From 8996b562bcd9bde74c4b0b18ba82b7baad1834b2 Mon Sep 17 00:00:00 2001
From: unknown <ajbura@gmail.com>
Date: Mon, 30 Aug 2021 21:03:59 +0530
Subject: [PATCH] created Postie

---
 src/util/Postie.js | 91 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 src/util/Postie.js

diff --git a/src/util/Postie.js b/src/util/Postie.js
new file mode 100644
index 0000000..c3bf806
--- /dev/null
+++ b/src/util/Postie.js
@@ -0,0 +1,91 @@
+class Postie {
+  constructor() {
+    this._topics = new Map();
+  }
+
+  _getSubscribers(topic) {
+    const subscribers = this._topics.get(topic);
+    if (typeof subscribers === 'undefined') {
+      throw new Error(`Topic:"${topic}" doesn't exist.`);
+    }
+    return subscribers;
+  }
+
+  _getSubscriber(topic, address) {
+    const subscribers = this._getSubscribers(topic);
+    const subscriber = subscribers.get(address);
+    if (typeof subscriber === 'undefined') {
+      throw new Error(`Subscriber on topic:"${topic}" at address:"${address}" doesn't exist.`);
+    }
+    return subscriber;
+  }
+
+  hasTopic(topic) {
+    return typeof this._topics.get(topic) !== 'undefined';
+  }
+
+  hasSubscriber(topic, address) {
+    const subscribers = this._getSubscribers(topic);
+    return typeof subscribers.get(address) !== 'undefined';
+  }
+
+  hasTopicAndSubscriber(topic, address) {
+    return (this.isTopicExist(topic))
+      ? this.isSubscriberExist(topic, address)
+      : false;
+  }
+
+  /**
+   * @param {string} topic - Subscription topic
+   * @param {string} address - Address of subscriber
+   * @param {function} inbox - The inbox function to receive post data
+   */
+  subscribe(topic, address, inbox) {
+    if (typeof inbox !== 'function') {
+      throw new TypeError('Inbox  must be a function.');
+    }
+
+    if (typeof this._topics.get(topic) === 'undefined') {
+      this._topics.set(topic, new Map());
+    }
+    const subscribers = this._topics.get(topic);
+    if (subscribers.get(address)) {
+      throw new Error(`Subscription on topic:"${topic}" at address:"${address}" already exist.`);
+    }
+    subscribers.set(address, inbox);
+  }
+
+  unsubscribe(topic, address) {
+    const subscribers = this._getSubscribers(topic);
+    if (subscribers.has(address)) {
+      subscribers.delete(address);
+    } else throw new Error(`Unable to unsubscribe. Subscriber on topic:"${topic}" at address:"${address}" doesn't exist`);
+    if (subscribers.size === 0) {
+      this._topics.delete(topic);
+    }
+  }
+
+  /**
+   * @param {string} topic - Subscription topic
+   * @param {string|string[]} address - Address of subscriber
+   * @param {*} data - Data to deliver to subscriber
+   */
+  post(topic, address, data) {
+    const sendPost = (subscriber, addr) => {
+      if (typeof subscriber === 'undefined') {
+        throw new Error(`Unable to post on topic:"${topic}" at address:"${addr}". Subscriber doesn't exist.`);
+      }
+      subscriber(data);
+    };
+    if (Array.isArray(address)) {
+      const subscribers = this._getSubscribers(topic);
+      address.forEach((addr) => {
+        sendPost(subscribers.get(addr), addr);
+      });
+      return;
+    }
+    sendPost(this._getSubscriber(topic, address), address);
+  }
+}
+
+export default Postie;