require 'yaml'

module HSS
  ##
  # Load values from an external YAML hash
  class Parser
    private

    def external(source, key)
      begin
        config = open(File.expand_path(source)) { |f| YAML.load f.read }
      rescue Psych::SyntaxError, Errno::ENOENT
        raise "Failed to open YAML file: #{source}"
      end
      begin
        key.split('.').reduce(config) { |a, e| a[e] } || fail
      rescue
        raise NameError, "Key not found in YAML: #{key}"
      end
    end
  end
end