1 files changed, 68 insertions, 0 deletions
diff --git a/packages/merchant-backend-ui/src/hooks/listener.ts b/packages/merchant-backend-ui/src/hooks/listener.ts
new file mode 100644
index 000000000..231ed6c87
--- /dev/null
+++ b/packages/merchant-backend-ui/src/hooks/listener.ts
@@ -0,0 +1,68 @@
+/*
+ This file is part of GNU Taler
+ (C) 2021 Taler Systems S.A.
+
+ GNU Taler is free software; you can redistribute it and/or modify it under the
+ terms of the GNU General Public License as published by the Free Software
+ Foundation; either version 3, or (at your option) any later version.
+
+ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License along with
+ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+/**
+*
+* @author Sebastian Javier Marchano (sebasjm)
+*/
+
+import { useState } from "preact/hooks";
+
+/**
+ * returns subscriber and activator
+ * subscriber will receive a method (listener) that will be call when the activator runs.
+ * the result of calling the listener will be sent to @action
+ *
+ * @param action from <T> to <R>
+ * @returns activator and subscriber, undefined activator means that there is not subscriber
+ */
+
+export function useListener<T, R = any>(action: (r: T) => Promise<R>): [undefined | (() => Promise<R>), (listener?: () => T) => void] {
+  type RunnerHandler = { toBeRan?: () => Promise<R>; };
+  const [state, setState] = useState<RunnerHandler>({});
+
+  /**
+   * subscriber will receive a method that will be call when the activator runs
+   *
+   * @param listener function to be run when the activator runs
+   */
+  const subscriber = (listener?: () => T) => {
+    if (listener) {
+      setState({
+        toBeRan: () => {
+          const whatWeGetFromTheListener = listener();
+          return action(whatWeGetFromTheListener);
+        }
+      });
+    } else {
+      setState({
+        toBeRan: undefined
+      })
+    }
+  };
+
+  /**
+   * activator will call runner if there is someone subscribed
+   */
+  const activator = state.toBeRan ? async () => {
+    if (state.toBeRan) {
+      return state.toBeRan();
+    }
+    return Promise.reject();
+  } : undefined;
+
+  return [activator, subscriber];
+}