# -*- coding: utf-8 -*-
import codecs
import warnings
import re
from contextlib import contextmanager

from parso.normalizer import Normalizer, NormalizerConfig, Issue, Rule
from parso.python.tree import search_ancestor

_BLOCK_STMTS = ('if_stmt', 'while_stmt', 'for_stmt', 'try_stmt', 'with_stmt')
_STAR_EXPR_PARENTS = ('testlist_star_expr', 'testlist_comp', 'exprlist')
# This is the maximal block size given by python.
_MAX_BLOCK_SIZE = 20
_MAX_INDENT_COUNT = 100
ALLOWED_FUTURES = (
    'all_feature_names', 'nested_scopes', 'generators', 'division',
    'absolute_import', 'with_statement', 'print_function', 'unicode_literals',
)
_COMP_FOR_TYPES = ('comp_for', 'sync_comp_for')


def _iter_stmts(scope):
    """
    Iterates over all statements and splits up  simple_stmt.
    """
    for child in scope.children:
        if child.type == 'simple_stmt':
            for child2 in child.children:
                if child2.type == 'newline' or child2 == ';':
                    continue
                yield child2
        else:
            yield child


def _get_comprehension_type(atom):
    first, second = atom.children[:2]
    if second.type == 'testlist_comp' and second.children[1].type in _COMP_FOR_TYPES:
        if first == '[':
            return 'list comprehension'
        else:
            return 'generator expression'
    elif second.type == 'dictorsetmaker' and second.children[-1].type in _COMP_FOR_TYPES:
        if second.children[1] == ':':
            return 'dict comprehension'
        else:
            return 'set comprehension'
    return None


def _is_future_import(import_from):
    # It looks like a __future__ import that is relative is still a future
    # import. That feels kind of odd, but whatever.
    # if import_from.level != 0:
    #     return False
    from_names = import_from.get_from_names()
    return [n.value for n in from_names] == ['__future__']


def _remove_parens(atom):
    """
    Returns the inner part of an expression like `(foo)`. Also removes nested
    parens.
    """
    try:
        children = atom.children
    except AttributeError:
        pass
    else:
        if len(children) == 3 and children[0] == '(':
            return _remove_parens(atom.children[1])
    return atom


def _iter_params(parent_node):
    return (n for n in parent_node.children if n.type == 'param')


def _is_future_import_first(import_from):
    """
    Checks if the import is the first statement of a file.
    """
    found_docstring = False
    for stmt in _iter_stmts(import_from.get_root_node()):
        if stmt.type == 'string' and not found_docstring:
            continue
        found_docstring = True

        if stmt == import_from:
            return True
        if stmt.type == 'import_from' and _is_future_import(stmt):
            continue
        return False


def _iter_definition_exprs_from_lists(exprlist):
    def check_expr(child):
        if child.type == 'atom':
            if child.children[0] == '(':
                testlist_comp = child.children[1]
                if testlist_comp.type == 'testlist_comp':
                    for expr in _iter_definition_exprs_from_lists(testlist_comp):
                        yield expr
                    return
                else:
                    # It's a paren that doesn't do anything, like 1 + (1)
                    for c in check_expr(testlist_comp):
                        yield c
                    return
            elif child.children[0] == '[':
                yield testlist_comp
                return
        yield child

    if exprlist.type in _STAR_EXPR_PARENTS:
        for child in exprlist.children[::2]:
            for c in check_expr(child):  # Python 2 sucks
                yield c
    else:
        for c in check_expr(exprlist):  # Python 2 sucks
            yield c


def _get_expr_stmt_definition_exprs(expr_stmt):
    exprs = []
    for list_ in expr_stmt.children[:-2:2]:
        if list_.type in ('testlist_star_expr', 'testlist'):
            exprs += _iter_definition_exprs_from_lists(list_)
        else:
            exprs.append(list_)
    return exprs


def _get_for_stmt_definition_exprs(for_stmt):
    exprlist = for_stmt.children[1]
    return list(_iter_definition_exprs_from_lists(exprlist))


class _Context(object):
    def __init__(self, node, add_syntax_error, parent_context=None):
        self.node = node
        self.blocks = []
        self.parent_context = parent_context
        self._used_name_dict = {}
        self._global_names = []
        self._nonlocal_names = []
        self._nonlocal_names_in_subscopes = []
        self._add_syntax_error = add_syntax_error

