function isObject(val: unknown): val is Record<string, unknown> {
  return typeof val === 'object' && val !== null
}
function isArray(val: unknown): val is unknown[] {
  return Array.isArray(val)
}

/** Simple diff function, retuns the values of the second object. */
export default function diff(item1: unknown, item2: unknown): unknown {
  const item1Type = typeof item2
  const item2Type = typeof item2
  const isSame = item1Type === item2Type

  // If the types aren't the same we always have a diff
  if (!isSame) return item2

  if (isArray(item1) && isArray(item2)) {
    const res = item1.map((val, idx) => diff(val, item2[idx])).filter((val) => !!val)
    return res.length ? res : undefined
  }

  if (isObject(item1) && isObject(item2)) {
    const entriesRight = Object.fromEntries(
      Object.entries(item1)
        .map(([key, val]) => [key, diff(val, item2[key])])
        .filter((entry) => !!entry[1]),
    )
    const entriesLeft = Object.fromEntries(
      Object.entries(item2)
        .map(([key, val]) => [key, diff(item1[key], val)])
        .filter((entry) => !!entry[1]),
    )
    const entries = { ...entriesRight, ...entriesLeft } as Record<string, unknown>

    return Object.keys(entries).length ? entries : undefined
  }

  return item2 === item1 ? undefined : item2
}