Add Amazon Product API "ItemLookup" endpoint (#173)

* Refactor AmazonProductAPI

In preparation for #62, this commit pulls the endpoint-specific
information out of the HTTPClient class and into and endpoint-specific
class.

Now HTTPClient is responsible only for managing the environment
information and directing the user to the relevant endpoint. Adding a
new endpoint is as simple as adding a method (ex. `item_search`) and
corresponding class (ex. `ItemSearchEndpoint).

The interface is *not* in its final form yet. This is just a good
breaking point for a commit.

* Add ItemSearch endpoint

Building on the last commit, this adds a new ItemLookup endpoint. Now we
can pull details on an individual item based on the ASIN.

The endpoints and responses include a lot of duplication. Some
refactoring will probably be needed.

* Extract spec for ItemSearchEndpoint

When the item search endpoint was extracted, the specs weren't extracted
with it; this means that the HTTPClientSpec was testing everything
relating to the item search endpoint.

This commit extracts all specs relating to the endpoint into a new file.
This can now be refactored and copied over for the
`ItemLookupEndpointSpec`.

* Add spec for ItemLookupEndpoint

* Fix CodeClimate issue

This is a bit of a hack solution, but I don't feel comfortable doing any
major abstraction here yet; I don't think we have enough information.

Hopefully this'll clear up the CodeClimate complaints about duplicated
code!

* Fix easy PR-related rubocop issues

Two big points:

  1. This only fixes easy rubocop issues related to this PR. This
     doesn't touch any of the new capistrano code; I want the diff for
     this PR to be fairly contained.

  2. This includes two rubocop config changes:
      i.  Exclude the vendor directory from linting
      ii. Allow multiline braces in tests (for exception checks, let, etc.)

There are a few more risky/controversial rubocop changes I omitted from
this commit. Those are coming next.

* Fix all Lint/UriEscapeUnescape violations

Fixes #56

This commit changes all the `URI.escape` calls to `CGI.escape`. All
tests pass and the app still works. As a bonus, this seems to resolve
issue #56 too-apostrophes are now properly escaped.

This resolves all rubocop issues relating to this PR.

* Give better name to AWS test credentials in specs

Following the review suggestions. This renames `env` to
`aws_credentials`. The latter is a better name because it represents a
credentials object (built from env vars), not the ENV object itself.

Hopefully this will be clearer!

* Fix item lookup hash

When I fixed the code style for Code Climate in #173, I used the wrong
hash leading to no update attributes being found. This fixes the bug,
adds a test, and renames some of the variables.

.rubocop.yml

@@ -5,6 +5,7 @@ AllCops:
   # directories or files.
   Exclude:
     - db/**/*
+    - vendor/**/*
   TargetRubyVersion: 2.4.1
   # Cop names are not displayed in offense messages by default. Change behavior
   # by overriding DisplayCopNames, or by giving the `-D/--display-cop-names`
@@ -16,4 +17,8 @@ AllCops:
   DisplayStyleGuide: true
 
 Style/NumericLiterals:
-  Enabled: false
+  Enabled: false
+
+Style/BlockDelimiters:
+  Exclude:
+    - spec/**/*

app/controllers/amazon_search_controller.rb

@@ -9,7 +9,7 @@ class AmazonSearchController < ApplicationController
 
   def show
     authorize :amazon_search, :show?
-    @response = amazon_client.search_response
+    @response = amazon_search_response
   end
 
   def new
@@ -18,9 +18,11 @@ def new
 
   private
 
-  def amazon_client
-    AmazonProductAPI::HTTPClient.new(query: params[:query],
-                                     page_num: params[:page_num] || 1)
+  def amazon_search_response
+    client = AmazonProductAPI::HTTPClient.new
+    query  = client.item_search(query: params[:query],
+                                page: params[:page_num] || 1)
+    query.response
   end
 
   def set_wishlist

lib/amazon_product_api/http_client.rb

@@ -1,56 +1,31 @@
 # frozen_string_literal: true
 
-require 'amazon_product_api/search_response'
+require 'amazon_product_api/item_search_endpoint'
+require 'amazon_product_api/item_lookup_endpoint'
 
 module AmazonProductAPI
-  # Responsible for building and executing the query to the Amazon Product API.
+  # Responsible for managing all Amazon Product API queries.
   #
-  # Any logic relating to endpoints, building the query string, authentication
-  # signatures, etc. should live in this class.
+  # All endpoints (returning query objects) should live in this class.
   class HTTPClient
-    require 'httparty'
-    require 'time'
-    require 'uri'
-    require 'openssl'
-    require 'base64'
+    attr_reader :env # injectable credentials
 
