feat: Puente Mayúscula-Minúscula + TTS SpeechSynthesis + E2E fixes

lib/fsrs.ts

@@ -0,0 +1,50 @@
+import { fsrs as createFSRS, createEmptyCard, Rating, type Card, type Grade } from "ts-fsrs"
+
+const scheduler = createFSRS({ maximum_interval: 365, request_retention: 0.9 })
+
+export type FsrsGrade = "again" | "hard" | "good" | "easy"
+
+const gradeMap: Record<FsrsGrade, Grade> = {
+  again: Rating.Again,
+  hard: Rating.Hard,
+  good: Rating.Good,
+  easy: Rating.Easy,
+}
+
+export function buildFsrsCard(params: {
+  stability?: number
+  difficulty?: number
+  reps?: number
+  lapses?: number
+  due?: Date
+}): Card {
+  const card = createEmptyCard(params.due ?? new Date())
+  return {
+    ...card,
+    stability: params.stability ?? card.stability,
+    difficulty: params.difficulty ?? card.difficulty,
+    reps: params.reps ?? 0,
+    lapses: params.lapses ?? 0,
+    due: params.due ?? card.due,
+  }
+}
+
+export function gradeCard(card: Card, grade: FsrsGrade, now: Date = new Date()) {
+  const result = scheduler.next(card, now, gradeMap[grade])
+  return {
+    card: result.card,
+    log: result.log,
+  }
+}
+
+export function getRetrievability(card: Card, now: Date = new Date()): number {
+  const r = scheduler.get_retrievability(card, now, false)
+  return typeof r === "number" ? r : parseFloat(r)
+}
+
+export function skillCodeFromGrade(correct: boolean, responseMs: number): FsrsGrade {
+  if (!correct) return "again"
+  if (responseMs > 8000) return "hard"
+  if (responseMs > 4000) return "good"
+  return "easy"
+}