require 'fileutils'

def album(song)
  if song =~ /\.ogg\Z/i
    File.open(song) { |f|
      f.read(2048)[/album=(( |[^\0-\63])+)/, 1]
    }
  elsif song =~ /\.mp3\Z/i
    `mp3info -p "%l" "#{song}"`
  end
end

def track(song)
  if song =~ /\.ogg\Z/i
    File.open(song) { |f|
      f.read(2048)[/tracknumber=(\d+)/, 1].to_i
    }
  elsif song =~ /\.mp3\Z/i
    `mp3info -p "%n" "#{song}"`.to_i
  end
end

count = 1
ARGV.each { |dir|
  unless File.directory? dir
    warn "`#{dir}' is not a directory.  Skipping."
  end

  songs = Dir[dir + "/**/*{ogg,mp3}"].map { |f| f.squeeze '/' }
  ordered = songs.sort_by { |song|
     [album(song), track(song)]
  }
  ordered.each { |song|
    dirname, basename = File.split song
    basename = basename[5..-1]  if basename =~ /\A\d{4}-/
    newname = File.join(dirname, "%04d-%s" % [count, basename])
    unless song == newname
      FileUtils.mv song, newname, :verbose => true
    end
    count += 1
  }
}