From 59751349b751db05ac89b94d0f8098fb63714958 Mon Sep 17 00:00:00 2001
From: Guido Schmit <scarriffle@MacBook-Pro.local>
Date: Tue, 7 Apr 2026 22:09:11 +0200
Subject: [PATCH] =?UTF-8?q?perf:=20Sliding-window=20Cache=20=E2=80=94=20Hi?=
 =?UTF-8?q?ntergrund-Prefetch=20bei=20Cache-Randn=C3=A4he=20Wenn=20die=20a?=
 =?UTF-8?q?ktuelle=20Ansicht=20weniger=20als=204=20Wochen=20vom=20Cache-Ra?=
 =?UTF-8?q?nd=20entfernt=20ist,=20werden=20im=20Hintergrund=208=20weitere?=
 =?UTF-8?q?=20Wochen=20in=20diese=20Richtung=20geladen=20und=20in=20den=20?=
 =?UTF-8?q?Cache=20gemergt.=20Der=20Cache=20w=C3=A4chst=20damit=20automati?=
 =?UTF-8?q?sch=20mit=20der=20Navigation=20mit=20=E2=80=94=20kein=20sichtba?=
 =?UTF-8?q?rer=20Ladevorgang=20auch=20bei=20langen=20Spr=C3=BCngen.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 frontend/js/calendar.js | 56 +++++++++++++++++++++++++++++++++++------
 1 file changed, 49 insertions(+), 7 deletions(-)

diff --git a/frontend/js/calendar.js b/frontend/js/calendar.js
index af88aaa..3dca0ac 100644
--- a/frontend/js/calendar.js
+++ b/frontend/js/calendar.js
@@ -73,12 +73,54 @@ export async function initCalendar() {
 }
 
 // ── Event cache ───────────────────────────────────────────
-const eventCache = { start: null, end: null, events: [] };
+const CACHE_BUF      = 56 * 86400000; // initial ±8 weeks
+const PREFETCH_EXT   = 56 * 86400000; // extend by 8 weeks when triggered
+const PREFETCH_EDGE  = 28 * 86400000; // trigger when within 4 weeks of cache edge
+
+const eventCache = {
+  start: null, end: null, events: [],
+  _fwdPending: false, _bwdPending: false,
+};
 
 function invalidateCache() {
-  eventCache.start  = null;
-  eventCache.end    = null;
-  eventCache.events = [];
+  eventCache.start      = null;
+  eventCache.end        = null;
+  eventCache.events     = [];
+  eventCache._fwdPending = false;
+  eventCache._bwdPending = false;
+}
+
+function _mergeEvents(newEvents) {
+  const seen = new Set(eventCache.events.map(e => e.id + '@@' + (e.url || '')));
+  for (const e of newEvents) {
+    const k = e.id + '@@' + (e.url || '');
+    if (!seen.has(k)) { seen.add(k); eventCache.events.push(e); }
+  }
+}
+
+// Fire-and-forget: extend the cache toward whichever edge the view is approaching
+function prefetchIfNeeded(viewStart, viewEnd) {
+  if (!eventCache.start || !eventCache.end) return;
+
+  if (!eventCache._fwdPending && (eventCache.end - viewEnd) < PREFETCH_EDGE) {
+    eventCache._fwdPending = true;
+    const from = new Date(eventCache.end);
+    const to   = new Date(eventCache.end.getTime() + PREFETCH_EXT);
+    api.get(`/caldav/events?start=${from.toISOString()}&end=${to.toISOString()}`)
+      .then(evs => { _mergeEvents(evs); eventCache.end = to; })
+      .catch(() => {})
+      .finally(() => { eventCache._fwdPending = false; });
+  }
+
+  if (!eventCache._bwdPending && (viewStart - eventCache.start) < PREFETCH_EDGE) {
+    eventCache._bwdPending = true;
+    const from = new Date(eventCache.start.getTime() - PREFETCH_EXT);
+    const to   = new Date(eventCache.start);
+    api.get(`/caldav/events?start=${from.toISOString()}&end=${to.toISOString()}`)
+      .then(evs => { _mergeEvents(evs); eventCache.start = from; })
+      .catch(() => {})
+      .finally(() => { eventCache._bwdPending = false; });
+  }
 }
 
 // ── Data fetching ─────────────────────────────────────────
@@ -92,13 +134,13 @@ async function fetchAndRender(force = false) {
     renderView();
     updateTitle();
     renderMiniCal();
+    prefetchIfNeeded(start, end); // extend cache in background if approaching an edge
     return;
   }
 
   // Cache miss: fetch a wider window (±8 weeks) so subsequent navigation is instant
-  const BUF = 56 * 86400000; // 8 weeks in ms
-  const fetchStart = new Date(start.getTime() - BUF);
-  const fetchEnd   = new Date(end.getTime()   + BUF);
+  const fetchStart = new Date(start.getTime() - CACHE_BUF);
+  const fetchEnd   = new Date(end.getTime()   + CACHE_BUF);
 
   showLoading();
   try {