#!/usr/bin/perl

use Getopt::Std;
use Time::ParseDate;

getopts("dhs");


if($opt_h || @ARGV != 2){
print <<USAGE;
usage: 
datediff [-d|-h|-s] 

-d	displays time in days, instead of years
-s	displays the time in seconds
-h	help (this)

USAGE
}

my $diff = abs(parsedate(@ARGV[1]) - parsedate(@ARGV[0]));

if( $opt_s ){
    print "$diff\n";
}else{
    print readableDelta( $diff )."\n";
}

sub readableDelta{
  my ($delta) = @_;

  my $diff = "";
    
  my $dy = int($delta / 24 / 60 / 60);
  my $yr = 0;
  unless($opt_d){
    $dy %= 365;
    $yr = int($delta / 24 / 60 / 60 / 365);

  if($yr > 0){
    $diff .= "$yr year";
    $diff .= "s" if $yr != 1;
    $diff .= ", ";
  }

  }
  if($dy > 0){
    $diff .= "$dy day";
    $diff .= "s" if $dy != 1;
    $diff .= ", ";
  }
  my $hr = ($delta / 60 / 60) % 24;
  if($hr > 0){
    $diff .= "$hr hour";
    $diff .= "s" if $hr != 1;
    $diff .= ", ";
  }

  my $mn = ($delta / 60 ) % 60;
  if($mn > 0){
    $diff .= "$mn minute";
    $diff .= "s" if $mn != 1;
    $diff .= ", ";
  }
  
  my $se = $delta % 60;
    
  $diff .= "and " if $diff ne "";
  $diff .= "$se second";
  $diff .= "s" if $se != 1;

  return $diff;    
}