From eae2e0587cf3c3f99352f9110ec45f4cc173440a Mon Sep 17 00:00:00 2001
From: Aden Linday <lindsaya542@gmail.com>
Date: Sat, 27 Jun 2026 14:19:28 +0930
Subject: [PATCH] feat: tweak calendar and clean it up

---
 src/background.ts                             |   3 +-
 src/background/googleCalendar.ts              |  64 ++++
 src/background/googleCalendarWeekly.ts        |  74 ++++
 src/config/googleCalendar.ts                  |   5 +-
 src/manifests/manifest.json                   |   2 +-
 .../CalendarDeleteEventsModal.svelte          | 140 ++++++++
 .../timetable/CalendarSyncControl.svelte      | 320 ++++++++++++------
 .../timetable/CalendarSyncProgress.svelte     |  67 ++++
 .../built-in/timetable/calendarSyncUi.ts      |   2 +
 .../googleCalendar/calendarSyncListener.ts    |  47 +++
 .../utils/googleCalendar/eventMapEntry.ts     |  29 ++
 .../utils/googleCalendar/fetchTimetable.ts    |  26 +-
 src/seqta/utils/googleCalendar/storage.ts     |   9 +-
 .../googleCalendar/syncDateRange.test.ts      |  31 ++
 .../utils/googleCalendar/syncDateRange.ts     |  45 +++
 .../utils/googleCalendar/syncEngine.test.ts   | 139 ++++++++
 src/seqta/utils/googleCalendar/syncEngine.ts  | 272 ++++++++++++++-
 src/seqta/utils/googleCalendar/syncRunner.ts  |  83 +++++
 .../utils/googleCalendar/syncSettings.ts      |  57 ++++
 src/seqta/utils/googleCalendar/types.ts       |  28 ++
 src/seqta/utils/googleCalendar/upsertEvent.ts |  19 ++
 21 files changed, 1336 insertions(+), 126 deletions(-)
 create mode 100644 src/background/googleCalendarWeekly.ts
 create mode 100644 src/plugins/built-in/timetable/CalendarDeleteEventsModal.svelte
 create mode 100644 src/plugins/built-in/timetable/CalendarSyncProgress.svelte
 create mode 100644 src/seqta/utils/googleCalendar/calendarSyncListener.ts
 create mode 100644 src/seqta/utils/googleCalendar/eventMapEntry.ts
 create mode 100644 src/seqta/utils/googleCalendar/syncDateRange.test.ts
 create mode 100644 src/seqta/utils/googleCalendar/syncDateRange.ts
 create mode 100644 src/seqta/utils/googleCalendar/syncEngine.test.ts
 create mode 100644 src/seqta/utils/googleCalendar/syncRunner.ts
 create mode 100644 src/seqta/utils/googleCalendar/syncSettings.ts

diff --git a/src/background.ts b/src/background.ts
index c4b5eda4..0ca8b442 100644
--- a/src/background.ts
+++ b/src/background.ts
@@ -13,7 +13,7 @@ import {
   withSuppressedCloudAutoUpload,
 } from "./background/cloudSettingsAutoSync";
 import { isAllowedFetchUrl } from "@/seqta/utils/allowedFetchUrl";
-import { registerGoogleCalendarMessageHandlers } from "./background/googleCalendar";
+import { registerGoogleCalendarMessageHandlers, initGoogleCalendarBackground } from "./background/googleCalendar";
 
 /**
  * Session-only dev-mode override of the content API base.
@@ -559,6 +559,7 @@ const MESSAGE_HANDLERS: Record<string, MessageHandler> = {
 };
 
 registerGoogleCalendarMessageHandlers(MESSAGE_HANDLERS, isTrustedSender);
+initGoogleCalendarBackground();
 
 browser.runtime.onMessage.addListener(
   // @ts-ignore - OnMessageListener expects literal true for async, we return boolean
diff --git a/src/background/googleCalendar.ts b/src/background/googleCalendar.ts
index edec6328..86ccb2f0 100644
--- a/src/background/googleCalendar.ts
+++ b/src/background/googleCalendar.ts
@@ -16,10 +16,20 @@ import {
   readGoogleCalendarState,
   writeGoogleCalendarState,
 } from "@/seqta/utils/googleCalendar/storage";
+import {
+  clampSyncWeeks,
+  getAutoSyncWeekly,
+  getSyncWeeksAhead,
+} from "@/seqta/utils/googleCalendar/syncSettings";
 import type {
   GoogleCalendarStatus,
   GoogleCalendarSyncResult,
 } from "@/seqta/utils/googleCalendar/types";
+import {
+  clearWeeklySyncAlarm,
+  ensureWeeklySyncAlarm,
+  registerWeeklySyncAlarmListener,
+} from "./googleCalendarWeekly";
 
 function base64UrlEncode(buffer: ArrayBuffer): string {
   const bytes = new Uint8Array(buffer);
@@ -197,6 +207,8 @@ async function connectGoogleCalendar(): Promise<GoogleCalendarSyncResult> {
       connectedAt: Date.now(),
     });
 
+    await ensureWeeklySyncAlarm();
+
     return { success: true, configured: true, connected: true };
   } catch (err) {
     return {
@@ -209,11 +221,16 @@ async function connectGoogleCalendar(): Promise<GoogleCalendarSyncResult> {
 
 async function getGoogleCalendarStatus(): Promise<GoogleCalendarStatus> {
   const state = await readGoogleCalendarState();
+  const syncWeeksAhead = await getSyncWeeksAhead();
+  const autoSyncWeekly = await getAutoSyncWeekly();
   return {
     configured: isGoogleCalendarConfigured(),
     connected: !!(state.refreshToken || state.accessToken),
     lastSyncAt: state.lastSyncAt,
+    lastWeeklySyncAt: state.lastWeeklySyncAt,
     lastSyncOrigin: state.lastSyncOrigin,
+    syncWeeksAhead,
+    autoSyncWeekly,
   };
 }
 
@@ -222,6 +239,7 @@ export async function handleGoogleCalendarConnect(): Promise<GoogleCalendarSyncR
 }
 
 export async function handleGoogleCalendarDisconnect(): Promise<{ success: boolean }> {
+  await clearWeeklySyncAlarm();
   await clearGoogleCalendarState();
   return { success: true };
 }
@@ -298,4 +316,50 @@ export function registerGoogleCalendarMessageHandlers(
       });
     return true;
   };
+
+  handlers.googleCalendarEnsureWeeklyAlarm = (_req, sendResponse, sender) => {
+    if (rejectUntrusted(sendResponse, sender)) return false;
+    void ensureWeeklySyncAlarm()
+      .then(() => sendResponse({ success: true }))
+      .catch((err) => {
+        sendResponse({
+          success: false,
+          error: err instanceof Error ? err.message : "Could not schedule weekly sync",
+        });
+      });
+    return true;
+  };
+
+  handlers.googleCalendarUpdateSyncSettings = (request, sendResponse, sender) => {
+    if (rejectUntrusted(sendResponse, sender)) return false;
+    void (async () => {
+      const body = request as {
+        syncWeeksAhead?: number;
+        autoSyncWeekly?: boolean;
+      };
+      const patch: Record<string, unknown> = {};
+      if (body.syncWeeksAhead != null) {
+        patch.syncWeeksAhead = clampSyncWeeks(body.syncWeeksAhead);
+      }
+      if (body.autoSyncWeekly != null) {
+        patch.autoSyncWeekly = !!body.autoSyncWeekly;
+      }
+      if (Object.keys(patch).length > 0) {
+        await writeGoogleCalendarState(patch);
+      }
+      await ensureWeeklySyncAlarm();
+      sendResponse({ success: true, ...(await getGoogleCalendarStatus()) });
+    })().catch((err) => {
+      sendResponse({
+        success: false,
+        error: err instanceof Error ? err.message : "Could not update sync settings",
+      });
+    });
+    return true;
+  };
+}
+
+export function initGoogleCalendarBackground(): void {
+  registerWeeklySyncAlarmListener();
+  void ensureWeeklySyncAlarm();
 }
diff --git a/src/background/googleCalendarWeekly.ts b/src/background/googleCalendarWeekly.ts
new file mode 100644
index 00000000..b1ece4b1
--- /dev/null
+++ b/src/background/googleCalendarWeekly.ts
@@ -0,0 +1,74 @@
+import browser from "webextension-polyfill";
+import { verboseLog } from "@/utils/verboseLog";
+import {
+  getAutoSyncWeekly,
+  GOOGLE_CALENDAR_WEEKLY_ALARM,
+  markWeeklySyncPending,
+} from "@/seqta/utils/googleCalendar/syncSettings";
+import { readGoogleCalendarState } from "@/seqta/utils/googleCalendar/storage";
+
+const WEEKLY_PERIOD_MINUTES = 7 * 24 * 60;
+
+function isSeqtaTab(tab: browser.Tabs.Tab): boolean {
+  const title = tab.title ?? "";
+  return title.includes("SEQTA Learn") || title.includes("SEQTA Engage");
+}
+
+async function isCalendarConnected(): Promise<boolean> {
+  const state = await readGoogleCalendarState();
+  return !!(state.refreshToken || state.accessToken);
+}
+
+export async function ensureWeeklySyncAlarm(): Promise<void> {
+  const connected = await isCalendarConnected();
+  const enabled = await getAutoSyncWeekly();
+  if (!connected || !enabled) {
+    await browser.alarms.clear(GOOGLE_CALENDAR_WEEKLY_ALARM);
+    return;
+  }
+
+  const existing = await browser.alarms.get(GOOGLE_CALENDAR_WEEKLY_ALARM);
+  if (!existing) {
+    await browser.alarms.create(GOOGLE_CALENDAR_WEEKLY_ALARM, {
+      periodInMinutes: WEEKLY_PERIOD_MINUTES,
+    });
+  }
+}
+
+export async function clearWeeklySyncAlarm(): Promise<void> {
+  await browser.alarms.clear(GOOGLE_CALENDAR_WEEKLY_ALARM);
+}
+
+export async function triggerWeeklySyncOnSeqtaTabs(): Promise<boolean> {
+  const tabs = await browser.tabs.query({});
+  const seqtaTabs = tabs.filter((tab) => tab.id != null && isSeqtaTab(tab));
+  if (seqtaTabs.length === 0) return false;
+
+  let delivered = false;
+  for (const tab of seqtaTabs) {
+    if (tab.id == null) continue;
+    try {
+      await browser.tabs.sendMessage(tab.id, { type: "googleCalendarRunWeeklySync" });
+      delivered = true;
+    } catch (err) {
+      verboseLog("[BetterSEQTA+] Weekly calendar sync message failed for tab:", tab.id, err);
+    }
+  }
+  return delivered;
+}
+
+export async function handleWeeklySyncAlarm(): Promise<void> {
+  if (!(await isCalendarConnected()) || !(await getAutoSyncWeekly())) return;
+
+  const delivered = await triggerWeeklySyncOnSeqtaTabs();
+  if (!delivered) {
+    await markWeeklySyncPending();
+  }
+}
+
+export function registerWeeklySyncAlarmListener(): void {
+  browser.alarms.onAlarm.addListener((alarm) => {
+    if (alarm.name !== GOOGLE_CALENDAR_WEEKLY_ALARM) return;
+    void handleWeeklySyncAlarm();
+  });
+}
diff --git a/src/config/googleCalendar.ts b/src/config/googleCalendar.ts
index 8a24bd14..9b669dc7 100644
--- a/src/config/googleCalendar.ts
+++ b/src/config/googleCalendar.ts
@@ -28,8 +28,11 @@ export const GOOGLE_CALENDAR_API = "https://www.googleapis.com/calendar/v3";
 
