From 10d45e8d14cdc3672cc65dc7f5ae79e63fb2da1a Mon Sep 17 00:00:00 2001
From: Mohamed Bassem <me@mbassem.com>
Date: Sat, 21 Jun 2025 11:32:42 +0000
Subject: fix: Change public image's signed tokens to be time aligned for
 better caching

---
 packages/shared/signedTokens.ts | 42 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 4 deletions(-)

(limited to 'packages/shared/signedTokens.ts')

diff --git a/packages/shared/signedTokens.ts b/packages/shared/signedTokens.ts
index b5e27f3e..14a26f60 100644
--- a/packages/shared/signedTokens.ts
+++ b/packages/shared/signedTokens.ts
@@ -1,8 +1,6 @@
 import crypto from "node:crypto";
 import { z } from "zod";
 
-import serverConfig from "./config";
-
 const zTokenPayload = z.object({
   payload: z.unknown(),
   expiresAt: z.number(),
@@ -13,10 +11,45 @@ const zSignedTokenPayload = z.object({
   signature: z.string(),
 });
 
+/**
+ * Returns the expiry date aligned to the specified interval.
+ * If the time left until the next interval is less than the grace period,
+ * it skips to the following interval.
+ *
+ * @param now - The current date and time (defaults to new Date()).
+ * @param intervalSeconds - The interval in seconds (e.g., 1800 for 30 mins).
+ * @param gracePeriodSeconds - The grace period in seconds.
+ * @returns The calculated expiry Date.
+ */
+export function getAlignedExpiry(
+  intervalSeconds: number,
+  gracePeriodSeconds: number,
+  now: Date = new Date(),
+): number {
+  const ms = now.getTime();
+  const intervalMs = intervalSeconds * 1000;
+
+  // Find the next interval
+  const nextIntervalTime =
+    Math.floor(ms / intervalMs) * intervalMs + intervalMs;
+
+  // Time left until the next interval
+  const timeLeft = nextIntervalTime - ms;
+
+  // Decide which interval to use
+  const finalIntervalTime =
+    timeLeft < gracePeriodSeconds * 1000
+      ? nextIntervalTime + intervalMs
+      : nextIntervalTime;
+
+  return finalIntervalTime;
+}
+
 export type SignedTokenPayload = z.infer<typeof zSignedTokenPayload>;
 
 export function createSignedToken(
   payload: unknown,
+  secret: string,
   expiryEpoch?: number,
 ): string {
   const expiresAt = expiryEpoch ?? Date.now() + 5 * 60 * 1000; // 5 minutes from now
@@ -28,7 +61,7 @@ export function createSignedToken(
 
   const payloadString = JSON.stringify(toBeSigned);
   const signature = crypto
-    .createHmac("sha256", serverConfig.signingSecret())
+    .createHmac("sha256", secret)
     .update(payloadString)
     .digest("hex");
 
@@ -42,6 +75,7 @@ export function createSignedToken(
 
 export function verifySignedToken<T>(
   token: string,
+  secret: string,
   schema: z.ZodSchema<T>,
 ): T | null {
   try {
@@ -52,7 +86,7 @@ export function verifySignedToken<T>(
 
     // Verify signature
     const expectedSignature = crypto
-      .createHmac("sha256", serverConfig.signingSecret())
+      .createHmac("sha256", secret)
       .update(JSON.stringify(payload))
       .digest("hex");
 
-- 
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