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#!/usr/bin/env ruby

# = ntpdate.rb - a Ruby port of argp's ntpdate.py[http://tinyurl.com/yb2pgy]
#
# URL::       http://agorf.void.gr/code/ntpdate.rb
# Author::    Aggelos Orfanakos (http://agorf.void.gr)
# Copyright:: 2006, Aggelos Orfanakos. All rights reserved.
# License::   MIT[http://agorf.void.gr/code/LICENSE]
#
# $Id: ntpdate.rb 610 2006-12-09 00:26:11Z agorf $
#--
# TODO: Network-oriented error checking!
#++

require 'optparse'
require 'socket'

SNTP_MSG = "\010" + "\0" * 47
SNTP_PORT = 123
NTP_UNIX_TIME = 2208988800

set_time = false

opts = OptionParser.new(nil, 15, ' ' * 2) do |opts|
  opts.banner = "Usage: #$0 [options] <(S)NTP server>"
  opts.separator ''
  opts.separator 'Options:'

  opts.on('-s', '--set-time', 'Set system time (needs root privileges)') do
    set_time = true
  end

  opts.on_tail('-h', '--help', 'Show this help message') do
    puts opts
    exit
  end
end

begin
  opts.parse!
rescue OptionParser::InvalidOption
  puts opts
  exit
end

unless ARGV[0]
  puts opts
  exit
end

data = UDPSocket.open do |sd|
  sd.send(SNTP_MSG, 0, ARGV[0], SNTP_PORT)
  sd.recvfrom(64)[0]
end

data = data.unpack('N12')[10].to_i - NTP_UNIX_TIME
time = Time.at(data)

if set_time
  system("date #{time.strftime('%m%d%H%M%Y.%S')}")
else
  puts time.asctime
end