Build an AI Study Assistant for Android

class AskUseCase(private val index: NotesIndex, private val llm: Llm) {

    fun ask(question: String, mode: Mode): Flow<String> = flow {
        val hits = index.search(question, topK = 5)
        if (hits.isEmpty()) { emit("I couldn't find this in your notes. Try importing the relevant chapter."); return@flow }
        val context = hits.joinToString("\n\n") { "[${it.id}] ${it.text}" }
        val style = when (mode) {
            Mode.EXPLAIN -> "Explain step by step for a student, then give one check-your-understanding question."
            Mode.HINT -> "Give a hint only, not the full answer. Encourage the student to try."
        }
        emitAll(llm.stream(
            "You are a study tutor. Use ONLY the notes below. Cite sources like [id]. " +
            "If the notes don't contain the answer, say so.\n$style\n\nNotes:\n$context\n\nQuestion: $question"
        ))
    }
    enum class Mode { EXPLAIN, HINT }
}

@Serializable
data class Question(val prompt: String, val options: List<String>, val correctIndex: Int, val explanation: String)

@Serializable
data class Quiz(val questions: List<Question>)

suspend fun generateQuiz(llm: Llm, chunk: String, count: Int = 5): List<Question> {
    val raw = llm.generateJson(
        "Create $count multiple-choice questions (4 options each) testing understanding of this text. " +
        "Include a one-sentence explanation citing the text. Use only facts in the text.\n\n$chunk"
    )
    return Json { ignoreUnknownKeys = true }.decodeFromString<Quiz>(raw).questions
        .filter { q -> q.options.size == 4 && q.correctIndex in 0..3 && q.options.toSet().size == 4 }
}

@Entity data class Card(
    @PrimaryKey val id: String,
    val front: String, val back: String,
    val intervalDays: Int = 0, val ease: Double = 2.5, val dueAt: Long = 0,
)

fun Card.review(grade: Int, now: Long): Card {       // grade: 0 = forgot, 1 = hard, 2 = good, 3 = easy
    val newEase = (ease + 0.1 - (3 - grade) * 0.08).coerceAtLeast(1.3)
    val newInterval = when {
        grade == 0 -> 1
        intervalDays == 0 -> 1
        intervalDays == 1 -> 3
        else -> (intervalDays * newEase).roundToInt()
    }
    return copy(intervalDays = newInterval, ease = newEase, dueAt = now + newInterval * 86_400_000L)
}