    def is_async_funcdef(self):
        # Stupidly enough async funcdefs can have two different forms,
        # depending if a decorator is used or not.
        return self.is_function() \
            and self.node.parent.type in ('async_funcdef', 'async_stmt')

    def is_function(self):
        return self.node.type == 'funcdef'

    def add_name(self, name):
        parent_type = name.parent.type
        if parent_type == 'trailer':
            # We are only interested in first level names.
            return

        if parent_type == 'global_stmt':
            self._global_names.append(name)
        elif parent_type == 'nonlocal_stmt':
            self._nonlocal_names.append(name)
        else:
            self._used_name_dict.setdefault(name.value, []).append(name)

    def finalize(self):
        """
        Returns a list of nonlocal names that need to be part of that scope.
        """
        self._analyze_names(self._global_names, 'global')
        self._analyze_names(self._nonlocal_names, 'nonlocal')

        global_name_strs = {n.value: n for n in self._global_names}
        for nonlocal_name in self._nonlocal_names:
            try:
                global_name = global_name_strs[nonlocal_name.value]
            except KeyError:
                continue

            message = "name '%s' is nonlocal and global" % global_name.value
            if global_name.start_pos < nonlocal_name.start_pos:
                error_name = global_name
            else:
                error_name = nonlocal_name
            self._add_syntax_error(error_name, message)

        nonlocals_not_handled = []
        for nonlocal_name in self._nonlocal_names_in_subscopes:
            search = nonlocal_name.value
            if search in global_name_strs or self.parent_context is None:
                message = "no binding for nonlocal '%s' found" % nonlocal_name.value
                self._add_syntax_error(nonlocal_name, message)
            elif not self.is_function() or \
                    nonlocal_name.value not in self._used_name_dict:
                nonlocals_not_handled.append(nonlocal_name)
        return self._nonlocal_names + nonlocals_not_handled

    def _analyze_names(self, globals_or_nonlocals, type_):
        def raise_(message):
            self._add_syntax_error(base_name, message % (base_name.value, type_))

        params = []
        if self.node.type == 'funcdef':
            params = self.node.get_params()

        for base_name in globals_or_nonlocals:
            found_global_or_nonlocal = False
            # Somehow Python does it the reversed way.
            for name in reversed(self._used_name_dict.get(base_name.value, [])):
                if name.start_pos > base_name.start_pos:
                    # All following names don't have to be checked.
                    found_global_or_nonlocal = True

                parent = name.parent
                if parent.type == 'param' and parent.name == name:
                    # Skip those here, these definitions belong to the next
                    # scope.
                    continue

                if name.is_definition():
                    if parent.type == 'expr_stmt' \
                            and parent.children[1].type == 'annassign':
                        if found_global_or_nonlocal:
                            # If it's after the global the error seems to be
                            # placed there.
                            base_name = name
                        raise_("annotated name '%s' can't be %s")
                        break
                    else:
                        message = "name '%s' is assigned to before %s declaration"
                else:
                    message = "name '%s' is used prior to %s declaration"

                if not found_global_or_nonlocal:
                    raise_(message)
                    # Only add an error for the first occurence.
                    break

            for param in params:
                if param.name.value == base_name.value:
                    raise_("name '%s' is parameter and %s"),

    @contextmanager
    def add_block(self, node):
        self.blocks.append(node)
        yield
        self.blocks.pop()

    def add_context(self, node):
        return _Context(node, self._add_syntax_error, parent_context=self)

    def close_child_context(self, child_context):
        self._nonlocal_names_in_subscopes += child_context.finalize()


class ErrorFinder(Normalizer):
    """
    Searches for errors in the syntax tree.
    """
    def __init__(self, *args, **kwargs):
        super(ErrorFinder, self).__init__(*args, **kwargs)
        self._error_dict = {}
        self.version = self.grammar.version_info

    def initialize(self, node):
        def create_context(node):
            if node is None:
                return None

            parent_context = create_context(node.parent)
            if node.type in ('classdef', 'funcdef', 'file_input'):
                return _Context(node, self._add_syntax_error, parent_context)
            return parent_context

        self.context = create_context(node) or _Context(node, self._add_syntax_error)
        self._indentation_count = 0

    def visit(self, node):
        if node.type == 'error_node':
            with self.visit_node(node):
                # Don't need to investigate the inners of an error node. We
                # might find errors in there that should be ignored, because
                # the error node itself already shows that there's an issue.
                return ''
        return super(ErrorFinder, self).visit(node)

