battery-level-server.rb

#!/usr/bin/ruby

require 'sinatra'
require 'json'
require 'thread'

class LevelStore
  def initialize
    @filename = 'battery-level.json'
    @mutex = Mutex.new
  end

  def load
    @mutex.synchronize do
      if File.exist?(@filename)
        JSON.parse(File.read(@filename))
      else
        {}
      end
    end
  end

  def save (obj)
    @mutex.synchronize do
      File.write(@filename, JSON.pretty_generate(obj))
    end
  end

  def modify (&block)
    save(block.call(load))
  end
end

set :bind, '0.0.0.0'

$level_store = LevelStore.new

get '/level' do
  $level_store.load.map do
    |name, level|
    "#{name} = #{level}"
  end.join("\n") + "\n"
end

get '/level/:name/:level' do
  |name, level|

  $level_store.modify do
    |stored|
    stored[name] = level.to_i
    stored
  end

  "ok #{level}"
end