#!/usr/bin/env ruby

def ngrams_it(s, n, fix=false)
  a = s.strip.split
  a.each_with_index { |tok, i|
    tok.strip!
    0.upto([n-1, a.size-i-1].min) { |m|
      yield a[i..i+m] if !(fix^(a[i..i+m].size==n))
    }
  }
end

def main(n, fix, sep)
  STDIN.set_encoding 'utf-8'
  STDOUT.set_encoding 'utf-8'
  while line = STDIN.gets
    a = []
    ngrams_it(line, n, fix) {|ng| a << ng.join(' ')}
    a.reject! {|i| i.strip.size==0 }
    puts a.join sep if a.size > 0
  end
end

def usage
  STDERR.write "./ng [-n <n>] [--fix] [--separator <s>] < <one number per line>\n"
  exit 1
end

if __FILE__ == $0
  require 'trollop'
  opts = Trollop::options do
    opt :n, "Ngrams", :type => :int, :default => 4
    opt :fix, "Don't output lower order Ngrams.", :type => :bool, :default => true
    opt :separator, "separte ngrams of a line by this string", :type => :string, :default => "\n"
  end
  usage if not [0,2,4,6].include? ARGV.size
  main(opts[:n], opts[:fix], opts[:separator])
end