Parse ruby error response body and add attributes

This commit updates the ApiError class in the generated Ruby gem. The
class has been updated to not pass hash arguments directly to the StandardError
constructor. Only a possible title or message hash attribute is passed
to StandardError. This prevents Ruby from stringifying a hash and using
that as the error message, which is both ugly and unusable.

Author: dhughes

swagger-config/marketing/ruby/templates/api_error.mustache

@@ -2,29 +2,55 @@
 {{> api_info}}
 =end
 
-module {{moduleName}}
+require 'json'
+
+module MailchimpMarketing
   class ApiError < StandardError
     attr_reader :status, :type, :title, :detail, :instance, :errors
 
+    attr_reader :response_headers, :response_body
+
     # Usage examples:
     #   ApiError.new
     #   ApiError.new("message")
     #   ApiError.new(:status => 500, :response_headers => {}, :response_body => "")
     #   ApiError.new(:status => 404, :message => "Not Found")
-    def initialize(arg = nil)
-      if arg.is_a? Hash
-        if arg.key?(:message) || arg.key?('message')
-          super(arg[:message] || arg['message'])
-        else
-          super arg
-        end
+    def initialize(arguments = nil)
+      @arguments = arguments
+      return super(@arguments) unless @arguments.is_a?(Hash)
+
+      @arguments.transform_keys!(&:to_sym)
 
-        arg.each do |k, v|
-          instance_variable_set "@#{k}", v
+      expand_response_body_into_arguments
+
+      super(@arguments[:title] || @arguments[:message])
+
+      @arguments.each do |key, value|
+        instance_variable_set("@#{key}", value)
+      end
+    end
+
+    private
+
+    def expand_response_body_into_arguments
+      @arguments.merge!(parsed_response_body) unless parsed_response_body.nil?
+    end
+
+    def parsed_response_body
+      @parsed_response_body ||= begin
+        parsed_response_body = JSON.parse(@arguments[:response_body]).transform_keys(&:to_sym)
+
+        if parsed_response_body[:errors].is_a?(Array)
+          parsed_response_body[:errors].map do |error|
+            error.transform_keys!(&:to_sym)
+          end
         end
-      else
-        super arg
+
+        parsed_response_body
+      rescue
+        nil
       end
     end
+
   end
 end