Finding the longest connection of ports (JS)

I can’t solve a problem.
We have an array. If we take a value, the index of it means port ID, and the value itself means the other port ID it is connected to. Need to find the start index of the longest sequential connection to element which value is -1.

I made a graphic explanation to describe the case for the array [2, 2, 1, 5, 3, -1, 4, 5, 2, 3]. On image the longest connection is purple (3 segments).

I need to make a solution by a function getResult(connections) with a single argument. I don’t know how to do it, so i decided to return another function with several arguments which allows me to make a recursive solution.

function getResult(connections) {
  return f(connections.findIndex(e => e == -1), connections, 0, []);
}

function f(index, cnx, counter, branches) {
  counter++;  
  for (let i = 0; i < cnx.length; i++) {
    if (cnx[i] === index) {
      branches.push([i, counter]);
      return f(i, cnx, counter, branches);
    }
  }
  return branches.sort((a, b) => b[1] - a[1])[0][0];
}

console.log(getResult([1, 2, -1])); // expected 0
console.log(getResult([1, -1, 1, 2])); // expected 3
console.log(getResult([2, 1, -1])); // expected 0
console.log(getResult([3, 4, 1, -1, 3])); // expected 2
console.log(getResult([1, 0, -1, 2])); // expected 3
console.log(getResult([3, 2, 1, -1])); // expected 0
console.log(getResult([2, 2, 1, 5, 3, -1, 4, 5, 2, 3])); // expected 6

Anyway, the code doesn’t work completely properly.
Would you please explain my mistakes?
Is it possible to solve the problem by a function with just one original argument?