Rename surrogate_keys_cache -> surrogate-keys-cache

lib/cache/surrogate-keys-cache.js

@@ -0,0 +1,55 @@
+'use strict';
+
+var queue = require('queue-async');
+
+/**
+ * @param {Array|Object} cacheBackends each backend backend should respond to `invalidate(cacheObject, callback)` method
+ * @constructor
+ */
+function SurrogateKeysCache(cacheBackends) {
+    this.cacheBackends = Array.isArray(cacheBackends) ? cacheBackends : [cacheBackends];
+}
+
+module.exports = SurrogateKeysCache;
+
+
+/**
+ * @param response should respond to `header(key, value)` method
+ * @param cacheObject should respond to `key() -> String` method
+ */
+SurrogateKeysCache.prototype.tag = function(response, cacheObject) {
+    var newKey = cacheObject.key();
+    response.set('Surrogate-Key', appendSurrogateKey(
+        response.get('Surrogate-Key'),
+        Array.isArray(newKey) ? cacheObject.key().join(' ') : newKey
+    ));
+
+};
+
+function appendSurrogateKey(currentKey, newKey) {
+    if (!!currentKey) {
+        newKey = currentKey + ' ' + newKey;
+    }
+    return newKey;
+}
+
+/**
+ * @param cacheObject should respond to `key() -> String` method
+ * @param {Function} callback
+ */
+SurrogateKeysCache.prototype.invalidate = function(cacheObject, callback) {
+    var invalidationQueue = queue(this.cacheBackends.length);
+
+    this.cacheBackends.forEach(function(cacheBackend) {
+        invalidationQueue.defer(function(cacheBackend, done) {
+            cacheBackend.invalidate(cacheObject, done);
+        }, cacheBackend);
+    });
+
+    invalidationQueue.awaitAll(function(err, result) {
+        if (err) {
+            return callback(err);
+        }
+        callback(null, result);
+    });
+};