Git-style namespaced key-value config file parser

config.rb

class NamespacedKeyValueConfigFile

  # This class parses a git-style config file of key=value configs grouped
  # by [namespaces].  Each namespace gets a method that returns a hash of
  # the key-value configs for the namespace.  So given:

  # [thing]
  #   key1 = val1
  #   key2 = val2
  # [other]
  #   cool = true
  # [nums]
  #   one = 1

  # You get:

  # NamespacedKeyValueConfigFile.thing #=> {'key1' => 'val1', 'key2' => 'val2'}
  # NamespacedKeyValueConfigFile.other #=> {'cool' => 'true'}
  # NamespacedKeyValueConfigFile.nums  #=> {'one'  => '1'}

  NAMESPACE_REGEX = /^\[(\w+)\].*/
  KEYVAL_REGEX    = /^\W*(\w+)\s*=\s*([\w|\.|-]+).*/
  VALID_NS_REGEX  = /^\w+$/

  attr_reader :__file__, :__data__

  def initialize(file)
    self.__parse_file__(file)
  end

  def method_missing(meth, *args, &block)
    if meth.to_s =~ VALID_NS_REGEX
      (self.__data__.keys.include?(meth.to_s) ? self.__data__[meth.to_s] : {}).tap do |v|
        block.call v if block
      end
    else
      super
    end
  end

  def respond_to?(*args)
    meth = args.first
    if meth.to_s =~ VALID_NS_REGEX && self.__data__.keys.include?(meth.to_s)
      true
    else
      super
    end
  end

  protected

  # reset and reparse the data when a new file is given
  def __parse_file__(file)
    @__file__ = file
    @__data__ = {}

    File.open(self.__file__, "r") do |file|
      file.readlines.each { |line| self.__parse_line__(line) }
    end if self.__file__ && File.exists?(self.__file__.to_s)
  end

  def __parse_line__(line)
    line.tap do
      __set_ns__(line =~ NAMESPACE_REGEX ? $1 : @ns)
      if @ns && line =~ KEYVAL_REGEX
        self.__data__[@ns][$1] = $2
      end
    end
  end

  private

  def __set_ns__(ns)
    return if ns.nil? || @ns == ns
    self.__data__[ns] ||= {}
    @ns = ns
  end

end

config_test.rb

# bundler: gem 'assert', '~> 0.7'
require 'assert'
require 'config'

class NamespacedKeyValueConfigFile

  class BasicTests < Assert::Context
    desc "the namespaced key-value config file"
    before do
      @config = NamespacedKeyValueConfigFile.new(File.expand_path("../testcfg", __FILE__))
    end
    subject { @config }

    should have_reader :__file__, :__data__

    should "store data as a nested hash of key-values" do
      assert_kind_of ::Hash, subject.__data__
      assert_kind_of ::Hash, subject.__data__[subject.__data__.keys.first]
    end

    should "parse out key value data for each config" do
      assert_equal 'true', subject.__data__['thing1']['status']
      assert_equal 'version1', subject.__data__['thing2']['v1']
      assert_equal 'version2', subject.__data__['thing2']['v2']
      assert_equal 'ver.sion3', subject.__data__['thing2']['v3']
      assert_equal 'ver-s4', subject.__data__['thing2']['v4']
      assert_equal 'cmd1', subject.__data__['line']['c1']
    end

    should "proxy its top-level __data__ hash keys as namespace methods" do
      subject.__data__.each do |ns, configs|
        assert_respond_to ns, subject
        assert_equal configs, subject.send(ns)
      end
    end

    should "return an empty hash for valid namespaces not configured" do
      assert_equal Hash.new, subject.not_configured
    end

    should "raise no method errors when accessing invalid namespaces" do
      assert_raises NoMethodError do
        subject.send(:'abc%&#')
      end
      assert_raises NoMethodError do
        subject.send(:'meth-with-hash-in-name')
      end
    end

  end

end

testcfg

[thing1]
    status=true
# comment line
[thing2]
v1 = version1
 v2    = version2
   # comment line
    v3 =    ver.sion3#comment line
    v4 = ver-s4 four

[line]
    c1 = cmd1, cmd2    # comment line
[ns]
    ns1 = 1