Having hard time doing this problem. I'm not even sure if I'm on the right track. All help is appreciated, thanks!

/** 
  For this code challenge, let’s define a math operation as a function that 
  carries out some work on two integers and returns an integer as well. An 
  example is the function below, `differenceBetweenNumbers`, which takes two 
  integers and calculates the difference between the numbers. After calculating, 
  it returns the difference.
*/


// Enter your code below
func mathOperation(o: Int) -> (Int) -> (Int) {
  if (o == 0) {
    func sumBetweenNumbers(a: Int, b: Int) -> (Int) {
      return a + b
    }
  }
  else if (o == 1) {
    func differenceBetweenNumbers(a: Int, b: Int) -> (Int) {
      return a - b
    }
  }
  else if (o == 2) {
    func productBetweenNumbers(a: Int, b: Int) -> (Int) {
      return a * b
    }
  }
  else if (o == 3) {
    func quotientBetweenNumbers(a: Int, b: Int) -> (Int) {
      return a / b
    }
  } 
}