program main

!*****************************************************************************80
!
!! drug_dosage_plots() plots the blood drug levels over time.
!
!  Discussion:
!
!    This program creates files that must be processed by gnuplot().
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    23 September 2026
!
!  Author:
!
!    John Burkardt
!
  implicit none

  character ( len = 255 ) command_filename
  integer command_unit
  character ( len = 255 ) data_filename
  character ( len = 255 ) graphic_filename

  call timestamp ( )
  write ( *, '(a)' ) ''
  write ( *, '(a)' ) 'drug_dosage_plots():'
  write ( *, '(a)' ) '  Fortran90 version'
  write ( *, '(a)' ) '  On a single picture, plot:'
  write ( *, '(a)' ) '  * the variation in blood levels of a medicinal drug.'
  write ( *, '(a)' ) '  * the minimal effective level.'
  write ( *, '(a)' ) '  * the toxic level.'
!
!  Set file names.
!
  command_filename = 'drug_dosage_commands.txt'
  data_filename = 'drug_dosage_data.txt'
  graphic_filename = 'drug_dosage_plots.png'
!
!  Create the command file.
!
  call get_unit ( command_unit )
  open ( unit = command_unit, file = command_filename, status = 'replace' )

  write ( command_unit, '(a)' ) '# ' // trim ( command_filename )
  write ( command_unit, '(a)' ) '#'
  write ( command_unit, '(a)' ) '# Usage:'
  write ( command_unit, '(a)' ) '#  gnuplot < ' // trim ( command_filename )
  write ( command_unit, '(a)' ) '#'
  write ( command_unit, '(a)' ) 'set term png'
  write ( command_unit, '(a)' ) 'set output "' // trim ( graphic_filename ) // '"'
  write ( command_unit, '(a)' ) 'set xlabel "<--- Hours --->"'
  write ( command_unit, '(a)' ) 'set ylabel "<--- Concentration (mg/l) --->"'
  write ( command_unit, '(a)' ) 'set title "Drug level variation over time"'
  write ( command_unit, '(a)' ) 'set grid'
  write ( command_unit, '(a)' ) 'set timestamp'
  write ( command_unit, '(a)' ) 'set key on'
  write ( command_unit, '(a)' ) 'set style data lines'
  write ( command_unit, '(a)' ) 'set yrange [0:1100]'

  write ( command_unit, '(a)' ) 'plot "' // trim ( data_filename ) &
    // '" using 1:2 with lines lw 3, \'
  write ( command_unit, '(a)' ) '     [y=800:800] 0,48 with lines lw 3 lt rgb "green" title "Minimal medicinal level", \' 
  write ( command_unit, '(a)' ) &
    '     1000 with lines lw 3 lt rgb "red" title "Toxic level"'

  write ( command_unit, '(a)' ) 'quit'

  close ( unit = command_unit )

  write ( *, '(a)' ) '  plot commands stored in "' &
    // trim ( command_filename ) // '".'
!
!  Terminate.
!
  write ( *, '(a)' ) ''
  write ( *, '(a)' ) 'drug_dosage_plots():'
  write ( *, '(a)' ) '  Normal end of execution.'
  call timestamp ( )

  stop 0
end
subroutine get_unit ( iunit )

!*****************************************************************************80
!
!! get_unit() returns a free Fortran unit number.
!
!  Discussion:
!
!    A "free" Fortran unit number is a value between 1 and 99 which
!    is not currently associated with an I/O device.  A free Fortran unit
!    number is needed in order to open a file with the OPEN command.
!
!    If IUNIT = 0, then no free Fortran unit could be found, although
!    all 99 units were checked (except for units 5, 6 and 9, which
!    are commonly reserved for console I/O).
!
!    Otherwise, IUNIT is a value between 1 and 99, representing a
!    free Fortran unit.  Note that GET_UNIT assumes that units 5 and 6
!    are special, and will never return those values.
!
!  Licensing:
!
!    This code is distributed under the MIT license. 
!
!  Modified:
!
!    26 October 2008
!
!  Author:
!
!    John Burkardt
!
!  Output:
!
!    integer IUNIT, the free unit number.
!
  implicit none

  integer i
  integer ios
  integer iunit
  logical lopen
 
  iunit = 0
 
  do i = 1, 99
 
    if ( i /= 5 .and. i /= 6 .and. i /= 9 ) then

      inquire ( unit = i, opened = lopen, iostat = ios )
 
      if ( ios == 0 ) then
        if ( .not. lopen ) then
          iunit = i
          return
        end if
      end if

    end if
 
  end do

  return
end
subroutine timestamp ( )

!*****************************************************************************80
!
!! timestamp() prints the current YMDHMS date as a time stamp.
!
!  Example:
!
!    31 May 2001   9:45:54.872 AM
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    06 August 2005
!
!  Author:
!
!    John Burkardt
!
  implicit none

  character ( len = 8 ) ampm
  integer d
  integer h
  integer m
  integer mm
  character ( len = 9 ), parameter, dimension(12) :: month = (/ &
    'January  ', 'February ', 'March    ', 'April    ', &
    'May      ', 'June     ', 'July     ', 'August   ', &
    'September', 'October  ', 'November ', 'December ' /)
  integer n
  integer s
  integer values(8)
  integer y

  call date_and_time ( values = values )

  y = values(1)
  m = values(2)
  d = values(3)
  h = values(5)
  n = values(6)
  s = values(7)
  mm = values(8)

  if ( h < 12 ) then
    ampm = 'AM'
  else if ( h == 12 ) then
    if ( n == 0 .and. s == 0 ) then
      ampm = 'Noon'
    else
      ampm = 'PM'
    end if
  else
    h = h - 12
    if ( h < 12 ) then
      ampm = 'PM'
    else if ( h == 12 ) then
      if ( n == 0 .and. s == 0 ) then
        ampm = 'Midnight'
      else
        ampm = 'AM'
      end if
    end if
  end if

  write ( *, '(i2,1x,a,1x,i4,2x,i2,a1,i2.2,a1,i2.2,a1,i3.3,1x,a)' ) &
    d, trim ( month(m) ), y, h, ':', n, ':', s, '.', mm, trim ( ampm )

  return
end