export function mergeDiffArray(pristine, current) {
  if (!Array.isArray(pristine)) {
    return current;
  }
  if (pristine.length !== current.length) {
    return current;
  }
  for (let i = 0; i < pristine.length; i++) {
    if (JSON.stringify(current[i]) !== JSON.stringify(pristine[i])) {
      return current;
    }
  }
}

export function mergeDiffObject(pristine, current) {
  if ('object' !== typeof pristine) {
    return current;
  }
  const diff = {};
  for (const i in current) {
    const value = mergeDiff(pristine[i], current[i]);
    if (undefined !== value) {
      diff[i] = value;
    }
  }
  if (0 === Object.keys(diff).length) {
    return undefined;
  }
  return diff;
}

export function mergeDiffPrimitive(pristine, current) {
  if (pristine !== current) {
    return current;
  }
}

export function mergeDiff(pristine, current) {
  if (Array.isArray(current)) {
    return mergeDiffArray(pristine, current);
  }
  else if ('object' === typeof current) {
    return mergeDiffObject(pristine, current);
  }
  else {
    return mergeDiffPrimitive(pristine, current);
  }
}