 export const BSPLUS_GOOGLE_CALENDAR_EVENT_PROP = "bsplusSeqtaKey";
 
-/** Weeks of timetable to sync (from start of current week). */
+/** Default weeks of timetable to sync forward (from start of current week). */
 export const GOOGLE_CALENDAR_SYNC_WEEKS = 12;
+export const GOOGLE_CALENDAR_SYNC_WEEKS_DEFAULT = GOOGLE_CALENDAR_SYNC_WEEKS;
+export const GOOGLE_CALENDAR_SYNC_WEEKS_MIN = 1;
+export const GOOGLE_CALENDAR_SYNC_WEEKS_MAX = 52;
 
 export function isGoogleCalendarConfigured(): boolean {
   return GOOGLE_OAUTH_CLIENT_ID.length > 0;
diff --git a/src/manifests/manifest.json b/src/manifests/manifest.json
index a96aa207..812f5de8 100644
--- a/src/manifests/manifest.json
+++ b/src/manifests/manifest.json
@@ -15,7 +15,7 @@
       "64": "resources/icons/icon-64.png"
     }
   },
-  "permissions": ["tabs", "notifications", "storage", "identity"],
+  "permissions": ["tabs", "notifications", "storage", "identity", "alarms"],
   "host_permissions": [
     "https://newsapi.org/",
     "https://betterseqta.org/",
diff --git a/src/plugins/built-in/timetable/CalendarDeleteEventsModal.svelte b/src/plugins/built-in/timetable/CalendarDeleteEventsModal.svelte
new file mode 100644
index 00000000..5accdd94
--- /dev/null
+++ b/src/plugins/built-in/timetable/CalendarDeleteEventsModal.svelte
@@ -0,0 +1,140 @@
+<script lang="ts">
+  import { fade } from "svelte/transition";
+
+  let {
+    open = false,
+    busy = false,
+    onConfirm,
+    onCancel,
+  } = $props<{
+    open?: boolean;
+    busy?: boolean;
+    onConfirm: () => void | Promise<void>;
+    onCancel: () => void;
+  }>();
+</script>
+
+{#if open}
+  <div
+    class="bsplus-cal-modal-backdrop"
+    onclick={(e) => {
+      if (e.target === e.currentTarget && !busy) onCancel();
+    }}
+    onkeydown={(e) => {
+      if (e.key === "Escape" && !busy) onCancel();
+    }}
+    role="presentation"
+    transition:fade={{ duration: 150 }}
+  >
+    <div
+      class="bsplus-cal-modal"
+      role="dialog"
+      aria-modal="true"
+      aria-labelledby="bsplus-cal-delete-title"
+      transition:fade={{ duration: 180 }}
+    >
+      <h2 id="bsplus-cal-delete-title" class="bsplus-cal-modal-title">
+        Remove synced events?
+      </h2>
+      <p class="bsplus-cal-modal-body">
+        This removes all BetterSEQTA+ timetable events from your Google Calendar for this school.
+        Your connection stays active — you can sync again later.
+      </p>
+      <div class="bsplus-cal-modal-actions">
+        <button
+          type="button"
+          class="bsplus-cal-btn bsplus-cal-btn--ghost"
+          disabled={busy}
+          onclick={onCancel}
+        >
+          Cancel
+        </button>
+        <button
+          type="button"
+          class="bsplus-cal-btn bsplus-cal-btn--danger"
+          disabled={busy}
+          onclick={() => void onConfirm()}
+        >
+          {busy ? "Removing…" : "Remove from calendar"}
+        </button>
+      </div>
+    </div>
+  </div>
+{/if}
+
+<style>
+  .bsplus-cal-modal-backdrop {
+    position: fixed;
+    inset: 0;
+    z-index: 2147483647;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    padding: 16px;
+    background: rgba(0, 0, 0, 0.5);
+    backdrop-filter: blur(4px);
+  }
+
+  .bsplus-cal-modal {
+    width: min(100%, 400px);
+    padding: 20px;
+    border-radius: 16px;
+    background: var(--bsplus-cal-surface, #fff);
+    color: var(--bsplus-cal-text, #111);
+    box-shadow: 0 24px 48px rgba(0, 0, 0, 0.22);
+    border: 1px solid color-mix(in srgb, var(--bsplus-cal-text, #111) 12%, transparent);
+  }
+
+  .bsplus-cal-modal-title {
+    margin: 0 0 8px;
+    font-size: 18px;
+    font-weight: 700;
+    line-height: 1.3;
+  }
+
+  .bsplus-cal-modal-body {
+    margin: 0 0 20px;
+    font-size: 14px;
+    line-height: 1.5;
+    color: color-mix(in srgb, var(--bsplus-cal-text, #111) 72%, transparent);
+  }
+
+  .bsplus-cal-modal-actions {
+    display: flex;
+    justify-content: flex-end;
+    gap: 8px;
+  }
+
+  .bsplus-cal-btn {
+    padding: 8px 14px;
+    border: none;
+    border-radius: 10px;
+    font-size: 13px;
+    font-weight: 600;
+    cursor: pointer;
+    transition: all 0.2s ease;
+  }
+
+  .bsplus-cal-btn:disabled {
+    opacity: 0.6;
+    cursor: not-allowed;
+  }
+
+  .bsplus-cal-btn--ghost {
+    background: color-mix(in srgb, var(--bsplus-cal-text, #111) 8%, transparent);
+    color: var(--bsplus-cal-text, #111);
+  }
+
+  .bsplus-cal-btn--ghost:hover:not(:disabled) {
+    background: color-mix(in srgb, var(--bsplus-cal-text, #111) 14%, transparent);
+  }
+
+  .bsplus-cal-btn--danger {
+    background: #dc2626;
+    color: #fff;
+  }
+
+  .bsplus-cal-btn--danger:hover:not(:disabled) {
+    background: #b91c1c;
+  }
+</style>
diff --git a/src/plugins/built-in/timetable/CalendarSyncControl.svelte b/src/plugins/built-in/timetable/CalendarSyncControl.svelte
index 7499b3a2..a79d99e4 100644
--- a/src/plugins/built-in/timetable/CalendarSyncControl.svelte
+++ b/src/plugins/built-in/timetable/CalendarSyncControl.svelte
@@ -2,20 +2,38 @@
   import { onMount } from "svelte";
   import { fade, fly } from "svelte/transition";
   import browser from "webextension-polyfill";
-  import { fetchTimetableForSync } from "@/seqta/utils/googleCalendar/fetchTimetable";
-  import { syncLessonsToGoogleCalendar } from "@/seqta/utils/googleCalendar/syncEngine";
-  import type { GoogleCalendarStatus, GoogleCalendarSyncResult } from "@/seqta/utils/googleCalendar/types";
+  import {
+    GOOGLE_CALENDAR_SYNC_WEEKS_MAX,
+    GOOGLE_CALENDAR_SYNC_WEEKS_MIN,
+  } from "@/config/googleCalendar";
+  import { maybeRunDueWeeklySync } from "@/seqta/utils/googleCalendar/calendarSyncListener";
+  import { deleteSyncedEventsFromGoogleCalendar } from "@/seqta/utils/googleCalendar/syncEngine";
+  import {
+    formatSyncResultMessage,
+    runGoogleCalendarSync,
+  } from "@/seqta/utils/googleCalendar/syncRunner";
+  import type {
+    GoogleCalendarStatus,
+    GoogleCalendarSyncProgress,
+    GoogleCalendarSyncResult,
+  } from "@/seqta/utils/googleCalendar/types";
+  import CalendarDeleteEventsModal from "./CalendarDeleteEventsModal.svelte";
   import CalendarDisconnectModal from "./CalendarDisconnectModal.svelte";
+  import CalendarSyncProgress from "./CalendarSyncProgress.svelte";
   import { settingsState } from "@/seqta/utils/listeners/SettingsState";
   import { syncCalendarSyncTheme } from "./calendarSyncTheme";
 
