lib/gooddata/bricks/middleware/base_middleware.rb in gooddata-0.6.10 vs lib/gooddata/bricks/middleware/base_middleware.rb in gooddata-0.6.11

@@ -1,12 +1,48 @@
 # encoding: UTF-8
+require 'hashie'
 
 module GoodData
   module Bricks
     class Middleware
       attr_accessor :app
 
       include Bricks::Utils
+
+      # Loads defaults to params from a json file in @config.
+      #
+      # The idea is to have a set of parameter defaults
+      # for a middleware. The defaults are loaded from a json file.
+      # If a brick user wants to override a default, they can
+      # do that in runtime params which come to the method in 'params'.
+      #
+      # A deep merge is done on the params. Arrays and other
+      # non-hash types are overwritten (params win).
+      #
+      # ### Examples
+      #
+      # A brick developer develops a SalesforceDownloaderMiddleware
+      # with default preset 'gse' having a configuration preset
+      # {"entities": ["Acount", "Event", "OpportunityLineItem", "Opportunity", "User"]}
+      #
+      # The brick user only wants to use Opportunity, so he passes
+      # runtime parameter {"entities": ["Opportunity"]} which overrides
+      # the default.
+      # See spec/bricks/bricks_spec.rb for usage.
+      def load_defaults(params)
+        # if default params given, fill what's not given in runtime params
+        if @config
+          # load it from file and merge it
+          defaults = { 'config' => MultiJson.load(File.read(@config)) }
+          default_params = defaults.extend(Hashie::Extensions::DeepMerge)
+          params = default_params.deep_merge(params)
+        end
+        params
+      end
+
+      def call(params)
+        load_defaults(params)
+      end
 
       def initialize(options = {})
         @app = options[:app]
       end
     end