Promise實現紅綠燈交替重複亮

紅燈3秒亮一次，黃燈2秒亮一次，綠燈1秒亮一次；如何讓三個燈不斷交替重複亮燈？（用Promise實現）三個亮燈函數已經存在：

function red() {
  console.log("red");
}
function green() {
  console.log("green");
}
function yellow() {
  console.log("yellow");
}
const light = function (timer, cb) {
  return new Promise(resolve => {
    setTimeout(() => {
      cb()
      resolve()
    }, timer)
  })
}
const step = function () {
  Promise.resolve().then(() => {
    return light(3000, red)
  }).then(() => {
    return light(2000, green)
  }).then(() => {
    return light(1000, yellow)
  }).then(() => {
    return step()
  })
}

step();