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feat: add an in-app keyboard widget for import mnemonic
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‎lib/core/utils/bip39.dart‎

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@@ -23,4 +23,36 @@ class Bip39WordList {
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return null;
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}
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}
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/// The letters that can extend [prefix] toward at least one word of
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/// [language].
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///
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/// This is what lets the in-app keyboard shrink to only the keys that keep a
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/// word possible: an empty prefix yields every letter some word begins with
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/// (so a letter no word starts with is never offered), and a prefix like
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/// `'a'` excludes `'a'` itself because no wordlist word starts with `'aa'`.
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/// A prefix that is already a complete word with no longer word extending it
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/// yields the empty set — the keyboard then offers backspace only.
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///
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/// Deliberately answered against the **whole** wordlist even when used on the
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/// last field: narrowing to the checksum candidates would let an earlier typo
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/// that happens to be another valid word hide the real last word, turning the
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/// one error the checksum exists to catch into a silently restored wrong
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/// wallet. The candidate narrowing stays a guidance-only concern of the
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/// suggestion chips.
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///
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/// A linear scan of the 2048-word list per keystroke is negligible, so no
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/// trie is warranted.
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static Set<String> allowedNextLetters({
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required String prefix,
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bip39.Language language = bip39.Language.english,
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}) {
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final letters = <String>{};
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for (final word in language.list) {
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if (word.length > prefix.length && word.startsWith(prefix)) {
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letters.add(word[prefix.length]);
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}
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}
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return letters;
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}
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}

