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Refactor Amazon Product API endpoints #174

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5 changes: 4 additions & 1 deletion README.md
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Expand Up @@ -175,7 +175,10 @@ account or login locally:

By the end of this section, you should be able to search Amazon products and
add items to wishlists on your local machine (when your logged-in user is an
admin or site manager).
admin or site manager). *Note: if you're adding a new API endpoint, read more
[here][API client README].*

[API client README]: lib/amazon_product_api/README.md

**This step is only required for site managers and admins searching/adding
Amazon products.** If your issue doesn't involve working with the Amazon
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68 changes: 68 additions & 0 deletions lib/amazon_product_api/README.md
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# Amazon Product Advertising API Client

This folder contains the wrapper code for the Amazon Product Advertising API.
For more details on the API, check the [Amazon documentation].

[Amazon documentation]: http://docs.aws.amazon.com/AWSECommerceService/latest/DG/Welcome.html

## Adding an Endpoint

All endpoints should be subclassed from `AmazonProductAPI::Endpoint`. In order
to add a new endpoint, you'll need to modify the template below in a few ways:

* Prepend any new attributes to the `#initialize` parameter list. Any
validations or processing can be done in `#initialize` as shown. Note:
setting `aws_credentials` is **required**!

* Add endpoint-specific request parameters to `#request_params`. These can
be found in the Amazon API documentation.

* Add any post-processing of the API response in `#process_response`.

* Update the class name and comments.

### Endpoint Template

```ruby
require 'amazon_product_api/endpoint'

module AmazonProductAPI
# Responsible for building and executing <...>
#
# <endpoint url>
#
# Contains all specialization logic for this endpoint including request
# parameters, parameter validation, and response parsing.
class TemplateEndpoint < Endpoint
# Add any parameters you need for the specific endpoint.
#
# Make sure you set `@aws_credentials`-the query won't work without it!
def initialize(aws_credentials)
# Attribute validations
# raise InvalidQueryError, 'reason' if ...

# Initialize attributes
@aws_credentials = aws_credentials
end

private

attr_accessor :aws_credentials # any other attrs

# Add any post-processing of the response hash.
def process_response(response_hash)
ExampleResponse.new(response_hash).item
end

# Include request parameters unique to this endpoint.
def request_params
{
# 'Operation' => 'ItemLookup',
# 'IdType' => 'ASIN',
# 'ItemId' => 'the item asin',
# ...
}
end
end
end
```
104 changes: 104 additions & 0 deletions lib/amazon_product_api/endpoint.rb
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# frozen_string_literal: true

module AmazonProductAPI
# Base representation of all Amazon Product Advertising API endpoints.
#
# http://docs.aws.amazon.com/AWSECommerceService/latest/DG/\
# CHAP_OperationListAlphabetical.html
#
# Any general logic relating to lookup, building the query string,
# authentication signatures, etc. should live in this class. Specializations
# (including specific request parameters and response parsing) should live in
# endpoint subclasses.
class Endpoint
require 'httparty'
require 'time'
require 'uri'
require 'openssl'
require 'base64'

# The region you are interested in
ENDPOINT = 'webservices.amazon.com'
REQUEST_URI = '/onca/xml'

# Generates the signed URL
def url
raise InvalidQueryError, 'Missing AWS credentials' unless aws_credentials

"http://#{ENDPOINT}#{REQUEST_URI}" + # base
"?#{canonical_query_string}" + # query
"&Signature=#{uri_escape(signature)}" # signature
end

# Sends the HTTP request
def get(http: HTTParty)
http.get(url)
end

# Performs the search query and returns the processed response
def response(http: HTTParty, logger: Rails.logger)
response = parse_response get(http: http)
logger.debug response
process_response(response)
end

private

attr_reader :aws_credentials

# Takes the response hash and returns the processed API response
#
# This must be implemented for each individual endpoint.
def process_response(_response_hash)
raise NotImplementedError, 'Implement this method in your subclass.'
end

# Returns a hash of request parameters unique to the endpoint
#
# This must be implemented for each individual endpoint.
def request_params
raise NotImplementedError, 'Implement this method in your subclass.'
end

def params
params = request_params.merge(
'Service' => 'AWSECommerceService',
'AWSAccessKeyId' => aws_credentials.access_key,
'AssociateTag' => aws_credentials.associate_tag
)

# Set current timestamp if not set
params['Timestamp'] ||= Time.now.gmtime.iso8601
params
end

def parse_response(response)
Hash.from_xml(response.body)
end

# Generates the signature required by the Product Advertising API
def signature
Base64.encode64(digest_with_key(string_to_sign)).strip
end

def string_to_sign
"GET\n#{ENDPOINT}\n#{REQUEST_URI}\n#{canonical_query_string}"
end

def canonical_query_string
params.sort
.map { |key, value| "#{uri_escape(key)}=#{uri_escape(value)}" }
.join('&')
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
85 changes: 13 additions & 72 deletions lib/amazon_product_api/item_lookup_endpoint.rb
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# frozen_string_literal: true

require 'amazon_product_api/endpoint'
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

# 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
@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
attr_reader :asin, :aws_credentials

# Generate the signature required by the Product Advertising API
def signature
Base64.encode64(digest_with_key(string_to_sign)).strip
def process_response(response_hash)
LookupResponse.new(response_hash).item
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
# Other request parameters for ItemLookup can be found here:
#
# http://docs.aws.amazon.com/AWSECommerceService/latest/DG/\
# ItemLookup.html#ItemLookup-rp
def request_params
{
'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
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