-    # The region you are interested in
-    ENDPOINT = 'webservices.amazon.com'
-    REQUEST_URI = '/onca/xml'
-
-    attr_reader :env
-    attr_writer :query, :page_num
-
-    def initialize(query:, page_num: 1, env: ENV)
-      @query = query
-      @page_num = page_num
+    def initialize(env: ENV)
       @env = env
       assign_env_vars
     end
 
-    # Generate the signed URL
-    def url
-      raise InvalidQueryError unless query && page_num
-
-      "http://#{ENDPOINT}#{REQUEST_URI}" +    # base
-        "?#{canonical_query_string}" +        # query
-        "&Signature=#{uri_escape(signature)}" # signature
-    end
-
-    # Performs the search query and returns the resulting SearchResponse
-    def search_response(http: HTTParty)
-      response = get(http: http)
-      SearchResponse.new parse_response(response)
+    def item_search(query:, page: 1)
+      ItemSearchEndpoint.new(query, page, aws_credentials)
     end
 
-    # Send the HTTP request
-    def get(http: HTTParty)
-      http.get(url)
+    def item_lookup(asin)
+      ItemLookupEndpoint.new(asin, aws_credentials)
     end
 
     private
 
-    attr_reader :query, :page_num, :aws_credentials
+    attr_reader :aws_credentials
 
     def assign_env_vars
       @aws_credentials = AWSCredentials.new(env['AWS_ACCESS_KEY'],
@@ -61,54 +36,6 @@ def assign_env_vars
               "they're set."
       raise InvalidQueryError, msg unless @aws_credentials.present?
     end
-
-    def parse_response(response)
-      Hash.from_xml(response.body)
-    end
-
-    def uri_escape(phrase)
-      URI.encode_www_form_component(phrase.to_s)
-    end
-
-    def params
-      params = {
-        'Service'         => 'AWSECommerceService',
-        'Operation'       => 'ItemSearch',
-        'AWSAccessKeyId'  => aws_credentials.access_key,
-        'AssociateTag'    => aws_credentials.associate_tag,
-        'SearchIndex'     => 'All',
-        'Keywords'        => query.to_s,
-        'ResponseGroup'   => 'ItemAttributes,Offers,Images',
-        'ItemPage'        => page_num.to_s
-      }
-
-      # Set current timestamp if not set
-      params['Timestamp'] ||= Time.now.gmtime.iso8601
-      params
-    end
-
-    # Generate the canonical query
-    def canonical_query_string
-      params.sort
-            .map { |key, value| "#{uri_escape(key)}=#{uri_escape(value)}" }
-            .join('&')
-    end
-
-    # Generate the string to be signed
-    def string_to_sign
-      "GET\n#{ENDPOINT}\n#{REQUEST_URI}\n#{canonical_query_string}"
-    end
-
-    # Generate the signature required by the Product Advertising API
-    def signature
-      Base64.encode64(digest_with_key(string_to_sign)).strip
-    end
-
-    def digest_with_key(string)
-      OpenSSL::HMAC.digest(OpenSSL::Digest.new('sha256'),
-                           aws_credentials.secret_key,
-                           string)
-    end
   end
 
   # Wrapper object to store/verify AWS credentials

lib/amazon_product_api/item_lookup_endpoint.rb

@@ -0,0 +1,98 @@
+# frozen_string_literal: true
+
+require 'amazon_product_api/lookup_response'
+
+module AmazonProductAPI
+  # Responsible for looking up an item listing on Amazon
+  #
+  # http://docs.aws.amazon.com/AWSECommerceService/latest/DG/ItemLookup.html
+  #
+  # Any logic relating to lookup, building the query string, authentication
+  # signatures, etc. should live in this class.
+  class ItemLookupEndpoint
+    require 'httparty'
+    require 'time'
+    require 'uri'
+    require 'openssl'
+    require 'base64'
+
+    # The region you are interested in
+    ENDPOINT = 'webservices.amazon.com'
+    REQUEST_URI = '/onca/xml'
+
+    attr_accessor :asin, :aws_credentials
+
+    def initialize(asin, aws_credentials)
+      @asin = asin
+      @aws_credentials = aws_credentials
+    end
+
+    # Generate the signed URL
+    def url
+      "http://#{ENDPOINT}#{REQUEST_URI}" +    # base
+        "?#{canonical_query_string}" +        # query
+        "&Signature=#{uri_escape(signature)}" # signature
+    end
+
+    # Send the HTTP request
+    def get(http: HTTParty)
+      http.get(url)
+    end
+
+    # Performs the search query and returns the resulting SearchResponse
+    def response(http: HTTParty, logger: Rails.logger)
+      response = parse_response get(http: http)
+      logger.debug(response)
+      LookupResponse.new(response).item
+    end
+
+    private
+
+    def parse_response(response)
+      Hash.from_xml(response.body)
+    end
+
+    # Generate the signature required by the Product Advertising API
+    def signature
+      Base64.encode64(digest_with_key(string_to_sign)).strip
+    end
+
+    # Generate the string to be signed
+    def string_to_sign
+      "GET\n#{ENDPOINT}\n#{REQUEST_URI}\n#{canonical_query_string}"
+    end
+
+    # Generate the canonical query
+    def canonical_query_string
+      params.sort
+            .map { |key, value| "#{uri_escape(key)}=#{uri_escape(value)}" }
+            .join('&')
+    end
+
+    def params
+      params = {
+        'Service'         => 'AWSECommerceService',
+        'AWSAccessKeyId'  => aws_credentials.access_key,
+        'AssociateTag'    => aws_credentials.associate_tag,
+        # endpoint-specific
+        'Operation'       => 'ItemLookup',
+        'ResponseGroup'   => 'ItemAttributes,Offers,Images',
+        'ItemId'          => asin.to_s
+      }
+
+      # Set current timestamp if not set
+      params['Timestamp'] ||= Time.now.gmtime.iso8601
+      params
+    end
+
+    def digest_with_key(string)
+      OpenSSL::HMAC.digest(OpenSSL::Digest.new('sha256'),
+                           aws_credentials.secret_key,
+                           string)
+    end
+
+    def uri_escape(phrase)
+      CGI.escape(phrase.to_s)
+    end
+  end
+end

