from smolagents.tools import Tool


class Calculator(Tool):
    name = "calculator"

    description = (
        "Performs deterministic arithmetic calculations. "
        "Use this when a research task requires numerical computation."
    )

    inputs = {
        "expression": {
            "type": "string",
            "description": (
                "A mathematical expression to evaluate, "
                "for example '125 * 0.18' or '(450 - 300) / 300 * 100'."
            ),
        }
    }

    output_type = "number"

    def forward(self, expression: str) -> float:
        try:
            # Restrict evaluation to arithmetic only.
            allowed = set("0123456789+-*/().% ")

            if not expression or any(char not in allowed for char in expression):
                raise ValueError("Expression contains unsupported characters.")

            expression = expression.replace("%", "/100")

            result = eval(expression, {"__builtins__": {}}, {})

            if not isinstance(result, (int, float)):
                raise ValueError("Expression did not produce a number.")

            return float(result)

        except Exception as e:
            raise ValueError(
                f"Could not evaluate expression '{expression}': {e}"
            ) from e