PROGRAM finiteMM1

IMPLICIT NONE

  INTEGER, DIMENSION(:), ALLOCATABLE :: seed
  INTEGER, PARAMETER :: DP=SELECTED_REAL_KIND(14)
  INTEGER :: I,K,N,queuelength,maxarrivals,numarrivals


  REAL(KIND=DP) :: Rand,lambda,mu

  CALL RANDOM_SEED(size=K)
  ALLOCATE (seed(K))
  WRITE(*, '(1x, a, i4, a)',ADVANCE="NO")'Enter ', K,&
       ' integers as random number seeds: '
  READ(*, *) seed
  CALL RANDOM_SEED(put=seed)

  PRINT *, "Input lambda: "
  READ *, lambda
  
  PRINT *, "Input mu: "
  READ*, mu

  PRINT *, "Input queue capacity N: "
  READ *, N


  maxarrivals = 500   ! will use PASTA and look at queuelength just before this

  DO I = 1,100000
     numarrivals = 0
     queuelength = 0  ! arbitrary starting point
     A_Loop : DO
        CALL RANDOM_NUMBER(Rand)
        IF(Rand <= lambda/(lambda+mu))THEN
           !next event is arrival
           numarrivals = numarrivals + 1
           queuelength = queuelength + 1
           queuelength = min(queuelength,N)
        ELSE
           !next event is a departure
           queuelength = queuelength-1
           queuelength = max(queuelength,0)
        END IF

        IF(numarrivals == maxarrivals) THEN
           queuelength = queuelength -1 !take away last arrival to look just before
           EXIT A_Loop
        END IF
     END DO A_Loop
     PRINT *, queuelength
  END DO


END PROGRAM finiteMM1