// .multi() / .exec() performs the operations as a transaction
// See https://github.com/redis/node-redis/blob/master/docs/transactions.md
const [_, cost] = await redisClient
  .multi()
  // Remove members from the sorted set which are older than the period
  // https://redis.io/docs/latest/commands/zremrangebyscore/
  .ZREMRANGEBYSCORE(key, '-inf', startRange)
  // Get the number of members in the sorted set
  // https://redis.io/docs/latest/commands/zcard/
  .ZCARD(key)
  .execTyped()

// Use pipelining instead of a transaction here: https://github.com/redis/node-redis/blob/master/packages/redis/README.md#auto-pipelining
// Pipelining sends multiple commands over a single request to Redis, however they're not guaranteed to be processed in order,
// or that other commands won't be processed in between.
// Adding the members to the sorted set and updating the expiry are not critical operations, and wouldn't benefit
// from the overhead of a transaction.
await Promise.all([
  // Add member to the sorted set
  // https://redis.io/docs/latest/commands/zadd/
  redisClient.ZADD(key, members),
  // Mark the key for expiry so Redis removes it if this user doesn't make a request within the defined period
  // https://redis.io/docs/latest/commands/expire/
  redisClient.EXPIRE(key, periodInSeconds),
])