"""

Implementation of the decompiler class.

"""

import ast
import cmath
from contextlib import contextmanager
import math
import sys
from typing import Any, Dict, Generator, Iterable, Optional, Sequence, Type, Union

_OP_TO_STR = {
    ast.Add: "+",
    ast.Sub: "-",
    ast.Mult: "*",
    ast.Div: "/",
    ast.Mod: "%",
    ast.Pow: "**",
    ast.LShift: "<<",
    ast.RShift: ">>",
    ast.BitOr: "|",
    ast.BitXor: "^",
    ast.BitAnd: "&",
    ast.FloorDiv: "//",
    ast.MatMult: "@",
    ast.Invert: "~",
    ast.Not: "not ",
    ast.UAdd: "+",
    ast.USub: "-",
    ast.Eq: "==",
    ast.NotEq: "!=",
    ast.Lt: "<",
    ast.LtE: "<=",
    ast.Gt: ">",
    ast.GtE: ">=",
    ast.Is: "is",
    ast.IsNot: "is not",
    ast.In: "in",
    ast.NotIn: "not in",
    ast.And: "and",
    ast.Or: "or",
}


class _CallArgs(ast.AST):
    """Used as an entry in the precedence table.

    Needed to convey the high precedence of the callee but low precedence of the arguments.

    """

    def __init__(self, args: Sequence[ast.AST]) -> None:
        self.args = args


_PRECEDENCE: Dict[Type[ast.AST], int] = {
    _CallArgs: -1,
    ast.Or: 0,
    ast.And: 1,
    ast.Not: 2,
    ast.Compare: 3,
    ast.BitOr: 4,
    ast.BitXor: 5,
    ast.BitAnd: 6,
    ast.LShift: 7,
    ast.RShift: 7,
    ast.Add: 8,
    ast.Sub: 8,
    ast.Mult: 9,
    ast.Div: 9,
    ast.FloorDiv: 9,
    ast.Mod: 9,
    ast.MatMult: 9,
    ast.UAdd: 10,
    ast.USub: 10,
    ast.Invert: 10,
    ast.Pow: 11,
    ast.Subscript: 12,
    ast.Call: 12,
    ast.Attribute: 12,
}


def decompile(
    ast: ast.AST,
    indentation: int = 4,
    line_length: int = 100,
    starting_indentation: int = 0,
) -> str:
    """Decompiles an AST into Python code.

    Arguments:
    - ast: code to decompile, using AST objects as generated by the standard library ast module
    - indentation: indentation level of lines
    - line_length: if lines become longer than this length, ast_decompiler will try to break them up
      (but it will not necessarily succeed in all cases)
    - starting_indentation: indentation level at which to start producing code

    """
    decompiler = Decompiler(
        indentation=indentation,
        line_length=line_length,
        starting_indentation=starting_indentation,
    )
    return decompiler.run(ast)


# helper ast nodes to make decompilation easier
class KeyValuePair(ast.AST):
    """A key-value pair as used in a dictionary display."""

    _fields = ("key", "value")

    def __init__(self, key: Optional[ast.AST], value: ast.AST) -> None:
        self.key = key
        self.value = value


class StarArg(ast.AST):
    """A * argument."""

    _fields = ("arg",)

    def __init__(self, arg: ast.arg) -> None:
        self.arg = arg


class DoubleStarArg(ast.AST):
    """A ** argument."""

    _fields = ("arg",)

    def __init__(self, arg: ast.arg) -> None:
        self.arg = arg


class KeywordArg(ast.AST):
    """A x=3 keyword argument in a function definition."""

    _fields = ("arg", "value")

    def __init__(self, arg: ast.arg, value: Optional[ast.AST]) -> None:
        self.arg = arg
        self.value = value


class Decompiler(ast.NodeVisitor):
    def __init__(
        self, indentation: int, line_length: int, starting_indentation: int
    ) -> None:
        self.lines = []
        self.current_line = []
        self.current_indentation = starting_indentation
        self.node_stack = []
        self.indentation = indentation
        self.max_line_length = line_length

    def run(self, ast: ast.AST) -> str:
        self.visit(ast)
        if self.current_line:
            self.lines.append("".join(self.current_line))
            self.current_line = []
        return "".join(self.lines)

    def visit(self, node: ast.AST) -> None:
        self.node_stack.append(node)
        try:
            super().visit(node)
        finally:
            self.node_stack.pop()

    def precedence_of_node(self, node: Optional[ast.AST]) -> int:
        if node is None:
            return -1
        if isinstance(node, (ast.BinOp, ast.UnaryOp, ast.BoolOp)):
            return _PRECEDENCE[type(node.op)]
        return _PRECEDENCE.get(type(node), -1)

