Add API resource instance methods to StripeClient

This change introduces a proof-of-concept to add convenience methods to
access API resources through a StripeClient for per-client
configuration. This first iteration only allows for the `api_key` to be
configured but can be extended to allow other options such as
`stripe_version`, which should solve stripe#872.

The primary workhorse for this feature is a new module called
`Stripe::ClientAPIOperations` that defines instance methods on
`StripeClient` when it is included. A `ClientProxy` is used to send any
method calls to an API resource with the instantiated client injected.
There are a few noteworthy aspects of this approach:

- Many resources are namespaced, which introduces a unique challenge
  when it comes to method chaining calls (e.g.
  client.issuing.authorizations).  In order to handle those cases, we
  create a `ClientProxy` object for the root namespace (e.g., "issuing")
  and define all resource methods (e.g. "authorizations") at once to
  avoid re-defining the proxy object when there are multiple resources
  per namespace.

- Sigma deviates from other namespaced API resources and does not have
  an `OBJECT_NAME` separated by a period. We account for that nuance
  directly.

- `method_missing` is substantially slower than direct calls. Therefore,
  methods are defined where possible but `method_missing` is still used
  at the last step when delegating resource methods to the actual
  resource.

lib/stripe.rb

@@ -30,18 +30,22 @@
 require "stripe/util"
 require "stripe/connection_manager"
 require "stripe/multipart_encoder"
-require "stripe/stripe_client"
 require "stripe/stripe_object"
 require "stripe/stripe_response"
 require "stripe/list_object"
 require "stripe/error_object"
 require "stripe/api_resource"
 require "stripe/singleton_api_resource"
 require "stripe/webhook"
+require "stripe/client_api_operations"
 
 # Named API resources
 require "stripe/resources"
 
+# StripeClient requires API Resources to be loaded
+# due to dynamic methods defined by ClientAPIOperations
+require "stripe/stripe_client"
+
 # OAuth
 require "stripe/oauth"
 

lib/stripe/client_api_operations.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module Stripe
+  # Define instance methods on the including class (i.e. StripeClient)
+  # to access API resources.
+  module ClientAPIOperations
+    # Proxy object to inject the client into API resources
+    class ClientProxy
+      def initialize(client:, resource: nil)
+        @client = client
+        @resource = resource
+      end
+
+      attr_reader :client
+
+      def with_client(client)
+        @client = client
+        self
+      end
+
+      def method_missing(method, *args)
+        super unless @resource
+        @resource.send(method, *args << { client: @client }) || super
+      end
+
+      def respond_to_missing?(symbol, include_private = false)
+        super unless @resource
+        @resource.respond_to?(symbol) || super
+      end
+    end
+
+    def self.included(base)
+      base.class_eval do
+        # Sigma, unlike other nested API objects, is not separated by a period
+        # so we modify the object name to follow the expected convention.
+        api_resources = Stripe::Util.api_object_classes.transform_keys do |key|
+          key == "scheduled_query_run" ? "sigma.scheduled_query_run" : key
+        end
+
+        # Group namespaces that have mutiple resourses
+        grouped_resources = api_resources.group_by do |key, _|
+          key.include?(".") ? key.split(".").first : key
+        end
+
+        grouped_resources.each do |resource_namespace, resources|
+          # Namespace resource names are separated with a period by convention.
+          if resources[0][0].include?(".")
+
+            # Defines the methods required for chaining calls for resources that
+            # are namespaced. A proxy object is created so that all resource
+            # methods can be defined at once.
+            proxy = ClientProxy.new(client: nil)
+            resources.each do |resource_name, resource_class|
+              method_name = resource_name.split(".").last
+              proxy.define_singleton_method("#{method_name}s") do
+                ClientProxy.new(client: proxy.client, resource: resource_class)
+              end
+            end
+
+            # Defines the first method for resources that are namespaced. By
+            # convention these methods are singular. A proxy object is returned
+            # so that the client can be injected along the method chain.
+            define_method(resource_namespace) do
+              proxy.with_client(self)
+            end
+          else
+            # Defines plural methods for non-namespaced resources
+            define_method("#{resource_namespace}s".to_sym) do
+              ClientProxy.new(client: self, resource: resources[0][1])
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/stripe/object_types.rb

@@ -1,15 +1,17 @@
 # frozen_string_literal: true
 
 # rubocop:disable Metrics/MethodLength
-
 module Stripe
   module ObjectTypes
     def self.object_names_to_classes
       {
         # data structures
         ListObject::OBJECT_NAME => ListObject,
+      }.merge(api_object_names_to_classes)
+    end
 
-        # business objects
+    def self.api_object_names_to_classes
+      {
         Account::OBJECT_NAME => Account,
         AccountLink::OBJECT_NAME => AccountLink,
         AlipayAccount::OBJECT_NAME => AlipayAccount,
@@ -95,5 +97,4 @@ def self.object_names_to_classes
     end
   end
 end
-
 # rubocop:enable Metrics/MethodLength

lib/stripe/stripe_client.rb

@@ -7,6 +7,8 @@ module Stripe
   # recover both a resource a call returns as well as a response object that
   # contains information on the HTTP call.
   class StripeClient
+    include Stripe::ClientAPIOperations
+
     # A set of all known thread contexts across all threads and a mutex to
     # synchronize global access to them.
     @thread_contexts_with_connection_managers = []
@@ -17,11 +19,14 @@ class StripeClient
     #
     # Takes a connection manager object for backwards compatibility only, and
     # that use is DEPRECATED.
-    def initialize(_connection_manager = nil)
+    def initialize(_connection_manager = nil, api_key: nil)
       @system_profiler = SystemProfiler.new
       @last_request_metrics = nil
+      @api_key = api_key
     end
 
