# encoding: utf-8

require 'digest'

require 'one_apm/agent/inbound_request_monitor'
require 'one_apm/agent/threading/agent_thread'
require 'one_apm/transaction/transaction_state'

module OneApm
  module Agent
    class CrossAppMonitor < InboundRequestMonitor

      ONEAPM_ID_HEADER      = 'X-OneApm-ID'
      ONEAPM_TXN_HEADER     = 'X-OneApm-Transaction'
      ONEAPM_APPDATA_HEADER = 'X-OneApm-App-Data'

      ONEAPM_ID_HEADER_KEY      = 'HTTP_X_ONEAPM_ID'.freeze
      ONEAPM_TXN_HEADER_KEY     = 'HTTP_X_ONEAPM_TRANSACTION'.freeze
      OA_CONTENT_LENGTH_HEADER_KEY = 'HTTP_CONTENT_LENGTH'.freeze

      def on_finished_configuring(events)
        register_event_listeners(events)
      end

      # Expected sequence of events:
      #   :before_call will save our cross application request id to the thread
      #   :after_call will write our response headers/metrics and clean up the thread
      def register_event_listeners(events)
        OneApm::Manager.logger.
          debug("Wiring up Cross Application Tracing to events after finished configuring")

        events.subscribe(:before_call) do |env|
          if should_process_request(env)
            state = OneApm::TransactionState.tl_get

            save_client_cross_app_id(state, env)
            save_referring_transaction_info(state, env)
            set_transaction_custom_parameters(state)
          end
        end

        events.subscribe(:after_call) do |env, (_status_code, headers, _body)|
          state = OneApm::TransactionState.tl_get

          insert_response_header(state, env, headers)
        end

        events.subscribe(:notice_error) do |_, options|
          state = OneApm::TransactionState.tl_get

          set_error_custom_parameters(state, options)
        end
      end

      def save_client_cross_app_id(state, request_headers)
        state.client_cross_app_id = decoded_id(request_headers)
      end

      def clear_client_cross_app_id(state)
        state.client_cross_app_id = nil
      end

      def save_referring_transaction_info(state, request_headers)
        txn_header = request_headers[ONEAPM_TXN_HEADER_KEY] or return
        txn_info = deserialize_header(txn_header, ONEAPM_TXN_HEADER)
        state.referring_transaction_info = txn_info
      end

      def client_referring_transaction_guid(state)
        info = state.referring_transaction_info or return nil
        return info[0]
      end

      def client_referring_transaction_record_flag(state)
        info = state.referring_transaction_info or return nil
        return info[1]
      end

      def client_referring_transaction_trip_id(state)
        info = state.referring_transaction_info or return nil
        return info[2].is_a?(String) && info[2]
      end

      def client_referring_transaction_path_hash(state)
        info = state.referring_transaction_info or return nil
        return info[3].is_a?(String) && info[3]
      end

      def insert_response_header(state, request_headers, response_headers)
        unless state.client_cross_app_id.nil?
          txn = state.current_transaction
          unless txn.nil?
            txn.freeze_name_and_execute_if_not_ignored do
              timings = state.timings
              content_length = content_length_from_request(request_headers)

              set_response_headers(state, response_headers, timings, content_length)
              set_metrics(state.client_cross_app_id, timings)
            end
          end
          clear_client_cross_app_id(state)
        end
      end

      def should_process_request(request_headers)
        return cross_app_enabled? && trusts?(request_headers)
      end

      def cross_app_enabled?
        OneApm::Agent::CrossAppTracing.cross_app_enabled?
      end

      # Expects an ID of format "12#345", and will only accept that!
      def trusts?(request)
        id = decoded_id(request)
        split_id = id.match(/(\d+)#\d+/)
        return false if split_id.nil?

        OneApm::Manager.config[:trusted_account_ids].include?(split_id.captures.first.to_i)
      end

      def set_response_headers(state, response_headers, timings, content_length)
        response_headers[ONEAPM_APPDATA_HEADER] = build_payload(state, timings, content_length)
      end

      def build_payload(state, timings, content_length)
        payload = [
          OneApm::Manager.config[:cross_process_id],
          timings.transaction_name,
          timings.queue_time_in_seconds.to_f,
          timings.app_time_in_seconds.to_f,
          content_length,
          state.request_guid
        ]
        payload = obfuscator.obfuscate(OneApm::JSONWrapper.dump(payload))
      end

      def set_transaction_custom_parameters(state)
        # We expect to get the before call to set the id (if we have it) before
        # this, and then write our custom parameter when the transaction starts
        OneApm::Manager.add_custom_parameters(:client_cross_process_id => state.client_cross_app_id) if state.client_cross_app_id

        referring_guid = client_referring_transaction_guid(state)
        if referring_guid
          OneApm::Manager.add_custom_parameters(:referring_transaction_guid => referring_guid)
        end
      end

      def set_error_custom_parameters(state, options)
        options[:client_cross_process_id] = state.client_cross_app_id if state.client_cross_app_id
      end

      def set_metrics(id, timings)
        metric_name = "ClientApplication/#{id}/all"
        OneApm::Manager.record_metric(metric_name, timings.app_time_in_seconds)
      end

      def decoded_id(request)
        encoded_id = request[ONEAPM_ID_HEADER_KEY]
        return "" if encoded_id.nil?

        obfuscator.deobfuscate(encoded_id)
      end

      def content_length_from_request(request)
        request[OA_CONTENT_LENGTH_HEADER_KEY] || -1
      end

      def hash_transaction_name(identifier)
        Digest::MD5.digest(identifier).unpack("@12N").first & 0xffffffff
      end

      def path_hash(txn_name, seed)
        rotated    = ((seed << 1) | (seed >> 31)) & 0xffffffff
        app_name   = OneApm::Manager.config.app_names.first
        identifier = "#{app_name};#{txn_name}"
        sprintf("%08x", rotated ^ hash_transaction_name(identifier))
      end
    end
  end
end