    @contextmanager
    def visit_node(self, node):
        self._check_type_rules(node)

        if node.type in _BLOCK_STMTS:
            with self.context.add_block(node):
                if len(self.context.blocks) == _MAX_BLOCK_SIZE:
                    self._add_syntax_error(node, "too many statically nested blocks")
                yield
            return
        elif node.type == 'suite':
            self._indentation_count += 1
            if self._indentation_count == _MAX_INDENT_COUNT:
                self._add_indentation_error(node.children[1], "too many levels of indentation")

        yield

        if node.type == 'suite':
            self._indentation_count -= 1
        elif node.type in ('classdef', 'funcdef'):
            context = self.context
            self.context = context.parent_context
            self.context.close_child_context(context)

    def visit_leaf(self, leaf):
        if leaf.type == 'error_leaf':
            if leaf.token_type in ('INDENT', 'ERROR_DEDENT'):
                # Indents/Dedents itself never have a prefix. They are just
                # "pseudo" tokens that get removed by the syntax tree later.
                # Therefore in case of an error we also have to check for this.
                spacing = list(leaf.get_next_leaf()._split_prefix())[-1]
                if leaf.token_type == 'INDENT':
                    message = 'unexpected indent'
                else:
                    message = 'unindent does not match any outer indentation level'
                self._add_indentation_error(spacing, message)
            else:
                if leaf.value.startswith('\\'):
                    message = 'unexpected character after line continuation character'
                else:
                    match = re.match('\\w{,2}("{1,3}|\'{1,3})', leaf.value)
                    if match is None:
                        message = 'invalid syntax'
                    else:
                        if len(match.group(1)) == 1:
                            message = 'EOL while scanning string literal'
                        else:
                            message = 'EOF while scanning triple-quoted string literal'
                self._add_syntax_error(leaf, message)
            return ''
        elif leaf.value == ':':
            parent = leaf.parent
            if parent.type in ('classdef', 'funcdef'):
                self.context = self.context.add_context(parent)

        # The rest is rule based.
        return super(ErrorFinder, self).visit_leaf(leaf)

    def _add_indentation_error(self, spacing, message):
        self.add_issue(spacing, 903, "IndentationError: " + message)

    def _add_syntax_error(self, node, message):
        self.add_issue(node, 901, "SyntaxError: " + message)

    def add_issue(self, node, code, message):
        # Overwrite the default behavior.
        # Check if the issues are on the same line.
        line = node.start_pos[0]
        args = (code, message, node)
        self._error_dict.setdefault(line, args)

    def finalize(self):
        self.context.finalize()

        for code, message, node in self._error_dict.values():
            self.issues.append(Issue(node, code, message))


class IndentationRule(Rule):
    code = 903

    def _get_message(self, message):
        message = super(IndentationRule, self)._get_message(message)
        return "IndentationError: " + message


@ErrorFinder.register_rule(type='error_node')
class _ExpectIndentedBlock(IndentationRule):
    message = 'expected an indented block'

    def get_node(self, node):
        leaf = node.get_next_leaf()
        return list(leaf._split_prefix())[-1]

    def is_issue(self, node):
        # This is the beginning of a suite that is not indented.
        return node.children[-1].type == 'newline'


class ErrorFinderConfig(NormalizerConfig):
    normalizer_class = ErrorFinder


class SyntaxRule(Rule):
    code = 901

    def _get_message(self, message):
        message = super(SyntaxRule, self)._get_message(message)
        return "SyntaxError: " + message


@ErrorFinder.register_rule(type='error_node')
class _InvalidSyntaxRule(SyntaxRule):
    message = "invalid syntax"

    def get_node(self, node):
        return node.get_next_leaf()

    def is_issue(self, node):
        # Error leafs will be added later as an error.
        return node.get_next_leaf().type != 'error_leaf'


@ErrorFinder.register_rule(value='await')
class _AwaitOutsideAsync(SyntaxRule):
    message = "'await' outside async function"

    def is_issue(self, leaf):
        return not self._normalizer.context.is_async_funcdef()

    def get_error_node(self, node):
        # Return the whole await statement.
        return node.parent


@ErrorFinder.register_rule(value='break')
class _BreakOutsideLoop(SyntaxRule):
    message = "'break' outside loop"

    def is_issue(self, leaf):
        in_loop = False
        for block in self._normalizer.context.blocks:
            if block.type in ('for_stmt', 'while_stmt'):
                in_loop = True
        return not in_loop


