module Pears 
  # A subject is a collection of settings.
  # You could different Pears::Subjects in your application for different parts
  # of its domain. for instance: application_settings, theming or translations.
  class Subject
    attr_reader :name

    def initialize(name, *layers)
      @name = name
      @layers = layers
      Pears.subjects << self
    end

    def [](key)
      project[key]
    end

    def keys
      project.keys
    end

    def has_key?(key)
      project.has_key? key
    end

    def push_layer(layer)
      @layers << layer
    end

    # Projects the layers to a hash that van be used as a single source of truth.
    def project
      layers.reverse.reduce(Hash.new) do |hash, layer|
        hash.deep_merge(layer.data)
      end
    end

    private

    def layers
      @layers
    end
  end
end