[FSSDK-11149] Ruby: Implement CMAB Client (#364)

* [FSSDK-11149] Ruby: Implement CMAB Client

* Implement copilot review

* Implement comments

* correct the name

* correct the sleep

* Correct the sleep

Author: esrakartalOpt

lib/optimizely/cmab/cmab_client.rb

@@ -0,0 +1,223 @@
+# frozen_string_literal: true
+
+#
+#    Copyright 2025 Optimizely and contributors
+#
+#    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 'optimizely/helpers/http_utils'
+require 'optimizely/helpers/constants'
+
+module Optimizely
+  # Default constants for CMAB requests
+  DEFAULT_MAX_RETRIES = 3
+  DEFAULT_INITIAL_BACKOFF = 0.1 # in seconds (100 ms)
+  DEFAULT_MAX_BACKOFF = 10 # in seconds
+  DEFAULT_BACKOFF_MULTIPLIER = 2.0
+  MAX_WAIT_TIME = 10
+
+  class CmabRetryConfig
+    # Configuration for retrying CMAB requests.
+    # Contains parameters for maximum retries, backoff intervals, and multipliers.
+    attr_reader :max_retries, :initial_backoff, :max_backoff, :backoff_multiplier
+
+    def initialize(max_retries: DEFAULT_MAX_RETRIES, initial_backoff: DEFAULT_INITIAL_BACKOFF, max_backoff: DEFAULT_MAX_BACKOFF, backoff_multiplier: DEFAULT_BACKOFF_MULTIPLIER)
+      @max_retries = max_retries
+      @initial_backoff = initial_backoff
+      @max_backoff = max_backoff
+      @backoff_multiplier = backoff_multiplier
+    end
+  end
+
+  class DefaultCmabClient
+    # Client for interacting with the CMAB service.
+    # Provides methods to fetch decisions with optional retry logic.
+
+    def initialize(http_client = nil, retry_config = nil, logger = nil)
+      # Initialize the CMAB client.
+      # Args:
+      #   http_client: HTTP client for making requests.
+      #   retry_config: Configuration for retry settings.
+      #   logger: Logger for logging errors and info.
+      @http_client = http_client || DefaultHttpClient.new
+      @retry_config = retry_config || CmabRetryConfig.new
+      @logger = logger || NoOpLogger.new
+    end
+
+    def fetch_decision(rule_id, user_id, attributes, cmab_uuid, timeout: MAX_WAIT_TIME)
+      # Fetches a decision from the CMAB service.
+      # Args:
+      #   rule_id: The rule ID for the experiment.
+      #   user_id: The user ID for the request.
+      #   attributes: User attributes for the request.
+      #   cmab_uuid: Unique identifier for the CMAB request.
+      #   timeout: Maximum wait time for the request to respond in seconds. (default is 10 seconds).
+      # Returns:
+      #   The variation ID.
+      url = "https://prediction.cmab.optimizely.com/predict/#{rule_id}"
+      cmab_attributes = attributes.map { |key, value| {'id' => key.to_s, 'value' => value, 'type' => 'custom_attribute'} }
+
+      request_body = {
+        instances: [{
+          visitorId: user_id,
+          experimentId: rule_id,
+          attributes: cmab_attributes,
+          cmabUUID: cmab_uuid
+        }]
+      }
+
+      if @retry_config && @retry_config.max_retries.to_i.positive?
+        _do_fetch_with_retry(url, request_body, @retry_config, timeout)
+      else
+        _do_fetch(url, request_body, timeout)
+      end
+    end
+
+    def _do_fetch(url, request_body, timeout)
+      # Perform a single fetch request to the CMAB prediction service.
+
+      # Args:
+      #   url: The endpoint URL.
+      #   request_body: The request payload.
+      #   timeout: Maximum wait time for the request to respond in seconds.
+      # Returns:
+      #   The variation ID from the response.
+
+      headers = {'Content-Type' => 'application/json'}
+      begin
+        response = @http_client.post(url, json: request_body, headers: headers, timeout: timeout.to_i)
+      rescue StandardError => e
+        error_message = Optimizely::Helpers::Constants::CMAB_FETCH_FAILED % e.message
+        @logger.log(Logger::ERROR, error_message)
+        raise CmabFetchError, error_message
+      end
+
+      unless (200..299).include?(response.status_code)
+        error_message = Optimizely::Helpers::Constants::CMAB_FETCH_FAILED % response.status_code
+        @logger.log(Logger::ERROR, error_message)
+        raise CmabFetchError, error_message
+      end
+
+      begin
+        body = response.json
+      rescue JSON::ParserError, Optimizely::CmabInvalidResponseError
+        error_message = Optimizely::Helpers::Constants::INVALID_CMAB_FETCH_RESPONSE
+        @logger.log(Logger::ERROR, error_message)
+        raise CmabInvalidResponseError, error_message
+      end
+
