perf: Reduce polling interval for read only users

Signed-off-by: Julius Härtl <jus@bitgrid.net>

src/services/PollingBackend.js

@@ -27,6 +27,12 @@ const FETCH_INTERVAL_MAX = 5000
  */
 const FETCH_INTERVAL_SINGLE_EDITOR = 5000
 
+/**
+ * Interval to check for changes for read only users
+ * @type {number}
+ */
+const FETCH_INTERVAL_READ_ONLY = 30000
+
 /**
  * Interval to fetch for changes when a browser window is considered invisible by the
  * page visibility API https://developer.mozilla.org/de/docs/Web/API/Page_Visibility_API
@@ -120,7 +126,9 @@ class PollingBackend {
 			}
 			const disconnect = Date.now() - COLLABORATOR_DISCONNECT_TIME
 			const alive = sessions.filter((s) => s.lastContact * 1000 > disconnect)
-			if (alive.length < 2) {
+			if (this.#syncService.connection.state.document.readOnly) {
+				this.maximumReadOnlyTimer()
+			} else if (alive.length < 2) {
 				this.maximumRefetchTimer()
 			} else {
 				this.increaseRefetchTimer()
@@ -193,6 +201,10 @@ class PollingBackend {
 		this.#fetchInterval = FETCH_INTERVAL_SINGLE_EDITOR
 	}
 
+	maximumReadOnlyTimer() {
+		this.#fetchInterval = FETCH_INTERVAL_READ_ONLY
+	}
+
 	visibilitychange() {
 		if (document.visibilityState === 'hidden') {
 			this.#fetchInterval = FETCH_INTERVAL_INVISIBLE