Add ability to use nested only parameter

- The only string works much the same as before with its comma separation
-- Nested includes are indicated with square brackets "[ ]"
-- The nested include is the value immediately preceding the square brackets
-- The only string is the comma separated string inside those brackets
- Default includes are split between format types when necessary
-- This prevents unnecessary includes from being added on page load
- Available includes are those items which are allowed to be accessible to the user
-- Some aren't because they are sensitive, such as the creator of a flag
-- Some aren't because the number of associated items is too large
- The amount of times the same model can be included to prevent recursions
-- One exception is the root model may include the same model once
--- e.g. the user model can include the inviter which is also the user model
-- Another exception is if the include is a has_many association
--- e.g. artist urls can include the artist, and then artist urls again

app/controllers/application_controller.rb

@@ -34,6 +34,25 @@ class ApplicationController < ActionController::Base
     end
   end
 
+  def model_includes(params, model = nil)
+    if params[:only] && ["json", "xml"].include?(params[:format])
+      includes_array = ParameterBuilder.includes_parameters(params[:only], model_name)
+    elsif params[:action] == "index"
+      includes_array = default_includes(params)
+    else
+      includes_array = []
+    end
+    includes_array
+  end
+
+  def default_includes(*)
+    []
+  end
+
+  def model_name
+    controller_name.classify
+  end
+
   def redirect_to_show(items)
     redirect_to send("#{controller_path.singularize}_path", items.first, format: request.format.symbol)
   end