Item lookup endpoint supports up to 10 ASINs

As a first step for batching the requests, this commit makes the client
endpoint take a list of asins instead of just an individual one. Other
files are changed in order to work with the new interface (asins ->
items)

Next up: bulk-searching with the items sync job!

Author: leesharma

app/jobs/item_sync_job.rb

@@ -13,6 +13,10 @@
 class ItemSyncJob < ApplicationJob
   queue_as :default
 
+  def initialize
+    @client = AmazonProductAPI::HTTPClient.new
+  end
+
   # Syncs all items and writes the results to the log
   def perform(*_args)
     Rails.logger.info bold_green('Syncing all items')
@@ -22,6 +26,8 @@ def perform(*_args)
 
   private
 
+  attr_reader :client
+
   def sync_all!
     # This is done in slices to avoid Amazon rate limits
     Item.all.each_slice(3) do |items|
@@ -41,8 +47,7 @@ def sync!(item)
   end
 
   def amazon_item!(item)
-    client = AmazonProductAPI::HTTPClient.new
-    client.item_lookup(item.asin).response
+    client.item_lookup(item.asin).response.first
   end
 
   # Some styles for log text. This is so minor that it's not worth

lib/amazon_product_api/http_client.rb

@@ -19,8 +19,8 @@ def item_search(query:, page: 1)
       ItemSearchEndpoint.new(query, page, aws_credentials)
     end
 
-    def item_lookup(asin)
-      ItemLookupEndpoint.new(asin, aws_credentials)
+    def item_lookup(*asin)
+      ItemLookupEndpoint.new(*asin, aws_credentials)
     end
 
     private

lib/amazon_product_api/item_lookup_endpoint.rb

@@ -11,17 +11,27 @@ module AmazonProductAPI
   # Contains all specialization logic for this endpoint including request
   # parameters, parameter validation, and response parsing.
   class ItemLookupEndpoint < Endpoint
-    def initialize(asin, aws_credentials)
-      @asin = asin
+    ASIN_LIMIT = 10 # max ASINs per request (from docs)
+
+    def initialize(*asins, aws_credentials)
+      validate_asin_count(asins)
+
+      @asins = asins
       @aws_credentials = aws_credentials
     end
 
     private
 
-    attr_reader :asin, :aws_credentials
+    attr_reader :asins, :aws_credentials
+
+    def validate_asin_count(asins)
+      return unless asins.count > ASIN_LIMIT
+      raise ArgumentError,
+            "Exceeded maximum ASIN limit: #{asins.length}/#{ASIN_LIMIT}"
+    end
 
     def process_response(response_hash)
-      LookupResponse.new(response_hash).item
+      LookupResponse.new(response_hash).items
     end
 
     # Other request parameters for ItemLookup can be found here:
@@ -32,7 +42,8 @@ def request_params
       {
         'Operation'       => 'ItemLookup',
         'ResponseGroup'   => 'ItemAttributes,Offers,Images',
-        'ItemId'          => asin.to_s
+        'IdType'          => 'ASIN',
+        'ItemId'          => asins.join(',')
       }
     end
   end

lib/amazon_product_api/lookup_response.rb

@@ -10,34 +10,34 @@ module AmazonProductAPI
   # file to touch if the API response changes.
   class LookupResponse
     def initialize(response_hash)
-      @hash = item_hash_for response_hash
+      @response_hash = response_hash
     end
 
-    def item(item_class: SearchItem)
-      item_class.new(**item_attrs)
+    def items(item_class: SearchItem)
+      item_hashes.map { |hash| item_class.new(**item_attrs_from(hash)) }
     end
 
     private
 
-    attr_reader :hash
+    attr_reader :response_hash
 
-    def item_attrs
+    def item_attrs_from(hash)
       {
         asin: hash['ASIN'],
 
-        price_cents: hash.dig('ItemAttributes', 'ListPrice', 'Amount').to_i,
+        detail_page_url: hash['DetailPageURL'],
+        title:           hash['ItemAttributes']['Title'],
+        price_cents:     hash['ItemAttributes']['ListPrice']['Amount'].to_i,
 
-        image_url:    hash.dig('SmallImage', 'URL') || '',
-        image_width:  hash.dig('SmallImage', 'Width') || '',
-        image_height: hash.dig('SmallImage', 'Height') || '',
-
-        title:              hash.dig('ItemAttributes', 'Title'),
-        detail_page_url:    hash['DetailPageURL']
+        image_url:    hash.dig('SmallImage', 'URL')    || '',
+        image_width:  hash.dig('SmallImage', 'Width')  || '',
+        image_height: hash.dig('SmallImage', 'Height') || ''
       }
     end
 
-    def item_hash_for(response_hash)
-      response_hash.dig('ItemLookupResponse', 'Items', 'Item') || []
+    def item_hashes
+      items = response_hash.dig('ItemLookupResponse', 'Items', 'Item') || []
+      items.is_a?(Array) ? items : [items] # wrap "naked" response
     end
   end
 end