python-app-rocketbot/rocketbot/pattern.py

"""
Statements that match messages based on an expression and have a list of actions
to take on them.
"""
import re
from abc import ABCMeta, abstractmethod
from typing import Any

from discord import Message, utils as discordutils
from discord.ext.commands import Context

from rocketbot.utils import is_user_id, str_from_quoted_str, timedelta_from_str, \
	user_id_from_mention

class PatternError(RuntimeError):
	"""
	Error thrown when parsing a pattern statement.
	"""

class PatternDeprecationError(PatternError):
	"""
	Error raised by PatternStatement.check_deprecated_syntax.
	"""

class PatternAction:
	"""
	Describes one action to take on a matched message or its author.
	"""
	def __init__(self, action: str, args: list[Any]):
		self.action = action
		self.arguments = list(args)

	def __str__(self) -> str:
		arg_str = ', '.join(self.arguments)
		return f'{self.action}({arg_str})'

class PatternExpression(metaclass=ABCMeta):
	"""
	Abstract message matching expression.
	"""
	def __init__(self):
		pass

	@abstractmethod
	def matches(self, message: Message) -> bool:
		"""
		Whether a message matches this expression.
		"""
		return False

class PatternSimpleExpression(PatternExpression):
	"""
	Message matching expression with a simple "<field> <operator> <value>"
	structure.
	"""
	def __init__(self, field: str, operator: str, value: Any):
		super().__init__()
		self.field = field
		self.operator = operator
		self.value = value

	def __field_value(self, message: Message) -> Any:
		if self.field in ('content.markdown', 'content'):
			return message.content
		if self.field == 'content.plain':
			return discordutils.remove_markdown(message.clean_content)
		if self.field == 'author':
			return str(message.author.id)
		if self.field == 'author.id':
			return str(message.author.id)
		if self.field == 'author.joinage':
			return message.created_at - message.author.joined_at
		if self.field == 'author.name':
			return message.author.name
		else:
			raise ValueError(f'Bad field name {self.field}')

	def matches(self, message: Message) -> bool:
		field_value = self.__field_value(message)
		if self.operator == '==':
			if isinstance(field_value, str) and isinstance(self.value, str):
				return field_value.lower() == self.value.lower()
			return field_value == self.value
		if self.operator == '!=':
			if isinstance(field_value, str) and isinstance(self.value, str):
				return field_value.lower() != self.value.lower()
			return field_value != self.value
		if self.operator == '<':
			return field_value < self.value
		if self.operator == '>':
			return field_value > self.value
		if self.operator == '<=':
			return field_value <= self.value
		if self.operator == '>=':
			return field_value >= self.value
		if self.operator == 'contains':
			return self.value.lower() in field_value.lower()
		if self.operator == '!contains':
			return self.value.lower() not in field_value.lower()
		if self.operator in ('matches', 'containsword'):
			return self.value.search(field_value.lower()) is not None
		if self.operator in ('!matches', '!containsword'):
			return self.value.search(field_value.lower()) is None
		raise ValueError(f'Bad operator {self.operator}')

	def __str__(self) -> str:
		return f'({self.field} {self.operator} {self.value})'

class PatternCompoundExpression(PatternExpression):
	"""
	Message matching expression that combines several child expressions with
	a boolean operator.
	"""
	def __init__(self, operator: str, operands: list[PatternExpression]):
		super().__init__()
		self.operator = operator
		self.operands = list(operands)

	def matches(self, message: Message) -> bool:
		if self.operator == '!':
			return not self.operands[0].matches(message)
		if self.operator == 'and':
			for op in self.operands:
				if not op.matches(message):
					return False
			return True
		if self.operator == 'or':
			for op in self.operands:
				if op.matches(message):
					return True
			return False
		raise ValueError(f'Bad operator "{self.operator}"')

	def __str__(self) -> str:
		if self.operator == '!':
			return f'(!( {self.operands[0]} ))'
		strs = map(str, self.operands)
		joined = f' {self.operator} '.join(strs)
		return f'( {joined} )'

class PatternStatement:
	"""
	A full message match statement. If a message matches the given expression,
	the given actions should be performed.
	"""
	def __init__(self,
			name: str,
			actions: list[PatternAction],
			expression: PatternExpression,
			original: str):
		self.name = name
		self.actions = list(actions)  # PatternAction[]
		self.expression = expression
		self.original = original

	def check_deprecations(self) -> None:
		"""
		Tests whether this statement uses any deprecated syntax. Will raise a
		PatternDeprecationError if one is found.
		"""
		self.__check_deprecations(self.expression)

