Feature: Global Config helper (#844) (#845)

* Added a global config helper to easily access installation/global configs
  * this will fetch the keys from cache with fallback to DB on cache miss
  * ability to query multiple keys simultaneously
  * interface to delete the existing global config cache
* Added tests for this new helper module

lib/global_config.rb

@@ -0,0 +1,44 @@
+class GlobalConfig
+  VERSION = 'V1'.freeze
+  KEY_PREFIX = 'GLOBAL_CONFIG'.freeze
+  DEFAULT_EXPIRY = 1.day
+
+  class << self
+    def get(*args)
+      config_keys = *args
+      config = {}
+
+      config_keys.each do |config_key|
+        config[config_key] = load_from_cache(config_key)
+      end
+
+      config.with_indifferent_access
+    end
+
+    def clear_cache
+      cached_keys = $alfred.keys("#{VERSION}:#{KEY_PREFIX}:*")
+      (cached_keys || []).each do |cached_key|
+        $alfred.expire(cached_key, 0)
+      end
+    end
+
+    private
+
+    def load_from_cache(config_key)
+      cache_key = "#{VERSION}:#{KEY_PREFIX}:#{config_key}"
+      cached_value = $alfred.get(cache_key)
+
+      if cached_value.blank?
+        value_from_db = db_fallback(config_key)
+        cached_value = { value: value_from_db }.to_json
+        $alfred.set(cache_key, cached_value, { expiry: DEFAULT_EXPIRY })
+      end
+
+      JSON.parse(cached_value)['value']
+    end
+
+    def db_fallback(config_key)
+      InstallationConfig.find_by(name: config_key)&.value
+    end
+  end
+end