Update SketchUp measurements that are marked up with a pair of brackets

measurements.rb

# coding: utf-8
require 'Logger'

# To turn on debugging, open Window → Ruby Console and say
#
#   UpdateMeasurements.log.level = Logger::DEBUG

module UpdateMeasurements
  # http://stackoverflow.com/a/6768164/435004
  def log
    UpdateMeasurements.log
  end

  def self.log
    # There is not really a STDOUT in SketchUp's Ruby:
    logWithPuts = Class.new do
      def write(*args)
        puts(*args)
      end
      def close
      end
    end
    u = logWithPuts.new
    @logger ||= Logger.new(u)
  end
end


class Sketchup::DimensionLinear
  include UpdateMeasurements
  
  def initialize
    # For debugging using the Ruby console:
    Sketchup::DimensionLinear::last_created = self
  end
  def measurement
    text_orig = self.text
    begin
      self.text = ""
      return self.text
    ensure
      self.text = text_orig
    end
  end

  def update_text_with_measurement
    log.debug("update_text_with_measurement " + self.to_s)
    matched = self.text.match('^(.*)\[.*?\](.*)$')
    return if (!matched)
    self.text = matched[1] + "[" + self.measurement + "]" + matched[2]
  end
end

class MeasurementsUpdater < Sketchup::EntitiesObserver
  include UpdateMeasurements

  def initialize
    super
    @pending = false
    @active = true
  end

  def toggle_active
    @active = ! @active
  end

  def active?
    @active
  end

  def onElementModified(entities, entity)
    if @active
      schedule
    end
  end

  # Idea borrowed from https://github.com/SketchUp/sketchup-safe-observer-events
  def schedule
    return if @pending
    timer_id = UI.start_timer(0, false) {
      break if ! @pending
      self.do_update
      @pending = false
    }
    @pending = true
  end

  def do_update
    log.debug "MeasurementsUpdater#do_update"
    Sketchup.active_model.entities.grep(Sketchup::DimensionLinear) {|dim|
      begin
        dim.update_text_with_measurement
      end
    }
  end
end

updater = MeasurementsUpdater.new
Sketchup.active_model.entities.add_observer(updater)

tools_menu = UI.menu("Tools")
item = tools_menu.add_item("Update measurements automatically") do
  updater.toggle_active
end
tools_menu.set_validation_proc(item) do
  if updater.active?
    MF_CHECKED
  else
    MF_UNCHECKED
  end
end