first commit

backend/src/lib/prisma.ts

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+import { PrismaClient } from "@prisma/client";
+
+export const prisma = new PrismaClient();

backend/src/lib/sm2.ts

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+// SM-2 spaced repetition algorithm (SuperMemo 2).
+// `quality` is 0-5: 0-2 = failed recall (reset), 3-5 = successful recall (grows interval).
+export interface SM2State {
+  easeFactor: number;
+  intervalDays: number;
+  repetitions: number;
+}
+
+export function sm2(state: SM2State, quality: number): SM2State {
+  const q = Math.max(0, Math.min(5, quality));
+  let { easeFactor, intervalDays, repetitions } = state;
+
+  if (q < 3) {
+    return { easeFactor, intervalDays: 1, repetitions: 0 };
+  }
+
+  repetitions += 1;
+  if (repetitions === 1) intervalDays = 1;
+  else if (repetitions === 2) intervalDays = 6;
+  else intervalDays = Math.round(intervalDays * easeFactor);
+
+  easeFactor = Math.max(
+    1.3,
+    easeFactor + (0.1 - (5 - q) * (0.08 + (5 - q) * 0.02)),
+  );
+
+  return { easeFactor, intervalDays, repetitions };
+}