Extract bits into a separate file for offline generation

app.rb

@@ -0,0 +1,21 @@
+require 'sinatra/base'
+require_relative 'cpi_fetcher'
+
+class App < Sinatra::Base
+  get '/' do
+    current_cpi = fetcher.cpi
+    halt 502 unless current_cpi
+
+    expires 300, :public, :must_revalidate
+    content_type :text
+    "#{current_cpi}\n"
+  end
+
+  run! if app_file == $PROGRAM_FILE
+
+  private
+
+  def fetcher
+    @fetcher ||= CPIFetcher.new
+  end
+end

config.ru

@@ -1,3 +1,3 @@
-require './cpi_feed'
+require './app'
 
-run CPIFeed
+run App

cpi_feed.rb

@@ -1,23 +0,0 @@
-require 'sinatra/base'
-require 'faraday'
-require 'json'
-
-class CPIFeed < Sinatra::Base
-  DEFAULT_CPI_SERIES_URL = 'http://api.bls.gov/publicAPI/v2/timeseries/data/CUUSA210SA0'
-
-  get '/' do
-    resp = JSON.parse(Faraday.get(cpi_series_url).body)
-
-    halt 502 unless resp['Results']['series']
-
-    expires 300, :public, :must_revalidate
-    content_type :csv
-    "#{resp['Results']['series'].first['data'].first['value']}\n"
-  end
-
-  def cpi_series_url
-    ENV['CPI_SERIES_URL'] || DEFAULT_CPI_SERIES_URL
-  end
-
-  run! if app_file == $PROGRAM_FILE
-end

cpi_fetcher.rb

@@ -0,0 +1,24 @@
+require 'faraday'
+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 = (ENV['CPI_SERIES_URL'] || DEFAULT_CPI_SERIES_URL)
+  end
+
+  def cpi
+    resp = JSON.parse(Faraday.get(cpi_series_url).body)
+
+    return nil unless resp['Results']['series']
+
+    resp['Results']['series'].first['data'].first['value']
+  end
+end
+
+if $PROGRAM_NAME == __FILE__
+  puts CPIFetcher.new.cpi
+  exit 0
+end