+    attr_reader :api_key
+
     # Gets a currently active `StripeClient`. Set for the current thread when
     # `StripeClient#request` is being run so that API operations being executed
     # inside of that block can find the currently active client. It's reset to
@@ -188,7 +193,7 @@ def execute_request(method, path,
         unless path.is_a?(String)
 
       api_base ||= Stripe.api_base
-      api_key ||= Stripe.api_key
+      api_key ||= self.api_key || Stripe.api_key
       params = Util.objects_to_ids(params)
 
       check_api_key!(api_key)

lib/stripe/util.rb

@@ -39,10 +39,16 @@ def self.objects_to_ids(obj)
       end
     end
 
+    # Returns a hash of all Stripe object classes.
     def self.object_classes
       @object_classes ||= Stripe::ObjectTypes.object_names_to_classes
     end
 
+    # Returns a hash containling only Stripe API object classes.
+    def self.api_object_classes
+      @api_object_classes ||= ::Stripe::ObjectTypes.api_object_names_to_classes
+    end
+
     def self.object_name_matches_class?(object_name, klass)
       Util.object_classes[object_name] == klass
     end
@@ -254,6 +260,20 @@ def self.secure_compare(str_a, str_b)
       res.zero?
     end
 
+    # Attempts to find API resource with provided string or symbol.
+    def self.resource_constantize(term)
+      Object.const_get("Stripe::#{resource_classify(term)}")
+    end
+
+    # Generates a class name based on the provided string. Accepts lowercase
+    # and camelcased strings.
+    def self.resource_classify(string)
+      string
+        .to_s
+        .gsub(/^(.+?)[s]{0,1}$/) { Regexp.last_match(1).capitalize }
+        .gsub(/(?:_)([a-z\d]*)/) { Regexp.last_match(1).capitalize }
+    end
+
     #
     # private
     #

test/stripe/stripe_client_test.rb

@@ -334,6 +334,46 @@ class StripeClientTest < Test::Unit::TestCase
         end
       end
 
+      context "API resource instance methods" do
+        should "define methods for all api resources" do
+          client = StripeClient.new
+
+          # Update Sigma name to account for nuance
+          api_resources = Stripe::Util.api_object_classes.transform_keys do |key|
+            key == "scheduled_query_run" ? "sigma.scheduled_query_run" : key
+          end
+
+          api_resources.each do |string, _|
+            if string.include?(".")
+              resource_module, resource_name = string.split(".")
+
+              assert client.respond_to?(resource_module), "#{resource_module} not found"
+              assert client.send(resource_module).respond_to?("#{resource_name}s"), "#{resource_name} not found"
+            else
+              assert client.respond_to?("#{string}s"), "#{string} not found"
+            end
+          end
+        end
+
+        should "make expected request on an API resource" do
+          client = StripeClient.new(api_key: "sk_test_local")
+          account = client.accounts.retrieve("acct_1234")
+          assert_requested(:get,
+                           "#{Stripe.api_base}/v1/accounts/acct_1234",
+                           headers: { "Authorization" => "Bearer sk_test_local" })
+          assert account.is_a?(Stripe::Account)
+        end
+
+        should "make expected request on a namespace API resource" do
+          client = StripeClient.new(api_key: "sk_test_local")
+          list = client.radar.value_lists.retrieve("rsl_123")
+          assert_requested(:get,
+                           "#{Stripe.api_base}/v1/radar/value_lists/rsl_123",
+                           headers: { "Authorization" => "Bearer sk_test_local" })
+          assert list.is_a?(Stripe::Radar::ValueList)
+        end
+      end
+
       context "logging" do
         setup do
           # Freeze time for the purposes of the `elapsed` parameter that we

test/stripe/util_test.rb

@@ -398,5 +398,25 @@ def isatty
         assert_equal "true", Util.send(:wrap_logfmt_value, true)
       end
     end
+
+    context ".resource_constantize" do
+      should "return an instance of the class" do
+        assert_equal Stripe::Account, Util.resource_constantize("accounts")
+        assert_equal Stripe::WebhookEndpoint, Util.resource_constantize(:webhook_endpoints)
+      end
+
+      should "raise when the String cannot be resolved" do
+        assert_raises(NameError) { Util.resource_constantize("not_real") }
+      end
+    end
+
+    context ".resource_classify" do
+      should "classify the string" do
+        assert_equal "Account", Util.resource_classify("accounts")
+        assert_equal "Account", Util.resource_classify(:accounts)
+        assert_equal "WebhookEndpoint", Util.resource_classify("webhook_endpoints")
+        assert_equal "Sigma", Util.resource_classify("sigma")
+      end
+    end
   end
 end