@ErrorFinder.register_rule(value='continue')
class _ContinueChecks(SyntaxRule):
    message = "'continue' not properly in loop"
    message_in_finally = "'continue' not supported inside 'finally' clause"

    def is_issue(self, leaf):
        in_loop = False
        for block in self._normalizer.context.blocks:
            if block.type in ('for_stmt', 'while_stmt'):
                in_loop = True
            if block.type == 'try_stmt':
                last_block = block.children[-3]
                if last_block == 'finally' and leaf.start_pos > last_block.start_pos:
                    self.add_issue(leaf, message=self.message_in_finally)
                    return False  # Error already added
        if not in_loop:
            return True


@ErrorFinder.register_rule(value='from')
class _YieldFromCheck(SyntaxRule):
    message = "'yield from' inside async function"

    def get_node(self, leaf):
        return leaf.parent.parent  # This is the actual yield statement.

    def is_issue(self, leaf):
        return leaf.parent.type == 'yield_arg' \
            and self._normalizer.context.is_async_funcdef()


@ErrorFinder.register_rule(type='name')
class _NameChecks(SyntaxRule):
    message = 'cannot assign to __debug__'
    message_none = 'cannot assign to None'

    def is_issue(self, leaf):
        self._normalizer.context.add_name(leaf)

        if leaf.value == '__debug__' and leaf.is_definition():
            return True
        if leaf.value == 'None' and self._normalizer.version < (3, 0) \
                and leaf.is_definition():
            self.add_issue(leaf, message=self.message_none)


@ErrorFinder.register_rule(type='string')
class _StringChecks(SyntaxRule):
    message = "bytes can only contain ASCII literal characters."

    def is_issue(self, leaf):
        string_prefix = leaf.string_prefix.lower()
        if 'b' in string_prefix \
                and self._normalizer.version >= (3, 0) \
                and any(c for c in leaf.value if ord(c) > 127):
            # b'ä'
            return True

        if 'r' not in string_prefix:
            # Raw strings don't need to be checked if they have proper
            # escaping.
            is_bytes = self._normalizer.version < (3, 0)
            if 'b' in string_prefix:
                is_bytes = True
            if 'u' in string_prefix:
                is_bytes = False

            payload = leaf._get_payload()
            if is_bytes:
                payload = payload.encode('utf-8')
                func = codecs.escape_decode
            else:
                func = codecs.unicode_escape_decode

            try:
                with warnings.catch_warnings():
                    # The warnings from parsing strings are not relevant.
                    warnings.filterwarnings('ignore')
                    func(payload)
            except UnicodeDecodeError as e:
                self.add_issue(leaf, message='(unicode error) ' + str(e))
            except ValueError as e:
                self.add_issue(leaf, message='(value error) ' + str(e))


@ErrorFinder.register_rule(value='*')
class _StarCheck(SyntaxRule):
    message = "named arguments must follow bare *"

    def is_issue(self, leaf):
        params = leaf.parent
        if params.type == 'parameters' and params:
            after = params.children[params.children.index(leaf) + 1:]
            after = [child for child in after
                     if child not in (',', ')') and not child.star_count]
            return len(after) == 0


@ErrorFinder.register_rule(value='**')
class _StarStarCheck(SyntaxRule):
    # e.g. {**{} for a in [1]}
    # TODO this should probably get a better end_pos including
    #      the next sibling of leaf.
    message = "dict unpacking cannot be used in dict comprehension"

    def is_issue(self, leaf):
        if leaf.parent.type == 'dictorsetmaker':
            comp_for = leaf.get_next_sibling().get_next_sibling()
            return comp_for is not None and comp_for.type in _COMP_FOR_TYPES


@ErrorFinder.register_rule(value='yield')
@ErrorFinder.register_rule(value='return')
class _ReturnAndYieldChecks(SyntaxRule):
    message = "'return' with value in async generator"
    message_async_yield = "'yield' inside async function"

    def get_node(self, leaf):
        return leaf.parent

    def is_issue(self, leaf):
        if self._normalizer.context.node.type != 'funcdef':
            self.add_issue(self.get_node(leaf), message="'%s' outside function" % leaf.value)
        elif self._normalizer.context.is_async_funcdef() \
                and any(self._normalizer.context.node.iter_yield_exprs()):
            if leaf.value == 'return' and leaf.parent.type == 'return_stmt':
                return True
            elif leaf.value == 'yield' \
                    and leaf.get_next_leaf() != 'from' \
                    and self._normalizer.version == (3, 5):
                self.add_issue(self.get_node(leaf), message=self.message_async_yield)