-  type BusyPhase = "connect" | "sync" | "disconnect" | null;
+  type BusyPhase = "connect" | "sync" | "delete" | "disconnect" | null;
 
   let status = $state<GoogleCalendarStatus>({ configured: true, connected: false });
   let busy = $state<BusyPhase>(null);
   let menuOpen = $state(false);
   let showDisconnect = $state(false);
+  let showDeleteEvents = $state(false);
   let toast = $state<{ message: string; error: boolean } | null>(null);
+  let syncProgress = $state<GoogleCalendarSyncProgress | null>(null);
+  let syncWeeksAhead = $state(12);
+  let autoSyncWeekly = $state(true);
 
   let rootEl = $state<HTMLDivElement | null>(null);
   let triggerEl = $state<HTMLButtonElement | null>(null);
@@ -38,6 +56,8 @@
     status = (await browser.runtime.sendMessage({
       type: "googleCalendarStatus",
     })) as GoogleCalendarStatus;
+    syncWeeksAhead = status.syncWeeksAhead ?? 12;
+    autoSyncWeekly = status.autoSyncWeekly !== false;
   }
 
   async function getAccessTokenFromBackground(): Promise<string> {
@@ -50,26 +70,42 @@
     return res.accessToken;
   }
 
-  async function performSync(): Promise<boolean> {
-    const lessons = await fetchTimetableForSync();
-    const result = await syncLessonsToGoogleCalendar(
-      { origin: location.origin, lessons },
-      getAccessTokenFromBackground,
-    );
+  function handleSyncProgress(progress: GoogleCalendarSyncProgress) {
+    syncProgress = progress;
+  }
+
+  async function saveSyncSettings(patch: {
+    syncWeeksAhead?: number;
+    autoSyncWeekly?: boolean;
+  }) {
+    const result = (await browser.runtime.sendMessage({
+      type: "googleCalendarUpdateSyncSettings",
+      ...patch,
+    })) as GoogleCalendarStatus & { success?: boolean };
+    if (result.syncWeeksAhead != null) syncWeeksAhead = result.syncWeeksAhead;
+    if (result.autoSyncWeekly != null) autoSyncWeekly = result.autoSyncWeekly;
+    status = { ...status, ...result };
+  }
+
+  async function performSync(mode: "full" | "incremental" = "full"): Promise<boolean> {
+    const result = await runGoogleCalendarSync({
+      mode,
+      onProgress: handleSyncProgress,
+    });
+
+    syncProgress = null;
 
     if (!result.success) {
       showToastMessage(result.error ?? "Calendar sync failed.", true);
       return false;
     }
 
-    const created = result.created ?? 0;
-    const updated = result.updated ?? 0;
     status = {
       ...status,
       connected: true,
       lastSyncAt: result.lastSyncAt ?? status.lastSyncAt,
     };
-    showToastMessage(`Google Calendar updated (${created} new, ${updated} updated).`);
+    showToastMessage(formatSyncResultMessage(result));
     return true;
   }
 
@@ -91,6 +127,7 @@
     } catch (err) {
       showToastMessage(err instanceof Error ? err.message : "Could not connect.", true);
     } finally {
+      syncProgress = null;
       busy = null;
     }
   }
@@ -108,10 +145,60 @@
     } catch (err) {
       showToastMessage(err instanceof Error ? err.message : "Calendar sync failed.", true);
     } finally {
+      syncProgress = null;
       busy = null;
     }
   }
 
+  async function confirmDeleteEvents() {
+    if (isBusy) return;
+    busy = "delete";
+    syncProgress = {
+      phase: "preparing",
+      current: 0,
+      total: 1,
+      message: "Preparing removal…",
+    };
+    try {
+      const result = await deleteSyncedEventsFromGoogleCalendar(
+        location.origin,
+        getAccessTokenFromBackground,
+        { onProgress: handleSyncProgress },
+      );
+
+      if (!result.success) {
+        showToastMessage(result.error ?? "Could not remove calendar events.", true);
+        return;
+      }
+
+      const removed = result.deleted ?? 0;
+      showDeleteEvents = false;
+      menuOpen = false;
+      if (removed === 0) {
+        showToastMessage("No synced events to remove.");
+      } else {
+        showToastMessage(`Removed ${removed} event${removed === 1 ? "" : "s"} from Google Calendar.`);
+      }
+    } catch (err) {
+      showToastMessage(err instanceof Error ? err.message : "Remove failed.", true);
+    } finally {
+      syncProgress = null;
+      busy = null;
+    }
+  }
+
+  async function onWeeksAheadChange(event: Event) {
+    const value = Number((event.currentTarget as HTMLInputElement).value);
+    if (!Number.isFinite(value)) return;
+    await saveSyncSettings({ syncWeeksAhead: value });
+  }
+
+  async function onAutoSyncToggle(event: Event) {
+    const checked = (event.currentTarget as HTMLInputElement).checked;
+    autoSyncWeekly = checked;
+    await saveSyncSettings({ autoSyncWeekly: checked });
+  }
+
   async function confirmDisconnect() {
     if (isBusy) return;
     busy = "disconnect";
@@ -198,7 +285,12 @@
   });
 
   onMount(() => {
-    void refreshStatus();
+    void refreshStatus().then(() => {
+      void maybeRunDueWeeklySync((message, isError) => {
+        showToastMessage(message, isError);
+        void refreshStatus();
+      });
+    });
 
     const themeKeys = [
       "selectedColor",
@@ -241,7 +333,7 @@
 <div class="bsplus-cal-sync" bind:this={rootEl}>
   <button
     type="button"
-    class="bsplus-cal-trigger"
+    class="uiButton bsplus-cal-trigger iconFamily"
     bind:this={triggerEl}
     class:bsplus-cal-trigger--open={menuOpen}
     class:bsplus-cal-trigger--connected={status.connected}
@@ -254,27 +346,11 @@
       if (!isBusy) toggleMenu();
     }}
   >
-    <span class="bsplus-cal-trigger-label" aria-hidden="true">
-      <span class="bsplus-google-word">
-        <span class="bsplus-google-g">G</span><span class="bsplus-google-o1">o</span><span class="bsplus-google-o2">o</span><span class="bsplus-google-g2">g</span><span class="bsplus-google-l">l</span><span class="bsplus-google-e">e</span>
-      </span>
-      <span class="bsplus-cal-word">Calendar</span>
-    </span>
+    <span class="bsplus-cal-trigger-icon" aria-hidden="true">&#xe9cd;</span>
+    <span class="bsplus-cal-trigger-text">Calendar</span>
     {#if status.connected}
       <span class="bsplus-cal-status-dot" aria-hidden="true"></span>
     {/if}
-    <span class="bsplus-cal-chevron" aria-hidden="true">
-      <svg viewBox="0 0 20 20" fill="currentColor">
-        <path
-          fill-rule="evenodd"
-          d="M5.23 7.21a.75.75 0 011.06.02L10 11.168l3.71-3.94a.75.75 0 111.08 1.04l-4.25 4.5a.75.75 0 01-1.08 0l-4.25-4.5a.75.75 0 01.02-1.06z"
-          clip-rule="evenodd"
-        />
-      </svg>
-    </span>
-    {#if isBusy}
-      <span class="bsplus-cal-spinner" aria-hidden="true"></span>
-    {/if}
   </button>
 
   {#if menuOpen}
@@ -332,6 +408,38 @@
           </div>
         </div>
 
+        {#if status.connected}
+          <div class="bsplus-cal-settings" role="group" aria-label="Sync settings">
+            <label class="bsplus-cal-setting">
+              <span class="bsplus-cal-setting-label">Weeks ahead</span>
+              <input
+                type="number"
+                class="bsplus-cal-setting-input"
+                min={GOOGLE_CALENDAR_SYNC_WEEKS_MIN}
+                max={GOOGLE_CALENDAR_SYNC_WEEKS_MAX}
+                value={syncWeeksAhead}
+                disabled={isBusy}
+                onchange={(e) => void onWeeksAheadChange(e)}
+              />
+            </label>
+            <label class="bsplus-cal-setting bsplus-cal-setting--toggle">
+              <span class="bsplus-cal-setting-label">Auto-sync weekly</span>
+              <input
+                type="checkbox"
+                class="bsplus-cal-setting-checkbox"
+                checked={autoSyncWeekly}
+                disabled={isBusy}
+                onchange={(e) => void onAutoSyncToggle(e)}
+              />
+            </label>
+            <p class="bsplus-cal-setting-hint">
+              Keeps a rolling {syncWeeksAhead}-week window. Each week adds the next week and removes the oldest.
+            </p>
+          </div>
+        {/if}
+
+        <CalendarSyncProgress progress={syncProgress} />
+
         <div class="bsplus-cal-provider-actions">
           {#if !status.connected}
             <button
@@ -355,6 +463,17 @@
             >
               {busy === "sync" ? "Syncing…" : "Sync now"}
             </button>
+            <button
+              type="button"
+              class="bsplus-cal-action bsplus-cal-action--ghost"
+              role="menuitem"
+              disabled={isBusy}
+              onclick={() => {
+                showDeleteEvents = true;
+              }}
+            >
+              {busy === "delete" ? "Removing…" : "Remove from calendar"}
+            </button>
             <button
               type="button"
               class="bsplus-cal-action bsplus-cal-action--ghost"
@@ -377,6 +496,15 @@
     </div>
   {/if}
 
+  <CalendarDeleteEventsModal
+    open={showDeleteEvents}
+    busy={busy === "delete"}
+    onCancel={() => {
+      if (busy !== "delete") showDeleteEvents = false;
+    }}
+    onConfirm={confirmDeleteEvents}
+  />
+
   <CalendarDisconnectModal
     open={showDisconnect}
     busy={busy === "disconnect"}
@@ -402,7 +530,7 @@
   .bsplus-cal-sync {
     position: relative;
     display: inline-flex;
-    font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
+    font-family: Rubik, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
     color: var(--bsplus-cal-text, var(--text-primary, #111));
   }
 
