// Stops one device from silently overwriting a study another device has saved since. The browser sends
// the `lastEdited` of the server copy it last saw (X-Base-Edited); if the server's copy has moved past
// that, the save is refused with 409 and the person chooses whose version to keep.

// stored: the server copy's lastEdited (null when there is none); base: what the client last saw
// (null/undefined when it never synced this study); force: the person chose "keep mine".
export function isSaveConflict({ stored, base, force = false }) {
  if (force || stored == null) return false;
  if (!Number.isFinite(base)) return false; // a device that never saw the server's copy has nothing to compare
  return stored > base;
}

// Reads the base header; anything that isn't a plain number is treated as "unknown".
export function parseBase(header) {
  if (header == null || header === '') return null;
  const n = Number(header);
  return Number.isFinite(n) ? n : null;
}