1 files changed, 78 insertions, 0 deletions
diff --git a/app/experiments/strategy/round_robin.rb b/app/experiments/strategy/round_robin.rb
new file mode 100644
index 00000000000..7b80c0e984d
--- /dev/null
+++ b/app/experiments/strategy/round_robin.rb
@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+module Strategy
+  class RoundRobin
+    CacheError = Class.new(StandardError)
+
+    COUNTER_EXPIRE_TIME = 86400 # one day
+
+    def initialize(key, variants)
+      @key = key
+      @variants = variants
+    end
+
+    def execute
+      increment_counter
+      resolve_variant_name
+    end
+
+    # When the counter would expire
+    #
+    # @api private Used internally by SRE and debugging purpose
+    # @return [Integer] Number in seconds until expiration or false if never
+    def counter_expires_in
+      Gitlab::Redis::SharedState.with do |redis|
+        redis.ttl(key)
+      end
+    end
+
+    # Return the actual counter value
+    #
+    # @return [Integer] value
+    def counter_value
+      Gitlab::Redis::SharedState.with do |redis|
+        (redis.get(key) || 0).to_i
+      end
+    end
+
+    # Reset the counter
+    #
+    # @private Used internally by SRE and debugging purpose
+    # @return [Boolean] whether reset was a success
+    def reset!
+      redis_cmd do |redis|
+        redis.del(key)
+      end
+    end
+
+    private
+
+    attr_reader :key, :variants
+
+    # Increase the counter
+    #
+    # @return [Boolean] whether operation was a success
+    def increment_counter
+      redis_cmd do |redis|
+        redis.incr(key)
+        redis.expire(key, COUNTER_EXPIRE_TIME)
+      end
+    end
+
+    def resolve_variant_name
+      remainder = counter_value % variants.size
+
+      variants[remainder]
+    end
+
+    def redis_cmd
+      Gitlab::Redis::SharedState.with { |redis| yield(redis) }
+
+      true
+    rescue CacheError => e
+      Gitlab::AppLogger.warn("GitLab: An unexpected error occurred in writing to Redis: #{e}")
+
+      false
+    end
+  end
+end