"""A module for unparsing ASTs back to source code.

NOTE: This is a verbatim copy of the code at https://github.com/python/cpython/blob/3.9/Lib/ast.py

This is only used for backwards compatiblity for python 3.8 as unparse was added in python 3.9.
"""

import ast
import sys
from ast import AsyncFunctionDef, ClassDef, Constant, Expr, FunctionDef, If, Module, Name, Starred, Tuple
from contextlib import contextmanager, nullcontext
from enum import IntEnum, auto

# Large float and imaginary literals get turned into infinities in the AST.
# We unparse those infinities to INFSTR.
_INFSTR = "1e" + repr(sys.float_info.max_10_exp + 1)


class _Precedence(IntEnum):
    """Precedence table that originated from python grammar."""

    TUPLE = auto()
    YIELD = auto()  # 'yield', 'yield from'
    TEST = auto()  # 'if'-'else', 'lambda'
    OR = auto()  # 'or'
    AND = auto()  # 'and'
    NOT = auto()  # 'not'
    CMP = auto()  # '<', '>', '==', '>=', '<=', '!=',
    # 'in', 'not in', 'is', 'is not'
    EXPR = auto()
    BOR = EXPR  # '|'
    BXOR = auto()  # '^'
    BAND = auto()  # '&'
    SHIFT = auto()  # '<<', '>>'
    ARITH = auto()  # '+', '-'
    TERM = auto()  # '*', '@', '/', '%', '//'
    FACTOR = auto()  # unary '+', '-', '~'
    POWER = auto()  # '**'
    AWAIT = auto()  # 'await'
    ATOM = auto()

    def next(self):
        try:
            return self.__class__(self + 1)
        except ValueError:
            return self


_SINGLE_QUOTES = ("'", '"')
_MULTI_QUOTES = ('"""', "'''")
_ALL_QUOTES = (*_SINGLE_QUOTES, *_MULTI_QUOTES)


class _Unparser(ast.NodeVisitor):
    """Methods in this class recursively traverse an AST and
    output source code for the abstract syntax; original formatting
    is disregarded.
    """

    def __init__(self, *, _avoid_backslashes=False):
        self._source = []
        self._buffer = []
        self._precedences = {}
        self._type_ignores = {}
        self._indent = 0
        self._avoid_backslashes = _avoid_backslashes

    def __call__(self, node):
        """Outputs a source code string that, if converted back to an ast
        (using ast.parse) will generate an AST equivalent to *node*
        .
        """
        self._source = []
        self.traverse(node)
        return "".join(self._source)

    def interleave(self, inter, f, seq):
        """Call f on each item in seq, calling inter() in between."""
        seq = iter(seq)
        try:
            f(next(seq))
        except StopIteration:
            pass
        else:
            for x in seq:
                inter()
                f(x)

    def items_view(self, traverser, items):
        """Traverse and separate the given *items* with a comma and append it to
        the buffer. If *items* is a single item sequence, a trailing comma
        will be added.
        """
        if len(items) == 1:
            traverser(items[0])
            self.write(",")
        else:
            self.interleave(lambda: self.write(", "), traverser, items)

    def maybe_newline(self):
        """Adds a newline if it isn't the start of generated source."""
        if self._source:
            self.write("\n")

    def fill(self, text=""):
        """Indent a piece of text and append it, according to the current
        indentation level
        .
        """
        self.maybe_newline()
        self.write("    " * self._indent + text)

    def write(self, text):
        """Append a piece of text."""
        self._source.append(text)

    def buffer_writer(self, text):
        self._buffer.append(text)

    @property
    def buffer(self):
        value = "".join(self._buffer)
        self._buffer.clear()
        return value

    @contextmanager
    def block(self, *, extra=None):
        """A context manager for preparing the source for blocks. It adds
        the character':', increases the indentation on enter and decreases
        the indentation on exit. If *extra* is given, it will be directly
        appended after the colon character.
        """
        self.write(":")
        if extra:
            self.write(extra)
        self._indent += 1
        yield
        self._indent -= 1

    @contextmanager
    def delimit(self, start, end):
        """A context manager for preparing the source for expressions. It adds
        *start* to the buffer and enters, after exit it adds *end*.
        """
        self.write(start)
        yield
        self.write(end)

    def delimit_if(self, start, end, condition):
        if condition:
            return self.delimit(start, end)
        else:
            return nullcontext()

    def require_parens(self, precedence, node):
        """Shortcut to adding precedence related parens."""
        return self.delimit_if("(", ")", self.get_precedence(node) > precedence)

    def get_precedence(self, node):
        return self._precedences.get(node, _Precedence.TEST)

    def set_precedence(self, precedence, *nodes):
        for node in nodes:
            self._precedences[node] = precedence

    def get_raw_docstring(self, node):
        """If a docstring node is found in the body of the *node* parameter,
        return that docstring node, None otherwise.