	@classmethod
	def __check_deprecations(cls, expression: PatternExpression) -> None:
		if isinstance(expression, PatternSimpleExpression):
			s: PatternSimpleExpression = expression
			if s.field in PatternCompiler.DEPRECATED_FIELDS:
				raise PatternDeprecationError(f'"{s.field}" field is deprecated')
		elif isinstance(expression, PatternCompoundExpression):
			c: PatternCompoundExpression = expression
			for oper in c.operands:
				cls.__check_deprecations(oper)

	def to_json(self) -> dict:
		"""
		Returns a JSON representation of this statement.
		"""
		return {
			'name': self.name,
			'statement': self.original,
		}

	@classmethod
	def from_json(cls, json: dict):
		"""
		Gets a PatternStatement from its JSON representation.
		"""
		return PatternCompiler.parse_statement(json['name'], json['statement'])

class PatternCompiler:
	"""
	Parses a user-provided message filter statement into a PatternStatement.
	"""
	TYPE_FLOAT = 'float'
	TYPE_ID = 'id'
	TYPE_INT = 'int'
	TYPE_MEMBER = 'Member'
	TYPE_REGEX = 'regex'
	TYPE_TEXT = 'text'
	TYPE_TIMESPAN = 'timespan'

	FIELD_TO_TYPE: dict[str, str] = {
		'content.plain': TYPE_TEXT,
		'content.markdown': TYPE_TEXT,
		'author': TYPE_MEMBER,
		'author.id': TYPE_ID,
		'author.name': TYPE_TEXT,
		'author.joinage': TYPE_TIMESPAN,

		'content': TYPE_TEXT, # deprecated, use content.markdown or content.plain
	}
	DEPRECATED_FIELDS: set[str] = set([ 'content' ])

	ACTION_TO_ARGS: dict[str, list[str]] = {
		'ban': [],
		'delete': [],
		'kick': [],
		'modinfo': [],
		'modwarn': [],
		'reply': [ TYPE_TEXT ],
	}

	OPERATORS_IDENTITY: set[str] = set([ '==', '!=' ])
	OPERATORS_COMPARISON: set[str] = set([ '<', '>', '<=', '>=' ])
	OPERATORS_NUMERIC = OPERATORS_IDENTITY | OPERATORS_COMPARISON
	OPERATORS_TEXT = OPERATORS_IDENTITY | set([
		'contains', '!contains',
		'containsword', '!containsword',
		'matches', '!matches',
	])
	OPERATORS_ALL = OPERATORS_IDENTITY | OPERATORS_COMPARISON | OPERATORS_TEXT

	TYPE_TO_OPERATORS: dict[str, set[str]] = {
		TYPE_ID: OPERATORS_IDENTITY,
		TYPE_MEMBER: OPERATORS_IDENTITY,
		TYPE_TEXT: OPERATORS_TEXT,
		TYPE_INT: OPERATORS_NUMERIC,
		TYPE_FLOAT: OPERATORS_NUMERIC,
		TYPE_TIMESPAN: OPERATORS_NUMERIC,
	}

	WHITESPACE_CHARS = ' \t\n\r'
	STRING_QUOTE_CHARS = '\'"'
	SYMBOL_CHARS = 'abcdefghijklmnopqrstuvwxyz.'
	VALUE_CHARS = '0123456789dhms<@!>'
	OP_CHARS = '<=>!(),'

	MAX_EXPRESSION_NESTING = 8

	@classmethod
	def expression_str_from_context(cls, context: Context, name: str) -> str:
		"""
		Extracts the statement string from an "add" command context.
		"""
		pattern_str = context.message.content
		command_chain = [ name ]
		cmd = context.command
		while cmd:
			command_chain.insert(0, cmd.name)
			cmd = cmd.parent
		command_chain[0] = f'{context.prefix}{command_chain[0]}'
		for cmd in command_chain:
			if pattern_str.startswith(cmd):
				pattern_str = pattern_str[len(cmd):].lstrip()
			elif pattern_str.startswith(f'"{cmd}"'):
				pattern_str = pattern_str[len(cmd) + 2:].lstrip()
		return pattern_str

	@classmethod
	def parse_statement(cls, name: str, statement: str) -> PatternStatement:
		"""
		Parses a user-provided message filter statement into a PatternStatement.
		Raises PatternError on failure.
		"""
		tokens = cls.__tokenize(statement)
		token_index = 0
		actions, token_index = cls.__read_actions(tokens, token_index)
		expression, token_index = cls.__read_expression(tokens, token_index)
		return PatternStatement(name, actions, expression, statement)

