C
C PURPOSE:
C       Read in the location of the Parker Solar Probe and the date it's
C       at that location.
C
C INPUTS:
C       None
C
C OUTPUTS:
C       npoints = integer, number of locations that were read from the
C                 file.
C       date    = real, dimension(2, npoints), row 1 = year,
C                 row 2 = day of year
C       coords  = real, dimension(3, npoints), row 1 = radius (AU),
C                 row 2 = SE_LAT, row 3 = SE_LON
C
C DEPENDENCIES:
C       None
C
C NOTES:
C       This assumes the data starts on the fourth line of the file, and
C       that the first three lines are headers. Thus, we will start
C       reading the data on the fourth line.
C
C       VARIABLES:
C               nmax    = integer, maximum number of points that will be
C                         read from the file.
C
C DATE:
C      February 13, 2020 @ 1:03 PM
C
C AUTHOR:
C      Luke Cota
C

      subroutine read_locations(nmax, infile, npoints, date, coords)
       implicit none
       integer, parameter                   :: INUNIT = 10
       integer                              :: io
       character(len=*)                     :: infile
       integer, intent(in)                  :: nmax
       integer, intent(out)                 :: npoints
       real, dimension(2,nmax), intent(out) :: date
       real, dimension(3,nmax), intent(out) :: coords

       infile = trim(infile)
c       print *, 'Reading locations from file: ', infile
       open(unit = INUNIT, file = infile, action = 'read', iostat = io)
       if (io .ne. 0) then
         print *, 'ERROR: Cannot open file "', infile, '"'
         stop
       end if

C Reading in the first 3 lines. They are not used.
       read(INUNIT,*)
       read(INUNIT,*)
       read(INUNIT,*)

       npoints = 1
       do while (io .eq. 0)
         read(INUNIT,*,iostat=io) date(1,npoints), date(2,npoints),
     &        coords(1,npoints), coords(2,npoints), coords(3,npoints)

         if (npoints .eq. NMAX) then
           print *, 'The number of data points in file: ', infile
           print *, 'has exeeded the max number (NMAX) that can be'
           print *, 'read. See subroutine Extractdvd to'
           print *, 'increase NMAX, and read more values'
           exit
         end if

         npoints = npoints + 1
       end do

       npoints = npoints - 1

       close(INUNIT)

       return
      end subroutine read_locations