Margin Calendar: a Google Calendar client for desktop and phone

Tauri 2, React 19 and zustand on the front, Rust behind. Rust owns auth,
all HTTP to Google, the SQLite store, the sync loop, recurrence expansion
and timezone maths. TypeScript owns rendering and never talks to Google,
which keeps the content security policy locked to ipc:.

Week, day and agenda views, and no month view: it would be a second layout
engine, and the fit and fold logic that makes a day fit the window without
scrolling is the whole point of the app.

Runs on macOS, Linux, Android and iOS. Desktop catches Google's OAuth
redirect on a loopback port. A phone cannot, and Google rejects loopback
for mobile client types anyway, so it redirects to a custom URI scheme and
needs its own public OAuth clients, which docs/mobile.md covers. Refresh
tokens are sealed with XChaCha20-Poly1305 in the app data directory on
every platform, with no OS credential store in the picture.

On a phone the chrome becomes a top bar and a bottom tab bar, overlays
become sheets, hover affordances become taps, and dragging out an event
waits for a long press. Navigation moves one day at a time everywhere,
a swipe included.

src/store/useAccounts.ts

@@ -0,0 +1,113 @@
+import { create } from "zustand";
+import { openUrl } from "@tauri-apps/plugin-opener";
+import { accountConnect, accountDisconnect, accountsList } from "../api/accounts";
+import { calendarSetSelected, calendarsList } from "../api/calendars";
+import { live, type Account, type Calendar } from "../ipc";
+import { notify } from "./useToast";
+
+type Phase = "idle" | "connecting" | "working" | "error";
+
+interface AccountsState {
+  accounts: Account[];
+  calendars: Calendar[];
+  phase: Phase;
+  error: string | null;
+  authUrl: string | null;
+  resolveConnect: ((ok: boolean) => void) | null;
+  refresh: () => Promise<void>;
+  connect: () => Promise<boolean>;
+  cancelConnect: () => void;
+  handleAuthEvent: (ok: boolean, error: string | null) => Promise<void>;
+  openAuthUrl: () => void;
+  copyAuthUrl: () => Promise<void>;
+  disconnect: (accountId: string) => Promise<void>;
+  setSelected: (calendarId: string, selected: boolean) => Promise<void>;
+}
+
+export const useAccounts = create<AccountsState>((set, get) => ({
+  accounts: [],
+  calendars: [],
+  phase: "idle",
+  error: null,
+  authUrl: null,
+  resolveConnect: null,
+  refresh: async () => {
+    if (!live()) return;
+    try {
+      const [accounts, calendars] = await Promise.all([accountsList(), calendarsList()]);
+      set({ accounts, calendars });
+    } catch (e) {
+      set({ error: String(e) });
+    }
+  },
+  // The promise holds its own resolver so a later Tauri `auth` event can settle it. Ported from
+  // margin/src/store/useBackup.ts:70.
+  connect: () =>
+    new Promise<boolean>((resolve) => {
+      get().resolveConnect?.(false);
+      set({ phase: "connecting", error: null, authUrl: null, resolveConnect: resolve });
+      accountConnect()
+        .then((url) => set({ authUrl: url }))
+        .catch((e) => {
+          set({ phase: "error", error: String(e), resolveConnect: null });
+          notify(`Could not connect: ${e}`);
+          resolve(false);
+        });
+    }),
+  cancelConnect: () => {
+    const resolve = get().resolveConnect;
+    set({ phase: "idle", authUrl: null, resolveConnect: null });
+    resolve?.(false);
+  },
+  handleAuthEvent: async (ok, error) => {
+    if (get().phase !== "connecting") return;
+    const resolve = get().resolveConnect;
+    if (ok) {
+      await get().refresh();
+      set({ phase: "idle", authUrl: null, error: null, resolveConnect: null });
+      notify("Connected to Google Calendar");
+    } else {
+      const message = error ?? "authorization failed";
+      set({ phase: "error", authUrl: null, error: message, resolveConnect: null });
+      notify(`Could not connect: ${message}`);
+    }
+    resolve?.(ok);
+  },
+  openAuthUrl: () => {
+    const url = get().authUrl;
+    if (url) openUrl(url).catch(() => {});
+  },
+  copyAuthUrl: async () => {
+    const url = get().authUrl;
+    if (!url) return;
+    try {
+      await navigator.clipboard.writeText(url);
+      notify("Authorization link copied");
+    } catch {
+      notify("Could not copy the link");
+    }
+  },
+  disconnect: async (accountId) => {
+    set({ phase: "working", error: null });
+    try {
+      await accountDisconnect(accountId);
+      await get().refresh();
+      set({ phase: "idle" });
+      notify("Disconnected");
+    } catch (e) {
+      set({ phase: "error", error: String(e) });
+      notify(`Could not disconnect: ${e}`);
+    }
+  },
+  setSelected: async (calendarId, selected) => {
+    set((s) => ({
+      calendars: s.calendars.map((c) => (c.id === calendarId ? { ...c, selected } : c)),
+    }));
+    try {
+      await calendarSetSelected(calendarId, selected);
+    } catch (e) {
+      await get().refresh();
+      notify(`Could not update the calendar: ${e}`);
+    }
+  },
+}));