Making constants consistent and mungeable in tests

gistfile1.rb

# config/initializers/app_config.rb

APP_CONFIG = AppConfig.new(YAML.load_file("#{Rails.root}/config/application.yml")[Rails.env])


# then you have application.yml or whatever you want to call it:

# config/application.yml (or some better name)
development:
  <<: *defaults
  default_audio_file_format: m4a
  media_path: 'public/media/development'
  media_path_clips: 'public/media/development/clips'

staging:
  ...

production: 
  ...

# usage

#  when need a constant, just use:
APP_CONFIG.constant_name

# of course the above works only for top level in the yml but nested you can still get
APP_CONFIG.constant_tree_name[:sub_value_one][:sub_value_two]

# ... in fact I think we could also make this more 'treeable' and have it traverse the yml and actually give us nested objects with a little bit of work, like:
APP_CONFIG.constant_tree_name.sub_value_one.sub_value_two


# whats cool about this is that it not only makes constants more consistent and easily 'seeable' from one file (vs in the environment files), but it also (and this is why I started doing it this way), allows us to easily change constant values for testing:

APP_CONFIG.stub(:constant_name).and_return('blah')



# the app config class file
# lib/app_config.rb (or whatever)

# this creates a class which will take hash from yaml application.yml file and simulate an
# instance method for each top level setting... this facilitates stubbing in tests

# class << hsh; def []=(key,val); return 'xxxx'; end; end;

class AppConfig

  def initialize(hash)
    hash.stringify_keys!

    # dynamic should be regular hash, updatable
    @dynamic = hash['dynamic'] || {}
    hash.delete('dynamic')

    # static uses AppConfigHash so we can control the setter
    freeze_hash(hash)
    @settings = hash
  end

  def dynamic
    @dynamic
  end


  private

    def method_missing(meth, *args, &block)
      return @settings[meth.to_s]
    end

    def freeze_hash(hash)
      disable_hash_setter(hash)
      hash.each do |key, value|
        if hash[key].is_a?(Hash)
          freeze_hash(value)
        end
      end
    end

    def disable_hash_setter(hash)
      class << hash
        def []=(key,val)
          raise 'Can not overwrite non-dynamic AppConfig constant!'
        end
      end
    end

end