R queue simulation: Finding a function whith two arguments the process and a state, which returns the amount of time spent in that state

Question

I have a code for a simulated birth/death process. And would like to find a function which takes a simluted process and a state of that process and returns the amount of time the process spent in that state.

I think I can use parts of the code i already have like the vector "time" in the code in some way. But I can't see it. For example I would like to find a function time_in_state <- function(s,process). Where the process can be for example process1 <- bd_process(2, 10, 0, 100) and the state s=2. Then the function should return the amount of time process1 spent in state 2.

bd_process <- function(lambda, mu, initial_state = 0, steps = 500) {

  time_now <- 0
  state_now <- initial_state


  time <- 0
  state <- initial_state

  for (i in 1:steps) { 

    if (state_now == 3) {
        lambda_now <- 0
        } else {
          lambda_now <- lambda
        }

    if (state_now == 0) {
        mu_now <- 0
        } else {
          mu_now <- mu
    }


  if (((mu_now + lambda_now )* runif(1)) < mu_now) {    
          state_now <- state_now - 1                        

     } else {
          state_now <- state_now + 1                    
            }
      time_now <- time_now + time_to_transition  

      time <- c(time, time_now)                 


      state <- c(state, state_now)                                                                            

  }


  list(tid = time, state = state, steps=steps)
}