move default modules from /modules/default to /defaultmodules (#4019)

Since the project's inception, I've missed a clear separation between
default and third-party modules.

This increases complexity within the project (exclude `modules`, but not
`modules/default`), but the mixed use is particularly problematic in
Docker setups.

Therefore, with this pull request, I'm moving the default modules to a
different directory.

~~I've chosen `default/modules`, but I'm not bothered about it;
`defaultmodules` or something similar would work just as well.~~

Changed to `defaultmodules`.

Let me know if there's a majority in favor of this change.

defaultmodules/calendar/node_helper.js

@@ -0,0 +1,101 @@
+const zlib = require("node:zlib");
+const NodeHelper = require("node_helper");
+const Log = require("logger");
+const CalendarFetcher = require("./calendarfetcher");
+
+module.exports = NodeHelper.create({
+	// Override start method.
+	start () {
+		Log.log(`Starting node helper for: ${this.name}`);
+		this.fetchers = [];
+	},
+
+	// Override socketNotificationReceived method.
+	socketNotificationReceived (notification, payload) {
+		if (notification === "ADD_CALENDAR") {
+			this.createFetcher(payload.url, payload.fetchInterval, payload.excludedEvents, payload.maximumEntries, payload.maximumNumberOfDays, payload.auth, payload.broadcastPastEvents, payload.selfSignedCert, payload.id);
+		} else if (notification === "FETCH_CALENDAR") {
+			const key = payload.id + payload.url;
+			if (typeof this.fetchers[key] === "undefined") {
+				Log.error("No fetcher exists with key: ", key);
+				this.sendSocketNotification("CALENDAR_ERROR", { error_type: "MODULE_ERROR_UNSPECIFIED" });
+				return;
+			}
+			this.fetchers[key].fetchCalendar();
+		}
+	},
+
+	/**
+	 * Creates a fetcher for a new url if it doesn't exist yet.
+	 * Otherwise it reuses the existing one.
+	 * @param {string} url The url of the calendar
+	 * @param {number} fetchInterval How often does the calendar needs to be fetched in ms
+	 * @param {string[]} excludedEvents An array of words / phrases from event titles that will be excluded from being shown.
+	 * @param {number} maximumEntries The maximum number of events fetched.
+	 * @param {number} maximumNumberOfDays The maximum number of days an event should be in the future.
+	 * @param {object} auth The object containing options for authentication against the calendar.
+	 * @param {boolean} broadcastPastEvents If true events from the past maximumNumberOfDays will be included in event broadcasts
+	 * @param {boolean} selfSignedCert If true, the server certificate is not verified against the list of supplied CAs.
+	 * @param {string} identifier ID of the module
+	 */
+	createFetcher (url, fetchInterval, excludedEvents, maximumEntries, maximumNumberOfDays, auth, broadcastPastEvents, selfSignedCert, identifier) {
+		try {
+			new URL(url);
+		} catch (error) {
+			Log.error("Malformed calendar url: ", url, error);
+			this.sendSocketNotification("CALENDAR_ERROR", { error_type: "MODULE_ERROR_MALFORMED_URL" });
+			return;
+		}
+
+		let fetcher;
+		let fetchIntervalCorrected;
+		if (typeof this.fetchers[identifier + url] === "undefined") {
+			if (fetchInterval < 60000) {
+				Log.warn(`fetchInterval for url ${url} must be >= 60000`);
+				fetchIntervalCorrected = 60000;
+			}
+			Log.log(`Create new calendarfetcher for url: ${url} - Interval: ${fetchIntervalCorrected || fetchInterval}`);
+			fetcher = new CalendarFetcher(url, fetchIntervalCorrected || fetchInterval, excludedEvents, maximumEntries, maximumNumberOfDays, auth, broadcastPastEvents, selfSignedCert);
+
+			fetcher.onReceive((fetcher) => {
+				this.broadcastEvents(fetcher, identifier);
+			});
+
+			fetcher.onError((fetcher, errorInfo) => {
+				Log.error("Calendar Error. Could not fetch calendar: ", fetcher.url, errorInfo.message || errorInfo);
+				this.sendSocketNotification("CALENDAR_ERROR", {
+					id: identifier,
+					error_type: errorInfo.translationKey
+				});
+			});
+
+			this.fetchers[identifier + url] = fetcher;
+			fetcher.fetchCalendar();
+		} else {
+			Log.log(`Use existing calendarfetcher for url: ${url}`);
+			fetcher = this.fetchers[identifier + url];
+			// Check if calendar data is stale and needs refresh
+			if (fetcher.shouldRefetch()) {
+				Log.log(`Calendar data is stale, fetching fresh data for url: ${url}`);
+				fetcher.fetchCalendar();
+			} else {
+				fetcher.broadcastEvents();
+			}
+		}
+	},
+
+	/**
+	 *
+	 * @param {object} fetcher the fetcher associated with the calendar
+	 * @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,
+			checksum: checksum
+		});
+	}
+});