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lib/rate-limit.ts

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+import { prisma } from "./prisma";
+
+type RateLimitResult = {
+  ok: boolean;
+  remaining: number;
+  resetAt: Date;
+};
+
+const parseNumber = (value: string | undefined, fallback: number) => {
+  if (!value) return fallback;
+  const parsed = Number(value);
+  return Number.isFinite(parsed) && parsed > 0 ? parsed : fallback;
+};
+
+export const getRateLimitConfig = (envKey: string, defaultLimit: number) => {
+  const limit = parseNumber(process.env[envKey], defaultLimit);
+  const windowMinutes = parseNumber(process.env.RATE_LIMIT_WINDOW_MINUTES, 15);
+  return { limit, windowMs: windowMinutes * 60 * 1000 };
+};
+
+export async function checkRateLimit({
+  key,
+  limit,
+  windowMs
+}: {
+  key: string;
+  limit: number;
+  windowMs: number;
+}): Promise<RateLimitResult> {
+  const now = new Date();
+  const resetAt = new Date(now.getTime() + windowMs);
+
+  const existing = await prisma.rateLimit.findUnique({ where: { key } });
+  if (!existing || existing.resetAt <= now) {
+    await prisma.rateLimit.upsert({
+      where: { key },
+      update: { count: 1, resetAt },
+      create: { key, count: 1, resetAt }
+    });
+    return { ok: true, remaining: Math.max(0, limit - 1), resetAt };
+  }
+
+  if (existing.count >= limit) {
+    return { ok: false, remaining: 0, resetAt: existing.resetAt };
+  }
+
+  const updated = await prisma.rateLimit.update({
+    where: { key },
+    data: { count: { increment: 1 } }
+  });
+
+  return {
+    ok: true,
+    remaining: Math.max(0, limit - updated.count),
+    resetAt: updated.resetAt
+  };
+}