SM-2 Spaced Repetition in Deno + Flashcard UI in Flutter Web
What We Built
A language learning feature for θͺεζ ͺεΌδΌη€Ύ competing with Duolingo and Anki:
- SM-2 spaced repetition algorithm (server-side in Deno)
- Flashcard flip UI with progress indicator
- Vocabulary deck management
- Streak tracking (π₯ consecutive days)
- Statistics tab: accuracy rate, total reviews, streak records
SM-2 Algorithm in the Edge Function
The SM-2 algorithm runs server-side in the language-learning Edge Function β not in Dart. This keeps the scheduling logic centralized and testable:
// SM-2 implementation in Deno
function calculateNextReview(
correct: boolean,
quality: number, // 0-5 response quality
interval: number, // current interval in days
ease: number, // ease factor (default 2.5)
): { interval: number; ease: number; nextReview: string } {
if (correct) {
if (interval === 1) interval = 6;
else interval = Math.round(interval * ease);
ease = ease + (0.1 - (5 - quality) * (0.08 + (5 - quality) * 0.02));
if (ease < 1.3) ease = 1.3; // minimum ease factor
} else {
interval = 1; // wrong answer β review again in 1 day
}
const nextReview = new Date(Date.now() + interval * 86400000).toISOString();
return { interval, ease, nextReview };
}
Key SM-2 mechanics:
- First correct answer β 6 days (not 1)
- Subsequent correct β
interval Γ ease(compounding) - Wrong answer β reset to 1 day, ease unchanged
- Ease floor at 1.3 prevents intervals from collapsing to 1 day permanently
Flutter UI: 3-Tab Structure
LanguageLearningPage
βββ Tab 1: Decks
β βββ Streak banner (π₯ N consecutive days)
β βββ Deck list (source language β target language)
β βββ Card list for selected deck
βββ Tab 2: Flashcard Review
β βββ LinearProgressIndicator (current session progress)
β βββ Flashcard (front / back with tap-to-flip)
β βββ "Got it!" / "Review again" buttons
βββ Tab 3: Statistics
βββ Streak (current + personal best)
βββ Stats grid: decks / total cards / total reviews / accuracy %
βββ Study tips card
Flashcard Flip
GestureDetector(
onTap: () => setState(() => _showBack = !_showBack),
child: AnimatedSwitcher(
duration: const Duration(milliseconds: 300),
child: _showBack
? _buildCardBack(_currentCard)
: _buildCardFront(_currentCard),
),
)
AnimatedSwitcher handles the flip animation. _showBack toggles on tap.
unnecessary_const Inside const Context
Inside a const constructor's argument list, inner const keywords are redundant and trigger the unnecessary_const lint:
// WRONG β unnecessary_const lint
const Column(
children: [
const Icon(Icons.book), // redundant const
const Text('Decks'), // redundant const
],
)
// CORRECT β outer const propagates inward
const Column(
children: [
Icon(Icons.book),
Text('Decks'),
],
)
When the outer widget is const, all children are implicitly const β remove the inner const keywords.
require_trailing_commas Pattern
// WRONG β missing trailing comma on multi-line
Text('text', textAlign: TextAlign.center,
style: TextStyle(color: Colors.grey)),
// CORRECT
Text(
'text',
textAlign: TextAlign.center,
style: TextStyle(color: Colors.grey),
),
Every multi-line argument list needs a trailing comma on the last argument. dart format auto-applies this when run with --fix.
Edge Function API Design
GET ?action=decks β deck list
GET ?action=cards&deck_id=xxx β cards due for review
GET ?action=stats β streak, accuracy, review counts
POST {action: "create_deck", ...} β create vocabulary deck
POST {action: "create_card", ...} β add card to deck
POST {action: "review", card_id, quality} β SM-2 update
Flutter:
// Review a card
final res = await _supabase.functions.invoke(
'language-learning',
body: {
'action': 'review',
'card_id': card['id'],
'quality': correct ? 4 : 1, // 4 = good, 1 = again
},
);
final data = res.data as Map<String, dynamic>?;
final nextReview = data?['nextReview'] as String?;
The Edge Function returns the next scheduled review date β the client just shows it. No scheduling logic in Dart.
Why SM-2 Server-Side
If SM-2 runs in Dart:
- Logic can drift across app versions
- Offline edits bypass the scheduling
- Can't batch-recalculate when the algorithm changes
Server-side SM-2: one implementation, one place to fix, no version drift.
Try it: θͺεζ ͺεΌδΌη€Ύ
