from dataclasses import dataclass
from typing import Any, List


class ParseError(Exception):
    pass


@dataclass
class Num:
    value: Any

    def __repr__(self):
        return f"Num({self.value!r})"


@dataclass
class BinOp:
    op: str
    left: Any
    right: Any

    def __repr__(self):
        return f"BinOp({self.op!r}, {self.left!r}, {self.right!r})"


@dataclass
class Unary:
    op: str
    operand: Any

    def __repr__(self):
        return f"Unary({self.op!r}, {self.operand!r})"


class _Parser:
    def __init__(self, tokens):
        self._tokens = tokens
        self._pos = 0

    def _peek(self):
        return self._tokens[self._pos]

    def _consume(self, kind=None):
        tok = self._tokens[self._pos]
        if kind is not None and tok.kind != kind:
            raise ParseError(f"expected {kind}, got {tok.kind!r} ({tok.value!r})")
        self._pos += 1
        return tok

    def _parse_expr(self):
        node = self._parse_term()
        while self._peek().kind in ('PLUS', 'MINUS'):
            op = self._consume().value
            right = self._parse_term()
            node = BinOp(op, node, right)
        return node

    def _parse_term(self):
        node = self._parse_unary()
        while self._peek().kind in ('STAR', 'SLASH'):
            op = self._consume().value
            right = self._parse_unary()
            node = BinOp(op, node, right)
        return node

    def _parse_unary(self):
        if self._peek().kind == 'MINUS':
            op = self._consume().value
            operand = self._parse_unary()
            return Unary(op, operand)
        return self._parse_primary()

    def _parse_primary(self):
        tok = self._peek()
        if tok.kind == 'NUMBER':
            self._consume()
            return Num(tok.value)
        if tok.kind == 'LPAREN':
            self._consume()
            node = self._parse_expr()
            if self._peek().kind != 'RPAREN':
                raise ParseError(f"expected ')', got {self._peek().kind!r}")
            self._consume()
            return node
        raise ParseError(f"unexpected token {tok.kind!r} ({tok.value!r})")


def parse(tokens: list):
    """Parse a token list produced by lexer.tokenize() into an AST.

    Returns one of: Num(value), BinOp(op, left, right), Unary(op, operand).
    Raises ParseError on malformed input.
    """
    p = _Parser(tokens)
    if p._peek().kind == 'EOF':
        raise ParseError("empty input")
    node = p._parse_expr()
    if p._peek().kind != 'EOF':
        raise ParseError(f"unexpected token {p._peek().kind!r} ({p._peek().value!r})")
    return node