require 'uri'
require 'net/http'
require 'json'

class CPIFetcher
  DEFAULT_CPI_SERIES_URL = 'http://api.bls.gov/publicAPI/v2/timeseries/data/CUUSA210SA0'
  attr_reader :cpi_series_url

  def initialize
    @cpi_series_url = URI(ENV['CPI_SERIES_URL'] || DEFAULT_CPI_SERIES_URL)
  end

  def cpi
    resp = fetch_raw_response

    return nil unless resp['Results']['series']

    resp['Results']['series'].first['data'].first['value']
  end

  private

  def fetch_raw_response
    JSON.parse(Net::HTTP.get_response(cpi_series_url).body)
  end
end

if $PROGRAM_NAME == __FILE__
  puts CPIFetcher.new.cpi
  exit 0
end