From cedec104a142962f365ced1d52699377a9922fb4 Mon Sep 17 00:00:00 2001
From: Yuri Tatishchev <itatishch@gmail.com>
Date: Fri, 6 Feb 2026 02:09:37 -0800
Subject: [PATCH] global player pt. 8 preload stuff

---
 src/lib/components/GlobalPlayer.svelte | 71 +++++++++++++++++++++-----
 1 file changed, 58 insertions(+), 13 deletions(-)

diff --git a/src/lib/components/GlobalPlayer.svelte b/src/lib/components/GlobalPlayer.svelte
index a16fd9d..e503262 100644
--- a/src/lib/components/GlobalPlayer.svelte
+++ b/src/lib/components/GlobalPlayer.svelte
@@ -26,6 +26,12 @@
 
 	let audioEl: HTMLAudioElement | null = null;
 
+	// Best-effort preload of the upcoming track's URL
+	let nextPreloadHref = $state<string | null>(null);
+
+	// Dedicated preloader element to warm the connection / decode pipeline a bit
+	let preloadEl = $state<HTMLAudioElement | null>(null);
+
 	let isPlaying = $state(false);
 	let currentTime = $state(0);
 	let duration = $state(0);
@@ -95,6 +101,41 @@
 		audioEl.volume = snap.volume;
 	}
 
+	function computeNextTrackToPreload(): Track | null {
+		// Prefer to preload the "linear next" item. For shuffle mode, we can still
+		// best-effort preload the first item in the upcoming order.
+		if (snap.queue.length === 0) return null;
+
+		if (snap.shuffleEnabled) {
+			const nextIdx = snap.order[0];
+			if (typeof nextIdx === "number") return snap.queue[nextIdx] ?? null;
+			return null;
+		}
+
+		if (snap.currentIndex == null) return snap.queue[0] ?? null;
+		const nextIdx = snap.currentIndex + 1;
+		return nextIdx >= 0 && nextIdx < snap.queue.length
+			? snap.queue[nextIdx]
+			: null;
+	}
+
+	function updatePreloadTargets() {
+		const nextTrack = computeNextTrackToPreload();
+		nextPreloadHref = nextTrack?.src ?? null;
+
+		// Also warm via an offscreen <audio> element. This may or may not help depending
+		// on browser caching policies, but it's safe and often reduces first-buffer delay.
+		if (!preloadEl) return;
+
+		if (nextTrack?.src) {
+			preloadEl.src = nextTrack.src;
+			preloadEl.load();
+		} else {
+			preloadEl.removeAttribute("src");
+			preloadEl.load();
+		}
+	}
+
 	async function waitForEvent(el: HTMLMediaElement, eventName: string) {
 		await new Promise<void>((resolve) => {
 			const onEvent = () => {
@@ -114,35 +155,25 @@
 
 		syncAudioToCurrentTrack();
 
-		// If the src changed, some browsers require a "load -> playing" sequence.
-		// Strategy:
-		// - if src changed: ensure load is kicked, then wait for loadedmetadata/canplay
-		// - call play()
-		// - if it's still paused, wait for 'playing' and retry play once
 		const afterSrc = el.currentSrc;
 
 		if (afterSrc !== beforeSrc) {
-			// Ensure metadata exists (duration available, etc.)
 			if (el.readyState < 1) {
 				await waitForEvent(el, "loadedmetadata");
 			}
-			// Ensure enough data to play.
 			if (el.readyState < 3) {
 				await waitForEvent(el, "canplay");
 			}
 		} else {
-			// Even if src didn't change, allow a minimal yield to let state settle.
 			await Promise.resolve();
 		}
 
 		try {
 			await el.play();
 		} catch {
-			// Autoplay may be blocked; bail out quietly.
 			return;
 		}
 
-		// If the browser didn't actually start playback, retry after 'canplay'/'playing'.
 		if (el.paused) {
 			if (el.readyState < 3) {
 				await waitForEvent(el, "canplay");
@@ -218,11 +249,11 @@
 
 	$effect(() => {
 		media.setTrack(snap.currentTrack);
-
-		// Persist queue/settings/UI state (throttled) from within a component-scoped effect
-		// to avoid orphaned module-level `$effect`.
 		schedulePersistNow();
 
+		// Keep preload targets updated as the queue/traversal state changes
+		updatePreloadTargets();
+
 		if (!audioEl) return;
 
 		audioEl.volume = snap.volume;
@@ -235,6 +266,13 @@
 			window.addEventListener("resize", updateIsMobile);
 		}
 
+		// Create the offscreen preloader audio element in the browser
+		if (browser) {
+			preloadEl = new Audio();
+			preloadEl.preload = "auto";
+			preloadEl.muted = true;
+		}
+
 		// Subscribe to player changes instead of polling
 		unsubscribe = subscribe((s) => {
 			snap = s;
@@ -252,6 +290,13 @@
 	});
 </script>
 
+<svelte:head>
+	<!-- Preload the next track (best-effort). We set this href reactively below. -->
+	{#if nextPreloadHref}
+		<link rel="preload" as="audio" href={nextPreloadHref} />
+	{/if}
+</svelte:head>
+
 {#if isMobile}
 	<!-- Mobile: mini bar + expandable drawer -->
 	<div