"""
Cog for matching messages against guild-configurable criteria and taking
automated actions on them.
"""
import re
from abc import ABCMeta, abstractmethod
from discord import Guild, Member, Message
from discord.ext import commands

from config import CONFIG
from rocketbot.cogs.basecog import BaseCog, BotMessage, BotMessageReaction
from rocketbot.storage import Storage
from rocketbot.utils import parse_timedelta

class PatternAction:
	"""
	Describes one action to take on a matched message or its author.
	"""
	def __init__(self, action: str, args: list):
		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):
		super().__init__()
		self.field = field
		self.operator = operator
		self.value = value

	def __field_value(self, message: Message):
		if self.field == 'content':
			return message.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 == 'matches':
			p = re.compile(self.value.lower())
			return p.match(field_value.lower()) is not None
		if self.operator == '!matches':
			p = re.compile(self.value.lower())
			return p.match(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):
		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 RuntimeError(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, expression: PatternExpression, original: str):
		self.name = name
		self.actions = list(actions)  # PatternAction[]
		self.expression = expression
		self.original = original

class PatternContext:
	"""
	Data about a message that has matched a configured statement and what
	actions have been carried out.
	"""
	def __init__(self, message: Message, statement: PatternStatement):
		self.message = message
		self.statement = statement
		self.is_deleted = False
		self.is_kicked = False
		self.is_banned = False

class PatternCog(BaseCog, name='Pattern Matching'):
	"""
	Highly flexible cog for performing various actions on messages that match
	various critera. Patterns can be defined by mods for each guild.
	"""

	def __get_patterns(self, guild: Guild) -> dict:
		patterns = Storage.get_state_value(guild, 'PatternCog.patterns')
		if patterns is None:
			patterns = {}
			patterns_encoded = Storage.get_config_value(guild, 'PatternCog.patterns')
			if patterns_encoded:
				for pe in patterns_encoded:
					name = pe.get('name')
					statement = pe.get('statement')
					try:
						ps = PatternCompiler.parse_statement(name, statement)
						patterns[name] = ps
					except PatternError as e:
						self.log(guild, 'Error parsing saved statement ' + \
							f'"{name}": "{e}" Statement: {statement}')
			Storage.set_state_value(guild, 'PatternCog.patterns', patterns)
		return patterns

	@classmethod
	def __save_patterns(cls, guild: Guild, patterns: dict) -> None:
		to_save = []
		for name, statement in patterns.items():
			to_save.append({
				'name': name,
				'statement': statement.original,
			})
		Storage.set_config_value(guild, 'PatternCog.patterns', to_save)

	@commands.Cog.listener()
	async def on_message(self, message: Message) -> None:
		'Event listener'
		if message.author is None or \
				message.author.bot or \
				message.channel is None or \
				message.guild is None or \
				message.content is None or \
				message.content == '':
			return
		if message.author.permissions_in(message.channel).ban_members:
			# Ignore mods
			return

		patterns = self.__get_patterns(message.guild)
		for _, statement in patterns.items():
			if statement.expression.matches(message):
				await self.__trigger_actions(message, statement)
				break


	async def __trigger_actions(self, message: Message, statement: PatternStatement) -> None:
		context = PatternContext(message, statement)
		should_alert_mods = False
		action_descriptions = []
		self.log(message.guild, f'Message from {message.author.name} matched pattern "{statement.name}"')
		for action in statement.actions:
			if action.action == 'ban':
				await message.author.ban(
					reason=f'Rocketbot: Message matched custom pattern named "{statement.name}"',
					delete_message_days=0)
				context.is_banned = True
				context.is_kicked = True
				action_descriptions.append('Author banned')
				self.log(message.guild, f'{message.author.name} banned')
			elif action.action == 'delete':
				await message.delete()
				context.is_deleted = True
				action_descriptions.append('Message deleted')
				self.log(message.guild, f'{message.author.name}\'s message deleted')
			elif action.action == 'kick':
				await message.author.kick(
					reason=f'Rocketbot: Message matched custom pattern named "{statement.name}"')
				context.is_kicked = True
				action_descriptions.append('Author kicked')
				self.log(message.guild, f'{message.author.name} kicked')
			elif action.action == 'modwarn':
				should_alert_mods = True
				action_descriptions.append('Mods alerted')
			elif action.action == 'reply':
				await message.reply(
					f'{action.arguments[0]}',
					mention_author=False)
				action_descriptions.append('Autoreplied')
				self.log(message.guild, f'{message.author.name} autoreplied to')
		bm = BotMessage(
			message.guild,
			f'User {message.author.name} tripped custom pattern ' + \
				f'`{statement.name}`.\n\nAutomatic actions taken:\n• ' + \
				('\n• '.join(action_descriptions)),
			type=BotMessage.TYPE_MOD_WARNING if should_alert_mods else BotMessage.TYPE_INFO,
			context=context)
		bm.quote = message.content
		await bm.set_reactions(BotMessageReaction.standard_set(
			did_delete=context.is_deleted,
			did_kick=context.is_kicked,
			did_ban=context.is_banned))
		await self.post_message(bm)

	async def on_mod_react(self,
			bot_message: BotMessage,
			reaction: BotMessageReaction,
			reacted_by: Member) -> None:
		context: PatternContext = bot_message.context
		if reaction.emoji == CONFIG['trash_emoji']:
			await context.message.delete()
			context.is_deleted = True
		elif reaction.emoji == CONFIG['kick_emoji']:
			await context.message.author.kick(
				reason='Rocketbot: Message matched custom pattern named ' + \
					f'"{context.statement.name}". Kicked by {reacted_by.name}.')
			context.is_kicked = True
		elif reaction.emoji == CONFIG['ban_emoji']:
			await context.message.author.ban(
				reason='Rocketbot: Message matched custom pattern named ' + \
					f'"{context.statement.name}". Banned by {reacted_by.name}.',
					delete_message_days=1)
			context.is_banned = True
		await bot_message.set_reactions(BotMessageReaction.standard_set(
			did_delete=context.is_deleted,
			did_kick=context.is_kicked,
			did_ban=context.is_banned))