lib/amazon_product_api/item_search_endpoint.rb

@@ -0,0 +1,103 @@
+# frozen_string_literal: true
+
+require 'amazon_product_api/search_response'
+
+module AmazonProductAPI
+  # Responsible for building and executing an Amazon Product API search query.
+  #
+  # http://docs.aws.amazon.com/AWSECommerceService/latest/DG/ItemSearch.html
+  #
+  # Any logic relating to searching, building the query string, authentication
+  # signatures, etc. should live in this class.
+  class ItemSearchEndpoint
+    require 'httparty'
+    require 'time'
+    require 'uri'
+    require 'openssl'
+    require 'base64'
+
+    # The region you are interested in
+    ENDPOINT = 'webservices.amazon.com'
+    REQUEST_URI = '/onca/xml'
+
+    attr_accessor :query, :page, :aws_credentials
+
+    def initialize(query, page, aws_credentials)
+      @query = query
+      @page = page
+      @aws_credentials = aws_credentials
+    end
+
+    # Generate the signed URL
+    def url
+      raise InvalidQueryError unless query && page
+
+      "http://#{ENDPOINT}#{REQUEST_URI}" +    # base
+        "?#{canonical_query_string}" +        # query
+        "&Signature=#{uri_escape(signature)}" # signature
+    end
+
+    # Send the HTTP request
+    def get(http: HTTParty)
+      http.get(url)
+    end
+
+    # Performs the search query and returns the resulting SearchResponse
+    def response(http: HTTParty, logger: Rails.logger)
+      response = parse_response get(http: http)
+      logger.debug response
+      SearchResponse.new response
+    end
+
+    private
+
+    def parse_response(response)
+      Hash.from_xml(response.body)
+    end
+
+    # Generate the signature required by the Product Advertising API
+    def signature
+      Base64.encode64(digest_with_key(string_to_sign)).strip
+    end
+
+    # Generate the string to be signed
+    def string_to_sign
+      "GET\n#{ENDPOINT}\n#{REQUEST_URI}\n#{canonical_query_string}"
+    end
+
+    # Generate the canonical query
+    def canonical_query_string
+      params.sort
+            .map { |key, value| "#{uri_escape(key)}=#{uri_escape(value)}" }
+            .join('&')
+    end
+
+    def params
+      params = {
+        'Service'         => 'AWSECommerceService',
+        'AWSAccessKeyId'  => aws_credentials.access_key,
+        'AssociateTag'    => aws_credentials.associate_tag,
+        # endpoint-specific
+        'Operation'       => 'ItemSearch',
+        'ResponseGroup'   => 'ItemAttributes,Offers,Images',
+        'SearchIndex'     => 'All',
+        'Keywords'        => query.to_s,
+        'ItemPage'        => page.to_s
+      }
+
+      # Set current timestamp if not set
+      params['Timestamp'] ||= Time.now.gmtime.iso8601
+      params
+    end
+
+    def digest_with_key(string)
+      OpenSSL::HMAC.digest(OpenSSL::Digest.new('sha256'),
+                           aws_credentials.secret_key,
+                           string)
+    end
+
+    def uri_escape(phrase)
+      CGI.escape(phrase.to_s)
+    end
+  end
+end