! Written by Chris Ding and Yun He at LBL

! Usage of function:  MPH_timer (flag, channel)  

! channel 0 is the default channel, using init_time.

!  ---------------------------------------------------------
!  timer calls to walk-clock dclock(), and do the following:
!  ---------------------------------------------------------
!  flag=0  : Sets initial time; init all channels. 
!
!  flag =1 : Calculates the most recent time interval; accure it to the
!            specified channel; 
!            Returns it to calling process. 
!	     Channel 0 is the default channel, which is automatically accrued.

!  flag =2 : Calculates the most recent time interval; accure it to the
!            specified channel; 
!	     Returns the curent total time in the specified channel; 
!            Channel 0 is the default channel, which is automatically accrued.
!  ---------------------------------------------------------


      module timer
      implicit none
      include 'mpif.h'

      integer N_CHANNELS
      parameter (N_CHANNELS=10)
      real (kind=8) :: init_time = -1.0
      real (kind=8) :: last_time, tot_time(0:N_CHANNELS)

      contains

! --- timer routine is MPH_timer(flag, channel) ---- 

      real (kind=8) function MPH_timer (flag, channel)
      integer :: flag, channel
      real (kind=8) :: new_time, delta_time, MPI_Wtime

      new_time = MPI_Wtime()

      if (flag == 0) then
         init_time = new_time
         last_time = new_time
         tot_time = 0.0
         MPH_timer = new_time - init_time
      else if (init_time == -1.0) then
!        Error Condition
         MPH_timer = init_time
      endif

! Timer is initialized and flag != 0 

      delta_time = new_time - last_time
      last_time = new_time

! For channel=0 or other undefined channels which is treated as 0 
      if ( channel < 0  .or. channel > N_CHANNELS) then
         write(*,*) 'Timer channel is not properly specified!' 
      endif

! channel != 0 
    
      if (flag == 1) then
	 tot_time(channel) = tot_time(channel) + delta_time 
         MPH_timer = delta_time
      else if (flag == 2) then
         tot_time(channel) = tot_time(channel) + delta_time 
         MPH_timer = tot_time(channel)
      else
!        Error Condition
         MPH_timer = -1.0  
      endif 

      end function 

      end module timer