"""Evaluator for the calc AST.

Result type rule: if the result is a whole number, return int; otherwise return float.
Division is always true division. Division by zero raises EvalError.
"""

from calc.parser import Num, BinOp, Unary


class EvalError(Exception):
    pass


def evaluate(node) -> int | float:
    if isinstance(node, Num):
        return node.value
    if isinstance(node, Unary):
        val = evaluate(node.operand)
        if node.op == '-':
            return _coerce(-val)
        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 _coerce(left + right)
        if node.op == '-':
            return _coerce(left - right)
        if node.op == '*':
            return _coerce(left * right)
        if node.op == '/':
            if right == 0:
                raise EvalError("Division by zero")
            return _coerce(left / right)
        raise EvalError(f"Unknown binary op: {node.op!r}")
    raise EvalError(f"Unknown node type: {type(node)!r}")


def _coerce(val: int | float) -> int | float:
    """Return int if val is whole-valued, otherwise float."""
    if isinstance(val, float) and val.is_integer():
        return int(val)
    return val