web-player: add Vitest, unit tests and pure queue operations

web-player/src/lib/player/queue.ts

@@ -0,0 +1,39 @@
+export function insertNext<T>(queue: T[], afterIndex: number, items: T[]): T[] {
+	const result = [...queue];
+	result.splice(afterIndex + 1, 0, ...items);
+	return result;
+}
+
+export function append<T>(queue: T[], items: T[]): T[] {
+	return [...queue, ...items];
+}
+
+export function move<T>(queue: T[], from: number, insertAt: number): T[] {
+	if (from < 0 || from >= queue.length) return queue;
+	const target = insertAt > from ? insertAt - 1 : insertAt;
+	if (target === from) return queue;
+	const result = [...queue];
+	const [item] = result.splice(from, 1);
+	result.splice(target, 0, item);
+	return result;
+}
+
+export function nextIndex(
+	length: number,
+	index: number,
+	shuffle: boolean,
+	random: () => number = Math.random
+): number {
+	if (shuffle && length > 1) {
+		let next: number;
+		do {
+			next = Math.floor(random() * length);
+		} while (next === index);
+		return next;
+	}
+	return (index + 1) % length;
+}
+
+export function previousIndex(length: number, index: number): number {
+	return (index - 1 + length) % length;
+}