        Logic mirrored from ``_PyAST_GetDocString``.
        """
        if not isinstance(node, (AsyncFunctionDef, FunctionDef, ClassDef, Module)) or len(node.body) < 1:
            return None
        node = node.body[0]
        if not isinstance(node, Expr):
            return None
        node = node.value
        if isinstance(node, Constant) and isinstance(node.value, str):
            return node

    def get_type_comment(self, node):
        comment = self._type_ignores.get(node.lineno) or node.type_comment
        if comment is not None:
            return f" # type: {comment}"

    def traverse(self, node):
        if isinstance(node, list):
            for item in node:
                self.traverse(item)
        else:
            super().visit(node)

    def _write_docstring_and_traverse_body(self, node):
        if docstring := self.get_raw_docstring(node):
            self._write_docstring(docstring)
            self.traverse(node.body[1:])
        else:
            self.traverse(node.body)

    def visit_Module(self, node):
        self._type_ignores = {ignore.lineno: f"ignore{ignore.tag}" for ignore in node.type_ignores}
        self._write_docstring_and_traverse_body(node)
        self._type_ignores.clear()

    def visit_FunctionType(self, node):
        with self.delimit("(", ")"):
            self.interleave(lambda: self.write(", "), self.traverse, node.argtypes)

        self.write(" -> ")
        self.traverse(node.returns)

    def visit_Expr(self, node):
        self.fill()
        self.set_precedence(_Precedence.YIELD, node.value)
        self.traverse(node.value)

    def visit_NamedExpr(self, node):
        with self.require_parens(_Precedence.TUPLE, node):
            self.set_precedence(_Precedence.ATOM, node.target, node.value)
            self.traverse(node.target)
            self.write(" := ")
            self.traverse(node.value)

    def visit_Import(self, node):
        self.fill("import ")
        self.interleave(lambda: self.write(", "), self.traverse, node.names)

    def visit_ImportFrom(self, node):
        self.fill("from ")
        self.write("." * node.level)
        if node.module:
            self.write(node.module)
        self.write(" import ")
        self.interleave(lambda: self.write(", "), self.traverse, node.names)

    def visit_Assign(self, node):
        self.fill()
        for target in node.targets:
            self.traverse(target)
            self.write(" = ")
        self.traverse(node.value)
        if type_comment := self.get_type_comment(node):
            self.write(type_comment)

    def visit_AugAssign(self, node):
        self.fill()
        self.traverse(node.target)
        self.write(" " + self.binop[node.op.__class__.__name__] + "= ")
        self.traverse(node.value)

    def visit_AnnAssign(self, node):
        self.fill()
        with self.delimit_if("(", ")", not node.simple and isinstance(node.target, Name)):
            self.traverse(node.target)
        self.write(": ")
        self.traverse(node.annotation)
        if node.value:
            self.write(" = ")
            self.traverse(node.value)

    def visit_Return(self, node):
        self.fill("return")
        if node.value:
            self.write(" ")
            self.traverse(node.value)

    def visit_Pass(self, node):
        self.fill("pass")

    def visit_Break(self, node):
        self.fill("break")

    def visit_Continue(self, node):
        self.fill("continue")

    def visit_Delete(self, node):
        self.fill("del ")
        self.interleave(lambda: self.write(", "), self.traverse, node.targets)

    def visit_Assert(self, node):
        self.fill("assert ")
        self.traverse(node.test)
        if node.msg:
            self.write(", ")
            self.traverse(node.msg)

    def visit_Global(self, node):
        self.fill("global ")
        self.interleave(lambda: self.write(", "), self.write, node.names)

