from abc import abstractmethod


class ParsingError(Exception):
	pass


class Token:
	is_skippable = False

	@abstractmethod
	def list_first(self):
		pass

	@abstractmethod
	def list_last(self):
		pass

	@abstractmethod
	def list_neighbours(self):
		pass


class Lambda(Token):
	is_skippable = True

	def list_first(self):
		yield from []

	def list_last(self):
		yield from []

	def list_neighbours(self):
		yield from []


class Symbol(Token):
	def __init__(self, position, value):
		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 Plus(Token):
	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 Asterisk(Plus):
	is_skippable = True
	
	def __str__(self):
		return str(self.content) + "*"


class Alternative(Token):
	def __init__(self, content: list):
		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:
	pass

class Chain(Token):
	def __init__(self, content: list):
		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, k):
	counter = 0

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

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


def parse(pattern, offset=0):
	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 == "+":
			try:
				token = res.pop()
			except IndexError as e:
				raise ParsingError(f'The plus operator is missing an argument. Pattern: "{pattern}", position {i}')
			res.append(Plus(token))
			i += 1
		elif c == ")":
			raise ParsingError(f'An opening parenthesis not found. Pattern: "{pattern}", position: {i}')
		elif 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)


class Regexp:
	def __init__(self, pattern):
		(self.rules, self.end_states) = self._parse(pattern)

	def _parse(self, s):
		r = parse(s)
		rules = dict()

		for i in r.list_first():
			c = s[i]
			key = (-1, c)
			if key not in rules:
				rules[key] = set()
			rules[key].add(i)

		for (i, j) in r.list_neighbours():
			c = s[j]
			key = (i, c)
			if key not in rules:
				rules[key] = set()
			rules[key].add(j)

		end_states = set(r.list_last())
		if r.is_skippable:
			end_states.add(-1)

		return rules, end_states

	def match(self, s):
		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):
		rules = dict()
		end_states = {(-1,)} if -1 in self.end_states else set()

		stack = [(-1,)]
		processed_states = set()
		while stack:
			multistate = stack.pop()
			new_rules = dict()
			
			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)
			
			for (c, target_set) in new_rules.items():
				new_target = tuple(sorted(target_set))
				rules[(multistate, c)] = new_target
				if any(st in self.end_states for st in new_target):
					end_states.add(new_target)
				if new_target not in processed_states:
					stack.append(new_target)
					processed_states.add(new_target)
		
		return (rules, end_states)


class RegexpDFA:
	def __init__(self, pattern):
		r = Regexp(pattern)
		(self.rules, self.end_states) = r.determinize()

	def match(self, s):
		st = (-1,)

		for c in s:
			key = (st, c)
			if key in self.rules:
				st = self.rules[key]
			else:
				return False

		return st in self.end_states


if __name__ == "__main__":
	tests = ["", "a", "ab", "aabb", "abab", "abcd", "abcbcdbcd"]
	for pattern in ["*", "((a)", "a)"]:
		print("#", pattern)
		try:
			r = RegexpDFA(pattern)
		except ParsingError as e:
			print("Failed to parse the regexp:")
			print(e)
			continue
		for t in tests:
			print(t, r.match(t))
		print()