#!/usr/bin/ruby

require 'set'

max_num = 1

Dir.foreach('/backups') { |file|
  if file.to_i > max_num then
    max_num = file.to_i
  end
}


#to_keep = Set.new(Range.new(max_num - 7, max_num).to_a)
to_keep = Set.new

start_exp = (Math.log(max_num)/Math.log(2)).to_i
largest = 2**start_exp
to_keep.add(largest)

(start_exp - 1).downto(0) { |e|
  pow = 2**e
  if largest + pow <= max_num then
    this_num = largest + pow
  else
    this_num = largest - pow
  end
  to_keep.add(this_num)
  if largest < this_num then
    largest = this_num
  end
}


Dir.foreach('/backups') { |file|
  if file == '.' or file == '..' then
    next
  end
  if to_keep.include?(file.to_i) then
    next
  end
  system('rm', '-r', "/backups/#{file}")
}