From ae3fcaf9e9f4b0f72d5664eb408291c7a4e6e70b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=A1s=20Hatcher?= <nicolas@theuniverse.today>
Date: Tue, 11 Nov 2025 06:56:45 +0100
Subject: [PATCH] FIX: New workbooks are created in the users TZ falling back
 to UTC

---
 webapp/app.ironcalc.com/frontend/src/App.tsx         |  3 ++-
 .../frontend/src/components/storage.ts               | 12 +++++++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/webapp/app.ironcalc.com/frontend/src/App.tsx b/webapp/app.ironcalc.com/frontend/src/App.tsx
index a55c4c7..402db67 100644
--- a/webapp/app.ironcalc.com/frontend/src/App.tsx
+++ b/webapp/app.ironcalc.com/frontend/src/App.tsx
@@ -10,6 +10,7 @@ import {
   uploadFile,
 } from "./components/rpc";
 import {
+  createModelWithSafeTimezone,
   createNewModel,
   deleteModelByUuid,
   deleteSelectedModel,
@@ -65,7 +66,7 @@ function App() {
         const newModel = loadSelectedModelFromStorage();
         if (!newModel) {
           setShowWelcomeDialog(true);
-          const createdModel = new Model("template", "en", "UTC");
+          const createdModel = createModelWithSafeTimezone();
           setModel(createdModel);
         } else {
           setModel(newModel);
diff --git a/webapp/app.ironcalc.com/frontend/src/components/storage.ts b/webapp/app.ironcalc.com/frontend/src/components/storage.ts
index 7bdb6b2..14833a1 100644
--- a/webapp/app.ironcalc.com/frontend/src/components/storage.ts
+++ b/webapp/app.ironcalc.com/frontend/src/components/storage.ts
@@ -85,11 +85,21 @@ function getNewName(existingNames: string[]): string {
   return "Workbook-Infinity";
 }
 
+export function createModelWithSafeTimezone(): Model {
+  try {
+    const tz = Intl.DateTimeFormat().resolvedOptions().timeZone;
+    return new Model("template", "en", tz);
+  } catch {
+    console.warn("Failed to get timezone, defaulting to UTC");
+    return new Model("template", "en", "UTC");
+  }
+}
+
 export function createNewModel(): Model {
   const models = getModelsMetadata();
   const name = getNewName(Object.values(models).map((m) => m.name));
 
-  const model = new Model(name, "en", "UTC");
+  const model = createModelWithSafeTimezone();
   const uuid = randomUUID();
   localStorage.setItem("selected", uuid);
   localStorage.setItem(uuid, bytesToBase64(model.toBytes()));