    def get_parent_node(self) -> Optional[ast.AST]:
        try:
            return self.node_stack[-2]
        except IndexError:
            return None

    def has_parent_of_type(self, node_type: Type[ast.AST]) -> bool:
        return any(isinstance(parent, node_type) for parent in self.node_stack)

    def write(self, code: str) -> None:
        assert isinstance(code, str), f"invalid code {code!r}"
        self.current_line.append(code)

    def write_indentation(self) -> None:
        self.write(" " * self.current_indentation)

    def write_newline(self) -> None:
        line = "".join(self.current_line) + "\n"
        self.lines.append(line)
        self.current_line = []

    def current_line_length(self) -> int:
        return sum(map(len, self.current_line))

    def write_expression_list(
        self,
        nodes: Sequence[ast.AST],
        *,
        separator: str = ", ",
        allow_newlines: bool = True,
        need_parens: bool = True,
        final_separator_if_multiline: bool = True,
    ) -> None:
        """Writes a list of nodes, separated by separator.

        If allow_newlines, will write the expression over multiple lines if necessary to say within
        max_line_length. If need_parens, will surround the expression with parentheses in this case.
        If final_separator_if_multiline, will write a separator at the end of the list if it is
        divided over multiple lines.

        """
        first = True
        last_line = len(self.lines)
        current_line = list(self.current_line)
        for node in nodes:
            if first:
                first = False
            else:
                self.write(separator)
            self.visit(node)
            if allow_newlines and (
                self.current_line_length() > self.max_line_length
                or last_line != len(self.lines)
            ):
                break
        else:
            return  # stayed within the limit

        # reset state
        del self.lines[last_line:]
        self.current_line = current_line

        separator = separator.rstrip()
        if need_parens:
            self.write("(")
        self.write_newline()
        with self.add_indentation():
            num_nodes = len(nodes)
            for i, node in enumerate(nodes):
                self.write_indentation()
                self.visit(node)
                if final_separator_if_multiline or i < num_nodes - 1:
                    self.write(separator)
                self.write_newline()

        self.write_indentation()
        if need_parens:
            self.write(")")

    def write_suite(self, nodes: Iterable[ast.AST]) -> None:
        with self.add_indentation():
            for line in nodes:
                self.visit(line)

    @contextmanager
    def add_indentation(self) -> Generator[None, None, None]:
        self.current_indentation += self.indentation
        try:
            yield
        finally:
            self.current_indentation -= self.indentation

    @contextmanager
    def parenthesize_if(self, condition: bool) -> Generator[None, None, None]:
        if condition:
            self.write("(")
            yield
            self.write(")")
        else:
            yield

    @contextmanager
    def f_literalise_if(self, condition: bool) -> Generator[None, None, None]:
        if condition:
            self.write("f'")
            yield
            self.write("'")
        else:
            yield

    def generic_visit(self, node: ast.AST) -> None:
        raise NotImplementedError(f"missing visit method for {node!r}")

    def visit_Module(self, node: Union[ast.Module, ast.Interactive]) -> None:
        for line in node.body:
            self.visit(line)

    visit_Interactive = visit_Module

    def visit_Expression(self, node: ast.Expression) -> None:
        self.visit(node.body)

    # Multi-line statements

    def visit_FunctionDef(
        self, node: Union[ast.FunctionDef, ast.AsyncFunctionDef]
    ) -> None:
        self.write_newline()
        for decorator in node.decorator_list:
            self.write_indentation()
            self.write("@")
            self.visit(decorator)
            self.write_newline()

        self.write_indentation()
        if isinstance(node, ast.AsyncFunctionDef):
            self.write("async ")
        self.write(f"def {node.name}")
        if sys.version_info >= (3, 12) and node.type_params:
            self.write("[")
            self.write_expression_list(node.type_params)
            self.write("]")
        self.write("(")
        self.visit(node.args)
        self.write(")")
        if node.returns is not None:
            self.write(" -> ")
            self.visit(node.returns)
        self.write(":")
        self.write_newline()

        self.write_suite(node.body)

    visit_AsyncFunctionDef = visit_FunctionDef

    def visit_ClassDef(self, node: ast.ClassDef) -> None:
        self.write_newline()
        self.write_newline()
        for decorator in node.decorator_list:
            self.write_indentation()
            self.write("@")
            self.visit(decorator)
            self.write_newline()

