/* A lemma's id — derived from what the word IS, not where it sorts.

   Ids used to be positions in the sorted build: the 12,000th entry got id
   12000. Cards point at lemmas by id, so any change to the dictionary —
   one entry added near the top — silently moved every card below it onto a
   different word. And a custom word took max(id)+1 on the device that added
   it, so the same id meant different words on a phone and a laptop.

   Hashing (headword, pos) makes the id a property of the word: stable across
   rebuilds, and identical on every device that adds the same word. The
   build asserts the whole dictionary is collision-free.

   cyrb53 (bryc, public domain): 53 bits, so the result is always a safe
   JavaScript integer and fits SQLite's INTEGER PRIMARY KEY. It hashes
   UTF-16 code units, which is deterministic across engines. The separator is
   written as an escape, never a literal control byte. */

export function lemmaId(headword, pos) {
  const str = `${headword}\u0001${pos}`;
  let h1 = 0xdeadbeef;
  let h2 = 0x41c6ce57;
  for (let i = 0; i < str.length; i++) {
    const ch = str.charCodeAt(i);
    h1 = Math.imul(h1 ^ ch, 2654435761);
    h2 = Math.imul(h2 ^ ch, 1597334677);
  }
  h1 = Math.imul(h1 ^ (h1 >>> 16), 2246822507);
  h1 ^= Math.imul(h2 ^ (h2 >>> 13), 3266489909);
  h2 = Math.imul(h2 ^ (h2 >>> 16), 2246822507);
  h2 ^= Math.imul(h1 ^ (h1 >>> 13), 3266489909);
  // 0 is never a valid rowid in practice; keep it out of the id space.
  return 4294967296 * (2097151 & h2) + (h1 >>> 0) || 1;
}