module Sinatra::ConfigFile

def self.registered(base)

traditional environments: development, test and production.
When the extension is registered sets the +environments+ setting to the 
def self.registered(base)
  base.set :environments, %w[test production development]
end

def config_file(*paths)

these +paths+ can actually be globs.
arguments, filtering the settings for the current environment. Note that
Loads the configuration from the YAML files whose +paths+ are passed as 
def config_file(*paths)
  Dir.chdir(root || '.') do
    paths.each do |pattern|
      Dir.glob(pattern) do |file|
        raise UnsupportedConfigType unless ['.yml', '.yaml', '.erb'].include?(File.extname(file))
        logger.info "loading config file '#{file}'" if logging? && respond_to?(:logger)
        document = ERB.new(File.read(file)).result
        yaml = YAML.respond_to?(:unsafe_load) ? YAML.unsafe_load(document) : YAML.load(document)
        config = config_for_env(yaml)
        config.each_pair { |key, value| set(key, value) }
      end
    end
  end
end

def config_for_env(hash)

precedence to environment settings defined at the root-level.
settings applicable to the current environment. Note: It gives
Given a +hash+ containing application configuration it returns 
def config_for_env(hash)
  return from_environment_key(hash) if environment_keys?(hash)
  hash.each_with_object(IndifferentHash[]) do |(k, v), acc|
    if environment_keys?(v)
      acc.merge!(k => v[environment.to_s]) if v.key?(environment.to_s)
    else
      acc.merge!(k => v)
    end
  end
end

def environment_keys?(hash)

+environments+ in its root keys.
Returns true if supplied with a hash that has any recognized 
def environment_keys?(hash)
  hash.is_a?(Hash) && hash.any? { |k, _| environments.include?(k.to_s) }
end

def from_environment_key(hash)

environment.
Given a +hash+ returns the settings corresponding to the current 
def from_environment_key(hash)
  hash[environment.to_s] || hash[environment.to_sym] || {}
end