#!/usr/bin/env ruby

require 'optparse'


options = { :minsize => 8 }

OptionParser.new do |opts|
  opts.banner = "Usage: #{__FILE__} [options]"

  opts.on("-h", "--help", "Show this message") do
    puts opts
    exit
  end

  opts.separator("Options:")
  opts.on("-m", "--min-size [n]", Integer, "Minimum password size (default: #{options[:minsize]})") {|n| options[:minsize] = n }
end.parse!

def pwgen(minsize = 8)
  elements = {
    :nums => ('0'..'9').to_a,
    :abc  => ['a'..'z','A'..'Z'].map(&:to_a).flatten
  }
  collection = []

  elements.each do |key,elements|
    min_node_size = minsize % 2 + minsize / 2
    (rand(min_node_size) + min_node_size).times { collection.push(elements[rand(elements.size)]) }
  end
  collection.shuffle.join
end

puts pwgen(options[:minsize])