# Copyright 2020 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

require 'addressable/uri'
require 'addressable/template'
require 'google/apis/options'
require 'google/apis/errors'
require 'retriable'
require 'google/apis/core/logging'
require 'pp'

module Google
  module Apis
    module Core
      # Command for HTTP request/response.
      class HttpCommand
        include Logging

        RETRIABLE_ERRORS = [Google::Apis::ServerError, Google::Apis::RateLimitError, Google::Apis::TransmissionError]

        begin
          require 'opencensus'
          OPENCENSUS_AVAILABLE = true
        rescue LoadError
          OPENCENSUS_AVAILABLE = false
        end

        # Request options
        # @return [Google::Apis::RequestOptions]
        attr_accessor :options

        # HTTP request URL
        # @return [String, Addressable::URI]
        attr_accessor :url

        # HTTP headers
        # @return [Hash]
        attr_accessor :header

        # Request body
        # @return [#read]
        attr_accessor :body

        # HTTP method
        # @return [symbol]
        attr_accessor :method

        # HTTP Client
        # @return [HTTPClient]
        attr_accessor :connection

        # Query params
        # @return [Hash]
        attr_accessor :query

        # Path params for URL Template
        # @return [Hash]
        attr_accessor :params

        # @param [symbol] method
        #   HTTP method
        # @param [String,Addressable::URI, Addressable::Template] url
        #   HTTP URL or template
        # @param [String, #read] body
        #   Request body
        def initialize(method, url, body: nil)
          self.options = Google::Apis::RequestOptions.default.dup
          self.url = url
          self.url = Addressable::Template.new(url) if url.is_a?(String)
          self.method = method
          self.header = Hash.new
          self.body = body
          self.query = {}
          self.params = {}
          @opencensus_span = nil
        end

        # Execute the command, retrying as necessary
        #
        # @param [HTTPClient] client
        #   HTTP client
        # @yield [result, err] Result or error if block supplied
        # @return [Object]
        # @raise [Google::Apis::ServerError] An error occurred on the server and the request can be retried
        # @raise [Google::Apis::ClientError] The request is invalid and should not be retried without modification
        # @raise [Google::Apis::AuthorizationError] Authorization is required
        def execute(client)
          prepare!
          opencensus_begin_span
          begin
            Retriable.retriable tries: options.retries + 1,
                                max_elapsed_time: options.max_elapsed_time,
                                base_interval: options.base_interval,
                                max_interval: options.max_interval,
                                multiplier: options.multiplier,
                                on: RETRIABLE_ERRORS do |try|
              # This 2nd level retriable only catches auth errors, and supports 1 retry, which allows
              # auth to be re-attempted without having to retry all sorts of other failures like
              # NotFound, etc
              auth_tries = (try == 1 && authorization_refreshable? ? 2 : 1)
              Retriable.retriable tries: auth_tries,
                                  on: [Google::Apis::AuthorizationError, Signet::AuthorizationError, Signet::RemoteServerError, Signet::UnexpectedStatusError],
                                  on_retry: proc { |*| refresh_authorization } do
                execute_once(client).tap do |result|
                  if block_given?
                    yield result, nil
                  end
                end
              end
            end
          rescue => e
            if block_given?
              yield nil, e
            else
              raise e
            end
          end
        ensure
          opencensus_end_span
          @http_res = nil
          release!
        end

        # Refresh the authorization authorization after a 401 error
        #
        # @private
        # @return [void]
        def refresh_authorization
          # Handled implicitly by auth lib, here in case need to override
          logger.debug('Retrying after authentication failure')
        end

        # Check if attached credentials can be automatically refreshed
        # @return [Boolean]
        def authorization_refreshable?
          options.authorization.respond_to?(:apply!)
        end

        # Prepare the request (e.g. calculate headers, add query params, serialize data, etc) before sending
        #
        # @private
        # @return [void]
        def prepare!
          normalize_unicode = true
          if options
            header.update(options.header) if options.header
            query.update(options.query) if options.query
            normalize_unicode = options.normalize_unicode
          end
          self.url = url.expand(params, nil, normalize_unicode) if url.is_a?(Addressable::Template)
          url.query_values = normalize_query_values(query).merge(url.query_values || {})

          if allow_form_encoding?
            @form_encoded = true
            self.body = Addressable::URI.form_encode(url.query_values(Array))
            self.header['Content-Type'] = 'application/x-www-form-urlencoded; charset=UTF-8'
            self.url.query_values = {}
          else
            @form_encoded = false
          end

          self.body = '' unless self.body
        end

        # Release any resources used by this command
        # @private
        # @return [void]
        def release!
        end