	@classmethod
	def __tokenize(cls, statement: str) -> list[str]:
		"""
		Converts a message filter statement into a list of tokens.
		"""
		tokens: list[str] = []
		in_quote = False
		in_escape = False
		all_token_types = set([ 'sym', 'op', 'val' ])
		possible_token_types = set(all_token_types)
		current_token = ''
		for ch in statement:
			if in_quote:
				if in_escape:
					if ch == 'n':
						current_token += '\n'
					elif ch == 't':
						current_token += '\t'
					else:
						current_token += ch
					in_escape = False
				elif ch == '\\':
					in_escape = True
				elif ch == in_quote:
					current_token += ch
					tokens.append(current_token)
					current_token = ''
					possible_token_types |= all_token_types
					in_quote = False
				else:
					current_token += ch
			else:
				if ch in cls.STRING_QUOTE_CHARS:
					if len(current_token) > 0:
						tokens.append(current_token)
						current_token = ''
						possible_token_types |= all_token_types
					in_quote = ch
					current_token = ch
				elif ch == '\\':
					raise PatternError("Unexpected \\ outside quoted string")
				elif ch in cls.WHITESPACE_CHARS:
					if len(current_token) > 0:
						tokens.append(current_token)
					current_token = ''
					possible_token_types |= all_token_types
				else:
					possible_ch_types = set()
					if ch in cls.SYMBOL_CHARS:
						possible_ch_types.add('sym')
					if ch in cls.VALUE_CHARS:
						possible_ch_types.add('val')
					if ch in cls.OP_CHARS:
						possible_ch_types.add('op')
					if len(current_token) > 0 and \
							possible_ch_types.isdisjoint(possible_token_types):
						if len(current_token) > 0:
							tokens.append(current_token)
							current_token = ''
							possible_token_types |= all_token_types
					possible_token_types &= possible_ch_types
					current_token += ch
		if len(current_token) > 0:
			tokens.append(current_token)

		# Some symbols might be glommed onto other tokens. Split 'em up.
		prefixes_to_split = [ '!', '(', ',' ]
		suffixes_to_split = [ ')', ',' ]
		i = 0
		while i < len(tokens):
			token = tokens[i]
			mutated = False
			for prefix in prefixes_to_split:
				if token.startswith(prefix) and len(token) > len(prefix):
					tokens.insert(i, prefix)
					tokens[i + 1] = token[len(prefix):]
					i += 1
					mutated = True
					break
			if mutated:
				continue
			for suffix in suffixes_to_split:
				if token.endswith(suffix) and len(token) > len(suffix):
					tokens[i] = token[0:-len(suffix)]
					tokens.insert(i + 1, suffix)
					mutated = True
					break
			if mutated:
				continue
			i += 1
		return tokens

	@classmethod
	def __read_actions(cls,
			tokens: list[str],
			token_index: int) -> tuple[list[PatternAction], int]:
		"""
		Reads the actions from a list of statement tokens. Returns a tuple
		containing a list of PatternActions and the token index this method
		left off at (the token after the "if").
		"""
		actions: list[PatternAction] = []
		current_action_tokens = []
		while token_index < len(tokens):
			token = tokens[token_index]
			if token == 'if':
				if len(current_action_tokens) > 0:
					a = PatternAction(current_action_tokens[0], \
						current_action_tokens[1:])
					cls.__validate_action(a)
					actions.append(a)
				token_index += 1
				return (actions, token_index)
			elif token == ',':
				if len(current_action_tokens) < 1:
					raise PatternError('Unexpected ,')
				a = PatternAction(current_action_tokens[0], \
					current_action_tokens[1:])
				cls.__validate_action(a)
				actions.append(a)
				current_action_tokens = []
			else:
				current_action_tokens.append(token)
			token_index += 1
		raise PatternError('Unexpected end of line in action list')

	@classmethod
	def __validate_action(cls, action: PatternAction) -> None:
		args: list[str] = cls.ACTION_TO_ARGS.get(action.action)
		if args is None:
			raise PatternError(f'Unknown action "{action.action}"')
		if len(action.arguments) != len(args):
			if len(args) == 0:
				raise PatternError(f'Action "{action.action}" expects no ' + \
					f'arguments, got {len(action.arguments)}.')
			raise PatternError(f'Action "{action.action}" expects ' + \
				f'{len(args)} arguments, got {len(action.arguments)}.')
		for i, datatype in enumerate(args):
			action.arguments[i] = cls.__parse_value(action.arguments[i], datatype)