	@commands.group(
		brief='Manages message pattern matching',
	)
	@commands.has_permissions(ban_members=True)
	@commands.guild_only()
	async def pattern(self, context: commands.Context):
		'Message pattern matching command group'
		if context.invoked_subcommand is None:
			await context.send_help()

	@pattern.command(
		brief='Adds a custom pattern',
		description='Adds a custom pattern. Patterns use a simplified ' + \
			'expression language. Full documentation found here: ' + \
			'https://git.rixafrix.com/ialbert/python-app-rocketbot/src/branch/master/patterns.md',
		usage='<pattern_name> <expression...>',
		ignore_extra=True
	)
	async def add(self, context: commands.Context, name: str):
		'Command handler'
		pattern_str = PatternCompiler.expression_str_from_context(context, name)
		try:
			statement = PatternCompiler.parse_statement(name, pattern_str)
			patterns = self.__get_patterns(context.guild)
			patterns[name] = statement
			self.__save_patterns(context.guild, patterns)
			await context.message.reply(
				f'{CONFIG["success_emoji"]} Pattern `{name}` added.',
				mention_author=False)
		except PatternError as e:
			await context.message.reply(
				f'{CONFIG["failure_emoji"]} Error parsing statement. {e}',
				mention_author=False)

	@pattern.command(
		brief='Removes a custom pattern',
		usage='<pattern_name>'
	)
	async def remove(self, context: commands.Context, name: str):
		'Command handler'
		patterns = self.__get_patterns(context.guild)
		if patterns.get(name) is not None:
			del patterns[name]
			self.__save_patterns(context.guild, patterns)
			await context.message.reply(
				f'{CONFIG["success_emoji"]} Pattern `{name}` deleted.',
				mention_author=False)
		else:
			await context.message.reply(
				f'{CONFIG["failure_emoji"]} No pattern named `{name}`.',
				mention_author=False)

	@pattern.command(
		brief='Lists all patterns'
	)
	async def list(self, context: commands.Context) -> None:
		'Command handler'
		patterns = self.__get_patterns(context.guild)
		if len(patterns) == 0:
			await context.message.reply('No patterns defined.', mention_author=False)
			return
		msg = ''
		for name, statement in sorted(patterns.items()):
			msg += f'Pattern `{name}`:\n```\n{statement.original}\n```\n'
		await context.message.reply(msg, mention_author=False)

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

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

	FIELD_TO_TYPE = {
		'content': TYPE_TEXT,
		'author': TYPE_MEMBER,
		'author.id': TYPE_ID,
		'author.name': TYPE_TEXT,
		'author.joinage': TYPE_TIMESPAN,
	}

	ACTION_TO_ARGS = {
		'ban': [],
		'delete': [],
		'kick': [],
		'modwarn': [],
		'reply': [ TYPE_TEXT ],
	}

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

	TYPE_TO_OPERATORS = {
		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 = '<=>!(),'

	@classmethod
	def expression_str_from_context(cls, context: commands.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.
		"""
		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:
		"""
		Converts a message filter statement into a list of tokens.
		"""
		tokens = []
		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, token_index: int) -> tuple:
		"""
		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 = []
		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 = 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 arguments, ' + \
					f'got {len(action.arguments)}.')
			else:
				raise PatternError(f'Action "{action.action}" expects {len(args)} ' + \
					f'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,
			token_index: int,
			depth: int = 0,
			one_subexpression: bool = False) -> tuple:
		"""
		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 readong 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
				else:
					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, token_index: int, depth: int = 0) -> tuple:
		"""
		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 > 8:
			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 field "{field}"')
			raise PatternError(f'Unrecognized operator "{op}" - allowed: {list(allowed_ops)}')

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

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

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

	@classmethod
	def parse_value(cls, value: str, datatype: str):
		"""
		Converts a value token to its Python value. Raises ValueError on failure.
		"""
		if datatype == cls.TYPE_ID:
			p = re.compile('^[0-9]+$')
			if p.match(value) is None:
				raise ValueError(f'Illegal id value "{value}"')
			# Store it as a str so it can be larger than an int
			return value
		if datatype == cls.TYPE_MEMBER:
			p = re.compile('^<@!?([0-9]+)>$')
			m = p.match(value)
			if m is None:
				raise ValueError('Illegal member value. Must be an @ mention.')
			return m.group(1)
		if datatype == cls.TYPE_TEXT:
			# Must be quoted.
			if len(value) < 2 or \
					value[0:1] not in cls.STRING_QUOTE_CHARS or \
					value[-1:] not in cls.STRING_QUOTE_CHARS or \
					value[0:1] != value[-1:]:
				raise ValueError(f'Not a quoted string value: {value}')
			return value[1:-1]
		if datatype == cls.TYPE_INT:
			return int(value)
		if datatype == cls.TYPE_FLOAT:
			return float(value)
		if datatype == cls.TYPE_TIMESPAN:
			return parse_timedelta(value)
		raise ValueError(f'Unhandled datatype {datatype}')