@@ -411,33 +539,31 @@
     display: inline-flex;
     align-items: center;
     justify-content: center;
-    gap: 8px;
-    min-width: 188px;
-    height: 42px;
-    padding: 0 12px 0 14px;
-    border: 1px solid color-mix(in srgb, var(--bsplus-cal-text, #111) 14%, transparent);
-    border-radius: 10px;
-    background: color-mix(in srgb, var(--bsplus-cal-surface, #fff) 88%, transparent);
-    color: var(--bsplus-cal-text, var(--text-primary, #111));
-    cursor: pointer;
+    gap: 6px;
+    min-width: auto;
+    height: auto;
+    padding: 0 10px;
+    margin-left: 4px;
+    border-radius: 16px !important;
     transition: all 0.2s ease;
-    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.06);
   }
 
-  .bsplus-cal-trigger-label {
-    display: inline-flex;
-    align-items: baseline;
-    gap: 6px;
-    font-size: 17px;
-    font-weight: 700;
-    letter-spacing: -0.01em;
+  .bsplus-cal-trigger-icon {
+    font-size: 16px;
+    line-height: 1;
+    opacity: 0.9;
+  }
+
+  .bsplus-cal-trigger-text {
+    font-size: 13px;
+    font-weight: 600;
     line-height: 1;
     white-space: nowrap;
   }
 
   .bsplus-google-word {
     display: inline-flex;
-    font-size: 18px;
+    font-size: 13px;
     font-weight: 700;
     letter-spacing: -0.02em;
   }
@@ -464,34 +590,20 @@
     color: #34a853;
   }
 
-  .bsplus-cal-word {
-    color: var(--bsplus-cal-text, var(--text-primary, #111));
-    font-weight: 700;
-  }
-
   .bsplus-cal-trigger:hover:not(.bsplus-cal-trigger--busy) {
     transform: scale(1.03);
-    border-color: color-mix(in srgb, var(--bsplus-cal-accent, var(--better-main, #3b82f6)) 45%, transparent);
-    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
   }
 
   .bsplus-cal-trigger:active:not(.bsplus-cal-trigger--busy) {
     transform: scale(0.97);
   }
 
-  .bsplus-cal-trigger:focus-visible {
-    outline: none;
-    box-shadow: 0 0 0 2px var(--bsplus-cal-surface, #fff),
-      0 0 0 4px var(--bsplus-cal-accent, var(--better-main, #3b82f6));
-  }
-
   .bsplus-cal-trigger--open {
-    border-color: color-mix(in srgb, var(--bsplus-cal-accent, var(--better-main, #3b82f6)) 55%, transparent);
-    background: color-mix(in srgb, var(--bsplus-cal-accent, var(--better-main, #3b82f6)) 10%, transparent);
+    background: color-mix(in srgb, var(--bsplus-cal-accent, var(--better-main, #3b82f6)) 14%, transparent) !important;
   }
 
-  .bsplus-cal-trigger--connected {
-    border-color: color-mix(in srgb, #22c55e 50%, transparent);
+  .bsplus-cal-trigger--connected .bsplus-cal-status-dot {
+    display: block;
   }
 
   .bsplus-cal-trigger--busy {
@@ -501,45 +613,61 @@
 
   .bsplus-cal-status-dot {
     position: absolute;
-    top: 7px;
-    right: 26px;
+    top: 4px;
+    right: 4px;
     width: 7px;
     height: 7px;
     border-radius: 999px;
     background: #22c55e;
     box-shadow: 0 0 0 2px var(--bsplus-cal-surface, #fff);
+    display: none;
   }
 
-  .bsplus-cal-chevron {
+  .bsplus-cal-settings {
+    margin: 8px 0 10px;
+    padding: 10px;
+    border-radius: 10px;
+    border: 1px solid var(--bsplus-cal-border, color-mix(in srgb, var(--bsplus-cal-text) 12%, transparent));
+    background: color-mix(in srgb, var(--bsplus-cal-surface, #fff) 92%, transparent);
+    display: grid;
+    gap: 8px;
+  }
+
+  .bsplus-cal-setting {
     display: flex;
-    flex: 0 0 auto;
+    align-items: center;
+    justify-content: space-between;
+    gap: 10px;
+    font-size: 12px;
+  }
+
+  .bsplus-cal-setting-label {
+    font-weight: 600;
+    color: var(--bsplus-cal-text, var(--text-primary, #111));
+  }
+
+  .bsplus-cal-setting-input {
+    width: 64px;
+    padding: 6px 8px;
+    border-radius: 10px;
+    border: 1px solid var(--bsplus-cal-border, color-mix(in srgb, var(--bsplus-cal-text) 18%, transparent));
+    background: var(--bsplus-cal-surface, #fff);
+    color: var(--bsplus-cal-text, var(--text-primary, #111));
+    font-size: 12px;
+    text-align: center;
+  }
+
+  .bsplus-cal-setting-checkbox {
     width: 16px;
     height: 16px;
-    margin-left: auto;
-    opacity: 0.6;
-    pointer-events: none;
+    accent-color: var(--bsplus-cal-accent, var(--better-main, #3b82f6));
   }
 
-  .bsplus-cal-chevron svg {
-    width: 100%;
-    height: 100%;
-  }
-
-  .bsplus-cal-spinner {
-    position: absolute;
-    right: 10px;
-    width: 16px;
-    height: 16px;
-    border-radius: 999px;
-    border: 2px solid color-mix(in srgb, var(--bsplus-cal-accent, #3b82f6) 25%, transparent);
-    border-top-color: var(--bsplus-cal-accent, #3b82f6);
-    animation: bsplus-cal-spin 0.7s linear infinite;
-  }
-
-  @keyframes bsplus-cal-spin {
-    to {
-      transform: rotate(360deg);
-    }
+  .bsplus-cal-setting-hint {
+    margin: 0;
+    font-size: 10px;
+    line-height: 1.4;
+    color: color-mix(in srgb, var(--bsplus-cal-text, #111) 58%, transparent);
   }
 
   .bsplus-cal-menu {
diff --git a/src/plugins/built-in/timetable/CalendarSyncProgress.svelte b/src/plugins/built-in/timetable/CalendarSyncProgress.svelte
new file mode 100644
index 00000000..7c7066df
--- /dev/null
+++ b/src/plugins/built-in/timetable/CalendarSyncProgress.svelte
@@ -0,0 +1,67 @@
+<script lang="ts">
+  import type { GoogleCalendarSyncProgress } from "@/seqta/utils/googleCalendar/types";
+
+  let {
+    progress = null,
+  } = $props<{
+    progress?: GoogleCalendarSyncProgress | null;
+  }>();
+
+  const percent = $derived(
+    progress && progress.total > 0
+      ? Math.min(100, Math.round((progress.current / progress.total) * 100))
+      : progress?.phase === "preparing"
+        ? 8
+        : 0,
+  );
+</script>
+
+{#if progress && progress.phase !== "done"}
+  <div class="bsplus-cal-progress" role="status" aria-live="polite" aria-busy="true">
+    <div class="bsplus-cal-progress-label">{progress.message}</div>
+    <div class="bsplus-cal-progress-track" aria-hidden="true">
+      <div class="bsplus-cal-progress-bar" style:width={`${percent}%`}></div>
+    </div>
+    {#if progress.total > 0}
+      <div class="bsplus-cal-progress-meta">{progress.current} / {progress.total}</div>
+    {/if}
+  </div>
+{/if}
+
+<style>
+  .bsplus-cal-progress {
+    margin-top: 8px;
+    padding: 10px;
+    border-radius: 10px;
+    background: color-mix(in srgb, var(--bsplus-cal-accent, var(--better-main, #3b82f6)) 10%, transparent);
+    border: 1px solid color-mix(in srgb, var(--bsplus-cal-accent, var(--better-main, #3b82f6)) 22%, transparent);
+  }
+
+  .bsplus-cal-progress-label {
+    font-size: 11px;
+    font-weight: 600;
+    color: var(--bsplus-cal-text, var(--text-primary, #111));
+    margin-bottom: 8px;
+  }
+
+  .bsplus-cal-progress-track {
+    height: 8px;
+    border-radius: 999px;
+    overflow: hidden;
+    background: color-mix(in srgb, var(--bsplus-cal-text, #111) 10%, transparent);
+  }
+
+  .bsplus-cal-progress-bar {
+    height: 100%;
+    border-radius: 999px;
+    background: var(--bsplus-cal-accent, var(--better-main, #3b82f6));
+    transition: width 0.25s ease;
+  }
+
+  .bsplus-cal-progress-meta {
+    margin-top: 6px;
+    font-size: 10px;
+    color: color-mix(in srgb, var(--bsplus-cal-text, #111) 62%, transparent);
+    text-align: right;
+  }
+</style>
diff --git a/src/plugins/built-in/timetable/calendarSyncUi.ts b/src/plugins/built-in/timetable/calendarSyncUi.ts
index a1059bb4..45fa003a 100644
--- a/src/plugins/built-in/timetable/calendarSyncUi.ts
+++ b/src/plugins/built-in/timetable/calendarSyncUi.ts
@@ -1,6 +1,7 @@
 import { mount, unmount } from "svelte";
 import CalendarSyncControl from "./CalendarSyncControl.svelte";
 import { syncCalendarSyncTheme } from "./calendarSyncTheme";
+import { registerGoogleCalendarContentHandlers } from "@/seqta/utils/googleCalendar/calendarSyncListener";
 import hostStyles from "./calendarSyncHost.css?inline";
 
 const CONTROLS_CLASS = "timetable-calendar-controls";
@@ -35,6 +36,7 @@ export async function mountGoogleCalendarButton(): Promise<void> {
   if (!toolbar) return;
 