        self.write_indentation()
        self.write(f"class {node.name}")
        if sys.version_info >= (3, 12) and node.type_params:
            self.write("[")
            self.write_expression_list(node.type_params)
            self.write("]")
        self.write("(")
        exprs = node.bases + getattr(node, "keywords", [])
        self.write_expression_list(exprs, need_parens=False)
        self.write("):")
        self.write_newline()
        self.write_suite(node.body)

    def visit_For(self, node: Union[ast.For, ast.AsyncFor]) -> None:
        self.write_indentation()
        if isinstance(node, ast.AsyncFor):
            self.write("async ")
        self.write("for ")
        self.visit(node.target)
        self.write(" in ")
        self.visit(node.iter)
        self.write(":")
        self.write_newline()
        self.write_suite(node.body)
        self.write_else(node.orelse)

    visit_AsyncFor = visit_For

    def visit_While(self, node: ast.While) -> None:
        self.write_indentation()
        self.write("while ")
        self.visit(node.test)
        self.write(":")
        self.write_newline()
        self.write_suite(node.body)
        self.write_else(node.orelse)

    def visit_If(self, node: ast.If) -> None:
        self.write_indentation()
        self.write("if ")
        self.visit(node.test)
        self.write(":")
        self.write_newline()
        self.write_suite(node.body)
        while (
            node.orelse and len(node.orelse) == 1 and isinstance(node.orelse[0], ast.If)
        ):
            node = node.orelse[0]
            self.write_indentation()
            self.write("elif ")
            self.visit(node.test)
            self.write(":")
            self.write_newline()
            self.write_suite(node.body)
        self.write_else(node.orelse)

    def write_else(self, orelse: Sequence[ast.AST]) -> None:
        if orelse:
            self.write_indentation()
            self.write("else:")
            self.write_newline()
            self.write_suite(orelse)

    def visit_With(self, node: Union[ast.With, ast.AsyncWith]) -> None:
        self.write_indentation()
        if isinstance(node, ast.AsyncWith):
            self.write("async ")
        self.write("with ")
        self.write_expression_list(node.items, allow_newlines=False)
        self.write(":")
        self.write_newline()
        self.write_suite(node.body)

    visit_AsyncWith = visit_With

    def visit_withitem(self, node: ast.withitem) -> None:
        self.visit(node.context_expr)
        if node.optional_vars:
            self.write(" as ")
            self.visit(node.optional_vars)

    def visit_Try(self, node: Union[ast.Try, "ast.TryStar"]) -> None:
        self.write_indentation()
        self.write("try:")
        self.write_newline()
        self.write_suite(node.body)
        is_trystar = sys.version_info >= (3, 11) and isinstance(node, ast.TryStar)
        for handler in node.handlers:
            self.visit_ExceptHandler(handler, is_trystar=is_trystar)
        self.write_else(node.orelse)
        if node.finalbody:
            self.write_finalbody(node.finalbody)

    visit_TryStar = visit_Try

    def write_finalbody(self, body: Sequence[ast.AST]) -> None:
        self.write_indentation()
        self.write("finally:")
        self.write_newline()
        self.write_suite(body)

    # One-line statements

    def visit_Return(self, node: ast.Return) -> None:
        self.write_indentation()
        self.write("return")
        if node.value:
            self.write(" ")
            self.visit(node.value)
        self.write_newline()

    def visit_Delete(self, node: ast.Delete) -> None:
        self.write_indentation()
        self.write("del ")
        self.write_expression_list(node.targets, allow_newlines=False)
        self.write_newline()

    def visit_Assign(self, node: ast.Assign) -> None:
        self.write_indentation()
        self.write_expression_list(node.targets, separator=" = ", allow_newlines=False)
        self.write(" = ")
        self.visit(node.value)
        self.write_newline()

    def visit_AugAssign(self, node: ast.AugAssign) -> None:
        self.write_indentation()
        self.visit(node.target)
        self.write(" ")
        self.visit(node.op)
        self.write("= ")
        self.visit(node.value)
        self.write_newline()

    if sys.version_info >= (3, 12):

        def visit_TypeAlias(self, node: ast.TypeAlias) -> None:
            self.write_indentation()
            self.write("type ")
            self.visit(node.name)
            if node.type_params:
                self.write("[")
                self.write_expression_list(node.type_params)
                self.write("]")
            self.write(" = ")
            self.visit(node.value)
            self.write_newline()

        def visit_TypeVar(self, node: ast.TypeVar) -> None:
            self.write(node.name)
            if node.bound:
                self.write(": ")
                self.visit(node.bound)
            if sys.version_info >= (3, 13) and node.default_value:
                self.write(" = ")
                self.visit(node.default_value)

