#!/usr/bin/perl
#
#  NAME OF SCRIPT FILE:
#   date1900
#
#  DESCRIPTION
#   Converts the day number since 1 Jan 1900 to a date in form YYMMDD, 
#   YYYY-MM-DD, or using the "date" command options.
#
#   Parameters are:
#   -dash        print output in YYYY-MM-DD format. This takes precedence
#                over the -o formats. 
#   -o "format"  print output in the "date" command output format.
#   day          day number since 1900-01-00,
#                (i.e., day 1 is 1900-01-01)
#
#  USAGE:
#   date1900 [-dash | -o "format"] day
#
#  HISTORY:
#   1992-10-27:nash:written
#   1995-08-10:nash:added -dash parameter
#   1996-12-05:nash:added -o parameter
#   $Header: /var/local/src/tmp/date1900,v 1.3 1996/12/06 15:39:26 root Exp $
#

require 'newgetopt.pl';

# parse options
  $message = 
    "\ndate1900 [-dash | -o 'format'] day\n\n".
    "  Converts the day number since 1 Jan 1900 to a date in form YYMMDD,\n".
    "    YYYY-MM-DD, or using the 'date' command options.\n\n".
    "Parameters are:\n".
    "  -dash        print output in YYYY-MM-DD format. This takes precedence\n".
    "               over the -o formats.\n".
    "  -o 'format'  print output in the 'date' command output format.\n".
    "  day          day number since 1900-01-00,\n".
    "               (i.e., day 1 is 1900-01-01)\n\n";
  die $message
    unless (&NGetOpt("dash","h","o=s") && (@ARGV) && (!$opt_h));

# get year
  $year = int(int($ARGV[0])/365.25);

# residual gives day of year
  $res = int($ARGV[0])-$year*365-int(($year-1)/4);

# set up beginning index of month for leap year
  $leap=(($year-int($year/4)*4 == 0) & ($year != 0));
  if  ($res > 334+$leap)  { $mo = 12; $dy = $res-334-$leap; }
  elsif  ($res > 304+$leap)  { $mo = 11; $dy = $res-304-$leap; }
  elsif  ($res > 273+$leap)  { $mo = 10; $dy = $res-273-$leap; }
  elsif  ($res > 243+$leap)  { $mo = 9; $dy = $res-243-$leap; }
  elsif  ($res > 212+$leap)  { $mo = 8; $dy = $res-212-$leap; }
  elsif  ($res > 181+$leap)  { $mo = 7; $dy = $res-181-$leap; }
  elsif  ($res > 151+$leap)  { $mo = 6; $dy = $res-151-$leap; }
  elsif  ($res > 120+$leap)  { $mo = 5; $dy = $res-120-$leap; }
  elsif  ($res > 90+$leap)  { $mo = 4; $dy = $res-90-$leap; }
  elsif  ($res > 59+$leap)  { $mo = 3; $dy = $res-59-$leap; }
  elsif  ($res > 31)  { $mo = 2; $dy = $res-31; }
  else  { $mo = 1; $dy = $res; }

# result in YYYY-MM-DD format
  if  (defined($opt_dash))
  { $add = ($year > 99);
    $year = $year-100*$add;
    print  19+$add,'0' x ($year < 10),$year,"-",'0' x ($mo < 10),$mo,
    "-",'0' x ($dy < 10),$dy."\n";
  }

# result in the 'date' command output format
  elsif  ($opt_o ne "")
  { chop ($today = `day1900`);
    $diff = $ARGV[0]-$today;
    # if  ($diff >= 0)  { $diff = "+".$diff; }
    $diff = ('+' x ($diff >= 0)).$diff;
    chop ($today = `date`);
    $command = "mdate $diff ".'"'.$today.'" "'.$opt_o.'"';
    print `$command`;
  }

# result in YYMMDD format
  else
  { print '0' x ($year < 10),$year,'0' x ($mo < 10),$mo,'0' x ($dy < 10),$dy,
    "\n";
  }
exit;