const FNV_OFFSET_BASIS_32 = 0x811c9dc5;
const FNV_PRIME_32 = 0x01000193;
const SECONDARY_HASH_SEED = 0x9e3779b9;
const SECONDARY_HASH_MULTIPLIER = 0x85ebca6b;

function fnv1a32(input: string, seed: number, multiplier: number): number {
  let hash = seed >>> 0;
  for (let index = 0; index < input.length; index += 1) {
    hash ^= input.charCodeAt(index);
    hash = Math.imul(hash, multiplier) >>> 0;
  }
  return hash >>> 0;
}

export function buildPatchCacheKey(patch: string, scope = "diff-panel"): string {
  const normalizedPatch = patch.trim();
  const primary = fnv1a32(normalizedPatch, FNV_OFFSET_BASIS_32, FNV_PRIME_32).toString(36);
  const secondary = fnv1a32(
    normalizedPatch,
    SECONDARY_HASH_SEED,
    SECONDARY_HASH_MULTIPLIER,
  ).toString(36);
  return `${scope}:${normalizedPatch.length}:${primary}:${secondary}`;
}