1 files changed, 64 insertions, 0 deletions
diff --git a/devtools/client/shared/redux/middleware/wait-service.js b/devtools/client/shared/redux/middleware/wait-service.js
new file mode 100644
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+++ b/devtools/client/shared/redux/middleware/wait-service.js
@@ -0,0 +1,64 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+/**
+ * A middleware which acts like a service, because it is stateful
+ * and "long-running" in the background. It provides the ability
+ * for actions to install a function to be run once when a specific
+ * condition is met by an action coming through the system. Think of
+ * it as a thunk that blocks until the condition is met. Example:
+ *
+ * ```js
+ * const services = { WAIT_UNTIL: require('wait-service').NAME };
+ *
+ * { type: services.WAIT_UNTIL,
+ *   predicate: action => action.type === constants.ADD_ITEM,
+ *   run: (dispatch, getState, action) => {
+ *     // Do anything here. You only need to accept the arguments
+ *     // if you need them. `action` is the action that satisfied
+ *     // the predicate.
+ *   }
+ * }
+ * ```
+ */
+const NAME = exports.NAME = "@@service/waitUntil";
+
+function waitUntilService({ dispatch, getState }) {
+  let pending = [];
+
+  function checkPending(action) {
+    let readyRequests = [];
+    let stillPending = [];
+
+    // Find the pending requests whose predicates are satisfied with
+    // this action. Wait to run the requests until after we update the
+    // pending queue because the request handler may synchronously
+    // dispatch again and run this service (that use case is
+    // completely valid).
+    for (let request of pending) {
+      if (request.predicate(action)) {
+        readyRequests.push(request);
+      } else {
+        stillPending.push(request);
+      }
+    }
+
+    pending = stillPending;
+    for (let request of readyRequests) {
+      request.run(dispatch, getState, action);
+    }
+  }
+
+  return next => action => {
+    if (action.type === NAME) {
+      pending.push(action);
+      return null;
+    }
+    let result = next(action);
+    checkPending(action);
+    return result;
+  };
+}
+exports.waitUntilService = waitUntilService;