add checksum to test whether calendar event list changed (#3988)

for issue #3971 add checksum to test if event list changed to
reduce/eliminate no change screen update
fixes #3971

crc32 checksum created in node helper, easy require, vs trying to do in
browser.
added to socket notification payload, used in browser

Author: sdetweil

modules/default/calendar/calendar.js

@@ -184,13 +184,27 @@ Module.register("calendar", {
 
 		if (notification === "CALENDAR_EVENTS") {
 			if (this.hasCalendarURL(payload.url)) {
-				this.calendarData[payload.url] = payload.events;
+				// have we received events for this url
+				if (!this.calendarData[payload.url]) {
+					// no, setup the structure to hold the info
+					this.calendarData[payload.url] = { events: null, checksum: null };
+				}
+				// save the event list
+				this.calendarData[payload.url].events = payload.events;
+
 				this.error = null;
 				this.loaded = true;
 
 				if (this.config.broadcastEvents) {
 					this.broadcastEvents();
 				}
+				// if the checksum is the same
+				if (this.calendarData[payload.url].checksum === payload.checksum) {
+					// then don't update the UI
+					return;
+				}
+				// haven't seen or the checksum is different
+				this.calendarData[payload.url].checksum = payload.checksum;
 
 				if (!this.config.updateOnFetch) {
 					if (this.calendarDisplayer[payload.url] === undefined) {
@@ -602,7 +616,7 @@ Module.register("calendar", {
 		let events = [];
 
 		for (const calendarUrl in this.calendarData) {
-			const calendar = this.calendarData[calendarUrl];
+			const calendar = this.calendarData[calendarUrl].events;
 			let remainingEntries = this.maximumEntriesForUrl(calendarUrl);
 			let maxPastDaysCompare = now.clone().subtract(this.maximumPastDaysForUrl(calendarUrl), "days");
 			let by_url_calevents = [];

modules/default/calendar/node_helper.js

@@ -1,3 +1,4 @@
+const zlib = require("node:zlib");
 const NodeHelper = require("node_helper");
 const Log = require("logger");
 const CalendarFetcher = require("./calendarfetcher");
@@ -90,10 +91,12 @@ module.exports = NodeHelper.create({
 	 * @param {string} identifier the identifier of the calendar
 	 */
 	broadcastEvents (fetcher, identifier) {
+		const checksum = zlib.crc32(Buffer.from(JSON.stringify(fetcher.events), "utf8"));
 		this.sendSocketNotification("CALENDAR_EVENTS", {
 			id: identifier,
 			url: fetcher.url,
-			events: fetcher.events
+			events: fetcher.events,
+			checksum: checksum
 		});
 	}
 });