	@classmethod
	def __read_expression(cls,
			tokens: list[str],
			token_index: int,
			depth: int = 0,
			one_subexpression: bool = False) -> tuple[PatternExpression, int]:
		"""
		Reads an expression from a list of statement tokens. Returns a tuple
		containing the PatternExpression and the token index it left off at.
		If one_subexpression is True then it will return after reading a
		single expression instead of joining multiples (for reading the
		subject of a NOT expression).
		"""
		subexpressions = []
		last_compound_operator = None
		while token_index < len(tokens):
			if one_subexpression:
				if len(subexpressions) == 1:
					return (subexpressions[0], token_index)
				if len(subexpressions) > 1:
					raise PatternError('Too many subexpressions')
			compound_operator = None
			if tokens[token_index] == ')':
				if len(subexpressions) == 0:
					raise PatternError('No subexpressions')
				if len(subexpressions) == 1:
					return (subexpressions[0], token_index)
				return (PatternCompoundExpression(last_compound_operator,
					subexpressions), token_index)
			if tokens[token_index] in set(["and", "or"]):
				compound_operator = tokens[token_index]
				if last_compound_operator and \
						compound_operator != last_compound_operator:
					subexpressions = [
						PatternCompoundExpression(last_compound_operator,
							subexpressions),
					]
				last_compound_operator = compound_operator
				token_index += 1
			if tokens[token_index] == '!':
				(exp, next_index) = cls.__read_expression(tokens, \
						token_index + 1, depth + 1, one_subexpression=True)
				subexpressions.append(PatternCompoundExpression('!', [exp]))
				token_index = next_index
			elif tokens[token_index] == '(':
				(exp, next_index) = cls.__read_expression(tokens,
					token_index + 1, depth + 1)
				if tokens[next_index] != ')':
					raise PatternError('Expected )')
				subexpressions.append(exp)
				token_index = next_index + 1
			else:
				(simple, next_index) = cls.__read_simple_expression(tokens,
					token_index, depth)
				subexpressions.append(simple)
				token_index = next_index
		if len(subexpressions) == 0:
			raise PatternError('No subexpressions')
		elif len(subexpressions) == 1:
			return (subexpressions[0], token_index)
		else:
			return (PatternCompoundExpression(last_compound_operator,
				subexpressions), token_index)

	@classmethod
	def __read_simple_expression(cls,
			tokens: list[str],
			token_index: int,
			depth: int = 0) -> tuple[PatternExpression, int]:
		"""
		Reads a simple expression consisting of a field name, operator, and
		comparison value. Returns a tuple of the PatternSimpleExpression and
		the token index it left off at.
		"""
		if depth > cls.MAX_EXPRESSION_NESTING:
			raise PatternError('Expression nests too deeply')
		if token_index >= len(tokens):
			raise PatternError('Expected field name, found EOL')
		field = tokens[token_index]
		token_index += 1

		datatype = cls.FIELD_TO_TYPE.get(field)
		if datatype is None:
			raise PatternError(f'No such field "{field}"')

		if token_index >= len(tokens):
			raise PatternError('Expected operator, found EOL')
		op = tokens[token_index]
		token_index += 1

		if op == '!':
			if token_index >= len(tokens):
				raise PatternError('Expected operator, found EOL')
			op = '!' + tokens[token_index]
			token_index += 1

		allowed_ops = cls.TYPE_TO_OPERATORS[datatype]
		if op not in allowed_ops:
			if op in cls.OPERATORS_ALL:
				raise PatternError(f'Operator {op} cannot be used with ' + \
					f'field "{field}"')
			raise PatternError(f'Unrecognized operator "{op}" - allowed: ' + \
				f'{sorted(list(allowed_ops))}')

		if token_index >= len(tokens):
			raise PatternError('Expected value, found EOL')
		value_str = tokens[token_index]

		try:
			value = cls.__parse_value(value_str, datatype, op)
		except ValueError as cause:
			raise PatternError(f'Bad value {value_str}') from cause

		token_index += 1
		exp = PatternSimpleExpression(field, op, value)
		return (exp, token_index)

	@classmethod
	def __parse_value(cls, value: str, datatype: str, op: str = None) -> Any:
		"""
		Converts a value token to its Python value. Raises ValueError on failure.
		"""
		if datatype == cls.TYPE_ID:
			if not is_user_id(value):
				raise ValueError(f'Illegal user id value: {value}')
			return value
		if datatype == cls.TYPE_MEMBER:
			return user_id_from_mention(value)
		if datatype == cls.TYPE_TEXT:
			s = str_from_quoted_str(value)
			if op in ('matches', '!matches'):
				try:
					return re.compile(s.lower())
				except re.error as e:
					raise ValueError(f'Invalid regex: {e}') from e
			if op in ('containsword', '!containsword'):
				try:
					return re.compile(f'\\b{re.escape(s.lower())}\\b')
				except re.error as e:
					raise ValueError(f'Invalid regex: {e}') from e
			return s
		if datatype == cls.TYPE_INT:
			return int(value)
		if datatype == cls.TYPE_FLOAT:
			return float(value)
		if datatype == cls.TYPE_TIMESPAN:
			return timedelta_from_str(value)
		raise ValueError(f'Unhandled datatype {datatype}')