   ensureHostStyles();
+  registerGoogleCalendarContentHandlers();
 
   const controls = document.createElement("div");
   controls.className = `${CONTROLS_CLASS} bsplus-timetable-control`;
diff --git a/src/seqta/utils/googleCalendar/calendarSyncListener.ts b/src/seqta/utils/googleCalendar/calendarSyncListener.ts
new file mode 100644
index 00000000..5a4911e7
--- /dev/null
+++ b/src/seqta/utils/googleCalendar/calendarSyncListener.ts
@@ -0,0 +1,47 @@
+import browser from "webextension-polyfill";
+import { shouldRunWeeklySync } from "@/seqta/utils/googleCalendar/syncSettings";
+import {
+  formatSyncResultMessage,
+  runGoogleCalendarSync,
+} from "@/seqta/utils/googleCalendar/syncRunner";
+import type { GoogleCalendarSyncResult } from "@/seqta/utils/googleCalendar/types";
+
+let listenerRegistered = false;
+
+export function registerGoogleCalendarContentHandlers(): void {
+  if (listenerRegistered) return;
+  listenerRegistered = true;
+
+  browser.runtime.onMessage.addListener((request, _sender, sendResponse) => {
+    if (request?.type !== "googleCalendarRunWeeklySync") return false;
+    void runGoogleCalendarSync({ mode: "incremental", silent: true })
+      .then((result: GoogleCalendarSyncResult) => sendResponse(result))
+      .catch((err: unknown) => {
+        sendResponse({
+          success: false,
+          error: err instanceof Error ? err.message : "Weekly sync failed",
+        });
+      });
+    return true;
+  });
+}
+
+export async function maybeRunDueWeeklySync(
+  onComplete?: (message: string, isError?: boolean) => void,
+): Promise<void> {
+  if (!(await shouldRunWeeklySync())) return;
+
+  const result = await runGoogleCalendarSync({ mode: "incremental", silent: true });
+  if (!onComplete) return;
+
+  if (!result.success) {
+    onComplete(result.error ?? "Weekly calendar sync failed.", true);
+    return;
+  }
+
+  const changed =
+    (result.created ?? 0) + (result.updated ?? 0) + (result.deleted ?? 0) > 0;
+  if (changed) {
+    onComplete(formatSyncResultMessage(result));
+  }
+}
diff --git a/src/seqta/utils/googleCalendar/eventMapEntry.ts b/src/seqta/utils/googleCalendar/eventMapEntry.ts
new file mode 100644
index 00000000..3428aa4c
--- /dev/null
+++ b/src/seqta/utils/googleCalendar/eventMapEntry.ts
@@ -0,0 +1,29 @@
+export interface GoogleCalendarEventMapEntry {
+  id: string;
+  date: string;
+}
+
+export function normalizeEventMapEntry(
+  value: string | GoogleCalendarEventMapEntry | undefined,
+): GoogleCalendarEventMapEntry | undefined {
+  if (value == null) return undefined;
+  if (typeof value === "string") return { id: value, date: "" };
+  if (typeof value.id === "string" && value.id.length > 0) {
+    return { id: value.id, date: value.date ?? "" };
+  }
+  return undefined;
+}
+
+export function getStoredEventId(
+  value: string | GoogleCalendarEventMapEntry | undefined,
+): string | undefined {
+  return normalizeEventMapEntry(value)?.id;
+}
+
+export function lessonDateFromSeqtaKey(seqtaKey: string): string | undefined {
+  const parts = seqtaKey.split(":");
+  for (const part of parts) {
+    if (/^\d{4}-\d{2}-\d{2}$/.test(part)) return part;
+  }
+  return undefined;
+}
diff --git a/src/seqta/utils/googleCalendar/fetchTimetable.ts b/src/seqta/utils/googleCalendar/fetchTimetable.ts
index 25c97c3e..ffbc0959 100644
--- a/src/seqta/utils/googleCalendar/fetchTimetable.ts
+++ b/src/seqta/utils/googleCalendar/fetchTimetable.ts
@@ -1,17 +1,7 @@
-import { GOOGLE_CALENDAR_SYNC_WEEKS } from "@/config/googleCalendar";
-import { toISODate, weekRangeContaining } from "@/seqta/utils/Loaders/engageParentTimetable";
+import type { SyncDateRange } from "./syncDateRange";
+import { syncWindowRange } from "./syncDateRange";
 import type { SeqtaTimetableLesson } from "./types";
 
-export function syncDateRange(weeksAhead = GOOGLE_CALENDAR_SYNC_WEEKS): {
-  from: string;
-  until: string;
-} {
-  const { from } = weekRangeContaining(new Date());
-  const end = new Date(from + "T12:00:00");
-  end.setDate(end.getDate() + weeksAhead * 7 - 1);
-  return { from, until: toISODate(end) };
-}
-
 async function postSeqtaJson<T>(path: string, body: Record<string, unknown>): Promise<T> {
   const res = await fetch(`${location.origin}${path}`, {
     method: "POST",
@@ -50,8 +40,10 @@ function isEngageParentContext(): boolean {
   );
 }
 
-export async function fetchTimetableForSync(): Promise<SeqtaTimetableLesson[]> {
-  const { from, until } = syncDateRange();
+export async function fetchTimetableLessons(
+  range: SyncDateRange,
+): Promise<SeqtaTimetableLesson[]> {
+  const { from, until } = range;
 
   if (isEngageParentContext()) {
     const listJson = await postSeqtaJson<{ payload?: { id?: string | number }[] }>(
@@ -80,3 +72,9 @@ export async function fetchTimetableForSync(): Promise<SeqtaTimetableLesson[]> {
   );
   return Array.isArray(data?.payload?.items) ? data.payload.items : [];
 }
+
+export async function fetchTimetableForSync(weeksAhead?: number): Promise<SeqtaTimetableLesson[]> {
+  return fetchTimetableLessons(syncWindowRange(weeksAhead));
+}
+
+export { syncWindowRange, trailingWeekRange, droppedWeekRange } from "./syncDateRange";
diff --git a/src/seqta/utils/googleCalendar/storage.ts b/src/seqta/utils/googleCalendar/storage.ts
index 1985d363..68b3bf60 100644
--- a/src/seqta/utils/googleCalendar/storage.ts
+++ b/src/seqta/utils/googleCalendar/storage.ts
@@ -1,4 +1,5 @@
 import browser from "webextension-polyfill";
+import type { GoogleCalendarEventMapEntry } from "./eventMapEntry";
 
 /** Never uploaded to BetterSEQTA Cloud (OAuth tokens + per-device event map). */
 export const BSPLUS_GOOGLE_CALENDAR_STORAGE_KEY = "bsplus_google_calendar";
@@ -9,9 +10,13 @@ export interface GoogleCalendarStoredState {
   expiresAt?: number;
   connectedAt?: number;
   lastSyncAt?: number;
+  lastWeeklySyncAt?: number;
   lastSyncOrigin?: string;
-  /** `${origin}::${seqtaKey}` → Google Calendar event id */
-  eventMap?: Record<string, string>;
+  syncWeeksAhead?: number;
+  autoSyncWeekly?: boolean;
+  pendingWeeklySync?: boolean;
+  /** `${origin}::${seqtaKey}` → Google event id (+ lesson date when known) */
+  eventMap?: Record<string, string | GoogleCalendarEventMapEntry>;
 }
 
