Use URL-based state management

index.html

@@ -53,7 +53,7 @@
       </ul>
       <p class="card-text">What this tool <strong>can't</strong> do:</p>
       <ul class="card-text">
-        <li>Store your TOTP secrets;</li>
+        <li>Store your TOTP secrets (you can try bookmarking this page with the secret in the URL, but it's not secure);</li>
         <li>Act as your general purpose authenticator app; and</li>
         <li>Scan TOTP QR codes.</li>
       </ul>

src/App.tsx

@@ -3,16 +3,22 @@ import {NumberInput, TextInput} from './Input';
 import OTPOutput, {HashAlgorithm} from './OTPOutput';
 import Select from './Select';
 import Collapsible from './Collapsible';
-import ActionLink from './ActionLink.tsx';
+import ActionLink from './ActionLink';
+import {type State, defaults, serializeState, deserializeState} from './state';
+
+function parseState() {
+  if (window.location.hash.startsWith('#!')) {
+    return deserializeState(window.location.hash.slice(2));
+  }
+  return null;
+}
 
 function App() {
   const [advanced, setAdvanced] = useState(false);
 
-  const [secret, setSecret] = React.useState('');
-  const [step, setStep] = React.useState(30);
+  const [state, setState] = React.useState(() => parseState() || defaults);
+  const {secret, step, digits, algorithm} = state;
   const [offset, setOffset] = React.useState(0);
-  const [digits, setDigits] = React.useState(6);
-  const [algorithm, setAlgorithm] = React.useState<HashAlgorithm>('sha1');
 
   const validStep = step > 0;
   const validDigits = digits > 0 && digits <= 10;
@@ -41,12 +47,47 @@ function App() {
     setAdvanced(false);
   }, []);
 
-  const onReset = React.useCallback(() => {
-    setStep(30);
-    setDigits(6);
-    setAlgorithm('sha1');
+  const setSecret = React.useCallback(
+    (secret: string) => setState((state) => ({...state, secret})),
+    [],
+  );
+
+  const setStep = React.useCallback(
+    (step: number) => setState((state) => ({...state, step})),
+    [],
+  );
+
+  const setDigits = React.useCallback(
+    (digits: number) => setState((state) => ({...state, digits})),
+    [],
+  );
+
+  const setAlgorithm = React.useCallback(
+    (algorithm: string) => setState((state) => ({...state, algorithm})),
+    [],
+  );
+
+  const onReset = React.useCallback(
+    () => setState((state) => ({...state, step: 30, digits: 6, algorithm: 'sha1'})),
+    [],
+  );
+
+  React.useEffect(() => {
+    const value = serializeState(state);
+    console.log(value);
+    history.replaceState(null, '', window.location.pathname + window.location.search + (value && `#!${value}`));
+  }, [state]);
+
+  const onHashChange = React.useCallback(() => {
+    const state = parseState();
+    state && setState(state);
   }, []);
 
+  React.useEffect(() => {
+    window.addEventListener('hashchange', onHashChange);
+    return () => window.removeEventListener('hashchange', onHashChange);
+  }, [onHashChange]);
+
   return (
     <div className="totp-app">
       <div className="totp-settings">

src/OTPOutput.tsx

@@ -4,7 +4,7 @@ import {createDigest} from '@otplib/plugin-crypto-js';
 import classNames from 'classnames';
 import CopyButton from './CopyButton.tsx';
 
-const ALGORITHMS = {
+export const ALGORITHMS = {
   sha1: HashAlgorithms.SHA1,
   sha256: HashAlgorithms.SHA256,
   sha512: HashAlgorithms.SHA512,

src/state.tsx

@@ -0,0 +1,35 @@
+import {ALGORITHMS, HashAlgorithm} from './OTPOutput';
+
+export type State = {
+  secret: string;
+  step: number;
+  digits: number;
+  algorithm: HashAlgorithm;
+};
+
+export const defaults: State = {
+  secret: '',
+  step: 30,
+  digits: 6,
+  algorithm: 'sha1',
+} as const;
+
+export function serializeState(state: State): string {
+  const values = ['secret', 'step', 'digits', 'algorithm'].map(
+    (key) => state[key] !== defaults[key] ? encodeURIComponent(state[key]) : '',
+  );
+  while (values[values.length - 1] === '') {
+    values.pop();
+  }
+  return values.join('/');
+}
+
+export function deserializeState(data: string): State {
+  const values = data.split('/').map(decodeURIComponent);
+  return {
+    secret: values[0] || defaults.secret,
+    step: +values[1] || defaults.step,
+    digits: +values[2] || defaults.digits,
+    algorithm: ALGORITHMS[values[3]] !== undefined ? values[3] : defaults.algorithm,
+  };
+}