    def visit_Nonlocal(self, node):
        self.fill("nonlocal ")
        self.interleave(lambda: self.write(", "), self.write, node.names)

    def visit_Await(self, node):
        with self.require_parens(_Precedence.AWAIT, node):
            self.write("await")
            if node.value:
                self.write(" ")
                self.set_precedence(_Precedence.ATOM, node.value)
                self.traverse(node.value)

    def visit_Yield(self, node):
        with self.require_parens(_Precedence.YIELD, node):
            self.write("yield")
            if node.value:
                self.write(" ")
                self.set_precedence(_Precedence.ATOM, node.value)
                self.traverse(node.value)

    def visit_YieldFrom(self, node):
        with self.require_parens(_Precedence.YIELD, node):
            self.write("yield from ")
            if not node.value:
                raise ValueError("Node can't be used without a value attribute.")
            self.set_precedence(_Precedence.ATOM, node.value)
            self.traverse(node.value)

    def visit_Raise(self, node):
        self.fill("raise")
        if not node.exc:
            if node.cause:
                raise ValueError("Node can't use cause without an exception.")
            return
        self.write(" ")
        self.traverse(node.exc)
        if node.cause:
            self.write(" from ")
            self.traverse(node.cause)

    def visit_Try(self, node):
        self.fill("try")
        with self.block():
            self.traverse(node.body)
        for ex in node.handlers:
            self.traverse(ex)
        if node.orelse:
            self.fill("else")
            with self.block():
                self.traverse(node.orelse)
        if node.finalbody:
            self.fill("finally")
            with self.block():
                self.traverse(node.finalbody)

    def visit_ExceptHandler(self, node):
        self.fill("except")
        if node.type:
            self.write(" ")
            self.traverse(node.type)
        if node.name:
            self.write(" as ")
            self.write(node.name)
        with self.block():
            self.traverse(node.body)

    def visit_ClassDef(self, node):
        self.maybe_newline()
        for deco in node.decorator_list:
            self.fill("@")
            self.traverse(deco)
        self.fill("class " + node.name)
        with self.delimit_if("(", ")", condition=node.bases or node.keywords):
            comma = False
            for e in node.bases:
                if comma:
                    self.write(", ")
                else:
                    comma = True
                self.traverse(e)
            for e in node.keywords:
                if comma:
                    self.write(", ")
                else:
                    comma = True
                self.traverse(e)

        with self.block():
            self._write_docstring_and_traverse_body(node)

    def visit_FunctionDef(self, node):
        self._function_helper(node, "def")

    def visit_AsyncFunctionDef(self, node):
        self._function_helper(node, "async def")

    def _function_helper(self, node, fill_suffix):
        self.maybe_newline()
        for deco in node.decorator_list:
            self.fill("@")
            self.traverse(deco)
        def_str = fill_suffix + " " + node.name
        self.fill(def_str)
        with self.delimit("(", ")"):
            self.traverse(node.args)
        if node.returns:
            self.write(" -> ")
            self.traverse(node.returns)
        with self.block(extra=self.get_type_comment(node)):
            self._write_docstring_and_traverse_body(node)

    def visit_For(self, node):
        self._for_helper("for ", node)

    def visit_AsyncFor(self, node):
        self._for_helper("async for ", node)

    def _for_helper(self, fill, node):
        self.fill(fill)
        self.traverse(node.target)
        self.write(" in ")
        self.traverse(node.iter)
        with self.block(extra=self.get_type_comment(node)):
            self.traverse(node.body)
        if node.orelse:
            self.fill("else")
            with self.block():
                self.traverse(node.orelse)

    def visit_If(self, node):
        self.fill("if ")
        self.traverse(node.test)
        with self.block():
            self.traverse(node.body)
        # collapse nested ifs into equivalent elifs.
        while node.orelse and len(node.orelse) == 1 and isinstance(node.orelse[0], If):
            node = node.orelse[0]
            self.fill("elif ")
            self.traverse(node.test)
            with self.block():
                self.traverse(node.body)
        # final else
        if node.orelse:
            self.fill("else")
            with self.block():
                self.traverse(node.orelse)

    def visit_While(self, node):
        self.fill("while ")
        self.traverse(node.test)
        with self.block():
            self.traverse(node.body)
        if node.orelse:
            self.fill("else")
            with self.block():
                self.traverse(node.orelse)