        # Check the response and either decode body or raise error
        #
        # @param [Fixnum] status
        #   HTTP status code of response
        # @param [Hash] header
        #   Response headers
        # @param [String, #read] body
        #  Response body
        # @return [Object]
        #   Response object
        # @raise [Google::Apis::ServerError] An error occurred on the server and the request can be retried
        # @raise [Google::Apis::ClientError] The request is invalid and should not be retried without modification
        # @raise [Google::Apis::AuthorizationError] Authorization is required
        def process_response(status, header, body)
          check_status(status, header, body)
          decode_response_body(header['Content-Type'].first, body)
        end

        # Check the response and raise error if needed
        #
        # @param [Fixnum] status
        #   HTTP status code of response
        # @param [Hash] header
        #   HTTP response headers
        # @param [String] body
        #   HTTP response body
        # @param [String] message
        #   Error message text
        # @return [void]
        # @raise [Google::Apis::ServerError] An error occurred on the server and the request can be retried
        # @raise [Google::Apis::ClientError] The request is invalid and should not be retried without modification
        # @raise [Google::Apis::AuthorizationError] Authorization is required
        def check_status(status, header = nil, body = nil, message = nil)
          # TODO: 304 Not Modified depends on context...
          case status
          when 200...300
            nil
          when 301, 302, 303, 307
            message ||= sprintf('Redirect to %s', header['Location'])
            raise Google::Apis::RedirectError.new(message, status_code: status, header: header, body: body)
          when 401
            message ||= 'Unauthorized'
            raise Google::Apis::AuthorizationError.new(message, status_code: status, header: header, body: body)
          when 429
            message ||= 'Rate limit exceeded'
            raise Google::Apis::RateLimitError.new(message, status_code: status, header: header, body: body)
          when 304, 400, 402...500
            message ||= 'Invalid request'
            raise Google::Apis::ClientError.new(message, status_code: status, header: header, body: body)
          when 500...600
            message ||= 'Server error'
            raise Google::Apis::ServerError.new(message, status_code: status, header: header, body: body)
          else
            logger.warn(sprintf('Encountered unexpected status code %s', status))
            message ||= 'Unknown error'
            raise Google::Apis::TransmissionError.new(message, status_code: status, header: header, body: body)
          end
        end

        # Process the actual response body. Intended to be overridden by subclasses
        #
        # @param [String] _content_type
        #  Content type of body
        # @param [String, #read] body
        #  Response body
        # @return [Object]
        def decode_response_body(_content_type, body)
          body
        end

        # Process a success response
        # @param [Object] result
        #  Result object
        # @return [Object] result if no block given
        # @yield [result, nil] if block given
        def success(result, &block)
          logger.debug { sprintf('Success - %s', safe_object_representation(result)) }
          block.call(result, nil) if block_given?
          result
        end

        # Process an error response
        # @param [StandardError] err
        #  Error object
        # @param [Boolean] rethrow
        #  True if error should be raised again after handling
        # @return [void]
        # @yield [nil, err] if block given
        # @raise [StandardError] if no block
        def error(err, rethrow: false, &block)
          logger.debug { sprintf('Error - %s', PP.pp(err, '')) }
          if err.is_a?(HTTPClient::BadResponseError)
            begin
              res = err.res
              raise Google::Apis::TransmissionError.new(err) if res.nil?
              check_status(res.status.to_i, res.header, res.body)
            rescue Google::Apis::Error => e
              err = e
            end
          elsif err.is_a?(HTTPClient::TimeoutError) || err.is_a?(SocketError)
            err = Google::Apis::TransmissionError.new(err)
          end
          block.call(nil, err) if block_given?
          fail err if rethrow || block.nil?
        end

        # Execute the command once.
        #
        # @private
        # @param [HTTPClient] client
        #   HTTP client
        # @return [Object]
        # @raise [Google::Apis::ServerError] An error occurred on the server and the request can be retried
        # @raise [Google::Apis::ClientError] The request is invalid and should not be retried without modification
        # @raise [Google::Apis::AuthorizationError] Authorization is required
        def execute_once(client)
          body.rewind if body.respond_to?(:rewind)
          begin
            logger.debug { sprintf('Sending HTTP %s %s', method, url) }
            request_header = header.dup
            apply_request_options(request_header)

