refactor: Changed the way reasons are being returned from decide APIs (…

…#279)

## Summary
Reasons were previously being collected by sending a reasons object down the stack to all the related functions which would mutate it by pushing their own reasons. This is now changed. Every related function now returns the reasons array along with the actual value.

## Test plan
- Manually tested thoroughly.
- Fixed all the affected unit test.
- FSC passing

lib/optimizely.rb

@@ -199,7 +199,8 @@ def decide(user_context, key, decide_options = [])
       experiment = nil
       decision_source = Optimizely::DecisionService::DECISION_SOURCES['ROLLOUT']
 
-      decision = @decision_service.get_variation_for_feature(config, feature_flag, user_id, attributes, decide_options, reasons)
+      decision, reasons_received = @decision_service.get_variation_for_feature(config, feature_flag, user_id, attributes, decide_options)
+      reasons.push(*reasons_received)
 
       # Send impression event if Decision came from a feature test and decide options doesn't include disableDecisionEvent
       if decision.is_a?(Optimizely::DecisionService::Decision)
@@ -405,7 +406,7 @@ def get_forced_variation(experiment_key, user_id)
       config = project_config
 
       forced_variation_key = nil
-      forced_variation = @decision_service.get_forced_variation(config, experiment_key, user_id)
+      forced_variation, = @decision_service.get_forced_variation(config, experiment_key, user_id)
       forced_variation_key = forced_variation['key'] if forced_variation
 
       forced_variation_key
@@ -489,7 +490,7 @@ def is_feature_enabled(feature_flag_key, user_id, attributes = nil)
         return false
       end
 
-      decision = @decision_service.get_variation_for_feature(config, feature_flag, user_id, attributes)
+      decision, = @decision_service.get_variation_for_feature(config, feature_flag, user_id, attributes)
 
       feature_enabled = false
       source_string = Optimizely::DecisionService::DECISION_SOURCES['ROLLOUT']
@@ -738,7 +739,7 @@ def get_all_feature_variables(feature_flag_key, user_id, attributes = nil)
         return nil
       end
 
-      decision = @decision_service.get_variation_for_feature(config, feature_flag, user_id, attributes)
+      decision, = @decision_service.get_variation_for_feature(config, feature_flag, user_id, attributes)
       variation = decision ? decision['variation'] : nil
       feature_enabled = variation ? variation['featureEnabled'] : false
       all_variables = {}
@@ -878,7 +879,7 @@ def get_variation_with_config(experiment_key, user_id, attributes, config)
 
       return nil unless user_inputs_valid?(attributes)
 
-      variation_id = @decision_service.get_variation(config, experiment_key, user_id, attributes)
+      variation_id, = @decision_service.get_variation(config, experiment_key, user_id, attributes)
       variation = config.get_variation_from_id(experiment_key, variation_id) unless variation_id.nil?
       variation_key = variation['key'] if variation
       decision_notification_type = if config.feature_experiment?(experiment['id'])
@@ -944,7 +945,7 @@ def get_feature_variable_for_type(feature_flag_key, variable_key, variable_type,
         return nil
       end
 
-      decision = @decision_service.get_variation_for_feature(config, feature_flag, user_id, attributes)
+      decision, = @decision_service.get_variation_for_feature(config, feature_flag, user_id, attributes)
       variation = decision ? decision['variation'] : nil
       feature_enabled = variation ? variation['featureEnabled'] : false
 

lib/optimizely/audience.rb

@@ -38,33 +38,23 @@ def user_meets_audience_conditions?(config, experiment, attributes, logger, logg
       #               This defaults to experiment['key'].
       #
       # Returns boolean representing if user satisfies audience conditions for the audiences or not.
+      decide_reasons = []
       logging_hash ||= 'EXPERIMENT_AUDIENCE_EVALUATION_LOGS'
       logging_key ||= experiment['key']
 
       logs_hash = Object.const_get "Optimizely::Helpers::Constants::#{logging_hash}"
 
       audience_conditions = experiment['audienceConditions'] || experiment['audienceIds']
 