@ErrorFinder.register_rule(type='strings')
class _BytesAndStringMix(SyntaxRule):
    # e.g. 's' b''
    message = "cannot mix bytes and nonbytes literals"

    def _is_bytes_literal(self, string):
        if string.type == 'fstring':
            return False
        return 'b' in string.string_prefix.lower()

    def is_issue(self, node):
        first = node.children[0]
        # In Python 2 it's allowed to mix bytes and unicode.
        if self._normalizer.version >= (3, 0):
            first_is_bytes = self._is_bytes_literal(first)
            for string in node.children[1:]:
                if first_is_bytes != self._is_bytes_literal(string):
                    return True


@ErrorFinder.register_rule(type='import_as_names')
class _TrailingImportComma(SyntaxRule):
    # e.g. from foo import a,
    message = "trailing comma not allowed without surrounding parentheses"

    def is_issue(self, node):
        if node.children[-1] == ',' and node.parent.children[-1] != ')':
            return True


@ErrorFinder.register_rule(type='import_from')
class _ImportStarInFunction(SyntaxRule):
    message = "import * only allowed at module level"

    def is_issue(self, node):
        return node.is_star_import() and self._normalizer.context.parent_context is not None


@ErrorFinder.register_rule(type='import_from')
class _FutureImportRule(SyntaxRule):
    message = "from __future__ imports must occur at the beginning of the file"

    def is_issue(self, node):
        if _is_future_import(node):
            if not _is_future_import_first(node):
                return True

            for from_name, future_name in node.get_paths():
                name = future_name.value
                allowed_futures = list(ALLOWED_FUTURES)
                if self._normalizer.version >= (3, 5):
                    allowed_futures.append('generator_stop')

                if name == 'braces':
                    self.add_issue(node, message="not a chance")
                elif name == 'barry_as_FLUFL':
                    m = "Seriously I'm not implementing this :) ~ Dave"
                    self.add_issue(node, message=m)
                elif name not in ALLOWED_FUTURES:
                    message = "future feature %s is not defined" % name
                    self.add_issue(node, message=message)


@ErrorFinder.register_rule(type='star_expr')
class _StarExprRule(SyntaxRule):
    message = "starred assignment target must be in a list or tuple"
    message_iterable_unpacking = "iterable unpacking cannot be used in comprehension"
    message_assignment = "can use starred expression only as assignment target"

    def is_issue(self, node):
        if node.parent.type not in _STAR_EXPR_PARENTS:
            return True
        if node.parent.type == 'testlist_comp':
            # [*[] for a in [1]]
            if node.parent.children[1].type in _COMP_FOR_TYPES:
                self.add_issue(node, message=self.message_iterable_unpacking)
        if self._normalizer.version <= (3, 4):
            n = search_ancestor(node, 'for_stmt', 'expr_stmt')
            found_definition = False
            if n is not None:
                if n.type == 'expr_stmt':
                    exprs = _get_expr_stmt_definition_exprs(n)
                else:
                    exprs = _get_for_stmt_definition_exprs(n)
                if node in exprs:
                    found_definition = True

            if not found_definition:
                self.add_issue(node, message=self.message_assignment)


@ErrorFinder.register_rule(types=_STAR_EXPR_PARENTS)
class _StarExprParentRule(SyntaxRule):
    def is_issue(self, node):
        if node.parent.type == 'del_stmt':
            self.add_issue(node.parent, message="can't use starred expression here")
        else:
            def is_definition(node, ancestor):
                if ancestor is None:
                    return False

                type_ = ancestor.type
                if type_ == 'trailer':
                    return False

                if type_ == 'expr_stmt':
                    return node.start_pos < ancestor.children[-1].start_pos

                return is_definition(node, ancestor.parent)

            if is_definition(node, node.parent):
                args = [c for c in node.children if c != ',']
                starred = [c for c in args if c.type == 'star_expr']
                if len(starred) > 1:
                    message = "two starred expressions in assignment"
                    self.add_issue(starred[1], message=message)
                elif starred:
                    count = args.index(starred[0])
                    if count >= 256:
                        message = "too many expressions in star-unpacking assignment"
                        self.add_issue(starred[0], message=message)