    def visit_With(self, node):
        self.fill("with ")
        self.interleave(lambda: self.write(", "), self.traverse, node.items)
        with self.block(extra=self.get_type_comment(node)):
            self.traverse(node.body)

    def visit_AsyncWith(self, node):
        self.fill("async with ")
        self.interleave(lambda: self.write(", "), self.traverse, node.items)
        with self.block(extra=self.get_type_comment(node)):
            self.traverse(node.body)

    def _str_literal_helper(self, string, *, quote_types=_ALL_QUOTES, escape_special_whitespace=False):
        """Helper for writing string literals, minimizing escapes.
        Returns the tuple (string literal to write, possible quote types).
        """

        def escape_char(c):
            # \n and \t are non-printable, but we only escape them if
            # escape_special_whitespace is True
            if not escape_special_whitespace and c in "\n\t":
                return c
            # Always escape backslashes and other non-printable characters
            if c == "\\" or not c.isprintable():
                return c.encode("unicode_escape").decode("ascii")
            return c

        escaped_string = "".join(map(escape_char, string))
        possible_quotes = quote_types
        if "\n" in escaped_string:
            possible_quotes = [q for q in possible_quotes if q in _MULTI_QUOTES]
        possible_quotes = [q for q in possible_quotes if q not in escaped_string]
        if not possible_quotes:
            # If there aren't any possible_quotes, fallback to using repr
            # on the original string. Try to use a quote from quote_types,
            # e.g., so that we use triple quotes for docstrings.
            string = repr(string)
            quote = next((q for q in quote_types if string[0] in q), string[0])
            return string[1:-1], [quote]
        if escaped_string:
            # Sort so that we prefer '''"''' over """\""""
            possible_quotes.sort(key=lambda q: q[0] == escaped_string[-1])
            # If we're using triple quotes and we'd need to escape a final
            # quote, escape it
            if possible_quotes[0][0] == escaped_string[-1]:
                assert len(possible_quotes[0]) == 3
                escaped_string = escaped_string[:-1] + "\\" + escaped_string[-1]
        return escaped_string, possible_quotes

    def _write_str_avoiding_backslashes(self, string, *, quote_types=_ALL_QUOTES):
        """Write string literal value with a best effort attempt to avoid backslashes."""
        string, quote_types = self._str_literal_helper(string, quote_types=quote_types)
        quote_type = quote_types[0]
        self.write(f"{quote_type}{string}{quote_type}")

    def visit_JoinedStr(self, node):
        self.write("f")
        if self._avoid_backslashes:
            self._fstring_JoinedStr(node, self.buffer_writer)
            self._write_str_avoiding_backslashes(self.buffer)
            return

        # If we don't need to avoid backslashes globally (i.e., we only need
        # to avoid them inside FormattedValues), it's cosmetically preferred
        # to use escaped whitespace. That is, it's preferred to use backslashes
        # for cases like: f"{x}\n". To accomplish this, we keep track of what
        # in our buffer corresponds to FormattedValues and what corresponds to
        # Constant parts of the f-string, and allow escapes accordingly.
        buffer = []
        for value in node.values:
            meth = getattr(self, "_fstring_" + type(value).__name__)
            meth(value, self.buffer_writer)
            buffer.append((self.buffer, isinstance(value, Constant)))
        new_buffer = []
        quote_types = _ALL_QUOTES
        for value, is_constant in buffer:
            # Repeatedly narrow down the list of possible quote_types
            value, quote_types = self._str_literal_helper(
                value, quote_types=quote_types, escape_special_whitespace=is_constant
            )
            new_buffer.append(value)
        value = "".join(new_buffer)
        quote_type = quote_types[0]
        self.write(f"{quote_type}{value}{quote_type}")

    def visit_FormattedValue(self, node):
        self.write("f")
        self._fstring_FormattedValue(node, self.buffer_writer)
        self._write_str_avoiding_backslashes(self.buffer)

    def _fstring_JoinedStr(self, node, write):
        for value in node.values:
            meth = getattr(self, "_fstring_" + type(value).__name__)
            meth(value, write)

