feat: allow for caching of specific config versions

fix: cached settings access

lib/middlewares/populateSettings.js

@@ -55,30 +55,64 @@ const populateSettings = function (req, res, next) {
   }
 
   try {
-    const operatorSettings = settingsCache.get(operatorId)
+    // Priority of configs to retrieve
-    if (!versionId && (!operatorSettings || !!needsSettingsReload[operatorId])) {
+    // 1. Machine is in the middle of a transaction and has the config-version header set, fetch that config from cache or database, depending on whether it exists in cache
+    // 2. The operator settings changed, so we must update the cache
+    // 3. There's a cached config, send the cached value
+    // 4. There's no cached config, cache and send the latest config
+
+    if (versionId) {
+      const cachedVersionedSettings = settingsCache.get(`${operatorId}-v${versionId}`)
+
+      if (!cachedVersionedSettings) {
+        logger.debug('Fetching a specific config version cached value')
+        return newSettingsLoader.load(versionId)
+          .then(settings => {
+            settingsCache.set(`${operatorId}-v${versionId}`, settings)
+            req.settings = settings
+          })
+          .then(() => next())
+          .catch(next)
+      }
+
+      logger.debug('Fetching and caching a specific config version')
+      req.settings = cachedVersionedSettings
+      return next()
+    }
+
+    const operatorSettings = settingsCache.get(`${operatorId}-latest`)
+
+    if (!versionId && !!needsSettingsReload[operatorId]) {
+      logger.debug('Fetching and caching a new latest config value, as a reload was requested')
       return newSettingsLoader.loadLatest()
         .then(settings => {
-          settingsCache.set(operatorId, settings)
+          settingsCache.set(`${operatorId}-latest`, settings)
           delete needsSettingsReload[operatorId]
           req.settings = settings
         })
         .then(() => next())
         .catch(next)
     }
-  
+
     if (!versionId && operatorSettings) {
+      logger.debug('Fetching the latest config value from cache')
       req.settings = operatorSettings
       return next()
     }
+
+    if (!versionId && !operatorSettings) {
+      logger.debug('Fetching the latest config version because there\'s no cached value')
+      return newSettingsLoader.loadLatest()
+        .then(settings => {
+          settingsCache.set(`${operatorId}-latest`, settings)
+          req.settings = settings
+        })
+        .then(() => next())
+        .catch(next)
+    }
   } catch (e) {
     logger.error(e)
   }
-
-  newSettingsLoader.load(versionId)
-    .then(settings => { req.settings = settings })
-    .then(() => next())
-    .catch(next)
 }
 
 module.exports = populateSettings