Add products cache integrity checker

Gemfile

@@ -55,6 +55,7 @@ gem 'figaro'
 gem 'blockenspiel'
 gem 'acts-as-taggable-on', '~> 3.4'
 gem 'paper_trail', '~> 3.0.8'
+gem 'diffy'
 
 gem 'wicked_pdf'
 gem 'wkhtmltopdf-binary'

Gemfile.lock

@@ -248,6 +248,7 @@ GEM
     devise-encryptable (0.1.2)
       devise (>= 2.1.0)
     diff-lcs (1.2.4)
+    diffy (3.1.0)
     em-websocket (0.5.0)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.5.3)
@@ -668,6 +669,7 @@ DEPENDENCIES
   debugger-linecache
   deface!
   delayed_job_active_record
+  diffy
   factory_girl_rails
   figaro
   foreigner

app/jobs/products_cache_integrity_checker_job.rb

@@ -0,0 +1,38 @@
+require 'open_food_network/products_renderer'
+
+ProductsCacheIntegrityCheckerJob = Struct.new(:distributor_id, :order_cycle_id) do
+  def perform
+    if diff.any?
+      Bugsnag.notify RuntimeError.new("Products JSON differs from cached version"), diff: diff.to_s(:color)
+    end
+  end
+
+
+  private
+
+  def diff
+    @diff ||= Diffy::Diff.new pretty(cached_json), pretty(rendered_json)
+  end
+
+  def pretty(json)
+    JSON.pretty_generate JSON.parse json
+  end
+
+  def cached_json
+    Rails.cache.read("products-json-#{distributor_id}-#{order_cycle_id}") || {}.to_json
+  end
+
+  def rendered_json
+    OpenFoodNetwork::ProductsRenderer.new(distributor, order_cycle).products_json
+  rescue OpenFoodNetwork::ProductsRenderer::NoProducts
+    nil
+  end
+
+  def distributor
+    Enterprise.find distributor_id
+  end
+
+  def order_cycle
+    OrderCycle.find order_cycle_id
+  end
+end

config/schedule.rb

@@ -7,6 +7,10 @@ env "MAILTO", "rohan@rohanmitchell.com"
 # If we use -e with a file containing specs, rspec interprets it and filters out our examples
 job_type :run_file, "cd :path; :environment_variable=:environment bundle exec script/rails runner :task :output"
 
+every 1.hour do
+  rake 'openfoodnetwork:cache:check_products_cache_integrity'
+end
+
 every 1.day, at: '12:05am' do
   run_file "lib/open_food_network/integrity_checker.rb"
 end

lib/tasks/cache.rake

@@ -0,0 +1,16 @@
+namespace :openfoodnetwork do
+  namespace :cache do
+    desc 'check the integrity of the products cache'
+    task :check_products_cache_integrity => :environment do
+      exchanges = Exchange.
+                  outgoing.
+                  joins(:order_cycle).
+                  merge(OrderCycle.dated).
+                  merge(OrderCycle.not_closed)
+
+      exchanges.each do |exchange|
+        Delayed::Job.enqueue ProductsCacheIntegrityCheckerJob.new(exchange.receiver, exchange.order_cycle), priority: 20
+      end
+    end
+  end
+end

spec/jobs/products_cache_integrity_checker_job_spec.rb

@@ -0,0 +1,26 @@
+require 'spec_helper'
+require 'open_food_network/products_renderer'
+
+describe ProductsCacheIntegrityCheckerJob do
+  describe "reporting on differences between the products cache and the current products" do
+    let(:distributor) { create(:distributor_enterprise) }
+    let(:order_cycle) { create(:simple_order_cycle) }
+    let(:job) { ProductsCacheIntegrityCheckerJob.new distributor.id, order_cycle.id }
+
+    before do
+      Rails.cache.write "products-json-#{distributor.id}-#{order_cycle.id}", "[1, 2, 3]\n"
+      OpenFoodNetwork::ProductsRenderer.stub(:new) { double(:pr, products_json: "[1, 3]\n") }
+    end
+
+    it "reports errors" do
+      expect(Bugsnag).to receive(:notify)
+      run_job job
+    end
+
+    it "deals with nil cached_json" do
+      Rails.cache.clear
+      expect(Bugsnag).to receive(:notify)
+      run_job job
+    end
+  end
+end