet_index: a mapping from letters to rules columns
		:return: a RegexpDFA over the unified alphabet"""
		if alphabet_index == self.alphabet_index:
			return self

		n1 = len(self.alphabet_index)
		m = len(self.rules) // n1

		combined_alphabet = set(self.alphabet_index.keys()) | set(alphabet_index.keys())
		# a new alphabet_index
		combined_index = {c: i for (i, c) in enumerate(sorted(combined_alphabet))}
		# a new letter key: the old letter key
		conversion_index = {combined_index[k]: v for (k, v) in self.alphabet_index.items()}
		n2 = len(combined_alphabet)

		# rewrite the rules into a new table, filling blanks with a new fail state
		rules = [
			self.rules[i*n1 + conversion_index[j]]
			if j in conversion_index else m
			for i in range(m) for j in range(n2)
		]
		rules.extend([m]*n2)

		return RegexpDFA(rules, self.end_states, combined_index).reduce().normalize()

	def _build_product_automaton(self, r: "RegexpDFA") -> "RegexpDFA":
		"""Create a new automaton, with a carthesian product of the arguments' states and corresponding transition rules.
		
		:param r: the other finite automaton. It must have the same `alphabet_index` as `self`"""
		assert self.alphabet_index == r.alphabet_index
		n = len(self.alphabet_index)
		m = len(r.rules) // n
		k = len(self.rules) // n

		rules = []
		end_states = set()

		# expand each self state into m new states, one for each of the r states
		for s1 in range(k):
			row1 = self.rules[s1*n:(s1+1)*n]
			for s2 in range(m):
				row2 = r.rules[s2*n:(s2+1)*n]
				rules.extend([x*m + y for (x, y) in zip(row1, row2)])
				if (s1 in self.end_states) != (s2 in r.end_states):
					end_states.add(s1*m + s2)

		return RegexpDFA(rules, end_states, self.alphabet_index).reduce().normalize()


def test():
	tests = ["", "a", "ab", "aabb", "abab", "abcd", "abcbcdbcd"]
	for pattern in ["", "a(b|c)", "a*b*", "(ab)*", "a((bc)*d)*", "(a|b)*a(a|b)(a|b)(a|b)", "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"]:
		print("#", pattern)
		try:
			r = RegexpDFA.create(pattern).reduce().normalize()
		except ParsingError as e:
			print("Failed to parse the regexp:")
			print(e)
			continue
		for t in tests:
			print(t, r.match(t))
		print()


if __name__ == "__main__":
	parser = argparse.ArgumentParser()
	subparsers = parser.add_subparsers()
	
	test_parser = subparsers.add_parser("test")
	test_parser.set_defaults(name="test")

	match_parser = subparsers.add_parser("match")
	match_parser.add_argument("pattern")
	match_parser.add_argument("string")
	match_parser.set_defaults(name="match")

	compare_parser = subparsers.add_parser("compare")
	compare_parser.add_argument("pattern1")
	compare_parser.add_argument("pattern2")
	compare_parser.set_defaults(name="compare")

	args = parser.parse_args()

	if args.name == "test":
		test()
	elif args.name == "match":
		try:
			r = RegexpDFA.create(args.pattern).reduce().normalize()
		except ParsingError as e:
			print("Failed to parse the regexp:")
			print(e)
		print(r.match(args.string))
	elif args.name == "compare":
		r1 = RegexpDFA.create(args.pattern1).reduce().normalize()
		r2 = RegexpDFA.create(args.pattern2).reduce().normalize()
		print(r1.find_distinguishing_string(r2))
	else:
		parser.print_help()