#!/usr/bin/env ruby

# d20+1    # 20 1 d 1 + p
# 10d6k8   # 6 10 d 10 8 keep 8 .+ p
# 3d6>2    # 6 3 d 3 2 > p
# 3d12/2   # 12 3 d + + 2 / p

stack = []

loop do
  print "> "
  gets.split.each do |token|
    case token
    when /[0-9]+/
      stack.push(token.to_i)
    when "+"
      a, b = stack.pop(2)
      stack.push(a + b)
    when ".+"
      l = stack.pop
      h = stack.pop(n)
      stack.push(h.sum)
    when "-"
      a, b = stack.pop(2)
      stack.push(a - b)
    when "*"
      a, b = stack.pop(2)
      stack.push(a * b)
    when "/"
      a, b = stack.pop(2)
      stack.push(a / b)
    when "%"
      a, b = stack.pop(2)
      stack.push(a % b)
    when "d", "roll"
      n = stack.pop
      d = stack.pop
      n.times { stack.push(rand(d) + 1) }
    when "p"
      puts stack.pop
    when "s"
      pp stack
    when "k", "keep"
      k = stack.pop
      n = stack.pop
      h = stack.pop(n).sort
      stack.push(*h.pop(k))
    when ">"
      t = stack.pop
      n = stack.pop
      h = stack.pop(n)
      stack.push(*h.select{|d|d > t})
    when "<"
      t = stack.pop
      n = stack.pop
      h = stack.pop(n)
      stack.push(*h.select{|d|d < t})
    when "q"
      exit
    else
      puts "I don't know how to #{token}!"
    end
  end
end