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;
}