Skip updates while the tab/window is not visible

Pause updates while the window is minimized or the tab is in the background, but immediately continue updating once the wall is visible again. This should avoid a ton of unnecessary requests to servers.

src/App.vue

@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import { computed, inject, onBeforeUnmount, onMounted, onUpdated, ref, watch } from 'vue';
 import Card, { type Post } from './components/Card.vue';
-import { useWindowSize, watchDebounced } from '@vueuse/core'
+import { useDocumentVisibility, useWindowSize, watchDebounced } from '@vueuse/core'
 import ConfigModal from './components/ConfigModal.vue';
 import { loadConfig, type Config } from './config';
 import InfoBar from './components/InfoBar.vue';
@@ -14,17 +14,18 @@ const hidden = ref<Array<string>>([])
 const banned = ref<Array<string>>([])
 const updateInProgress = ref(false)
 
-var updateIntervalHandle: number;
 const accountToLocalId: Record<string, string | null> = {}
+var updateIntervalHandle: number;
+var lastUpdate = 0;
 
 onMounted(async () => {
   config.value = await loadConfig()
-  // Trigger update once. Timed updates are started by a watcher below.
-  await updateWall()
+  if (visibilityState.value !== "hidden")
+    restartUpdates()
 })
 
 onBeforeUnmount(() => {
-  clearInterval(updateIntervalHandle)
+  stopUpdates()
 })
 
 // Re-layout Masonry on dom updates or window size changes
@@ -39,19 +40,15 @@ watch(() => config.value?.theme, () => {
 })
 
 // Watch for a update interval changes
-watch(() => config.value?.interval, () => {
-  clearInterval(updateIntervalHandle)
-  if (!config.value) return
+watch(() => config.value?.interval, () => restartUpdates())
 
-  // Update  interval is large enough to not hit the mastodon default rate limit
-  const rqPerUpdate = config.value.accounts.length * 2 + config.value.tags.length
-  const maxPerSecond = 300 / (5 * 60) / 2 // Be nice, use only half rate limit
-  const minInternal = Math.ceil(rqPerUpdate / maxPerSecond)
-  const interval = Math.max(minInternal, config.value.interval)
-
-  updateIntervalHandle = setInterval(() => {
-    updateWall()
-  }, interval * 1000)
+// Pause updates while tab/window is hidden
+const visibilityState = useDocumentVisibility()
+watch(visibilityState, () => {
+  if (visibilityState.value === "hidden")
+    stopUpdates()
+  else
+    restartUpdates()
 })
 
 // Souces grouped by server
@@ -259,6 +256,35 @@ async function fetchAllPosts() {
   return posts
 }
 
+/**
+ * Starts or restarts the update interval timer.
+ */
+const restartUpdates = () => {
+  stopUpdates()
+  if (!config.value) return
+
+  // Mastodon default rate limit is 1/s (300/5m)
+  // Be nice, only send one request every 2 seconds on average.
+  const rqPerUpdate = config.value.accounts.length + config.value.tags.length
+  const minInternal = Math.ceil(rqPerUpdate * 2)
+  const interval = Math.max(minInternal, config.value.interval)
+
+  updateIntervalHandle = setInterval(() => {
+    updateWall()
+  }, interval * 1000)
+
+  // Trigger update immediately if new interval allows it
+  if (lastUpdate + interval < new Date().getTime())
+    updateWall()
+}
+
+/**
+ * Stops the update interval
+ */
+const stopUpdates = () => {
+  clearInterval(updateIntervalHandle)
+}
+
 /**
  * Trigger a wall update.
  * 
@@ -273,14 +299,16 @@ async function updateWall() {
     return
   }
 
-  console.debug("Startung wall update...")
+  console.debug("Updating wall...")
   updateInProgress.value = true
+
   try {
     allPosts.value = await fetchAllPosts()
     console.debug("Update completed")
   } catch (e) {
     console.warn("Update failed", e)
   } finally {
+    lastUpdate = Date.now()
     updateInProgress.value = false;
   }
 
@@ -386,7 +414,8 @@ const privacyLink = computed(() => {
     <ConfigModal v-if="config" v-model="config" id="configModal" />
 
     <footer>
-      <button class="btn btn-link text-muted" @click="toggleTheme(); false">[{{ config?.theme == "dark" ? "Light" : "Dark" }} mode]</button>
+      <button class="btn btn-link text-muted" @click="toggleTheme(); false">[{{ config?.theme == "dark" ? "Light" : "Dark"
+      }} mode]</button>
       <button class="btn btn-link text-muted" data-bs-toggle="modal" data-bs-target="#configModal">[Customize]</button>
       <div>
         <a :href="privacyLink" target="_blank" class="mx-1">Privacy policy</a>