Add library configuration object (#17)

* Add library configuration object

Implements a global configuration object so that we can conditionally
register things such as the renderer, parameter parser and mime type.

Author: ezekg

lib/jsonapi/rails/configuration.rb

@@ -0,0 +1,19 @@
+module JSONAPI
+  module Rails
+    class Configuration < ActiveSupport::InheritableOptions; end
+
+    DEFAULT_CONFIG = {
+      register_parameter_parser: true,
+      register_mime_type: true,
+      register_renderers: true
+    }.freeze
+
+    def self.configure
+      yield config
+    end
+
+    def self.config
+      @config ||= JSONAPI::Rails::Configuration.new(DEFAULT_CONFIG)
+    end
+  end
+end

lib/jsonapi/rails/railtie.rb

@@ -2,9 +2,10 @@
 require 'action_controller'
 require 'active_support'
 
+require 'jsonapi/rails/configuration'
+require 'jsonapi/rails/controller'
 require 'jsonapi/rails/parser'
 require 'jsonapi/rails/renderer'
-require 'jsonapi/rails/controller'
 
 module JSONAPI
   module Rails
@@ -19,20 +20,26 @@ class Railtie < ::Rails::Railtie
         ActiveSupport.on_load(:action_controller) do
           include ::JSONAPI::Rails::Controller
 
-          Mime::Type.register MEDIA_TYPE, :jsonapi
+          if JSONAPI::Rails.config.register_mime_type
+            Mime::Type.register MEDIA_TYPE, :jsonapi
+          end
 
-          if ::Rails::VERSION::MAJOR >= 5
-            ::ActionDispatch::Request.parameter_parsers[:jsonapi] = PARSER
-          else
-            ::ActionDispatch::ParamsParser::DEFAULT_PARSERS[Mime[:jsonapi]] = PARSER
+          if JSONAPI::Rails.config.register_parameter_parser
+            if ::Rails::VERSION::MAJOR >= 5
+              ::ActionDispatch::Request.parameter_parsers[:jsonapi] = PARSER
+            else
+              ::ActionDispatch::ParamsParser::DEFAULT_PARSERS[Mime[:jsonapi]] = PARSER
+            end
           end
 
-          RENDERERS.each do |name, renderer|
-            ::ActionController::Renderers.add(name) do |resources, options|
-              # Renderer proc is evaluated in the controller context.
-              self.content_type ||= Mime[:jsonapi]
+          if JSONAPI::Rails.config.register_renderers
+            RENDERERS.each do |name, renderer|
+              ::ActionController::Renderers.add(name) do |resources, options|
+                # Renderer proc is evaluated in the controller context.
+                self.content_type ||= Mime[:jsonapi]
 
-              renderer.render(resources, options, self).to_json
+                renderer.render(resources, options, self).to_json
+              end
             end
           end
         end

spec/config_spec.rb

@@ -0,0 +1,39 @@
+require 'rails_helper'
+
+describe JSONAPI::Rails.config do
+  context 'when the default configuration is used' do
+    it 'should register the jsonapi parameter parser' do
+      expect(JSONAPI::Rails.config.register_parameter_parser).to be true
+    end
+
+    it 'should register the jsonapi mime type' do
+      expect(JSONAPI::Rails.config.register_mime_type).to be true
+    end
+
+    it 'should register the jsonapi renderers' do
+      expect(JSONAPI::Rails.config.register_renderers).to be true
+    end
+  end
+
+  context 'when a custom configuration is used' do
+    before do
+      JSONAPI::Rails.configure do |config|
+        config.register_parameter_parser = false
+        config.register_mime_type = false
+        config.register_renderers = false
+      end
+    end
+
+    it 'should not register the jsonapi parameter parser' do
+      expect(JSONAPI::Rails.config.register_parameter_parser).to be false
+    end
+
+    it 'should not register the jsonapi mime type' do
+      expect(JSONAPI::Rails.config.register_mime_type).to be false
+    end
+
+    it 'should not register the jsonapi renderers' do
+      expect(JSONAPI::Rails.config.register_renderers).to be false
+    end
+  end
+end