-      logger.log(
-        Logger::DEBUG,
-        format(
-          logs_hash['EVALUATING_AUDIENCES_COMBINED'],
-          logging_key,
-          audience_conditions
-        )
-      )
+      message = format(logs_hash['EVALUATING_AUDIENCES_COMBINED'], logging_key, audience_conditions)
+      logger.log(Logger::DEBUG, message)
 
       # Return true if there are no audiences
       if audience_conditions.empty?
-        logger.log(
-          Logger::INFO,
-          format(
-            logs_hash['AUDIENCE_EVALUATION_RESULT_COMBINED'],
-            logging_key,
-            'TRUE'
-          )
-        )
-        return true
+        message = format(logs_hash['AUDIENCE_EVALUATION_RESULT_COMBINED'], logging_key, 'TRUE')
+        logger.log(Logger::INFO, message)
+        decide_reasons.push(message)
+        return true, decide_reasons
       end
 
       attributes ||= {}
@@ -80,39 +70,28 @@ def user_meets_audience_conditions?(config, experiment, attributes, logger, logg
         return nil unless audience
 
         audience_conditions = audience['conditions']
-        logger.log(
-          Logger::DEBUG,
-          format(
-            logs_hash['EVALUATING_AUDIENCE'],
-            audience_id,
-            audience_conditions
-          )
-        )
+        message = format(logs_hash['EVALUATING_AUDIENCE'], audience_id, audience_conditions)
+        logger.log(Logger::DEBUG, message)
+        decide_reasons.push(message)
 
         audience_conditions = JSON.parse(audience_conditions) if audience_conditions.is_a?(String)
         result = ConditionTreeEvaluator.evaluate(audience_conditions, evaluate_custom_attr)
         result_str = result.nil? ? 'UNKNOWN' : result.to_s.upcase
-        logger.log(
-          Logger::DEBUG,
-          format(logs_hash['AUDIENCE_EVALUATION_RESULT'], audience_id, result_str)
-        )
+        message = format(logs_hash['AUDIENCE_EVALUATION_RESULT'], audience_id, result_str)
+        logger.log(Logger::DEBUG, message)
+        decide_reasons.push(message)
+
         result
       end
 
       eval_result = ConditionTreeEvaluator.evaluate(audience_conditions, evaluate_audience)
-
       eval_result ||= false
 
-      logger.log(
-        Logger::INFO,
-        format(
-          logs_hash['AUDIENCE_EVALUATION_RESULT_COMBINED'],
-          logging_key,
-          eval_result.to_s.upcase
-        )
-      )
+      message = format(logs_hash['AUDIENCE_EVALUATION_RESULT_COMBINED'], logging_key, eval_result.to_s.upcase)
+      logger.log(Logger::INFO, message)
+      decide_reasons.push(message)
 
-      eval_result
+      [eval_result, decide_reasons]
     end
   end
 end

lib/optimizely/bucketer.rb

@@ -35,7 +35,7 @@ def initialize(logger)
       @bucket_seed = HASH_SEED
     end
 
-    def bucket(project_config, experiment, bucketing_id, user_id, decide_reasons = nil)
+    def bucket(project_config, experiment, bucketing_id, user_id)
       # Determines ID of variation to be shown for a given experiment key and user ID.
       #
       # project_config - Instance of ProjectConfig
@@ -44,7 +44,9 @@ def bucket(project_config, experiment, bucketing_id, user_id, decide_reasons = n
       # user_id - String ID for user.
       #
       # Returns variation in which visitor with ID user_id has been placed. Nil if no variation.
-      return nil if experiment.nil?
+      return nil, [] if experiment.nil?
+
+      decide_reasons = []
 