        def visit_TypeVarTuple(self, node: ast.TypeVarTuple) -> None:
            self.write("*")
            self.write(node.name)
            if sys.version_info >= (3, 13) and node.default_value:
                self.write(" = ")
                self.visit(node.default_value)

        def visit_ParamSpec(self, node: ast.ParamSpec) -> None:
            self.write("**")
            self.write(node.name)
            if sys.version_info >= (3, 13) and node.default_value:
                self.write(" = ")
                self.visit(node.default_value)

    def visit_AnnAssign(self, node: ast.AnnAssign) -> None:
        self.write_indentation()
        if not node.simple:
            self.write("(")
        self.visit(node.target)
        if not node.simple:
            self.write(")")
        self.write(": ")
        self.visit(node.annotation)
        if node.value is not None:
            self.write(" = ")
            self.visit(node.value)
        self.write_newline()

    def visit_Raise(self, node: ast.Raise) -> None:
        self.write_indentation()
        self.write("raise")
        if node.exc is not None:
            self.write(" ")
            self.visit(node.exc)
            if node.cause is not None:
                self.write(" from ")
                self.visit(node.cause)
        self.write_newline()

    def visit_Assert(self, node: ast.Assert) -> None:
        self.write_indentation()
        self.write("assert ")
        self.visit(node.test)
        if node.msg:
            self.write(", ")
            self.visit(node.msg)
        self.write_newline()

    def visit_Import(self, node: ast.Import) -> None:
        self.write_indentation()
        self.write("import ")
        self.write_expression_list(node.names, allow_newlines=False)
        self.write_newline()

    def visit_ImportFrom(self, node: ast.ImportFrom) -> None:
        self.write_indentation()
        dots = "." * (node.level or 0)
        self.write(f"from {dots}")
        if node.module:
            self.write(node.module)
        self.write(" import ")
        self.write_expression_list(node.names)
        self.write_newline()

    def visit_Global(self, node: ast.Global) -> None:
        self.write_indentation()
        self.write(f"global {', '.join(node.names)}")
        self.write_newline()

    def visit_Nonlocal(self, node: ast.Nonlocal) -> None:
        self.write_indentation()
        self.write(f"nonlocal {', '.join(node.names)}")
        self.write_newline()

    def visit_Expr(self, node: ast.Expr) -> None:
        self.write_indentation()
        self.visit(node.value)
        self.write_newline()

    def visit_Pass(self, node: ast.Pass) -> None:
        self.write_indentation()
        self.write("pass")
        self.write_newline()

    def visit_Break(self, node: ast.Break) -> None:
        self.write_indentation()
        self.write("break")
        self.write_newline()

    def visit_Continue(self, node: ast.Continue) -> None:
        self.write_indentation()
        self.write("continue")
        self.write_newline()

    # Expressions

    def visit_BoolOp(self, node: ast.BoolOp) -> None:
        my_prec = self.precedence_of_node(node)
        parent_prec = self.precedence_of_node(self.get_parent_node())
        with self.parenthesize_if(my_prec <= parent_prec):
            op = "and" if isinstance(node.op, ast.And) else "or"
            self.write_expression_list(
                node.values, separator=f" {op} ", final_separator_if_multiline=False
            )

    def visit_BinOp(self, node: ast.BinOp) -> None:
        parent_node = self.get_parent_node()
        my_prec = self.precedence_of_node(node)
        parent_prec = self.precedence_of_node(parent_node)
        if my_prec < parent_prec:
            should_parenthesize = True
        elif my_prec == parent_prec and isinstance(parent_node, ast.BinOp):
            if isinstance(node.op, ast.Pow):
                should_parenthesize = node == parent_node.left
            else:
                should_parenthesize = node == parent_node.right
        else:
            should_parenthesize = False

        with self.parenthesize_if(should_parenthesize):
            self.visit(node.left)
            self.write(" ")
            self.visit(node.op)
            self.write(" ")
            self.visit(node.right)

    def visit_UnaryOp(self, node: ast.UnaryOp) -> None:
        my_prec = self.precedence_of_node(node)
        parent_prec = self.precedence_of_node(self.get_parent_node())
        with self.parenthesize_if(my_prec < parent_prec):
            self.visit(node.op)
            self.visit(node.operand)