@ErrorFinder.register_rule(type='annassign')
class _AnnotatorRule(SyntaxRule):
    # True: int
    # {}: float
    message = "illegal target for annotation"

    def get_node(self, node):
        return node.parent

    def is_issue(self, node):
        type_ = None
        lhs = node.parent.children[0]
        lhs = _remove_parens(lhs)
        try:
            children = lhs.children
        except AttributeError:
            pass
        else:
            if ',' in children or lhs.type == 'atom' and children[0] == '(':
                type_ = 'tuple'
            elif lhs.type == 'atom' and children[0] == '[':
                type_ = 'list'
            trailer = children[-1]

        if type_ is None:
            if not (lhs.type == 'name'
                    # subscript/attributes are allowed
                    or lhs.type in ('atom_expr', 'power')
                    and trailer.type == 'trailer'
                    and trailer.children[0] != '('):
                return True
        else:
            # x, y: str
            message = "only single target (not %s) can be annotated"
            self.add_issue(lhs.parent, message=message % type_)


@ErrorFinder.register_rule(type='argument')
class _ArgumentRule(SyntaxRule):
    def is_issue(self, node):
        first = node.children[0]
        if node.children[1] == '=' and first.type != 'name':
            if first.type == 'lambdef':
                # f(lambda: 1=1)
                if self._normalizer.version < (3, 8):
                    message = "lambda cannot contain assignment"
                else:
                    message = 'expression cannot contain assignment, perhaps you meant "=="?'
            else:
                # f(+x=1)
                if self._normalizer.version < (3, 8):
                    message = "keyword can't be an expression"
                else:
                    message = 'expression cannot contain assignment, perhaps you meant "=="?'
            self.add_issue(first, message=message)


@ErrorFinder.register_rule(type='nonlocal_stmt')
class _NonlocalModuleLevelRule(SyntaxRule):
    message = "nonlocal declaration not allowed at module level"

    def is_issue(self, node):
        return self._normalizer.context.parent_context is None


@ErrorFinder.register_rule(type='arglist')
class _ArglistRule(SyntaxRule):
    @property
    def message(self):
        if self._normalizer.version < (3, 7):
            return "Generator expression must be parenthesized if not sole argument"
        else:
            return "Generator expression must be parenthesized"

    def is_issue(self, node):
        first_arg = node.children[0]
        if first_arg.type == 'argument' \
                and first_arg.children[1].type in _COMP_FOR_TYPES:
            # e.g. foo(x for x in [], b)
            return len(node.children) >= 2
        else:
            arg_set = set()
            kw_only = False
            kw_unpacking_only = False
            is_old_starred = False
            # In python 3 this would be a bit easier (stars are part of
            # argument), but we have to understand both.
            for argument in node.children:
                if argument == ',':
                    continue

                if argument in ('*', '**'):
                    # Python < 3.5 has the order engraved in the grammar
                    # file.  No need to do anything here.
                    is_old_starred = True
                    continue
                if is_old_starred:
                    is_old_starred = False
                    continue

                if argument.type == 'argument':
                    first = argument.children[0]
                    if first in ('*', '**'):
                        if first == '*':
                            if kw_unpacking_only:
                                # foo(**kwargs, *args)
                                message = "iterable argument unpacking " \
                                          "follows keyword argument unpacking"
                                self.add_issue(argument, message=message)
                        else:
                            kw_unpacking_only = True
                    else:  # Is a keyword argument.
                        kw_only = True
                        if first.type == 'name':
                            if first.value in arg_set:
                                # f(x=1, x=2)
                                self.add_issue(first, message="keyword argument repeated")
                            else:
                                arg_set.add(first.value)
                else:
                    if kw_unpacking_only:
                        # f(**x, y)
                        message = "positional argument follows keyword argument unpacking"
                        self.add_issue(argument, message=message)
                    elif kw_only:
                        # f(x=2, y)
                        message = "positional argument follows keyword argument"
                        self.add_issue(argument, message=message)


@ErrorFinder.register_rule(type='parameters')
@ErrorFinder.register_rule(type='lambdef')
class _ParameterRule(SyntaxRule):
    # def f(x=3, y): pass
    message = "non-default argument follows default argument"

    def is_issue(self, node):
        param_names = set()
        default_only = False
        for p in _iter_params(node):
            if p.name.value in param_names:
                message = "duplicate argument '%s' in function definition"
                self.add_issue(p.name, message=message % p.name.value)
            param_names.add(p.name.value)

            if p.default is None and not p.star_count:
                if default_only:
                    return True
            else:
                default_only = True


@ErrorFinder.register_rule(type='try_stmt')
class _TryStmtRule(SyntaxRule):
    message = "default 'except:' must be last"

    def is_issue(self, try_stmt):
        default_except = None
        for except_clause in try_stmt.children[3::3]:
            if except_clause in ('else', 'finally'):
                break
            if except_clause == 'except':
                default_except = except_clause
            elif default_except is not None:
                self.add_issue(default_except, message=self.message)