       # check if experiment is in a group; if so, check if user is bucketed into specified experiment
       # this will not affect evaluation of rollout rules.
@@ -55,72 +57,77 @@ def bucket(project_config, experiment, bucketing_id, user_id, decide_reasons = n
         group = project_config.group_id_map.fetch(group_id)
         if Helpers::Group.random_policy?(group)
           traffic_allocations = group.fetch('trafficAllocation')
-          bucketed_experiment_id = find_bucket(bucketing_id, user_id, group_id, traffic_allocations)
+          bucketed_experiment_id, find_bucket_reasons = find_bucket(bucketing_id, user_id, group_id, traffic_allocations)
+          decide_reasons.push(*find_bucket_reasons)
+
           # return if the user is not bucketed into any experiment
           unless bucketed_experiment_id
             message = "User '#{user_id}' is in no experiment."
             @logger.log(Logger::INFO, message)
-            decide_reasons&.push(message)
-            return nil
+            decide_reasons.push(message)
+            return nil, decide_reasons
           end
 
           # return if the user is bucketed into a different experiment than the one specified
           if bucketed_experiment_id != experiment_id
             message = "User '#{user_id}' is not in experiment '#{experiment_key}' of group #{group_id}."
             @logger.log(Logger::INFO, message)
-            decide_reasons&.push(message)
-            return nil
+            decide_reasons.push(message)
+            return nil, decide_reasons
           end
 
           # continue bucketing if the user is bucketed into the experiment specified
           message = "User '#{user_id}' is in experiment '#{experiment_key}' of group #{group_id}."
           @logger.log(Logger::INFO, message)
-          decide_reasons&.push(message)
+          decide_reasons.push(message)
         end
       end
 
       traffic_allocations = experiment['trafficAllocation']
-      variation_id = find_bucket(bucketing_id, user_id, experiment_id, traffic_allocations, decide_reasons)
+      variation_id, find_bucket_reasons = find_bucket(bucketing_id, user_id, experiment_id, traffic_allocations)
+      decide_reasons.push(*find_bucket_reasons)
+
       if variation_id && variation_id != ''
         variation = project_config.get_variation_from_id(experiment_key, variation_id)
-        return variation
+        return variation, decide_reasons
       end
 
       # Handle the case when the traffic range is empty due to sticky bucketing
       if variation_id == ''
         message = 'Bucketed into an empty traffic range. Returning nil.'
         @logger.log(Logger::DEBUG, message)
-        decide_reasons&.push(message)
+        decide_reasons.push(message)
       end
 
-      nil
+      [nil, decide_reasons]
     end
 
-    def find_bucket(bucketing_id, user_id, parent_id, traffic_allocations, decide_reasons = nil)
+    def find_bucket(bucketing_id, user_id, parent_id, traffic_allocations)
       # Helper function to find the matching entity ID for a given bucketing value in a list of traffic allocations.
       #
       # bucketing_id - String A customer-assigned value user to generate bucketing key
       # user_id - String ID for user
       # parent_id - String entity ID to use for bucketing ID
       # traffic_allocations - Array of traffic allocations
       #
-      # Returns entity ID corresponding to the provided bucket value or nil if no match is found.
+      # Returns and array of two values where first value is the entity ID corresponding to the provided bucket value
+      # or nil if no match is found. The second value contains the array of reasons stating how the deicision was taken
+      decide_reasons = []
       bucketing_key = format(BUCKETING_ID_TEMPLATE, bucketing_id: bucketing_id, entity_id: parent_id)
       bucket_value = generate_bucket_value(bucketing_key)
 
       message = "Assigned bucket #{bucket_value} to user '#{user_id}' with bucketing ID: '#{bucketing_id}'."
       @logger.log(Logger::DEBUG, message)
-      decide_reasons&.push(message)
 
       traffic_allocations.each do |traffic_allocation|
         current_end_of_range = traffic_allocation['endOfRange']
         if bucket_value < current_end_of_range
           entity_id = traffic_allocation['entityId']
-          return entity_id
+          return entity_id, decide_reasons
         end
       end
 
-      nil
+      [nil, decide_reasons]
     end
 
     private