from flask import Flask, render_template, request

app = Flask(__name__)


def _calculate(a: float, b: float, op: str) -> float:
    if op == "+":
        return a + b
    if op == "-":
        return a - b
    if op == "*":
        return a * b
    if op == "/":
        if b == 0:
            raise ZeroDivisionError("Division by zero")
        return a / b
    raise ValueError("Unknown operation")


@app.route("/", methods=["GET", "POST"])
def index():
    result = None
    error = None
    a_val = ""
    b_val = ""
    op = "+"

    if request.method == "POST":
        a_val = request.form.get("a", "")
        b_val = request.form.get("b", "")
        op = request.form.get("op", "+")
        try:
            a = float(a_val)
            b = float(b_val)
            result = _calculate(a, b, op)
        except Exception as exc:  # noqa: BLE001 - show a friendly message
            error = str(exc)

    return render_template(
        "index.html",
        result=result,
        error=error,
        a_val=a_val,
        b_val=b_val,
        op=op,
    )


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000, debug=False)