Aurora SpotiRip desktop and web app

- Spotify playlist, library, album and artist browsing with in-app playback
- Song, playlist and album downloads via spotdl with YouTube and Bandcamp fallbacks
- Electron desktop app (castLabs Widevine) with a permanent sidebar layout
- Linux and Windows packaging scripts

helpers/libraryIdentity.tsx

@@ -0,0 +1,41 @@
+export type LibraryIdentityInput = {
+  isrc?: string;
+  title?: string;
+  artist?: string;
+  album?: string;
+};
+
+function normalize(value?: string) {
+  return (value || "")
+    .toLowerCase()
+    .normalize("NFKD")
+    .replace(/[\u0300-\u036f]/g, "")
+    .replace(/[^a-z0-9]+/g, " ")
+    .trim();
+}
+
+export function makeLibraryIdentity(input: LibraryIdentityInput) {
+  if (input.isrc?.trim()) return `isrc:${input.isrc.trim().toUpperCase()}`;
+  return [
+    "meta",
+    normalize(input.artist),
+    normalize(input.title),
+    normalize(input.album),
+  ].join(":");
+}
+
+export function findDuplicateIdentities(items: LibraryIdentityInput[]) {
+  const seen = new Map<string, number>();
+  const duplicates = new Set<number>();
+  items.forEach((item, index) => {
+    const identity = makeLibraryIdentity(item);
+    const first = seen.get(identity);
+    if (typeof first === "number") {
+      duplicates.add(first);
+      duplicates.add(index);
+    } else {
+      seen.set(identity, index);
+    }
+  });
+  return duplicates;
+}