    def _fstring_Constant(self, node, write):
        if not isinstance(node.value, str):
            raise ValueError("Constants inside JoinedStr should be a string.")
        value = node.value.replace("{", "{{").replace("}", "}}")
        write(value)

    def _fstring_FormattedValue(self, node, write):
        write("{")
        unparser = type(self)(_avoid_backslashes=True)
        unparser.set_precedence(_Precedence.TEST.next(), node.value)
        expr = unparser.visit(node.value)
        if expr.startswith("{"):
            write(" ")  # Separate pair of opening brackets as "{ {"
        if "\\" in expr:
            raise ValueError("Unable to avoid backslash in f-string expression part")
        write(expr)
        if node.conversion != -1:
            conversion = chr(node.conversion)
            if conversion not in "sra":
                raise ValueError("Unknown f-string conversion.")
            write(f"!{conversion}")
        if node.format_spec:
            write(":")
            meth = getattr(self, "_fstring_" + type(node.format_spec).__name__)
            meth(node.format_spec, write)
        write("}")

    def visit_Name(self, node):
        self.write(node.id)

    def _write_docstring(self, node):
        self.fill()
        if node.kind == "u":
            self.write("u")
        self._write_str_avoiding_backslashes(node.value, quote_types=_MULTI_QUOTES)

    def _write_constant(self, value):
        if isinstance(value, (float, complex)):
            # Substitute overflowing decimal literal for AST infinities,
            # and inf - inf for NaNs.
            self.write(repr(value).replace("inf", _INFSTR).replace("nan", f"({_INFSTR}-{_INFSTR})"))
        elif self._avoid_backslashes and isinstance(value, str):
            self._write_str_avoiding_backslashes(value)
        else:
            self.write(repr(value))

    def visit_Constant(self, node):
        value = node.value
        if isinstance(value, tuple):
            with self.delimit("(", ")"):
                self.items_view(self._write_constant, value)
        elif value is ...:
            self.write("...")
        else:
            if node.kind == "u":
                self.write("u")
            self._write_constant(node.value)

    def visit_List(self, node):
        with self.delimit("[", "]"):
            self.interleave(lambda: self.write(", "), self.traverse, node.elts)

    def visit_ListComp(self, node):
        with self.delimit("[", "]"):
            self.traverse(node.elt)
            for gen in node.generators:
                self.traverse(gen)

    def visit_GeneratorExp(self, node):
        with self.delimit("(", ")"):
            self.traverse(node.elt)
            for gen in node.generators:
                self.traverse(gen)

    def visit_SetComp(self, node):
        with self.delimit("{", "}"):
            self.traverse(node.elt)
            for gen in node.generators:
                self.traverse(gen)

    def visit_DictComp(self, node):
        with self.delimit("{", "}"):
            self.traverse(node.key)
            self.write(": ")
            self.traverse(node.value)
            for gen in node.generators:
                self.traverse(gen)

    def visit_comprehension(self, node):
        if node.is_async:
            self.write(" async for ")
        else:
            self.write(" for ")
        self.set_precedence(_Precedence.TUPLE, node.target)
        self.traverse(node.target)
        self.write(" in ")
        self.set_precedence(_Precedence.TEST.next(), node.iter, *node.ifs)
        self.traverse(node.iter)
        for if_clause in node.ifs:
            self.write(" if ")
            self.traverse(if_clause)

    def visit_IfExp(self, node):
        with self.require_parens(_Precedence.TEST, node):
            self.set_precedence(_Precedence.TEST.next(), node.body, node.test)
            self.traverse(node.body)
            self.write(" if ")
            self.traverse(node.test)
            self.write(" else ")
            self.set_precedence(_Precedence.TEST, node.orelse)
            self.traverse(node.orelse)

    def visit_Set(self, node):
        if node.elts:
            with self.delimit("{", "}"):
                self.interleave(lambda: self.write(", "), self.traverse, node.elts)
        else:
            # `{}` would be interpreted as a dictionary literal, and
            # `set` might be shadowed. Thus:
            self.write("{*()}")

    def visit_Dict(self, node):
        def write_key_value_pair(k, v):
            self.traverse(k)
            self.write(": ")
            self.traverse(v)

        def write_item(item):
            k, v = item
            if k is None:
                # for dictionary unpacking operator in dicts {**{'y': 2}}
                # see PEP 448 for details
                self.write("**")
                self.set_precedence(_Precedence.EXPR, v)
                self.traverse(v)
            else:
                write_key_value_pair(k, v)

