From 27ebec8c8b679104bedd605b451cc56e24c1e931 Mon Sep 17 00:00:00 2001
From: Brandon Keepers <brandon@opensoul.org>
Date: Thu, 25 Apr 2024 20:01:39 -0400
Subject: [PATCH] export syncClock, perform 5 iterations

---
 demo.ts      | 13 ++++---------
 src/clock.ts | 37 ++++++++++++++++++++++---------------
 src/index.ts |  2 ++
 3 files changed, 28 insertions(+), 24 deletions(-)

diff --git a/demo.ts b/demo.ts
index 6b68298..b84708a 100644
--- a/demo.ts
+++ b/demo.ts
@@ -1,13 +1,8 @@
-import { createMetronome } from "./src"
-import { sync } from "./src/clock.ts"
+import { createMetronome, syncClock } from "./src"
 
-async function doSync() {
-  const offset = await sync()
-  document.getElementById('offset')!.innerText = offset.toString()
-  setTimeout(doSync, 5000)
-}
-
-setTimeout(doSync(), 1000)
+setTimeout(async () => {
+  document.getElementById('offset')!.innerText = (await syncClock()).toString()
+}, 1000)
 
 const tempoEl = document.getElementById("tempo")! as HTMLInputElement
 const visualizerEl = document.getElementById("visualizer")! as HTMLInputElement
diff --git a/src/clock.ts b/src/clock.ts
index 7dcf2e4..2046e63 100644
--- a/src/clock.ts
+++ b/src/clock.ts
@@ -1,35 +1,42 @@
 // The number of milliseconds that this client's clock is offset from the server's clock.
-export let offset = 0;
-let delay = Infinity;
+export let offset = 0
+let latency = Infinity
 
 // the NTP algorithm
 // t0 - client's timestamp of the request packet transmission,
 // t1 - server's timestamp of the request packet reception,
 // t2 - server's timestamp of the response packet transmission and
 // t3 - client's timestamp of the response packet reception.
-export function ntp(t0, t1, t2, t3) {
+export function ntp(t0: number, t1: number, t2: number, t3: number) {
   return {
-    delay: (t3 - t0) - (t2 - t1),
+    latency: (t3 - t0) - (t2 - t1),
     offset: ((t1 - t0) + (t2 - t3)) / 2
-  };
+  }
 }
 
-export async function sync () {
-  const t0 = Date.now()
-  const response = await fetch('https://clock.zone/_/_offset')
-  const t3 = Date.now()
-  const { val } = await response.json();
+export async function sync ({ iterations, wait } = { iterations: 5, wait: 1000 }) {
+  for (let i = 0; i < iterations; i++) {
+    const t0 = Date.now()
+    const response = await fetch('https://clock.zone/_/_offset')
+    const t3 = Date.now()
+    const { val } = await response.json();
+
+    const latest = ntp(t0, val, val, t3)
 
-  const latest = ntp(t0, val, val, t3)
+    // Less latency is likely higher accuracy
+    if(latest.latency < latency) {
+      offset = latest.offset
+      latency = latest.latency
+    }
 
-  if(latest.delay < delay) {
-    offset = latest.offset
-    delay = latest.delay
+    if(i < iterations) {
+      await new Promise(resolve => setTimeout(resolve, wait))
+    }
   }
 
   return offset
 }
 
 export function now() {
-  return Date.now() + offset;
+  return Date.now() + offset
 }
diff --git a/src/index.ts b/src/index.ts
index b91aacc..9b5d07d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,6 +1,8 @@
 import { setInterval, clearInterval } from "./timers"
 import { now } from "./clock"
 
+export { sync as syncClock } from "./clock"
+
 export interface Beat {
   note: number
   time: number