@ErrorFinder.register_rule(type='fstring')
class _FStringRule(SyntaxRule):
    _fstring_grammar = None
    message_expr = "f-string expression part cannot include a backslash"
    message_nested = "f-string: expressions nested too deeply"
    message_conversion = "f-string: invalid conversion character: expected 's', 'r', or 'a'"

    def _check_format_spec(self, format_spec, depth):
        self._check_fstring_contents(format_spec.children[1:], depth)

    def _check_fstring_expr(self, fstring_expr, depth):
        if depth >= 2:
            self.add_issue(fstring_expr, message=self.message_nested)

        expr = fstring_expr.children[1]
        if '\\' in expr.get_code():
            self.add_issue(expr, message=self.message_expr)

        conversion = fstring_expr.children[2]
        if conversion.type == 'fstring_conversion':
            name = conversion.children[1]
            if name.value not in ('s', 'r', 'a'):
                self.add_issue(name, message=self.message_conversion)

        format_spec = fstring_expr.children[-2]
        if format_spec.type == 'fstring_format_spec':
            self._check_format_spec(format_spec, depth + 1)

    def is_issue(self, fstring):
        self._check_fstring_contents(fstring.children[1:-1])

    def _check_fstring_contents(self, children, depth=0):
        for fstring_content in children:
            if fstring_content.type == 'fstring_expr':
                self._check_fstring_expr(fstring_content, depth)


class _CheckAssignmentRule(SyntaxRule):
    def _check_assignment(self, node, is_deletion=False, is_namedexpr=False):
        error = None
        type_ = node.type
        if type_ == 'lambdef':
            error = 'lambda'
        elif type_ == 'atom':
            first, second = node.children[:2]
            error = _get_comprehension_type(node)
            if error is None:
                if second.type == 'dictorsetmaker':
                    if self._normalizer.version < (3, 8):
                        error = 'literal'
                    else:
                        if second.children[1] == ':':
                            error = 'dict display'
                        else:
                            error = 'set display'
                elif first in ('(', '['):
                    if second.type == 'yield_expr':
                        error = 'yield expression'
                    elif second.type == 'testlist_comp':
                        # ([a, b] := [1, 2])
                        # ((a, b) := [1, 2])
                        if is_namedexpr:
                            if first == '(':
                                error = 'tuple'
                            elif first == '[':
                                error = 'list'

                        # This is not a comprehension, they were handled
                        # further above.
                        for child in second.children[::2]:
                            self._check_assignment(child, is_deletion, is_namedexpr)
                    else:  # Everything handled, must be useless brackets.
                        self._check_assignment(second, is_deletion, is_namedexpr)
        elif type_ == 'keyword':
            if self._normalizer.version < (3, 8):
                error = 'keyword'
            else:
                error = str(node.value)
        elif type_ == 'operator':
            if node.value == '...':
                error = 'Ellipsis'
        elif type_ == 'comparison':
            error = 'comparison'
        elif type_ in ('string', 'number', 'strings'):
            error = 'literal'
        elif type_ == 'yield_expr':
            # This one seems to be a slightly different warning in Python.
            message = 'assignment to yield expression not possible'
            self.add_issue(node, message=message)
        elif type_ == 'test':
            error = 'conditional expression'
        elif type_ in ('atom_expr', 'power'):
            if node.children[0] == 'await':
                error = 'await expression'
            elif node.children[-2] == '**':
                error = 'operator'
            else:
                # Has a trailer
                trailer = node.children[-1]
                assert trailer.type == 'trailer'
                if trailer.children[0] == '(':
                    error = 'function call'
                elif is_namedexpr and trailer.children[0] == '[':
                    error = 'subscript'
                elif is_namedexpr and trailer.children[0] == '.':
                    error = 'attribute'
        elif type_ in ('testlist_star_expr', 'exprlist', 'testlist'):
            for child in node.children[::2]:
                self._check_assignment(child, is_deletion, is_namedexpr)
        elif ('expr' in type_ and type_ != 'star_expr'  # is a substring
              or '_test' in type_
              or type_ in ('term', 'factor')):
            error = 'operator'

        if error is not None:
            if is_namedexpr:
                message = 'cannot use assignment expressions with %s' % error
            else:
                cannot = "can't" if self._normalizer.version < (3, 8) else "cannot"
                message = ' '.join([cannot, "delete" if is_deletion else "assign to", error])
            self.add_issue(node, message=message)