            @http_res = client.request(method.to_s.upcase,
                                       url.to_s,
                                       query: nil,
                                       body: body,
                                       header: request_header,
                                       follow_redirect: true)
            logger.debug { @http_res.status }
            logger.debug { safe_response_representation @http_res }
            response = process_response(@http_res.status.to_i, @http_res.header, @http_res.body)
            success(response)
          rescue => e
            logger.debug { sprintf('Caught error %s', e) }
            error(e, rethrow: true)
          end
        end

        # Update the request with any specified options.
        # @param [Hash] req_header
        #  HTTP headers
        # @return [void]
        def apply_request_options(req_header)
          if options.authorization.respond_to?(:apply!)
            options.authorization.apply!(req_header)
          elsif options.authorization.is_a?(String)
            req_header['Authorization'] = sprintf('Bearer %s', options.authorization)
          end
          req_header.update(header)
        end

        def allow_form_encoding?
          [:post, :put].include?(method) && body.nil?
        end

        private

        UNSAFE_CLASS_NAMES = [
          "Google::Apis::CloudkmsV1::DecryptResponse"
        ]

        def safe_object_representation obj
          name = obj.class.name
          if UNSAFE_CLASS_NAMES.include? name
            "#<#{name} (fields redacted)>"
          else
            PP.pp(obj, "")
          end
        end

        def safe_response_representation http_res
          if respond_to?(:response_class) && response_class.is_a?(Class) &&
             UNSAFE_CLASS_NAMES.include?(response_class.name)
            return "#<#{http_res.class.name} (fields redacted)>"
          end
          http_res.inspect
        end

        def opencensus_begin_span
          return unless OPENCENSUS_AVAILABLE && options.use_opencensus
          return if @opencensus_span
          return unless OpenCensus::Trace.span_context

          @opencensus_span = OpenCensus::Trace.start_span url.path.to_s
          @opencensus_span.kind = OpenCensus::Trace::SpanBuilder::CLIENT
          @opencensus_span.put_attribute "http.host", url.host.to_s
          @opencensus_span.put_attribute "http.method", method.to_s.upcase
          @opencensus_span.put_attribute "http.path", url.path.to_s
          if body.respond_to? :bytesize
            @opencensus_span.put_message_event \
              OpenCensus::Trace::SpanBuilder::SENT, 1, body.bytesize
          end

          formatter = OpenCensus::Trace.config.http_formatter
          if formatter.respond_to? :header_name
            header[formatter.header_name] = formatter.serialize @opencensus_span.context.trace_context
          end
        rescue StandardError => e
          # Log exceptions and continue, so opencensus failures don't cause
          # the entire request to fail.
          logger.debug { sprintf('Error opening OpenCensus span: %s', e) }
        end

        def opencensus_end_span
          return unless OPENCENSUS_AVAILABLE
          return unless @opencensus_span
          return unless OpenCensus::Trace.span_context

          if @http_res
            if @http_res.body.respond_to? :bytesize
              @opencensus_span.put_message_event \
                OpenCensus::Trace::SpanBuilder::RECEIVED, 1, @http_res.body.bytesize
            end
            status = @http_res.status.to_i
            if status > 0
              @opencensus_span.set_status map_http_status status
              @opencensus_span.put_attribute "http.status_code", status
            end
          end

          OpenCensus::Trace.end_span @opencensus_span
          @opencensus_span = nil
        rescue StandardError => e
          # Log exceptions and continue, so failures don't cause leaks by
          # aborting cleanup.
          logger.debug { sprintf('Error finishing OpenCensus span: %s', e) }
        end

        def form_encoded?
          @form_encoded
        end

        def map_http_status http_status
          case http_status
          when 200..399 then 0 # OK
          when 400 then 3 # INVALID_ARGUMENT
          when 401 then 16 # UNAUTHENTICATED
          when 403 then 7 # PERMISSION_DENIED
          when 404 then 5 # NOT_FOUND
          when 429 then 8 # RESOURCE_EXHAUSTED
          when 501 then 12 # UNIMPLEMENTED
          when 503 then 14 # UNAVAILABLE
          when 504 then 4 # DEADLINE_EXCEEDED
          else 2 # UNKNOWN
          end
        end

        def normalize_query_values(input)
          input.inject({}) do |h, (k, v)|
            h[k] = normalize_query_value(v)
            h
          end
        end

        def normalize_query_value(v)
          case v
          when Array
            v.map { |v2| normalize_query_value(v2) }
          when nil
            nil
          else
            v.to_s
          end
        end
      end
    end
  end
end