This directory contains code shared between frontend and backend.

• types.ts - TypeScript interfaces and spaced repetition algorithm

Code in this directory must work in both environments:

• ✅ Standard JavaScript/TypeScript
• ❌ No Deno-specific APIs (Deno.*)
• ❌ No browser-specific APIs (window, document)
• ✅ Use only standard ES modules

• Deck - Flashcard deck
• Card - Individual flashcard with SR parameters
• StudySession - Completed study session record
• UserStats - Calculated statistics
• UserData - Complete user data structure

• Rating - Enum for card difficulty ratings (1-4)
• ReviewResult - Result of SR calculation

Implements the SM-2 algorithm to determine:

• Next review date
• Updated ease factor
• Updated interval

Checks if a card should be shown for review.

Creates unique IDs for new records.

The SM-2 (SuperMemo 2) algorithm is the foundation of Anki's spaced repetition:

• easeFactor: How "easy" the card is (higher = longer intervals)
• interval: Days until next review
• nextReview: Specific date/time for next review

See ARCHITECTURE.md for full algorithm documentation.