"""Evaluator: walks the AST produced by calc.parser and returns a numeric result."""

from __future__ import annotations
from .parser import Num, BinOp, Unary


class EvalError(Exception):
    pass


def evaluate(node) -> int | float:
    """Recursively evaluate an AST node and return int or float."""
    if isinstance(node, Num):
        return node.value
    if isinstance(node, Unary):
        operand = evaluate(node.operand)
        if node.op == "-":
            return -operand
        raise EvalError(f"unknown unary op: {node.op!r}")
    if isinstance(node, BinOp):
        left = evaluate(node.left)
        right = evaluate(node.right)
        if node.op == "+":
            return left + right
        if node.op == "-":
            return left - right
        if node.op == "*":
            return left * right
        if node.op == "/":
            if right == 0:
                raise EvalError("division by zero")
            return left / right
        raise EvalError(f"unknown binary op: {node.op!r}")
    raise EvalError(f"unknown node type: {type(node).__name__!r}")