[AI-FSSDK] [FSSDK-12337] Add Feature Rollout support (#392)

* [AI-FSSDK] [FSSDK-12337] Add Feature Rollout support

Add Feature Rollout support to the Ruby SDK. During project config
parsing, inject the "everyone else" variation from the flag's rollout
into any experiment with type "feature_rollout", enabling correct
evaluation without changes to decision logic.

- Added config parsing logic to inject the everyone else rollout
  variation into feature_rollout experiments
- Added traffic allocation entry (endOfRange=10000) for injected variation
- Added get_everyone_else_variation helper to extract the last rollout
  rule's first variation
- Added 6 unit tests covering injection, variation maps, edge cases,
  and backward compatibility

* [AI-FSSDK] [FSSDK-12337] Add type field to experiment JSON schema

Add optional 'type' string field to the experiment properties in the
datafile JSON schema validation constants.

* [AI-FSSDK] [FSSDK-12337] Add test for experiment type field parsing

Verify that the type field from the datafile is correctly preserved
on experiment hashes after config parsing.

* [AI-FSSDK] [FSSDK-12337] Move flag_variation_map after rollout injection

Move @flag_variation_map generation to after the feature rollout
injection block so the everyone-else variation is included in
get_variation_from_flag lookups used by forced decisions.

* [AI-FSSDK] [FSSDK-12337] Add tests for featureEnabled and variables propagation

Add tests verifying:
- Injected everyone-else variation preserves featureEnabled=false
- Variables from the rollout variation carry through to the injected
  variation and populate variation_id_to_variable_usage_map

* [AI-FSSDK] [FSSDK-12337] Fix pre-existing rubocop Lint/Void offense in spec_params

Remove redundant else clause in deep_clone that referenced a variable
in void context (Lint/Void: Variable new_obj used in void context).

* [AI-FSSDK] [FSSDK-12337] Add EXPERIMENT_TYPES constant with enum validation

- Define EXPERIMENT_TYPES constant with valid experiment type values
  (ab, mab, cmab, td, fr) in Constants module
- Use enum constraint in JSON schema to validate the type field
- Reference constant in injection check instead of raw string literal
- Add flag_variation_map assertion to variation maps test

* [AI-FSSDK] [FSSDK-12337] Remove tests not in ticket spec

Remove 3 tests not in updated Jira ticket test requirements:
- LAST rollout rule selection
- featureEnabled preservation
- Variables propagation

* [AI-FSSDK] [FSSDK-12337] Fix rubocop EmptyLinesAroundBlockBody offense

* [FSSDK-12337] Fix experiment type values to match backend

Update EXPERIMENT_TYPES to use actual backend values:
'multi_armed_bandit' and 'contextual_multi_armed_bandit'
instead of shorthand 'mab' and 'cmab'. Restore accidentally
removed else branch in spec_params deep_clone.

* [AI-FSSDK] [FSSDK-12337] Fix rubocop Lint/Void offense in spec_params

Remove redundant else clause in deep_clone that was accidentally
restored in a previous commit.

* [AI-FSSDK] [FSSDK-12337] Update experiment type values to short-form abbreviations

Author: FarhanAnjum-opti

lib/optimizely/config/datafile_project_config.rb

@@ -180,7 +180,6 @@ def initialize(datafile, logger, error_handler)
         @all_segments.concat Audience.get_segments(audience['conditions'])
       end
 
-      @flag_variation_map = generate_feature_variation_map(@feature_flags)
       @all_experiments = @experiment_id_map.merge(@rollout_experiment_id_map)
       @all_experiments.each do |id, exp|
         variations = exp.fetch('variations')
@@ -205,8 +204,33 @@ def initialize(datafile, logger, error_handler)
         feature_flag['experimentIds'].each do |experiment_id|
           @experiment_feature_map[experiment_id] = [feature_flag['id']]
         end
+
+        # Feature Rollout support: inject the "everyone else" variation
+        # into any experiment with type == "feature_rollout"
+        everyone_else_variation = get_everyone_else_variation(feature_flag)
+        next if everyone_else_variation.nil?
+
+        feature_flag['experimentIds'].each do |exp_id|
+          experiment = @experiment_id_map[exp_id]
+          next unless experiment && experiment['type'] == Helpers::Constants::EXPERIMENT_TYPES['fr']
+
+          experiment['variations'].push(everyone_else_variation)
+          experiment['trafficAllocation'].push(
+            'entityId' => everyone_else_variation['id'],
+            'endOfRange' => 10_000
+          )
+          @variation_key_map[experiment['key']][everyone_else_variation['key']] = everyone_else_variation
+          @variation_id_map[experiment['key']][everyone_else_variation['id']] = everyone_else_variation
+          @variation_id_map_by_experiment_id[exp_id][everyone_else_variation['id']] = everyone_else_variation
+          @variation_key_map_by_experiment_id[exp_id][everyone_else_variation['key']] = everyone_else_variation
+          variation_variables = everyone_else_variation['variables']
+          @variation_id_to_variable_usage_map[everyone_else_variation['id']] = generate_key_map(variation_variables, 'id') if variation_variables
+        end
       end
 
+      # Generate flag_variation_map after injection so it includes everyone-else variations
+      @flag_variation_map = generate_feature_variation_map(@feature_flags)
+
       # Adding Holdout variations in variation id and key maps
       return unless @holdouts && !@holdouts.empty?
 
@@ -690,6 +714,38 @@ def get_holdout(holdout_id)
 
     private
 
+    def get_everyone_else_variation(feature_flag)
+      # Get the "everyone else" variation for a feature flag.
+      #
+      # The "everyone else" rule is the last experiment in the flag's rollout,
+      # and its first variation is the "everyone else" variation.
+      #
+      # feature_flag - Feature flag hash
+      #
+      # Returns the "everyone else" variation hash, or nil if not available.
+
+      rollout_id = feature_flag['rolloutId']
+      return nil if rollout_id.nil? || rollout_id.empty?
+
+      rollout = @rollout_id_map[rollout_id]
+      return nil if rollout.nil?
+
+      experiments = rollout['experiments']
+      return nil if experiments.nil? || experiments.empty?
+
+      everyone_else_rule = experiments.last
+      variations = everyone_else_rule['variations']
+      return nil if variations.nil? || variations.empty?
+
+      variation = variations.first
+      {
+        'id' => variation['id'],
+        'key' => variation['key'],
+        'featureEnabled' => variation['featureEnabled'] == true,
+        'variables' => variation.fetch('variables', [])
+      }
+    end
+
     def generate_feature_variation_map(feature_flags)
       flag_variation_map = {}
       feature_flags.each do |flag|

lib/optimizely/helpers/constants.rb

@@ -18,6 +18,14 @@
 module Optimizely
   module Helpers
     module Constants
+      EXPERIMENT_TYPES = {
+        'ab' => 'ab',
+        'mab' => 'mab',
+        'cmab' => 'cmab',
+        'td' => 'td',
+        'fr' => 'fr'
+      }.freeze
+
       JSON_SCHEMA_V2 = {
         'type' => 'object',
         'properties' => {
@@ -205,6 +213,10 @@ module Constants
                 'cmab' => {
                   'type' => 'object'
                 },
+                'type' => {
+                  'type' => %w[string null],
+                  'enum' => EXPERIMENT_TYPES.values + [nil]
+                },
                 'holdouts' => {
                   'type' => 'array'
                 }