time_utc.rb

# Preparation
# gem install sinatra
# gem install timezone
#
# Launch
# RACK_ENV=production ruby time_utc.rb
#
# Check working
# curl http://localhost:4567/time?Moscow,New%20York
#
# Stress testing
# siege -c100 http://localhost:4567/time?Moscow,New%20York -b -t10s

require 'sinatra'
require 'timezone'
require 'find'

module Timezone
  module Loader
    def self.get_zone_data(zone)
      path = ''
      Find.find ZONE_FILE_PATH do |_path|
        if _path =~ /.*#{zone}$/
          path = _path
          break
        end
      end
      unless File.exists? path
        raise Timezone::Error::InvalidZone, "'#{zone}' is not a valid zone."
      end
      File.read path
    end
  end
end

class TimeUTC
  class << self
    def default
      Time.now.utc
    end

    def by_city(city)
      timezone = Timezone::Zone.new zone: prepare_city(city)
      timezone.time Time.now
    rescue Timezone::Error::InvalidZone => e
      puts e.message
    end

    private

    def prepare_city(city)
      city.sub ' ', '_'
    end
  end
end

class TimePresenter
  def initialize(cities)
    @cities = cities || ''
  end

  def to_s
    text = "UTC: #{TimeUTC.default}\n"
    @cities.split(',').each do |city|
      time = TimeUTC.by_city city
      text += "#{city}: #{time}\n" if time
    end
    text
  end
end

get '/time' do
  "#{TimePresenter.new params.keys[0]}"
end