#!/usr/bin/env ruby
#
# Copyright (C) 2013 Red Hat, GmbH
# 
# This file is released under the GPL
#
#
# Script to calculate device-mapper thin privisioning
# metadata device size based on pool, block size and
# maximum expected thin provisioned devices.
#

require 'optparse'
require 'pathname'

#----------------------------------------------------------------

$prg = Pathname.new($0).basename
$btree_entrysize = 16
$btree_nodesize = 4096

def init_units
  units = Hash.new
  units[:chars] = "sKkMmGgTtPpEeZzYy"
  units[:strings] = [ 'sectors',
                      'kilobytes', 'kibibytes', 'megabytes',  'mebibytes',
                      'gigabytes', 'gibibytes', 'terabytes',  'tebibytes',
                      'petabytes', 'pebibytes', 'exabytes',   'ebibytes',
                      'zetabytes', 'zebibytes', 'yottabytes', 'yobibytes' ]
  units[:factors] =  Array.new

  units[:factors][0] = 512
  1.step(8) do |e|
    units[:factors][(e - 1) * 2 + 1] = 1024**e
    units[:factors][(e - 1) * 2 + 2] = 1000**e
  end
  units
end

def check_opts(opts)
  abort "#{$prg} - 3 arguments required!" if opts.length < 3
  abort "#{$prg} - poolsize must be much larger than blocksize" if opts[:poolsize] < opts[:blocksize] * 16
  abort "#{$prg} - maximum number of thin provisioned devices must be > 0" if opts[:maxthins].nil? || opts[:maxthins] == 0
end

def to_sectors(size, units)
  unit_chars = units[:chars]

  a = size.split(/[#{unit_chars}]/)
  s = size.to_i.to_s
  abort "#{$prg} - only one unit character allowed!" if a.length > 1 || size.length - s.length > 1
  abort "#{$prg} - invalid unit specifier!" if s != a[0]
  idx = unit_chars.index(size[a[0].length])
  r = size.to_i * units[:factors][idx] / 512
  r
end

def parse_command_line(argv, units)
  opts = {}
  unit_chars = units[:chars]

  os = OptionParser.new do |o|
    o.banner = "Thin Provisioning Metadata Size Calculator.\nUsage: #{$prg} [opts]"
    o.on('-b', '--blocksize BLOCKSIZE', String,
         "Block size, ie. allocation unit size for thin provisioned devices.") do |bs|
      opts[:blocksize] = to_sectors(bs, units)
    end
    o.on('-s', '--poolsize SIZE', String, "Size of the pool device.") do |ps|
      opts[:poolsize] = to_sectors(ps, units)
    end
    o.on('-m', '--maxthins MAXTHINS', Integer, "Size of the pool device.") do |mt|
      opts[:maxthins] = mt
    end
    o.on('-u', '--units [skKmMgGtTpP]', String, "Output unit specifier.") do |u|
      if u =~ /[#{unit_chars}]/
        opts[:units] = u
      else
        abort "#{$prg} - output unit specifier invalid."
      end
    end
    o.on('-n', '--numeric-only', "Output numeric value only.") do
      opts[:numeric] = true || nil
    end
    o.on('-h', '--help', "Outout this help.") do
      puts o
      exit
    end
  end

  begin
    os.parse(argv)
  rescue OptionParser::ParseError => e
    abort "#{$prg} #{e}\n#{$prg} #{os}"
  end

  check_opts(opts)
  opts
end

def entries_per_node
  btree_node_headersize = 64
  ($btree_nodesize - btree_node_headersize) / $btree_entrysize
end

def estimated_result(opts, units)
  idx = opts[:units] ? units[:chars].index(opts[:units]) : 0
  r = 1.0 + ((opts[:poolsize] / opts[:blocksize] / entries_per_node) + opts[:maxthins]) * 512 / 8
  r /= units[:factors][idx]
  tmp = "%.2f" % r
  # FIXME: avoid zero decimal places
  r = tmp.to_f > 0.0 ? tmp : "%.4e" % r
  r = "#{$prg} estimated metadata area size is #{r} #{units[:strings][idx]}." if !opts[:numeric]
  r
end


#----------------------------------------------------------------
# Main

units = init_units
puts estimated_result(parse_command_line(ARGV, units), units)