    def visit_Lambda(self, node: ast.Lambda) -> None:
        parent_node = self.get_parent_node()
        should_parenthesize = isinstance(
            parent_node,
            (
                ast.BinOp,
                ast.UnaryOp,
                ast.Compare,
                ast.IfExp,
                ast.Attribute,
                ast.Subscript,
                ast.Call,
                ast.BoolOp,
            ),
        ) or (
            # Parens are required in 3.9+, but let's just always add them.
            isinstance(parent_node, ast.comprehension)
            and node in parent_node.ifs
        )
        with self.parenthesize_if(should_parenthesize):
            self.write("lambda")
            if node.args.args or node.args.vararg or node.args.kwarg:
                self.write(" ")
            self.visit(node.args)
            self.write(": ")
            self.visit(node.body)

    def visit_NamedExpr(self, node: "ast.NamedExpr") -> None:
        self.write("(")
        self.visit(node.target)
        self.write(" := ")
        # := has the lowest precedence, so we should never need to parenthesize this
        self.visit(node.value)
        self.write(")")

    def visit_IfExp(self, node: ast.IfExp) -> None:
        parent_node = self.get_parent_node()
        if isinstance(
            parent_node,
            (
                ast.BinOp,
                ast.UnaryOp,
                ast.Compare,
                ast.Attribute,
                ast.Subscript,
                ast.Call,
                ast.BoolOp,
                ast.comprehension,
            ),
        ):
            should_parenthesize = True
        elif isinstance(parent_node, ast.IfExp) and (
            node is parent_node.test or node is parent_node.body
        ):
            should_parenthesize = True
        else:
            should_parenthesize = False

        with self.parenthesize_if(should_parenthesize):
            self.visit(node.body)
            self.write(" if ")
            self.visit(node.test)
            self.write(" else ")
            self.visit(node.orelse)

    def visit_Dict(self, node: ast.Dict) -> None:
        self.write("{")
        items = [KeyValuePair(key, value) for key, value in zip(node.keys, node.values)]
        self.write_expression_list(items, need_parens=False)
        self.write("}")

    def visit_KeyValuePair(self, node: KeyValuePair) -> None:
        if node.key is None:
            self.write("**")
        else:
            self.visit(node.key)
            self.write(": ")
        self.visit(node.value)

    def visit_Set(self, node: ast.Set) -> None:
        self.write("{")
        self.write_expression_list(node.elts, need_parens=False)
        self.write("}")

    def visit_ListComp(self, node: ast.ListComp) -> None:
        self.visit_comp(node, "[", "]")

    def visit_SetComp(self, node: ast.SetComp) -> None:
        self.visit_comp(node, "{", "}")

    def visit_DictComp(self, node: ast.DictComp) -> None:
        self.write("{")
        elts = [KeyValuePair(node.key, node.value)] + node.generators
        self.write_expression_list(elts, separator=" ", need_parens=False)
        self.write("}")

    def visit_GeneratorExp(self, node: ast.GeneratorExp) -> None:
        parent_node = self.get_parent_node()
        # if this is the only argument to a function, omit the extra parentheses
        if (
            isinstance(parent_node, _CallArgs)
            and len(parent_node.args) == 1
            and node == parent_node.args[0]
        ):
            start = end = ""
        else:
            start = "("
            end = ")"
        self.visit_comp(node, start, end)

    def visit_comp(
        self,
        node: Union[ast.GeneratorExp, ast.ListComp, ast.SetComp],
        start: str,
        end: str,
    ) -> None:
        self.write(start)
        self.write_expression_list(
            [node.elt] + node.generators, separator=" ", need_parens=False
        )
        self.write(end)

    def visit_Await(self, node: ast.Await) -> None:
        with self.parenthesize_if(
            not isinstance(
                self.get_parent_node(), (ast.Expr, ast.Assign, ast.AugAssign)
            )
        ):
            self.write("await ")
            self.visit(node.value)

    def visit_Yield(self, node: ast.Yield) -> None:
        with self.parenthesize_if(
            not isinstance(
                self.get_parent_node(), (ast.Expr, ast.Assign, ast.AugAssign)
            )
        ):
            self.write("yield")
            if node.value:
                self.write(" ")
                self.visit(node.value)

    def visit_YieldFrom(self, node: ast.YieldFrom) -> None:
        with self.parenthesize_if(
            not isinstance(
                self.get_parent_node(), (ast.Expr, ast.Assign, ast.AugAssign)
            )
        ):
            self.write("yield from ")
            self.visit(node.value)

    def visit_Compare(self, node: ast.Compare) -> None:
        my_prec = self.precedence_of_node(node)
        parent_prec = self.precedence_of_node(self.get_parent_node())
        with self.parenthesize_if(my_prec <= parent_prec):
            self.visit(node.left)
            for op, expr in zip(node.ops, node.comparators):
                self.write(" ")
                self.visit(op)
                self.write(" ")
                self.visit(expr)

