#!/usr/bin/env ruby

# $Id: ruby 1708 2006-02-24 10:09:22Z ward $
# $URL$

#
# Copyright (c) 2007 Ward Wouts <ward@wouts.nl>
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
#

require 'getoptlong'

def usage
	puts <<EOT
Usage: #{$0.sub(/.*\//, "")} [options]

-h, --help			Show this message
-s, --source <source>		Source file
-t, --target <target>		Target file; default "<source>.trimmed"

EOT
	exit 1
end

def cmdline
	options = Hash.new
	begin
		opts = GetoptLong.new(
			[ "-s", "--source",	GetoptLong::REQUIRED_ARGUMENT ],
			[ "-t", "--target",	GetoptLong::REQUIRED_ARGUMENT ],
			[ "-h", "--help",	GetoptLong::NO_ARGUMENT ]
		)
		opts.quiet=true

		opts.each do |opt, arg|
			options[opt] = arg
		end

	rescue
		print "#{$!}\n"
		usage
	end
	if options["-h"]
		usage
	elsif options["-s"].nil?
		usage
	end
	if options["-t"].nil?
		options["-t"] = "#{options["-s"]}.trimmed"
	end
	return options
end

options = cmdline

if FileTest.exists?(options["-t"])
	puts "Target #{options["-t"]} already exists, not overwriting"
	exit 1
end

if ! FileTest.readable?(options["-s"])
	puts "Source #{options["-s"]} not readable, exiting"
	exit 1
end

size = File.stat(options["-s"]).size
trimpos = size

# read last 1KB, check if all bytes are all te same
sourcefile = File.new(options["-s"], "r")
sourcefile.seek(-1024, IO::SEEK_END)
block = sourcefile.read(1024)
byte = block[0]
block.each_byte{ |b|
	if b != byte
		puts "Last 1KB of #{source} doesn't appear to be filler"
		exit 1
	end
}

# scan backwards in blocks of 1KB until a byte differs
while true do
	sourcefile.seek(-2048, IO::SEEK_CUR)
	block2 = sourcefile.read(1024)
	if block2 != block
		trimpos = sourcefile.pos
		break
	end
end

puts "Trimming to #{trimpos} bytes"

# back to the beginning
sourcefile.seek(0, IO::SEEK_SET)

# open target
targetfile = File.new(options["-t"], "w")
while sourcefile.pos < trimpos do
	targetfile.write(sourcefile.read(1024))
end