+      unless validate_response(body)
+        error_message = Optimizely::Helpers::Constants::INVALID_CMAB_FETCH_RESPONSE
+        @logger.log(Logger::ERROR, error_message)
+        raise CmabInvalidResponseError, error_message
+      end
+
+      body['predictions'][0]['variationId']
+    end
+
+    def validate_response(body)
+      # Validate the response structure from the CMAB service.
+      # Args:
+      #   body: The JSON response body to validate.
+      # Returns:
+      #   true if valid, false otherwise.
+
+      body.is_a?(Hash) &&
+        body.key?('predictions') &&
+        body['predictions'].is_a?(Array) &&
+        !body['predictions'].empty? &&
+        body['predictions'][0].is_a?(Hash) &&
+        body['predictions'][0].key?('variationId')
+    end
+
+    def _do_fetch_with_retry(url, request_body, retry_config, timeout)
+      # Perform a fetch request with retry logic.
+      # Args:
+      #   url: The endpoint URL.
+      #   request_body: The request payload.
+      #   retry_config: Configuration for retry settings.
+      #   timeout: Maximum wait time for the request to respond in seconds.
+      # Returns:
+      #   The variation ID from the response.
+
+      backoff = retry_config.initial_backoff
+
+      (0..retry_config.max_retries).each do |attempt|
+        variation_id = _do_fetch(url, request_body, timeout)
+        return variation_id
+      rescue StandardError => e
+        if attempt < retry_config.max_retries
+          @logger.log(Logger::INFO, "Retrying CMAB request (attempt #{attempt + 1}) after #{backoff} seconds...")
+          Kernel.sleep(backoff)
+
+          backoff = [
+            backoff * retry_config.backoff_multiplier,
+            retry_config.max_backoff
+          ].min
+        else
+          @logger.log(Logger::ERROR, "Max retries exceeded for CMAB request: #{e.message}")
+          raise Optimizely::CmabFetchError, "CMAB decision fetch failed (#{e.message})."
+        end
+      end
+    end
+  end
+
+  class DefaultHttpClient
+    # Default HTTP client for making requests.
+    # Uses Optimizely::Helpers::HttpUtils to make requests.
+
+    def post(url, json: nil, headers: {}, timeout: nil)
+      # Makes a POST request to the specified URL with JSON body and headers.
+      # Args:
+      #   url: The endpoint URL.
+      #   json: The JSON payload to send in the request body.
+      #   headers: Additional headers for the request.
+      #   timeout: Maximum wait time for the request to respond in seconds.
+      # Returns:
+      #   The response object.
+
+      response = Optimizely::Helpers::HttpUtils.make_request(url, :post, json.to_json, headers, timeout)
+
+      HttpResponseAdapter.new(response)
+    end
+
+    class HttpResponseAdapter
+      # Adapter for HTTP response to provide a consistent interface.
+      # Args:
+      #   response: The raw HTTP response object.
+
+      def initialize(response)
+        @response = response
+      end
+
+      def status_code
+        @response.code.to_i
+      end
+
+      def json
+        JSON.parse(@response.body)
+      rescue JSON::ParserError
+        raise Optimizely::CmabInvalidResponseError, Optimizely::Helpers::Constants::INVALID_CMAB_FETCH_RESPONSE
+      end
+
+      def body
+        @response.body
+      end
+    end
+  end
+
+  class NoOpLogger
+    # A no-operation logger that does nothing.
+    def log(_level, _message); end
+  end
+end

lib/optimizely/exceptions.rb

@@ -190,4 +190,28 @@ def initialize(msg = 'Provided semantic version is invalid.')
       super
     end
   end
+
+  class CmabError < Error
+    # Base exception for CMAB errors
+
+    def initialize(msg = 'CMAB error occurred.')
+      super
+    end
+  end
+
+  class CmabFetchError < CmabError
+    # Exception raised when CMAB fetch fails
+
+    def initialize(msg = 'CMAB decision fetch failed with status:')
+      super
+    end
+  end
+
+  class CmabInvalidResponseError < CmabError
+    # Exception raised when CMAB fetch returns an invalid response
+
+    def initialize(msg = 'Invalid CMAB fetch response')
+      super
+    end
+  end
 end

lib/optimizely/helpers/constants.rb

@@ -469,6 +469,9 @@ module Constants
         'IF_MODIFIED_SINCE' => 'If-Modified-Since',
         'LAST_MODIFIED' => 'Last-Modified'
       }.freeze
+
+      CMAB_FETCH_FAILED = 'CMAB decision fetch failed (%s).'
+      INVALID_CMAB_FETCH_RESPONSE = 'Invalid CMAB fetch response'
     end
   end
 end