snapWhenToSteps: support snapping forward

lib/snap-when.js

@@ -1,10 +1,18 @@
+import {strictEqual} from 'node:assert'
+
 // snap `when` to 10s steps for a better cache hit ratio
 // Note: With most HAFAs instances, this will yield slightly different results because it all it will return results <=10s in the past.
-const snapWhenTo10sSteps = () => {
-	const now = Date.now()
-	return now - now % 10 * 1000
+const snapWhenTo10sSteps = (t = Date.now(), snapForward = false) => {
+	t -= t % (10 * 1000)
+	if (snapForward) t += 10 * 1000
+	return t
 }
 
+strictEqual(snapWhenTo10sSteps(Date.parse('2024-01-29T16:10:50.000+01:00')), Date.parse('2024-01-29T16:10:50+01:00'))
+strictEqual(snapWhenTo10sSteps(Date.parse('2024-01-29T16:10:57.812+01:00')), Date.parse('2024-01-29T16:10:50+01:00'))
+strictEqual(snapWhenTo10sSteps(Date.parse('2024-01-29T16:11:00.000+01:00')), Date.parse('2024-01-29T16:11:00+01:00'))
+strictEqual(snapWhenTo10sSteps(Date.parse('2024-01-29T16:10:57.812+01:00'), true), Date.parse('2024-01-29T16:11:00+01:00'))
+
 export {
 	snapWhenTo10sSteps as snapWhenToSteps,
 }