 export async function readGoogleCalendarState(): Promise<GoogleCalendarStoredState> {
diff --git a/src/seqta/utils/googleCalendar/syncDateRange.test.ts b/src/seqta/utils/googleCalendar/syncDateRange.test.ts
new file mode 100644
index 00000000..d6b21839
--- /dev/null
+++ b/src/seqta/utils/googleCalendar/syncDateRange.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, it } from "@jest/globals";
+import {
+  droppedWeekRange,
+  syncWindowRange,
+  trailingWeekRange,
+} from "./syncDateRange";
+
+describe("syncDateRange", () => {
+  it("builds a 12-week rolling window from the current week", () => {
+    const range = syncWindowRange(12);
+    expect(range.from <= range.until).toBe(true);
+
+    const start = new Date(`${range.from}T12:00:00`);
+    const end = new Date(`${range.until}T12:00:00`);
+    const days = Math.round((end.getTime() - start.getTime()) / 86_400_000) + 1;
+    expect(days).toBe(12 * 7);
+  });
+
+  it("places the trailing week at the end of the window", () => {
+    const window = syncWindowRange(12);
+    const trailing = trailingWeekRange(12);
+    expect(trailing.from >= window.from).toBe(true);
+    expect(trailing.until <= window.until).toBe(true);
+  });
+
+  it("places the dropped week before the window start", () => {
+    const window = syncWindowRange(12);
+    const dropped = droppedWeekRange(12);
+    expect(dropped.until < window.from).toBe(true);
+  });
+});
diff --git a/src/seqta/utils/googleCalendar/syncDateRange.ts b/src/seqta/utils/googleCalendar/syncDateRange.ts
new file mode 100644
index 00000000..cd9b87ab
--- /dev/null
+++ b/src/seqta/utils/googleCalendar/syncDateRange.ts
@@ -0,0 +1,45 @@
+import {
+  GOOGLE_CALENDAR_SYNC_WEEKS_DEFAULT,
+} from "@/config/googleCalendar";
+import { toISODate, weekRangeContaining } from "@/seqta/utils/Loaders/engageParentTimetable";
+
+export interface SyncDateRange {
+  from: string;
+  until: string;
+}
+
+function parseLocalDate(iso: string): Date {
+  return new Date(`${iso}T12:00:00`);
+}
+
+/** Full rolling sync window from the start of the current week. */
+export function syncWindowRange(weeksAhead = GOOGLE_CALENDAR_SYNC_WEEKS_DEFAULT): SyncDateRange {
+  const { from } = weekRangeContaining(new Date());
+  const end = parseLocalDate(from);
+  end.setDate(end.getDate() + weeksAhead * 7 - 1);
+  return { from, until: toISODate(end) };
+}
+
+/** The trailing week at the end of the sync window (added each weekly roll). */
+export function trailingWeekRange(weeksAhead = GOOGLE_CALENDAR_SYNC_WEEKS_DEFAULT): SyncDateRange {
+  const { from: windowStart } = syncWindowRange(weeksAhead);
+  const start = parseLocalDate(windowStart);
+  start.setDate(start.getDate() + (weeksAhead - 1) * 7);
+  const end = new Date(start);
+  end.setDate(end.getDate() + 6);
+  return { from: toISODate(start), until: toISODate(end) };
+}
+
+/** The week that rolled off when the window advances (removed each weekly roll). */
+export function droppedWeekRange(weeksAhead = GOOGLE_CALENDAR_SYNC_WEEKS_DEFAULT): SyncDateRange {
+  const { from: windowStart } = syncWindowRange(weeksAhead);
+  const end = parseLocalDate(windowStart);
+  end.setDate(end.getDate() - 1);
+  const start = new Date(end);
+  start.setDate(start.getDate() - 6);
+  return { from: toISODate(start), until: toISODate(end) };
+}
+
+export function isDateInRange(date: string, range: SyncDateRange): boolean {
+  return date >= range.from && date <= range.until;
+}
diff --git a/src/seqta/utils/googleCalendar/syncEngine.test.ts b/src/seqta/utils/googleCalendar/syncEngine.test.ts
new file mode 100644
index 00000000..40eb921b
--- /dev/null
+++ b/src/seqta/utils/googleCalendar/syncEngine.test.ts
@@ -0,0 +1,139 @@
+import { beforeEach, describe, expect, it, jest } from "@jest/globals";
+import type { SeqtaTimetableLesson } from "./types";
+
+jest.mock("@/config/googleCalendar", () => ({
+  isGoogleCalendarConfigured: jest.fn(() => true),
+}));
+
+jest.mock("@/utils/verboseLog", () => ({
+  verboseLog: jest.fn(),
+}));
+
+jest.mock("@/seqta/utils/googleCalendar/storage", () => ({
+  eventMapKey: (origin: string, seqtaKey: string) => `${origin}::${seqtaKey}`,
+  readGoogleCalendarState: jest.fn(),
+  writeGoogleCalendarState: jest.fn(async (patch: unknown) => patch),
+}));
+
+jest.mock("@/seqta/utils/googleCalendar/syncSettings", () => ({
+  getSyncWeeksAhead: jest.fn(async () => 12),
+}));
+
+jest.mock("@/seqta/utils/googleCalendar/upsertEvent", () => ({
+  upsertGoogleCalendarEvent: jest.fn(),
+  deleteGoogleCalendarEvent: jest.fn(),
+}));
+
+import { readGoogleCalendarState } from "@/seqta/utils/googleCalendar/storage";
+import {
+  deleteGoogleCalendarEvent,
+  upsertGoogleCalendarEvent,
+} from "@/seqta/utils/googleCalendar/upsertEvent";
+import { deleteSyncedEventsFromGoogleCalendar, syncLessonsToGoogleCalendar } from "./syncEngine";
+
+const ORIGIN = "https://school.seqta.com.au";
+const getAccessToken = async () => "test-token";
+
+const baseLesson: SeqtaTimetableLesson = {
+  date: "2026-06-27",
+  from: "09:00:00",
+  until: "10:00:00",
+  description: "10 Mathematics",
+  staff: "Mr Smith",
+  room: "MA1",
+  code: "10MAT",
+  type: "class",
+  calendarid: 12345,
+};
+
+describe("syncLessonsToGoogleCalendar", () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    jest.mocked(readGoogleCalendarState).mockResolvedValue({
+      refreshToken: "refresh",
+      eventMap: {
+        [`${ORIGIN}::${ORIGIN}:cal:12345`]: { id: "google-existing", date: "2026-06-27" },
+        [`${ORIGIN}::${ORIGIN}:cal:99999`]: { id: "google-stale", date: "2020-01-06" },
+      },
+    });
+    jest.mocked(upsertGoogleCalendarEvent).mockResolvedValue("google-existing");
+    jest.mocked(deleteGoogleCalendarEvent).mockResolvedValue(undefined);
+  });
+
+  it("updates existing events and removes stale tracked events on full sync", async () => {
+    const result = await syncLessonsToGoogleCalendar(
+      { origin: ORIGIN, lessons: [baseLesson], mode: "full" },
+      getAccessToken,
+    );
+
+    expect(deleteGoogleCalendarEvent).toHaveBeenCalled();
+    expect(upsertGoogleCalendarEvent).toHaveBeenCalledTimes(1);
+    expect(result).toMatchObject({
+      success: true,
+      created: 0,
+      updated: 1,
+      failed: 0,
+    });
+  });
+
+  it("creates events that are not yet tracked", async () => {
+    jest.mocked(readGoogleCalendarState).mockResolvedValue({
+      refreshToken: "refresh",
+      eventMap: {},
+    });
+    jest.mocked(upsertGoogleCalendarEvent).mockResolvedValue("google-new");
+
+    const result = await syncLessonsToGoogleCalendar(
+      { origin: ORIGIN, lessons: [baseLesson], mode: "full" },
+      getAccessToken,
+    );
+
+    expect(deleteGoogleCalendarEvent).not.toHaveBeenCalled();
+    expect(result).toMatchObject({
+      success: true,
+      created: 1,
+      updated: 0,
+      deleted: 0,
+    });
+  });
+
+  it("reports progress while syncing", async () => {
+    const progress: Array<{ phase: string; current: number; total: number }> = [];
+    await syncLessonsToGoogleCalendar(
+      { origin: ORIGIN, lessons: [baseLesson], mode: "full" },
+      getAccessToken,
+      {
+        onProgress: (entry) => progress.push(entry),
+      },
+    );
+
+    expect(progress.some((entry) => entry.phase === "upserting")).toBe(true);
+    expect(progress.at(-1)?.phase).toBe("done");
+  });
+});
+
+describe("deleteSyncedEventsFromGoogleCalendar", () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    jest.mocked(readGoogleCalendarState).mockResolvedValue({
+      refreshToken: "refresh",
+      eventMap: {
+        [`${ORIGIN}::${ORIGIN}:cal:12345`]: { id: "google-1", date: "2026-06-27" },
+        [`${ORIGIN}::${ORIGIN}:cal:99999`]: { id: "google-2", date: "2026-06-28" },
+        "https://other.seqta.com.au::other:key": { id: "google-other", date: "2026-06-28" },
+      },
+    });
+    jest.mocked(deleteGoogleCalendarEvent).mockResolvedValue(undefined);
+  });
+
+  it("deletes only events for the requested origin", async () => {
+    const result = await deleteSyncedEventsFromGoogleCalendar(ORIGIN, getAccessToken);
+
+    expect(deleteGoogleCalendarEvent).toHaveBeenCalledTimes(2);
+    expect(result).toMatchObject({
+      success: true,
+      deleted: 2,
+      failed: 0,
+    });
+  });
+});
diff --git a/src/seqta/utils/googleCalendar/syncEngine.ts b/src/seqta/utils/googleCalendar/syncEngine.ts
index 9ee4045b..503be74a 100644
--- a/src/seqta/utils/googleCalendar/syncEngine.ts
+++ b/src/seqta/utils/googleCalendar/syncEngine.ts
@@ -1,20 +1,154 @@
 import { verboseLog } from "@/utils/verboseLog";
 import { isGoogleCalendarConfigured } from "@/config/googleCalendar";
 import { googleApiEventBody, mapLessonsToGoogleEvents } from "@/seqta/utils/googleCalendar/eventMapper";
+import {
+  getStoredEventId,
+  lessonDateFromSeqtaKey,
+  normalizeEventMapEntry,
+} from "@/seqta/utils/googleCalendar/eventMapEntry";
+import {
+  droppedWeekRange,
+  isDateInRange,
+  syncWindowRange,
+} from "@/seqta/utils/googleCalendar/syncDateRange";
+import { getSyncWeeksAhead } from "@/seqta/utils/googleCalendar/syncSettings";
 import {
   eventMapKey,
   readGoogleCalendarState,
   writeGoogleCalendarState,
 } from "@/seqta/utils/googleCalendar/storage";
-import type { GoogleCalendarSyncRequest, GoogleCalendarSyncResult } from "@/seqta/utils/googleCalendar/types";
-import { upsertGoogleCalendarEvent } from "@/seqta/utils/googleCalendar/upsertEvent";
+import type {
+  GoogleCalendarDeleteResult,
+  GoogleCalendarSyncOptions,
+  GoogleCalendarSyncProgress,
+  GoogleCalendarSyncRequest,
+  GoogleCalendarSyncResult,
+} from "@/seqta/utils/googleCalendar/types";
+import {
+  deleteGoogleCalendarEvent,
+  upsertGoogleCalendarEvent,
+} from "@/seqta/utils/googleCalendar/upsertEvent";
 
