"""AST evaluator for calc expressions.

evaluate(node) -> int | float

Result-type rule:
  - Whole-valued results (including float 2.0) are returned/displayed as int.
  - Non-whole results are returned as float.
  Division by zero raises EvalError, not a bare ZeroDivisionError.
"""

from calc.parser import Num, BinOp, Unary, Node


class EvalError(Exception):
    pass


def evaluate(node: Node) -> "int | float":
    if isinstance(node, Num):
        return node.value
    if isinstance(node, Unary):
        if node.op == "-":
            return -evaluate(node.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")
            result = left / right
            return int(result) if result == int(result) else result
        raise EvalError(f"unknown binary op {node.op!r}")
    raise EvalError(f"unknown node type {type(node).__name__}")