@ErrorFinder.register_rule(type='sync_comp_for')
class _CompForRule(_CheckAssignmentRule):
    message = "asynchronous comprehension outside of an asynchronous function"

    def is_issue(self, node):
        expr_list = node.children[1]
        if expr_list.type != 'expr_list':  # Already handled.
            self._check_assignment(expr_list)

        return node.parent.children[0] == 'async' \
            and not self._normalizer.context.is_async_funcdef()


@ErrorFinder.register_rule(type='expr_stmt')
class _ExprStmtRule(_CheckAssignmentRule):
    message = "illegal expression for augmented assignment"

    def is_issue(self, node):
        for before_equal in node.children[:-2:2]:
            self._check_assignment(before_equal)

        augassign = node.children[1]
        if augassign != '=' and augassign.type != 'annassign':  # Is augassign.
            return node.children[0].type in ('testlist_star_expr', 'atom', 'testlist')


@ErrorFinder.register_rule(type='with_item')
class _WithItemRule(_CheckAssignmentRule):
    def is_issue(self, with_item):
        self._check_assignment(with_item.children[2])


@ErrorFinder.register_rule(type='del_stmt')
class _DelStmtRule(_CheckAssignmentRule):
    def is_issue(self, del_stmt):
        child = del_stmt.children[1]

        if child.type != 'expr_list':  # Already handled.
            self._check_assignment(child, is_deletion=True)


@ErrorFinder.register_rule(type='expr_list')
class _ExprListRule(_CheckAssignmentRule):
    def is_issue(self, expr_list):
        for expr in expr_list.children[::2]:
            self._check_assignment(expr)


@ErrorFinder.register_rule(type='for_stmt')
class _ForStmtRule(_CheckAssignmentRule):
    def is_issue(self, for_stmt):
        # Some of the nodes here are already used, so no else if
        expr_list = for_stmt.children[1]
        if expr_list.type != 'expr_list':  # Already handled.
            self._check_assignment(expr_list)


@ErrorFinder.register_rule(type='namedexpr_test')
class _NamedExprRule(_CheckAssignmentRule):
    # namedexpr_test: test [':=' test]

    def is_issue(self, namedexpr_test):
        # assigned name
        first = namedexpr_test.children[0]

        def search_namedexpr_in_comp_for(node):
            while True:
                parent = node.parent
                if parent is None:
                    return parent
                if parent.type == 'sync_comp_for' and parent.children[3] == node:
                    return parent
                node = parent

        if search_namedexpr_in_comp_for(namedexpr_test):
            # [i+1 for i in (i := range(5))]
            # [i+1 for i in (j := range(5))]
            # [i+1 for i in (lambda: (j := range(5)))()]
            message = 'assignment expression cannot be used in a comprehension iterable expression'
            self.add_issue(namedexpr_test, message=message)

        # defined names
        exprlist = list()

        def process_comp_for(comp_for):
            if comp_for.type == 'sync_comp_for':
                comp = comp_for
            elif comp_for.type == 'comp_for':
                comp = comp_for.children[1]
            exprlist.extend(_get_for_stmt_definition_exprs(comp))

        def search_all_comp_ancestors(node):
            has_ancestors = False
            while True:
                node = search_ancestor(node, 'testlist_comp', 'dictorsetmaker')
                if node is None:
                    break
                for child in node.children:
                    if child.type in _COMP_FOR_TYPES:
                        process_comp_for(child)
                        has_ancestors = True
                        break
            return has_ancestors

        # check assignment expressions in comprehensions
        search_all = search_all_comp_ancestors(namedexpr_test)
        if search_all:
            if self._normalizer.context.node.type == 'classdef':
                message = 'assignment expression within a comprehension ' \
                          'cannot be used in a class body'
                self.add_issue(namedexpr_test, message=message)

            namelist = [expr.value for expr in exprlist if expr.type == 'name']
            if first.type == 'name' and first.value in namelist:
                # [i := 0 for i, j in range(5)]
                # [[(i := i) for j in range(5)] for i in range(5)]
                # [i for i, j in range(5) if True or (i := 1)]
                # [False and (i := 0) for i, j in range(5)]
                message = 'assignment expression cannot rebind ' \
                          'comprehension iteration variable %r' % first.value
                self.add_issue(namedexpr_test, message=message)

        self._check_assignment(first, is_namedexpr=True)