#!/usr/bin/env ruby
# Author Eric Monti (emonti at matasano)
#
# len prepends a binary length number in front of its input and writes it
# raw on STDOUT
#
# Usage: len [options] <data | blank for stdin>
#     -h, --help                       Show this message
#     -v, --version                    Show version and exit
#     -f, --file FILENAME              Input from FILENAME
#     -n, --nudge INT                  Add integer to length
#     -s, --size=SIZE                  Size of length field in bytes
#     -x, --[no-]swap                  Swap endianness. Default=big
#     -t, --[no-]total                 Include size word in size
#     -l, --length=LEN                 Ignore all else and use LEN
#

require 'rbkb'
require 'rbkb/command_line'

include RBkB::CommandLine

#-------------------------------------------------------------------------------
# Init options and arg parsing

# endianness pair. index 0 is always the default
endpair = [:big, :little]

OPTS = {:nudge => 0, :size => 4, :endian => endpair[0]}

arg = bkb_stdargs(nil, OPTS)
arg = bkb_inputargs(arg, OPTS)

arg.banner += " <data | blank for stdin>"

#------------------------------------------------------------------------------
# Add local options
arg.on("-n", "--nudge INT", Numeric, "Add integer to length") do |n|
  OPTS[:nudge] += n
end

arg.on("-s", "--size=SIZE", Numeric, "Size of length field in bytes")  do |s|
  bail("Size must be greater than 0") unless (OPTS[:size] = s) > 0
end

arg.on("-x", "--[no-]swap", "Swap endianness. Default=#{OPTS[:endian]}") do |x|
  OPTS[:endian] = endpair[(x)? 1 : 0]
end

arg.on("-t", "--[no-]total", "Include size word in size") do |t|
  OPTS[:tot]=t
end

arg.on("-l", "--length=LEN", Numeric, "Ignore all else and use LEN") do |l|
  OPTS[:static]=l
end

#------------------------------------------------------------------------------
# Parse arguments
arg.parse!(ARGV) rescue bail "Error: #{$!}\n#{arg}"

OPTS[:indat] ||= ARGV.shift
OPTS[:indat] ||= STDIN.read

bail "Error: Too many arguments\n##{arg}" if ARGV.shift

unless len=OPTS[:static]
  len = OPTS[:indat].size
  len += OPTS[:size] if OPTS[:tot]
  len += OPTS[:nudge]
end

STDOUT.write len.to_bytes(OPTS[:endian], OPTS[:size]) << OPTS[:indat]