 const EVENT_MAP_PERSIST_EVERY = 10;
+const CALENDAR_ID = "primary";
+
+type DeleteTrackedEventsResult = {
+  deleted: number;
+  failed: number;
+};
+
+function reportProgress(
+  onProgress: GoogleCalendarSyncOptions["onProgress"],
+  progress: GoogleCalendarSyncProgress,
+) {
+  onProgress?.(progress);
+}
+
+function lessonDateForEvent(startDateTime: string, seqtaKey: string): string {
+  return startDateTime.slice(0, 10) || lessonDateFromSeqtaKey(seqtaKey) || "";
+}
+
+async function deleteTrackedEventsFromGoogle(
+  entries: Array<[string, string]>,
+  eventMap: Record<string, string | { id: string; date: string }>,
+  getAccessToken: () => Promise<string>,
+  persistProgress = false,
+  onProgress?: GoogleCalendarSyncOptions["onProgress"],
+  progressOffset = 0,
+  progressTotal = 0,
+): Promise<DeleteTrackedEventsResult> {
+  if (entries.length === 0) return { deleted: 0, failed: 0 };
+
+  let accessToken = await getAccessToken();
+  let deleted = 0;
+  let failed = 0;
+
+  for (let i = 0; i < entries.length; i++) {
+    const [mapKey, eventId] = entries[i];
+    try {
+      await deleteGoogleCalendarEvent(accessToken, CALENDAR_ID, eventId, async () => {
+        accessToken = await getAccessToken();
+        return accessToken;
+      });
+      delete eventMap[mapKey];
+      deleted += 1;
+
+      reportProgress(onProgress, {
+        phase: "deleting",
+        current: progressOffset + deleted + failed,
+        total: progressTotal,
+        message: `Removing old events (${deleted + failed}/${entries.length})…`,
+      });
+
+      if (persistProgress && (deleted + failed) % EVENT_MAP_PERSIST_EVERY === 0) {
+        await writeGoogleCalendarState({ eventMap });
+      }
+    } catch (err) {
+      verboseLog("[BetterSEQTA+] Google Calendar event delete failed:", err);
+      failed += 1;
+      reportProgress(onProgress, {
+        phase: "deleting",
+        current: progressOffset + deleted + failed,
+        total: progressTotal,
+        message: `Removing old events (${deleted + failed}/${entries.length})…`,
+      });
+    }
+  }
+
+  return { deleted, failed };
+}
+
+function originEventMapEntries(
+  eventMap: Record<string, string | { id: string; date: string }>,
+  origin: string,
+): Array<[string, string]> {
+  const prefix = `${origin}::`;
+  const entries: Array<[string, string]> = [];
+  for (const [key, value] of Object.entries(eventMap)) {
+    if (!key.startsWith(prefix)) continue;
+    const id = getStoredEventId(value);
+    if (id) entries.push([key, id]);
+  }
+  return entries;
+}
+
+function entriesToPrune(
+  eventMap: Record<string, string | { id: string; date: string }>,
+  origin: string,
+  mode: "full" | "incremental",
+  weeksAhead: number,
+  currentMapKeys: Set<string>,
+): Array<[string, string]> {
+  const window = syncWindowRange(weeksAhead);
+  const dropped = droppedWeekRange(weeksAhead);
+  const prefix = `${origin}::`;
+  const entries: Array<[string, string]> = [];
+
+  for (const [mapKey, raw] of Object.entries(eventMap)) {
+    if (!mapKey.startsWith(prefix)) continue;
+    const entry = normalizeEventMapEntry(raw);
+    if (!entry) continue;
+
+    let shouldDelete = false;
+    if (mode === "incremental") {
+      shouldDelete = !!entry.date && isDateInRange(entry.date, dropped);
+    } else if (entry.date) {
+      shouldDelete = !isDateInRange(entry.date, window);
+    } else {
+      shouldDelete = !currentMapKeys.has(mapKey);
+    }
+
+    if (shouldDelete) entries.push([mapKey, entry.id]);
+  }
+
+  return entries;
+}
 
 /** Runs in the content script tab so long syncs are not killed by the MV3 service worker. */
 export async function syncLessonsToGoogleCalendar(
   request: GoogleCalendarSyncRequest,
   getAccessToken: () => Promise<string>,
+  options: GoogleCalendarSyncOptions = {},
 ): Promise<GoogleCalendarSyncResult> {
   if (!isGoogleCalendarConfigured()) {
     return {
@@ -29,9 +163,12 @@ export async function syncLessonsToGoogleCalendar(
     return { success: false, configured: true, connected: false, error: "Connect Google Calendar first." };
   }
 
+  const mode = request.mode ?? "full";
+  const weeksAhead = request.weeksAhead ?? (await getSyncWeeksAhead());
   const timeZone = Intl.DateTimeFormat().resolvedOptions().timeZone || "UTC";
   const events = mapLessonsToGoogleEvents(request.origin, request.lessons, timeZone);
-  if (events.length === 0) {
+
+  if (events.length === 0 && mode === "full") {
     return {
       success: false,
       configured: true,
@@ -40,23 +177,42 @@ export async function syncLessonsToGoogleCalendar(
     };
   }
 
+  reportProgress(options.onProgress, {
+    phase: "preparing",
+    current: 0,
+    total: Math.max(events.length, 1),
+    message: mode === "incremental" ? "Preparing weekly sync…" : "Preparing sync…",
+  });
+
   let accessToken = await getAccessToken();
-  const calendarId = "primary";
   const eventMap = { ...(state.eventMap ?? {}) };
+  const currentMapKeys = new Set(events.map((event) => eventMapKey(request.origin, event.seqtaKey)));
+  const staleEntries = entriesToPrune(eventMap, request.origin, mode, weeksAhead, currentMapKeys);
+  const totalSteps = staleEntries.length + events.length;
+
+  const staleResult = await deleteTrackedEventsFromGoogle(
+    staleEntries,
+    eventMap,
+    getAccessToken,
+    false,
+    options.onProgress,
+    0,
+    totalSteps,
+  );
 
   let created = 0;
   let updated = 0;
-  let failed = 0;
+  let failed = staleResult.failed;
   const lastSyncAt = Date.now();
 
   for (let i = 0; i < events.length; i++) {
     const event = events[i];
     const mapKey = eventMapKey(request.origin, event.seqtaKey);
-    const existingId = eventMap[mapKey];
+    const existingId = getStoredEventId(eventMap[mapKey]);
     try {
       const googleId = await upsertGoogleCalendarEvent(
         accessToken,
-        calendarId,
+        CALENDAR_ID,
         existingId,
         googleApiEventBody(event),
         async () => {
@@ -66,7 +222,17 @@ export async function syncLessonsToGoogleCalendar(
       );
       if (existingId) updated += 1;
       else created += 1;
-      eventMap[mapKey] = googleId;
+      eventMap[mapKey] = {
+        id: googleId,
+        date: lessonDateForEvent(event.startDateTime, event.seqtaKey),
+      };
+
+      reportProgress(options.onProgress, {
+        phase: "upserting",
+        current: staleEntries.length + i + 1,
+        total: totalSteps,
+        message: `Syncing events (${i + 1}/${events.length})…`,
+      });
 
       if ((i + 1) % EVENT_MAP_PERSIST_EVERY === 0 || i === events.length - 1) {
         await writeGoogleCalendarState({
@@ -78,15 +244,37 @@ export async function syncLessonsToGoogleCalendar(
     } catch (err) {
       verboseLog("[BetterSEQTA+] Google Calendar event sync failed:", err);
       failed += 1;
+      reportProgress(options.onProgress, {
+        phase: "upserting",
+        current: staleEntries.length + i + 1,
+        total: totalSteps,
+        message: `Syncing events (${i + 1}/${events.length})…`,
+      });
     }
   }
 
