nested_query.rb

# Helper methods to encode and parse nested query strings without a
# third-party library (e.g. ActiveSupport, Addressable, or Rack).
module NestedQuery
  autoload :CGI, 'cgi'
  extend self

  # Dumps a hash into a nested query string.
  #
  #   NestedQuery.encode a: [1, 3], b: { 2 => 4 }, c: 5
  #   # => "a%5B%5D=1&a%5B%5D=3&b%5B2%5D=4&c=5"
  def encode object, key = nil
    case object
    when Hash
      object.map { |k, v| encode v, key ? "#{key}[#{k}]" : k }.sort * '&'
    when Array
      object.map { |o| encode o, "#{key}[]" } * '&'
    else
      "#{CGI.escape key.to_s}=#{CGI.escape object.to_s}"
    end
  end

  # Parses a nested query string into a params hash.
  #
  #   NestedQuery.parse "a%5B%5D=1&a%5B%5D=3&b%5B2%5D=4&c=5"
  #   # => {"a"=>["1", "3"], "b"=>{"2"=>"4"}, "c"=>"5"}
  def parse string
    string.scan(/([^=&]+)=([^=&]*)/).inject({}) do |hash, pair|
      key, value = pair.map(&CGI.method(:unescape))
      keypath, array = key.scan(/[^\[\]]+/), key[/\[\]$/]
      keypath.inject(hash) do |nest, component|
        next nest[component] ||= {} unless keypath.last == component
        array ? (nest[component] ||= []) << value : nest[component] = value
      end
      hash
    end
  end
end