class Hash
  # Return a new hash with all keys converted to strings.
  def stringify_keys
    inject({}) do |options, (key, value)|
      options[key.to_s] = value
      options
    end
  end

  # Destructively convert all keys to strings.
  def stringify_keys!
    keys.each do |key|
      self[key.to_s] = delete(key)
    end
    self
  end

  # Return a new hash with all keys converted to symbols, as long as
  # they respond to +to_sym+.
  def symbolize_keys
    inject({}) do |options, (key, value)|
      options[(key.to_sym rescue key) || key] = value
      options
    end
  end

  # Destructively convert all keys to symbols, as long as they respond
  # to +to_sym+.
  def symbolize_keys!
    self.replace(self.symbolize_keys)
  end

  alias_method :to_options,  :symbolize_keys
  alias_method :to_options!, :symbolize_keys!

  # Validate all keys in a hash match *valid keys, raising ArgumentError on a mismatch.
  # Note that keys are NOT treated indifferently, meaning if you use strings for keys but assert symbols
  # as keys, this will fail.
  #
  # ==== Examples
  #   { :name => "Rob", :years => "28" }.assert_valid_keys(:name, :age) # => raises "ArgumentError: Unknown key(s): years"
  #   { :name => "Rob", :age => "28" }.assert_valid_keys("name", "age") # => raises "ArgumentError: Unknown key(s): name, age"
  #   { :name => "Rob", :age => "28" }.assert_valid_keys(:name, :age) # => passes, raises nothing
  def assert_valid_keys(*valid_keys)
    unknown_keys = keys - [valid_keys].flatten
    raise(ArgumentError, "Unknown key(s): #{unknown_keys.join(", ")}") unless unknown_keys.empty?
  end
end