-  const syncResult: GoogleCalendarSyncResult = {
+  if (staleResult.deleted > 0 || staleEntries.length > 0 || events.length > 0) {
+    await writeGoogleCalendarState({
+      eventMap,
+      lastSyncAt,
+      lastSyncOrigin: request.origin,
+    });
+  }
+
+  reportProgress(options.onProgress, {
+    phase: "done",
+    current: totalSteps,
+    total: totalSteps,
+    message: "Sync complete",
+  });
+
+  return {
     success: failed === 0,
     configured: true,
     connected: true,
     created,
     updated,
+    deleted: staleResult.deleted,
     skipped: 0,
     failed,
     lastSyncAt,
@@ -95,6 +283,68 @@ export async function syncLessonsToGoogleCalendar(
         ? `Synced with ${failed} error${failed === 1 ? "" : "s"}. Check the console for details.`
         : undefined,
   };
-
-  return syncResult;
+}
+
+/** Delete all tracked BetterSEQTA+ events for this SEQTA origin from Google Calendar. */
+export async function deleteSyncedEventsFromGoogleCalendar(
+  origin: string,
+  getAccessToken: () => Promise<string>,
+  options: GoogleCalendarSyncOptions = {},
+): Promise<GoogleCalendarDeleteResult> {
+  if (!isGoogleCalendarConfigured()) {
+    return {
+      success: false,
+      configured: false,
+      error: "Google Calendar is not configured in this extension build.",
+    };
+  }
+
+  const state = await readGoogleCalendarState();
+  if (!state.refreshToken && !state.accessToken) {
+    return { success: false, configured: true, connected: false, error: "Connect Google Calendar first." };
+  }
+
+  const entries = originEventMapEntries(state.eventMap ?? {}, origin);
+  if (entries.length === 0) {
+    return { success: true, configured: true, connected: true, deleted: 0, failed: 0 };
+  }
+
+  reportProgress(options.onProgress, {
+    phase: "preparing",
+    current: 0,
+    total: entries.length,
+    message: "Preparing removal…",
+  });
+
+  const eventMap = { ...(state.eventMap ?? {}) };
+  const { deleted, failed } = await deleteTrackedEventsFromGoogle(
+    entries,
+    eventMap,
+    getAccessToken,
+    true,
+    options.onProgress,
+    0,
+    entries.length,
+  );
+
+  await writeGoogleCalendarState({ eventMap });
+
+  reportProgress(options.onProgress, {
+    phase: "done",
+    current: entries.length,
+    total: entries.length,
+    message: "Removal complete",
+  });
+
+  return {
+    success: failed === 0,
+    configured: true,
+    connected: true,
+    deleted,
+    failed,
+    error:
+      failed > 0
+        ? `Removed ${deleted} event${deleted === 1 ? "" : "s"} with ${failed} error${failed === 1 ? "" : "s"}.`
+        : undefined,
+  };
 }
diff --git a/src/seqta/utils/googleCalendar/syncRunner.ts b/src/seqta/utils/googleCalendar/syncRunner.ts
new file mode 100644
index 00000000..d3c80543
--- /dev/null
+++ b/src/seqta/utils/googleCalendar/syncRunner.ts
@@ -0,0 +1,83 @@
+import browser from "webextension-polyfill";
+import {
+  fetchTimetableForSync,
+  fetchTimetableLessons,
+  trailingWeekRange,
+} from "@/seqta/utils/googleCalendar/fetchTimetable";
+import {
+  getSyncWeeksAhead,
+  markWeeklySyncComplete,
+} from "@/seqta/utils/googleCalendar/syncSettings";
+import { syncLessonsToGoogleCalendar } from "@/seqta/utils/googleCalendar/syncEngine";
+import type {
+  GoogleCalendarSyncOptions,
+  GoogleCalendarSyncProgress,
+  GoogleCalendarSyncResult,
+} from "@/seqta/utils/googleCalendar/types";
+
+export type GoogleCalendarRunMode = "full" | "incremental";
+
+export interface RunGoogleCalendarSyncParams {
+  mode?: GoogleCalendarRunMode;
+  silent?: boolean;
+  onProgress?: (progress: GoogleCalendarSyncProgress) => void;
+}
+
+async function getAccessTokenFromBackground(): Promise<string> {
+  const res = (await browser.runtime.sendMessage({
+    type: "googleCalendarGetAccessToken",
+  })) as { success?: boolean; accessToken?: string; error?: string };
+  if (!res?.success || !res.accessToken) {
+    throw new Error(res?.error ?? "Could not get Google Calendar access token.");
+  }
+  return res.accessToken;
+}
+
+export async function runGoogleCalendarSync(
+  params: RunGoogleCalendarSyncParams = {},
+): Promise<GoogleCalendarSyncResult> {
+  const mode = params.mode ?? "full";
+  const weeksAhead = await getSyncWeeksAhead();
+
+  params.onProgress?.({
+    phase: "preparing",
+    current: 0,
+    total: 1,
+    message: mode === "incremental" ? "Fetching new week…" : "Fetching timetable…",
+  });
+
+  const lessons =
+    mode === "incremental"
+      ? await fetchTimetableLessons(trailingWeekRange(weeksAhead))
+      : await fetchTimetableForSync(weeksAhead);
+
+  const options: GoogleCalendarSyncOptions = { onProgress: params.onProgress };
+  const result = await syncLessonsToGoogleCalendar(
+    {
+      origin: location.origin,
+      lessons,
+      mode,
+      weeksAhead,
+    },
+    getAccessTokenFromBackground,
+    options,
+  );
+
+  if (result.success && mode === "incremental") {
+    await markWeeklySyncComplete();
+  }
+
+  return result;
+}
+
+export function formatSyncResultMessage(result: GoogleCalendarSyncResult): string {
+  const created = result.created ?? 0;
+  const updated = result.updated ?? 0;
+  const deleted = result.deleted ?? 0;
+  const parts: string[] = [];
+  if (created > 0) parts.push(`${created} new`);
+  if (updated > 0) parts.push(`${updated} updated`);
+  if (deleted > 0) parts.push(`${deleted} removed`);
+  if (parts.length === 0) return "Google Calendar is up to date.";
+  return `Google Calendar updated (${parts.join(", ")}).`;
+}
diff --git a/src/seqta/utils/googleCalendar/syncSettings.ts b/src/seqta/utils/googleCalendar/syncSettings.ts
new file mode 100644
index 00000000..492685ec
--- /dev/null
+++ b/src/seqta/utils/googleCalendar/syncSettings.ts
@@ -0,0 +1,57 @@
+import {
+  GOOGLE_CALENDAR_SYNC_WEEKS_DEFAULT,
+  GOOGLE_CALENDAR_SYNC_WEEKS_MAX,
+  GOOGLE_CALENDAR_SYNC_WEEKS_MIN,
+} from "@/config/googleCalendar";
+import { readGoogleCalendarState, writeGoogleCalendarState } from "./storage";
+
+export const GOOGLE_CALENDAR_WEEKLY_ALARM = "bsplus_google_calendar_weekly";
+export const WEEKLY_SYNC_INTERVAL_MS = 7 * 24 * 60 * 60 * 1000;
+
+export function clampSyncWeeks(weeks: number): number {
+  if (!Number.isFinite(weeks)) return GOOGLE_CALENDAR_SYNC_WEEKS_DEFAULT;
+  return Math.min(
+    GOOGLE_CALENDAR_SYNC_WEEKS_MAX,
+    Math.max(GOOGLE_CALENDAR_SYNC_WEEKS_MIN, Math.round(weeks)),
+  );
+}
+
+export async function getSyncWeeksAhead(): Promise<number> {
+  const state = await readGoogleCalendarState();
+  return clampSyncWeeks(state.syncWeeksAhead ?? GOOGLE_CALENDAR_SYNC_WEEKS_DEFAULT);
+}
+
+export async function setSyncWeeksAhead(weeks: number): Promise<number> {
+  const syncWeeksAhead = clampSyncWeeks(weeks);
+  await writeGoogleCalendarState({ syncWeeksAhead });
+  return syncWeeksAhead;
+}
+
+export async function getAutoSyncWeekly(): Promise<boolean> {
+  const state = await readGoogleCalendarState();
+  return state.autoSyncWeekly !== false;
+}
+
+export async function setAutoSyncWeekly(enabled: boolean): Promise<void> {
+  await writeGoogleCalendarState({ autoSyncWeekly: enabled });
+}
+
+export async function shouldRunWeeklySync(): Promise<boolean> {
+  const state = await readGoogleCalendarState();
+  if (!state.refreshToken && !state.accessToken) return false;
+  if (state.autoSyncWeekly === false) return false;
+  if (state.pendingWeeklySync) return true;
+  const last = state.lastWeeklySyncAt ?? state.lastSyncAt ?? 0;
+  return Date.now() - last >= WEEKLY_SYNC_INTERVAL_MS;
+}
+
+export async function markWeeklySyncComplete(): Promise<void> {
+  await writeGoogleCalendarState({
+    lastWeeklySyncAt: Date.now(),
+    pendingWeeklySync: false,
+  });
+}
+
+export async function markWeeklySyncPending(): Promise<void> {
+  await writeGoogleCalendarState({ pendingWeeklySync: true });
+}
diff --git a/src/seqta/utils/googleCalendar/types.ts b/src/seqta/utils/googleCalendar/types.ts
index cd645a3d..c7c14465 100644
--- a/src/seqta/utils/googleCalendar/types.ts
+++ b/src/seqta/utils/googleCalendar/types.ts
@@ -25,6 +25,21 @@ export interface GoogleCalendarEventInput {
 export interface GoogleCalendarSyncRequest {
   origin: string;
   lessons: SeqtaTimetableLesson[];
+  mode?: "full" | "incremental";
+  weeksAhead?: number;
+}
+
+export type GoogleCalendarSyncPhase = "preparing" | "deleting" | "upserting" | "done";
+
+export interface GoogleCalendarSyncProgress {
+  phase: GoogleCalendarSyncPhase;
+  current: number;
+  total: number;
+  message: string;
+}
+
+export interface GoogleCalendarSyncOptions {
+  onProgress?: (progress: GoogleCalendarSyncProgress) => void;
 }
 
 export interface GoogleCalendarSyncResult {
@@ -33,6 +48,7 @@ export interface GoogleCalendarSyncResult {
   configured?: boolean;
   created?: number;
   updated?: number;
+  deleted?: number;
   skipped?: number;
   failed?: number;
   lastSyncAt?: number;
@@ -43,5 +59,17 @@ export interface GoogleCalendarStatus {
   configured: boolean;
   connected: boolean;
   lastSyncAt?: number;
+  lastWeeklySyncAt?: number;
   lastSyncOrigin?: string;
+  syncWeeksAhead?: number;
+  autoSyncWeekly?: boolean;
+}
+
+export interface GoogleCalendarDeleteResult {
+  success: boolean;
+  configured?: boolean;
+  connected?: boolean;
+  deleted?: number;
+  failed?: number;
+  error?: string;
 }
diff --git a/src/seqta/utils/googleCalendar/upsertEvent.ts b/src/seqta/utils/googleCalendar/upsertEvent.ts
index 7737ee3c..81a0c7bb 100644
--- a/src/seqta/utils/googleCalendar/upsertEvent.ts
+++ b/src/seqta/utils/googleCalendar/upsertEvent.ts
@@ -42,3 +42,22 @@ export async function upsertGoogleCalendarEvent(
   }
   return json.id;
 }
+
+export async function deleteGoogleCalendarEvent(
+  accessToken: string,
+  calendarId: string,
+  eventId: string,
+  refreshAccessToken?: () => Promise<string>,
+): Promise<void> {
+  const res = await fetch(
+    `${GOOGLE_CALENDAR_API}/calendars/${encodeURIComponent(calendarId)}/events/${encodeURIComponent(eventId)}`,
+    { method: "DELETE", headers: { Authorization: `Bearer ${accessToken}` } },
+  );
+  if (res.status === 401 && refreshAccessToken) {
+    const nextToken = await refreshAccessToken();
+    return deleteGoogleCalendarEvent(nextToken, calendarId, eventId);
+  }
+  if (res.ok || res.status === 404 || res.status === 410) return;
+  const err = (await res.json().catch(() => ({}))) as { error?: { message?: string } };
+  throw new Error(err?.error?.message ?? `Google Calendar delete failed (${res.status})`);
+}