chore: refactor redis config (#1310)

- refactor Redis config in Redis::Config Module
-  unit tests for Redis::Config module

lib/redis/config.rb

@@ -0,0 +1,48 @@
+module Redis::Config
+  DEFAULT_SENTINEL_PORT = '26379'.freeze
+  SIDEKIQ_SIZE = 25
+
+  class << self
+    def app
+      return BASE_CONFIG if const_defined? 'BASE_CONFIG'
+
+      reload_config
+    end
+
+    def sidekiq
+      config = begin
+        if const_defined? 'BASE_CONFIG'
+          BASE_CONFIG
+        else
+          reload_config
+        end
+      end
+      config.merge(size: SIDEKIQ_SIZE)
+    end
+
+    def reload_config
+      config = {
+        url: ENV.fetch('REDIS_URL', 'redis://127.0.0.1:6379'),
+        password: ENV.fetch('REDIS_PASSWORD', nil).presence
+      }
+
+      sentinel_string = ENV.fetch('REDIS_SENTINELS', nil)
+      if sentinel_string.presence
+        # expected format for REDIS_SENTINELS url string is host1:port1, host2:port2
+        sentinels = sentinel_string.split(',').map do |sentinel_url|
+          host, port = sentinel_url.split(':').map(&:strip)
+          { host: host, port: port || DEFAULT_SENTINEL_PORT, password: config[:password] }
+        end
+
+        master_name = ENV.fetch('REDIS_SENTINEL_MASTER_NAME', 'mymaster')
+        # over-write redis url as redis://:<your-redis-password>@<master-name>/ when using sentinel
+        # more at https://github.com/redis/redis-rb/issues/531#issuecomment-263501322
+        config[:url] = "redis://#{master_name}"
+        config[:sentinels] = sentinels
+      end
+      send(:remove_const, 'BASE_CONFIG') if const_defined? 'BASE_CONFIG'
+      const_set('BASE_CONFIG', config)
+      BASE_CONFIG
+    end
+  end
+end