// Kept transport-independent so all late session completions use the same rule.
export type SessionIdentity = {
  accessToken: string
  user: { id: number }
}

export function isSameSession(expected: SessionIdentity | null, current: SessionIdentity | null) {
  return Boolean(expected && current && expected.accessToken === current.accessToken && expected.user.id === current.user.id)
}

export function createSessionRequestGuard(readCurrent: () => SessionIdentity | null) {
  let generation = 0
  return {
    invalidate() { generation += 1 },
    begin(session: SessionIdentity) {
      const requestGeneration = ++generation
      return () => generation === requestGeneration && isSameSession(session, readCurrent())
    },
  }
}