‎lib/core/widgets/mnemonic_keyboard.dart‎

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import 'package:bb_mobile/core/themes/app_theme.dart';
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import 'package:bb_mobile/core/widgets/text/text.dart';
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import 'package:flutter/material.dart';
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/// Letters-only keyboard for mnemonic entry.
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///
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/// It exists to keep the recovery phrase off the platform IME: on the seed
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/// entry screen the word fields are read-only, and this widget is the only
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/// path from a tap to a character. A third-party keyboard, the OS
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/// autocorrect cache, and any accessibility keylogger therefore never see a
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/// keystroke of the seed.
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///
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/// Deliberately dumb: it knows nothing about BIP39. It renders the 26 letters
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/// of [layout] in three rows, enables a key only when its letter is in
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/// [enabledLetters], and reports taps through [onLetter] / [onBackspace]. All
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/// the wordlist intelligence — which letters keep a word possible, auto fill,
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/// focus advance — stays with the owner that computes [enabledLetters].
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///
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/// [layout] is just the display order: pass [qwerty] for a familiar keyboard,
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/// or a shuffled alphabet for the paranoid mode, where randomised key
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/// positions defeat shoulder-surfing and tap-position inference.
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class MnemonicKeyboard extends StatelessWidget {
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/// A familiar QWERTY order, split 10 / 9 / 7 across the three rows.
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static const List<String> qwerty = [
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'q', 'w', 'e', 'r', 't', 'y', 'u', 'i', 'o', 'p', //
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'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l', //
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'z', 'x', 'c', 'v', 'b', 'n', 'm', //
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];
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/// The 26 lowercase letters in display order. Split 10 / 9 / 7 into rows.
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final List<String> layout;
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/// The lowercase letters a tap may currently produce. A key outside this set
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/// is shown disabled: the owner has determined it cannot extend the word.
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final Set<String> enabledLetters;
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/// Whether the backspace key is active — false only when the focused field
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/// is already empty, so there is nothing to delete.
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final bool canBackspace;
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final void Function(String letter) onLetter;
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final VoidCallback onBackspace;
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/// Paranoid mode toggle, shown as a key next to backspace.
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final bool shuffleActive;
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final VoidCallback onToggleShuffle;
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/// Tooltip for the shuffle key. Passed in so this widget stays free of
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/// localization.
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final String shuffleHint;
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const MnemonicKeyboard({
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super.key,
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required this.enabledLetters,
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required this.canBackspace,
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required this.onLetter,
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required this.onBackspace,
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required this.shuffleActive,
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required this.onToggleShuffle,
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required this.shuffleHint,
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this.layout = qwerty,
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});
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@override
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Widget build(BuildContext context) {
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return Material(
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color: context.appColors.surfaceContainer,
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child: SafeArea(
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top: false,
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child: Padding(
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padding: const EdgeInsets.symmetric(horizontal: 4, vertical: 8),
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child: Column(
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mainAxisSize: MainAxisSize.min,
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children: [
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_LetterRow(
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letters: layout.sublist(0, 10),
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enabledLetters: enabledLetters,
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onLetter: onLetter,
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paranoid: shuffleActive,
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),
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_LetterRow(
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letters: layout.sublist(10, 19),
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enabledLetters: enabledLetters,
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onLetter: onLetter,
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paranoid: shuffleActive,
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),
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_LetterRow(
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letters: layout.sublist(19, 26),
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enabledLetters: enabledLetters,
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onLetter: onLetter,
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paranoid: shuffleActive,
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// Backspace shares its slot with the shuffle toggle
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trailing: Row(
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children: [
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Expanded(
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child: _BackspaceKey(
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enabled: canBackspace,
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onTap: onBackspace,
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),
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),
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Expanded(
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child: _ShuffleKey(
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active: shuffleActive,
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hint: shuffleHint,
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onTap: onToggleShuffle,
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),
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),
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],
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),
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),
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],
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),
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),
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),
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);
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}
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}
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class _LetterRow extends StatelessWidget {
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final List<String> letters;
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final Set<String> enabledLetters;
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final void Function(String letter) onLetter;
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final bool paranoid;
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final Widget? trailing;
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const _LetterRow({
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required this.letters,
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required this.enabledLetters,
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required this.onLetter,
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required this.paranoid,
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this.trailing,
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});
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@override
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Widget build(BuildContext context) {
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return Padding(
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padding: const EdgeInsets.symmetric(vertical: 3),
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child: Row(
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children: [
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for (final letter in letters)
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Expanded(
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child: _LetterKey(
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letter: letter,
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enabled: enabledLetters.contains(letter),
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paranoid: paranoid,
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onTap: () => onLetter(letter),
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),
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),
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if (trailing != null) Expanded(flex: 2, child: trailing!),
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],
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),
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);
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}
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}
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class _LetterKey extends StatelessWidget {
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final String letter;
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final bool enabled;
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final bool paranoid;
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final VoidCallback onTap;
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const _LetterKey({
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required this.letter,
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required this.enabled,
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required this.paranoid,
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required this.onTap,
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});
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@override
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Widget build(BuildContext context) {
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// ExcludeSemantics: the key's letter must not reach the accessibility tree,
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// where a malicious accessibility service would read the seed letter by
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// letter as it is typed. This makes the keyboard unusable with a screen
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// reader by design — the recovery phrase is too sensitive to narrate.
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return ExcludeSemantics(
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child: _KeyCap(
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enabled: enabled,
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onTap: onTap,
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suppressAnimation: paranoid,
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child: BBText(
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letter,
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style: context.font.headlineLarge,
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color: enabled
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? context.appColors.onSurface
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: context.appColors.textMuted,
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),
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),
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);
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}
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}
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class _BackspaceKey extends StatelessWidget {
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final bool enabled;
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final VoidCallback onTap;
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const _BackspaceKey({required this.enabled, required this.onTap});
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@override
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Widget build(BuildContext context) {
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return _KeyCap(
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enabled: enabled,
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onTap: onTap,
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child: Icon(
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Icons.backspace_outlined,
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size: 20,
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color: enabled
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? context.appColors.onSurface
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: context.appColors.textMuted,
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),
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);
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}
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}
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/// Toggles the paranoid, randomised-layout mode. Accent-coloured while active.
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class _ShuffleKey extends StatelessWidget {
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final bool active;
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final String hint;
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final VoidCallback onTap;
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const _ShuffleKey({
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required this.active,
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required this.hint,
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required this.onTap,
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});
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@override
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Widget build(BuildContext context) {
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return Tooltip(
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message: hint,
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child: _KeyCap(
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key: const Key('mnemonicParanoidToggle'),
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enabled: true,
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onTap: onTap,
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child: Icon(
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Icons.shuffle,
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size: 20,
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color: active
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? context.appColors.primary
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: context.appColors.onSurface,
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),
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),
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);
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}
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}
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/// The shared key shell: sizing, colour, and tap surface. A disabled key has
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/// no tap handler at all, so it cannot fire even through automation.
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class _KeyCap extends StatelessWidget {
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final bool enabled;
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final VoidCallback onTap;
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final Widget child;
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/// When true, the key changes appearance as an instant cut with no ink
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/// splash. Used while the layout is reshuffling on every tap: an animated
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/// colour fade or a splash that outlives the reshuffle would mark, for a
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/// frame, which slot was just pressed — letting an observer follow a letter
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/// across the shuffle and defeating it.
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final bool suppressAnimation;
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const _KeyCap({
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super.key,
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required this.enabled,
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required this.onTap,
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required this.child,
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this.suppressAnimation = false,
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});
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@override
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Widget build(BuildContext context) {
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return Padding(
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padding: const EdgeInsets.symmetric(horizontal: 2),
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child: Material(
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// Zero duration: even in basic mode an enable/disable colour tween is
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// an extra frame of state history for a camera; there is no reason to
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// animate a key cap.
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animationDuration: Duration.zero,
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color: enabled
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? context.appColors.surface
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: context.appColors.surfaceContainerHighest,
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borderRadius: BorderRadius.circular(6),
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child: InkWell(
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// A key must never take focus from the word field being typed into.
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canRequestFocus: false,
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borderRadius: BorderRadius.circular(6),
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splashFactory: suppressAnimation ? NoSplash.splashFactory : null,
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highlightColor: suppressAnimation ? Colors.transparent : null,
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onTap: enabled ? onTap : null,
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child: Container(
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height: 44,
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alignment: Alignment.center,
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child: child,
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),
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),
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),
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);
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}
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}

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