#!/usr/bin/env ruby

$stdout.sync = true # persistent process

require 'json'
opt = ARGV[0] ? JSON::parse(ARGV[0]) : {'interval' => 1, 'count' => 2}

cmd = %w{iostat -xd}
if opt['interval']
  cmd.push(opt['interval'].to_s)
  cmd.push(opt['count'].to_s) if opt['count']
end
p = IO.popen(cmd, 'r')

[1,2].each { x = p.readline until x == "\n" } # header + first sample

puts '{}' # beep

def parse_header l
  want = {
    'kb_read/s'  => 'rkB/s',
    'kb_write/s' => 'wkB/s',
    'rrqm/s'     => 'rrqm/s',
    'wrqm/s'     => 'wrqm/s',
    'reads/s'    => 'r/s',
    'writes/s'   => 'w/s',
    'avgrq-sz'   => 'avgrq-sz',
    'avgqu-sz'   => 'avgqu-sz',
    'await'      => 'await',
    'r_await'    => 'r_await',
    'w_await'    => 'w_await',
    'util'       => '%util',
  }
  head = l.chomp.split(/\s+/)
  head = Hash[*head.zip(0..(head.length-1)).flatten]
  want.values.find_all{|x| not(head[x])}.tap {|missed|
    warn "missing headers: "+ missed.join(', ') if missed.length > 0
  }
  o = {}; want.each {|k,v| o[k] = head[v] if head[v]}
  return o
end

omap = nil
group = {}

until p.eof?
  l = p.readline("\n\n").split(/\n/)
  omap ||= parse_header(l[0])
  puts JSON::generate(Hash[*l.drop(1).map {|x|
    r = x.split(/\s+/)
    [r[0], # device name
      Hash[*omap.keys.map {|k| [k, r[omap[k]].to_f]}.flatten]]
  }.flatten])

end