    def visit_Call(self, node: ast.Call) -> None:
        self.visit(node.func)
        self.write("(")

        args = node.args + node.keywords
        self.node_stack.append(_CallArgs(args))
        try:
            if args:
                self.write_expression_list(
                    args,
                    need_parens=False,
                    final_separator_if_multiline=False,  # it's illegal after *args and **kwargs
                )

            self.write(")")
        finally:
            self.node_stack.pop()

    def visit_StarArg(self, node: StarArg) -> None:
        self.write("*")
        self.visit(node.arg)

    def visit_DoubleStarArg(self, node: DoubleStarArg) -> None:
        self.write("**")
        self.visit(node.arg)

    def visit_KeywordArg(self, node: KeywordArg) -> None:
        self.visit(node.arg)
        if node.value is not None:
            self.write("=")
            self.visit(node.value)

    def write_number(self, number: Union[int, float, complex]) -> None:
        should_parenthesize = (
            isinstance(number, int)
            and number >= 0
            and isinstance(self.get_parent_node(), ast.Attribute)
        )
        if not should_parenthesize:
            should_parenthesize = (
                isinstance(number, complex)
                and number.real == 0.0
                and (number.imag < 0 or number.imag == -0.0)
            )
        with self.parenthesize_if(should_parenthesize):
            if isinstance(number, float) and math.isinf(number):
                # otherwise we write inf, which won't be parsed back right
                # I don't know of any way to write nan with a literal
                self.write("1e1000" if number > 0 else "-1e1000")
            elif isinstance(number, complex) and cmath.isinf(number):
                self.write("1e1000j" if number.imag > 0 else "-1e1000j")
            elif isinstance(number, (int, float)) and number < 0:
                # needed for precedence to work correctly
                me = self.node_stack.pop()
                if isinstance(number, int):
                    val = str(-number)
                else:
                    val = repr(type(number)(-number))  # - of long may be int
                self.visit(
                    ast.UnaryOp(op=ast.USub(), operand=ast.Name(id=val, ctx=ast.Load()))
                )
                self.node_stack.append(me)
            else:
                self.write(repr(number))

    def write_string(self, string_value: str, kind: Optional[str] = None) -> None:
        if kind is not None:
            self.write(kind)
        if isinstance(self.get_parent_node(), ast.Expr) and '"""' not in string_value:
            self.write('"""')
            s = string_value.encode("unicode-escape").decode("ascii")
            s = s.replace("\\n", "\n")
            self.write(s)
            self.write('"""')
            return
        if self.has_parent_of_type(ast.FormattedValue):
            delimiter = '"'
        else:
            delimiter = "'"
        self.write(delimiter)
        s = string_value.encode("unicode-escape").decode("ascii")
        s = s.replace(delimiter, "\\" + delimiter)
        self.write(s)
        self.write(delimiter)

    def visit_FormattedValue(self, node: ast.FormattedValue) -> None:
        has_parent = isinstance(self.get_parent_node(), ast.JoinedStr)
        with self.f_literalise_if(not has_parent):
            self.write("{")
            if isinstance(node.value, ast.JoinedStr):
                raise NotImplementedError(
                    "ast_decompiler does not support nested f-strings yet"
                )
            add_space = isinstance(
                node.value, (ast.Set, ast.Dict, ast.SetComp, ast.DictComp)
            )
            if add_space:
                self.write(" ")
            self.visit(node.value)
            if node.conversion != -1:
                self.write(f"!{chr(node.conversion)}")
            if node.format_spec is not None:
                self.write(":")
                if isinstance(node.format_spec, ast.JoinedStr):
                    self.visit(node.format_spec)
                elif isinstance(node.format_spec, ast.Constant) and isinstance(
                    node.format_spec.value, str
                ):
                    self.write(node.format_spec.value)
                else:
                    raise TypeError(
                        f"format spec must be a string, not {node.format_spec}"
                    )
            if add_space:
                self.write(" ")
            self.write("}")

    def visit_JoinedStr(self, node: ast.JoinedStr) -> None:
        has_parent = isinstance(self.get_parent_node(), ast.FormattedValue)
        with self.f_literalise_if(not has_parent):
            for value in node.values:
                if isinstance(value, ast.Constant) and isinstance(value.value, str):
                    # always escape '
                    self.write(
                        value.value.encode("unicode-escape")
                        .decode("ascii")
                        .replace("'", r"\'")
                        .replace("{", "{{")
                        .replace("}", "}}")
                    )
                else:
                    self.visit(value)