        with self.delimit("{", "}"):
            self.interleave(lambda: self.write(", "), write_item, zip(node.keys, node.values))

    def visit_Tuple(self, node):
        with self.delimit("(", ")"):
            self.items_view(self.traverse, node.elts)

    unop = {"Invert": "~", "Not": "not", "UAdd": "+", "USub": "-"}
    unop_precedence = {
        "not": _Precedence.NOT,
        "~": _Precedence.FACTOR,
        "+": _Precedence.FACTOR,
        "-": _Precedence.FACTOR,
    }

    def visit_UnaryOp(self, node):
        operator = self.unop[node.op.__class__.__name__]
        operator_precedence = self.unop_precedence[operator]
        with self.require_parens(operator_precedence, node):
            self.write(operator)
            # factor prefixes (+, -, ~) shouldn't be seperated
            # from the value they belong, (e.g: +1 instead of + 1)
            if operator_precedence is not _Precedence.FACTOR:
                self.write(" ")
            self.set_precedence(operator_precedence, node.operand)
            self.traverse(node.operand)

    binop = {
        "Add": "+",
        "Sub": "-",
        "Mult": "*",
        "MatMult": "@",
        "Div": "/",
        "Mod": "%",
        "LShift": "<<",
        "RShift": ">>",
        "BitOr": "|",
        "BitXor": "^",
        "BitAnd": "&",
        "FloorDiv": "//",
        "Pow": "**",
    }

    binop_precedence = {
        "+": _Precedence.ARITH,
        "-": _Precedence.ARITH,
        "*": _Precedence.TERM,
        "@": _Precedence.TERM,
        "/": _Precedence.TERM,
        "%": _Precedence.TERM,
        "<<": _Precedence.SHIFT,
        ">>": _Precedence.SHIFT,
        "|": _Precedence.BOR,
        "^": _Precedence.BXOR,
        "&": _Precedence.BAND,
        "//": _Precedence.TERM,
        "**": _Precedence.POWER,
    }

    binop_rassoc = frozenset(("**",))

    def visit_BinOp(self, node):
        operator = self.binop[node.op.__class__.__name__]
        operator_precedence = self.binop_precedence[operator]
        with self.require_parens(operator_precedence, node):
            if operator in self.binop_rassoc:
                left_precedence = operator_precedence.next()
                right_precedence = operator_precedence
            else:
                left_precedence = operator_precedence
                right_precedence = operator_precedence.next()

            self.set_precedence(left_precedence, node.left)
            self.traverse(node.left)
            self.write(f" {operator} ")
            self.set_precedence(right_precedence, node.right)
            self.traverse(node.right)

    cmpops = {
        "Eq": "==",
        "NotEq": "!=",
        "Lt": "<",
        "LtE": "<=",
        "Gt": ">",
        "GtE": ">=",
        "Is": "is",
        "IsNot": "is not",
        "In": "in",
        "NotIn": "not in",
    }

    def visit_Compare(self, node):
        with self.require_parens(_Precedence.CMP, node):
            self.set_precedence(_Precedence.CMP.next(), node.left, *node.comparators)
            self.traverse(node.left)
            for o, e in zip(node.ops, node.comparators):
                self.write(" " + self.cmpops[o.__class__.__name__] + " ")
                self.traverse(e)

    boolops = {"And": "and", "Or": "or"}
    boolop_precedence = {"and": _Precedence.AND, "or": _Precedence.OR}

    def visit_BoolOp(self, node):
        operator = self.boolops[node.op.__class__.__name__]
        operator_precedence = self.boolop_precedence[operator]

        def increasing_level_traverse(node):
            nonlocal operator_precedence
            operator_precedence = operator_precedence.next()
            self.set_precedence(operator_precedence, node)
            self.traverse(node)

        with self.require_parens(operator_precedence, node):
            s = f" {operator} "
            self.interleave(lambda: self.write(s), increasing_level_traverse, node.values)

