controller.js

"use strict";

exports.calculate = function (req, res) {
  req.app.use(function (err, _req, res, next) {
    if (res.headersSent) {
      return next(err);
    }

    res.status(400);
    res.json({ error: err.message });
  });

  var operations = {
    add: function (a, b) {
      return Number(a) + Number(b);
    },
    subtract: function (a, b) {
      return a - b;
    },
    multiply: function (a, b) {
      return a * b;
    },
    divide: function (a, b) {
      return a / b;
    },
    power: function (a, b) {
      return Math.pow(a, b);
    },
    // natural logarithm (ln) - uses only operand1
    ln: function (a) {
      return Math.log(Number(a));
    },
  };

  if (!req.query.operation) {
    throw new Error("Unspecified operation");
  }

  var operation = operations[req.query.operation];

  if (!operation) {
    throw new Error("Invalid operation: " + req.query.operation);
  }

  if (
    !req.query.operand1 ||
    !req.query.operand1.match(/^(-)?[0-9\.]+(e(-)?[0-9]+)?$/) ||
    req.query.operand1.replace(/[-0-9e]/g, "").length > 1
  ) {
    throw new Error("Invalid operand1: " + req.query.operand1);
  }

  // For unary ops like ln we don't require operand2; for others we do
  if (req.query.operation !== "ln") {
    if (
      !req.query.operand2 ||
      !req.query.operand2.match(/^(-)?[0-9\.]+(e(-)?[0-9]+)?$/) ||
      req.query.operand2.replace(/[-0-9e]/g, "").length > 1
    ) {
      throw new Error("Invalid operand2: " + req.query.operand2);
    }
  }

  res.json({ result: operation(req.query.operand1, req.query.operand2) });
};