    def visit_Constant(self, node: ast.Constant) -> None:
        if isinstance(node.value, str):
            kind = node.kind
        else:
            kind = None
        self.write_constant(node.value, kind)

    def write_constant(self, value: object, kind: Optional[str] = None) -> None:
        if value is Ellipsis:
            self.write("...")
        elif isinstance(value, str):
            self.write_string(value, kind)
        elif isinstance(value, bytes):
            self.write(repr(value))
        elif isinstance(value, (int, float, complex)):
            self.write_number(value)
        elif isinstance(value, (bool, type(None))):
            self.write(repr(value))
        else:
            raise NotImplementedError(repr(value))

    def visit_Attribute(self, node: ast.Attribute) -> None:
        self.visit(node.value)
        self.write(f".{node.attr}")

    def visit_Subscript(self, node: ast.Subscript) -> None:
        self.visit(node.value)
        self.write("[")
        self.visit(node.slice)
        self.write("]")

    def visit_Starred(self, node: ast.Starred) -> None:
        # TODO precedence
        self.write("*")
        self.visit(node.value)

    def visit_Name(self, node: ast.Name) -> None:
        self.write(node.id)

    def visit_List(self, node: ast.List) -> None:
        self.write("[")
        self.write_expression_list(node.elts, need_parens=False)
        self.write("]")

    def visit_Tuple(self, node: ast.Tuple) -> None:
        if not node.elts:
            self.write("()")
        else:
            parent_node = self.get_parent_node()
            allow_parens = True
            should_parenthesize = not isinstance(
                parent_node,
                (ast.Expr, ast.Assign, ast.AugAssign, ast.Return, ast.Yield, ast.Index),
            )
            if (
                isinstance(parent_node, ast.comprehension)
                and node is parent_node.target
            ):
                should_parenthesize = False
            # Only relevant on 3.9+, where the ExtSlice class no longer exists.
            if isinstance(parent_node, ast.Subscript) and node is parent_node.slice:
                should_parenthesize = False
                allow_parens = False
            # https://bugs.python.org/issue32117
            if (
                isinstance(parent_node, (ast.Return, ast.Yield))
                and any(isinstance(elt, ast.Starred) for elt in node.elts)
                and sys.version_info < (3, 8)
            ):
                should_parenthesize = True
            with self.parenthesize_if(should_parenthesize):
                if len(node.elts) == 1:
                    self.visit(node.elts[0])
                    self.write(",")
                else:
                    self.write_expression_list(
                        node.elts, need_parens=allow_parens and not should_parenthesize
                    )

    # slice

    def visit_Slice(self, node: ast.Slice) -> None:
        if node.lower:
            self.visit(node.lower)
        self.write(":")
        if node.upper:
            self.visit(node.upper)
        if node.step:
            self.write(":")
            self.visit(node.step)

    if sys.version_info < (3, 9):
        # Any to avoid version-dependent errors from pyanalyze.
        def visit_ExtSlice(self, node: Any) -> None:
            if len(node.dims) == 1:
                self.visit(node.dims[0])
                self.write(",")
            else:
                self.write_expression_list(node.dims, need_parens=False)

        def visit_Index(self, node: Any) -> None:
            self.visit(node.value)

    # operators
    for op, string in _OP_TO_STR.items():
        exec(f"def visit_{op.__name__}(self, node): self.write({string!r})")

    # Other types

    visit_Load = visit_Store = visit_Del = visit_AugLoad = visit_AugStore = (
        visit_Param
    ) = lambda self, node: None

    def visit_comprehension(self, node: ast.comprehension) -> None:
        if node.is_async:
            self.write("async ")
        self.write("for ")
        self.visit(node.target)
        self.write(" in ")
        self.visit(node.iter)
        for expr in node.ifs:
            self.write(" if ")
            self.visit(expr)

    def visit_ExceptHandler(
        self, node: ast.ExceptHandler, *, is_trystar: bool = False
    ) -> None:
        self.write_indentation()
        self.write("except")
        if is_trystar:
            self.write("*")
        if node.type:
            self.write(" ")
            self.visit(node.type)
            if node.name:
                self.write(" as ")
                self.write(node.name)
        self.write(":")
        self.write_newline()
        self.write_suite(node.body)

    def visit_arguments(self, node: ast.arguments) -> None:
        args = []
        if node.posonlyargs:
            args += node.posonlyargs
            args.append(ast.Name(id="/", ctx=ast.Load()))

        num_defaults = len(node.defaults)
        if num_defaults:
            args += node.args[:-num_defaults]
            default_args = zip(node.args[-num_defaults:], node.defaults)
        else:
            args += list(node.args)
            default_args = []
        for name, value in default_args:
            args.append(KeywordArg(name, value))

        if node.vararg:
            args.append(StarArg(node.vararg))

