module ActionController
  class UrlEncodedPairParser < StringScanner #:nodoc:
    class << self
      def parse_query_parameters(query_string)
        return {} if query_string.blank?

        pairs = query_string.split('&').collect do |chunk|
          next if chunk.empty?
          key, value = chunk.split('=', 2)
          next if key.empty?
          value = value.nil? ? nil : CGI.unescape(value)
          [ CGI.unescape(key), value ]
        end.compact

        new(pairs).result
      end

      def parse_hash_parameters(params)
        parser = new

        params = params.dup
        until params.empty?
          for key, value in params
            if key.blank?
              params.delete(key)
            elsif value.is_a?(Array)
              parser.parse(key, get_typed_value(value.shift))
              params.delete(key) if value.empty?
            else
              parser.parse(key, get_typed_value(value))
              params.delete(key)
            end
          end
        end

        parser.result
      end

      private
        def get_typed_value(value)
          case value
          when String
            value
          when NilClass
            ''
          when Array
            value.map { |v| get_typed_value(v) }
          when Hash
            if value.has_key?(:tempfile) && value[:filename].any?
              upload = value[:tempfile]
              upload.extend(UploadedFile)
              upload.original_path = value[:filename]
              upload.content_type = value[:type]
              upload
            else
              nil
            end
          else
            raise "Unknown form value: #{value.inspect}"
          end
        end
    end

    attr_reader :top, :parent, :result

    def initialize(pairs = [])
      super('')
      @result = {}
      pairs.each { |key, value| parse(key, value) }
    end

    KEY_REGEXP = %r{([^\[\]=&]+)}
    BRACKETED_KEY_REGEXP = %r{\[([^\[\]=&]+)\]}

    # Parse the query string
    def parse(key, value)
      self.string = key
      @top, @parent = result, nil

      # First scan the bare key
      key = scan(KEY_REGEXP) or return
      key = post_key_check(key)

      # Then scan as many nestings as present
      until eos?
        r = scan(BRACKETED_KEY_REGEXP) or return
        key = self[1]
        key = post_key_check(key)
      end

      bind(key, value)
    end

    private
      # After we see a key, we must look ahead to determine our next action. Cases:
      #
      #   [] follows the key. Then the value must be an array.
      #   = follows the key. (A value comes next)
      #   & or the end of string follows the key. Then the key is a flag.
      #   otherwise, a hash follows the key.
      def post_key_check(key)
        if scan(/\[\]/) # a[b][] indicates that b is an array
          container(key, Array)
          nil
        elsif check(/\[[^\]]/) # a[b] indicates that a is a hash
          container(key, Hash)
          nil
        else # End of key? We do nothing.
          key
        end
      end

      # Add a container to the stack.
      def container(key, klass)
        type_conflict! klass, top[key] if top.is_a?(Hash) && top.key?(key) && ! top[key].is_a?(klass)
        value = bind(key, klass.new)
        type_conflict! klass, value unless value.is_a?(klass)
        push(value)
      end

      # Push a value onto the 'stack', which is actually only the top 2 items.
      def push(value)
        @parent, @top = @top, value
      end

      # Bind a key (which may be nil for items in an array) to the provided value.
      def bind(key, value)
        if top.is_a? Array
          if key
            if top[-1].is_a?(Hash) && ! top[-1].key?(key)
              top[-1][key] = value
            else
              top << {key => value}.with_indifferent_access
            end
            push top.last
            return top[key]
          else
            top << value
            return value
          end
        elsif top.is_a? Hash
          key = CGI.unescape(key)
          parent << (@top = {}) if top.key?(key) && parent.is_a?(Array)
          top[key] ||= value
          return top[key]
        else
          raise ArgumentError, "Don't know what to do: top is #{top.inspect}"
        end
      end

      def type_conflict!(klass, value)
        raise TypeError, "Conflicting types for parameter containers. Expected an instance of #{klass} but found an instance of #{value.class}. This can be caused by colliding Array and Hash parameters like qs[]=value&qs[key]=value. (The parameters received were #{value.inspect}.)"
      end
  end
end