    def visit_Attribute(self, node):
        self.set_precedence(_Precedence.ATOM, node.value)
        self.traverse(node.value)
        # Special case: 3.__abs__() is a syntax error, so if node.value
        # is an integer literal then we need to either parenthesize
        # it or add an extra space to get 3 .__abs__().
        if isinstance(node.value, Constant) and isinstance(node.value.value, int):
            self.write(" ")
        self.write(".")
        self.write(node.attr)

    def visit_Call(self, node):
        self.set_precedence(_Precedence.ATOM, node.func)
        self.traverse(node.func)
        with self.delimit("(", ")"):
            comma = False
            for e in node.args:
                if comma:
                    self.write(", ")
                else:
                    comma = True
                self.traverse(e)
            for e in node.keywords:
                if comma:
                    self.write(", ")
                else:
                    comma = True
                self.traverse(e)

    def visit_Subscript(self, node):
        def is_simple_tuple(slice_value):
            # when unparsing a non-empty tuple, the parentheses can be safely
            # omitted if there aren't any elements that explicitly requires
            # parentheses (such as starred expressions).
            return (
                isinstance(slice_value, Tuple)
                and slice_value.elts
                and not any(isinstance(elt, Starred) for elt in slice_value.elts)
            )

        self.set_precedence(_Precedence.ATOM, node.value)
        self.traverse(node.value)
        with self.delimit("[", "]"):
            if is_simple_tuple(node.slice):
                self.items_view(self.traverse, node.slice.elts)
            else:
                self.traverse(node.slice)

    def visit_Starred(self, node):
        self.write("*")
        self.set_precedence(_Precedence.EXPR, node.value)
        self.traverse(node.value)

    def visit_Ellipsis(self, node):
        self.write("...")

    def visit_Slice(self, node):
        if node.lower:
            self.traverse(node.lower)
        self.write(":")
        if node.upper:
            self.traverse(node.upper)
        if node.step:
            self.write(":")
            self.traverse(node.step)

    def visit_arg(self, node):
        self.write(node.arg)
        if node.annotation:
            self.write(": ")
            self.traverse(node.annotation)

    def visit_arguments(self, node):
        first = True
        # normal arguments
        all_args = node.posonlyargs + node.args
        defaults = [None] * (len(all_args) - len(node.defaults)) + node.defaults
        for index, elements in enumerate(zip(all_args, defaults), 1):
            a, d = elements
            if first:
                first = False
            else:
                self.write(", ")
            self.traverse(a)
            if d:
                self.write("=")
                self.traverse(d)
            if index == len(node.posonlyargs):
                self.write(", /")

        # varargs, or bare '*' if no varargs but keyword-only arguments present
        if node.vararg or node.kwonlyargs:
            if first:
                first = False
            else:
                self.write(", ")
            self.write("*")
            if node.vararg:
                self.write(node.vararg.arg)
                if node.vararg.annotation:
                    self.write(": ")
                    self.traverse(node.vararg.annotation)

        # keyword-only arguments
        if node.kwonlyargs:
            for a, d in zip(node.kwonlyargs, node.kw_defaults):
                self.write(", ")
                self.traverse(a)
                if d:
                    self.write("=")
                    self.traverse(d)

        # kwargs
        if node.kwarg:
            if first:
                first = False
            else:
                self.write(", ")
            self.write("**" + node.kwarg.arg)
            if node.kwarg.annotation:
                self.write(": ")
                self.traverse(node.kwarg.annotation)

    def visit_keyword(self, node):
        if node.arg is None:
            self.write("**")
        else:
            self.write(node.arg)
            self.write("=")
        self.traverse(node.value)

    def visit_Lambda(self, node):
        with self.require_parens(_Precedence.TEST, node):
            self.write("lambda ")
            self.traverse(node.args)
            self.write(": ")
            self.set_precedence(_Precedence.TEST, node.body)
            self.traverse(node.body)

    def visit_alias(self, node):
        self.write(node.name)
        if node.asname:
            self.write(" as " + node.asname)

    def visit_withitem(self, node):
        self.traverse(node.context_expr)
        if node.optional_vars:
            self.write(" as ")
            self.traverse(node.optional_vars)


def unparse(ast_obj):
    unparser = _Unparser()
    return unparser(ast_obj)


def roundtrip(source):
    tree = ast.parse(source)
    if hasattr(ast, "unparse"):
        return ast.unparse(tree)
    return unparse(tree)