        # TODO write a * if there are kwonly args but no vararg
        if node.kw_defaults:
            if node.kwonlyargs and not node.vararg:
                args.append(StarArg(ast.arg(arg="", annotation=None)))
            num_kwarg_defaults = len(node.kw_defaults)
            if num_kwarg_defaults:
                args += node.kwonlyargs[:-num_kwarg_defaults]
                default_kwargs = zip(
                    node.kwonlyargs[-num_kwarg_defaults:], node.kw_defaults
                )
            else:
                args += node.kwonlyargs
                default_kwargs = []
            for name, value in default_kwargs:
                args.append(KeywordArg(name, value))

        if node.kwarg:
            args.append(DoubleStarArg(node.kwarg))

        if args:
            # lambdas can't have a multiline arglist
            allow_newlines = not isinstance(self.get_parent_node(), ast.Lambda)
            self.write_expression_list(
                args,
                allow_newlines=allow_newlines,
                need_parens=False,
                final_separator_if_multiline=False,  # illegal after **kwargs
            )

    def visit_arg(self, node: ast.arg) -> None:
        self.write(node.arg)
        if node.annotation:
            self.write(": ")
            # TODO precedence
            self.visit(node.annotation)

    def visit_keyword(self, node: ast.keyword) -> None:
        if node.arg is None:
            # in py3, **kwargs is a keyword whose arg is None
            self.write("**")
        else:
            self.write(node.arg + "=")
        self.visit(node.value)

    def visit_alias(self, node: ast.alias) -> None:
        self.write(node.name)
        if node.asname is not None:
            self.write(f" as {node.asname}")

    def visit_Match(self, node: "ast.Match") -> None:
        self.write_indentation()
        self.write("match ")
        self.visit(node.subject)
        self.write(":")
        self.write_newline()
        self.write_suite(node.cases)

    def visit_match_case(self, node: "ast.match_case") -> None:
        self.write_indentation()
        self.write("case ")
        self.visit(node.pattern)
        if node.guard is not None:
            self.write(" if ")
            self.visit(node.guard)
        self.write(":")
        self.write_newline()
        self.write_suite(node.body)

    def visit_MatchValue(self, node: "ast.MatchValue") -> None:
        self.visit(node.value)

    def visit_MatchSingleton(self, node: "ast.MatchSingleton") -> None:
        self.write_constant(node.value)

    def visit_MatchSequence(self, node: "ast.MatchSequence") -> None:
        self.write("[")
        self.write_expression_list(node.patterns, need_parens=False)
        self.write("]")

    def visit_MatchMapping(self, node: "ast.MatchMapping") -> None:
        self.write("{")
        items = [
            KeyValuePair(key, value) for key, value in zip(node.keys, node.patterns)
        ]
        self.write_expression_list(items, need_parens=False)
        if node.rest is not None:
            if node.keys:
                self.write(", ")
            self.write(f"**{node.rest}")
        self.write("}")

    def visit_MatchClass(self, node: "ast.MatchClass") -> None:
        self.visit(node.cls)
        self.write("(")
        self.write_expression_list(node.patterns, need_parens=False)
        for i, (attr, pattern) in enumerate(zip(node.kwd_attrs, node.kwd_patterns)):
            if i > 0 or node.patterns:
                self.write(", ")
            self.write(attr)
            self.write("=")
            self.visit(pattern)
        self.write(")")

    def visit_MatchAs(self, node: "ast.MatchAs") -> None:
        if node.pattern is None:
            if node.name is None:
                self.write("_")
            else:
                self.write(node.name)
        else:
            parent_node = self.get_parent_node()
            with self.parenthesize_if(
                isinstance(parent_node, (ast.MatchOr, ast.MatchAs))
            ):
                self.visit(node.pattern)
                self.write(" as ")
                self.write(node.name)

    def visit_MatchOr(self, node: "ast.MatchOr") -> None:
        parent_node = self.get_parent_node()
        with self.parenthesize_if(isinstance(parent_node, ast.MatchOr)):
            self.write_expression_list(
                node.patterns, need_parens=False, separator=" | "
            )

    def visit_MatchStar(self, node: "ast.MatchStar") -> None:
        self.write("*")
        if node.name is None:
            self.write("_")
        else:
            self.write(node.name)