Add items:sync rake task

`rake items:sync` will sync all items in the database. Some chunking was
done in `ItemSyncJob` in order to get around Amazon's rate limitations.

TODO:
  * Batch the Amazon query (ItemLookup can take up to 10 ASINs)
  * Add a delayed job queue (new issue?)
  * Add specs

Author: leesharma

app/jobs/item_sync_job.rb

@@ -0,0 +1,61 @@
+require 'amazon_product_api'
+
+# This job is responsible for syncing items with Amazon.
+#
+# Amazon changes prices, details, etc. pretty frequently, so this job will
+# query the Amazon record associated with the ASIN and make any required local
+# updates.
+#
+# Bang methods (ex. `#amazon_item!`) perform an HTTP request.
+#
+class ItemSyncJob < ApplicationJob
+  queue_as :default
+
+  # Syncs all items and writes the results to the log
+  def perform(*_args)
+    Rails.logger.info bold_green('Syncing all items')
+    sync_all!
+    Rails.logger.info bold_green('Done syncing!')
+  end
+
+  private
+
+  def sync_all!
+    # This is done in slices to avoid Amazon rate limits
+    Item.all.each_slice(3) do |items|
+      items.each { |item| sync! item }
+      sleep 2.seconds
+    end
+  end
+
+  def sync!(item)
+    Rails.logger.info green("Syncing item #{item.id}: #{item.name}")
+    update_hash = amazon_item!(item).update_hash
+    item.assign_attributes(update_hash)
+
+    if item.changed?
+      Rails.logger.info bold_green("Changed:\n") + item.changes.pretty_inspect
+      item.save!
+    end
+  end
+
+  def amazon_item!(item)
+    client = AmazonProductAPI::HTTPClient.new
+    client.item_lookup(item.asin).response
+  end
+
+  # Some styles for log text. This is so minor that it's not worth
+  # bringing in a full library.
+
+  def bold_green(text)
+    bold(green(text))
+  end
+
+  def green(text)
+    "\e[32m#{text}\e[0m"
+  end
+
+  def bold(text)
+    "\e[1m#{text}\e[22m"
+  end
+end

lib/tasks/items.rake

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+namespace :items do
+  desc 'Check Amazon listings and update local items accordingly.'
+  task sync: :environment do
+    ItemSyncJob.perform_now
+  end
+end