# Call an API with given options.
    #
    # @return [Array<(Object, Integer, Hash)>] an array of 3 elements:
    #   the data deserialized from response body (could be nil), response status code and response headers.
    def call_api(http_method, path, opts = {})
      ssl_options = {
        :ca_file => @config.ssl_ca_file,
        :verify => @config.ssl_verify,
        :verify_mode => @config.ssl_verify_mode,
        :client_cert => @config.ssl_client_cert,
        :client_key => @config.ssl_client_key
      }

      connection = Faraday.new(:url => config.base_url, :ssl => ssl_options) do |conn|
        conn.request(:basic_auth, config.username, config.password)
        @config.configure_middleware(conn)
        if opts[:header_params]["Content-Type"] == "multipart/form-data"
          conn.request :multipart
          conn.request :url_encoded
        end
        conn.adapter(Faraday.default_adapter)
      end

      begin
        response = connection.public_send(http_method.to_sym.downcase) do |req|
          build_request(http_method, path, req, opts)
        end

        if @config.debugging
          @config.logger.debug "HTTP response body ~BEGIN~\n#{response.body}\n~END~\n"
        end

        unless response.success?
          if response.status == 0
            # Errors from libcurl will be made visible here
            fail ApiError.new(:code => 0,
                              :message => response.return_message)
          else
            fail ApiError.new(:code => response.status,
                              :response_headers => response.headers,
                              :response_body => response.body),
                 response.reason_phrase
          end
        end
      rescue Faraday::TimeoutError
        fail ApiError.new('Connection timed out')
      end

      if opts[:return_type]
        data = deserialize(response, opts[:return_type])
      else
        data = nil
      end
      return data, response.status, response.headers
    end

    # Builds the HTTP request
    #
    # @param [String] http_method HTTP method/verb (e.g. POST)
    # @param [String] path URL path (e.g. /account/new)
    # @option opts [Hash] :header_params Header parameters
    # @option opts [Hash] :query_params Query parameters
    # @option opts [Hash] :form_params Query parameters
    # @option opts [Object] :body HTTP body (JSON/XML)
    # @return [Typhoeus::Request] A Typhoeus Request
    def build_request(http_method, path, request, opts = {})
      url = build_request_url(path, opts)
      http_method = http_method.to_sym.downcase

      header_params = @default_headers.merge(opts[:header_params] || {})
      query_params = opts[:query_params] || {}
      form_params = opts[:form_params] || {}

      update_params_for_auth! header_params, query_params, opts[:auth_names]

      req_opts = {
        :params_encoding => @config.params_encoding,
        :timeout => @config.timeout,
        :verbose => @config.debugging
      }

      if [:post, :patch, :put, :delete].include?(http_method)
        req_body = build_request_body(header_params, form_params, opts[:body])
        if @config.debugging
          @config.logger.debug "HTTP request body param ~BEGIN~\n#{req_body}\n~END~\n"
        end
      end
      request.headers = header_params
      request.body = req_body
      request.options = OpenStruct.new(req_opts)
      request.url url
      request.params = query_params
      download_file(request) if opts[:return_type] == 'File'
      request
    end

    # Builds the HTTP request body
    #
    # @param [Hash] header_params Header parameters
    # @param [Hash] form_params Query parameters
    # @param [Object] body HTTP body (JSON/XML)
    # @return [String] HTTP body data in the form of string
    def build_request_body(header_params, form_params, body)
      # http form
      if header_params['Content-Type'] == 'application/x-www-form-urlencoded'
        data = URI.encode_www_form(form_params)
      elsif header_params['Content-Type'] == 'multipart/form-data'
        data = {}
        form_params.each do |key, value|
          case value
          when ::File, ::Tempfile
            # TODO hardcode to application/octet-stream, need better way to detect content type
            data[key] = Faraday::UploadIO.new(value.path, 'application/octet-stream', value.path)
          when ::Array, nil
            # let Faraday handle Array and nil parameters
            data[key] = value
          else
            data[key] = value.to_s
          end
        end
      elsif body
        data = body.is_a?(String) ? body : body.to_json
      else
        data = nil
      end
      data
    end

    def download_file(request)
      @stream = []

      # handle streaming Responses
      request.options.on_data = Proc.new do |chunk, overall_received_bytes|
        @stream << chunk
      end
    end