range.js

const { client, key } = require('./utils')
const date = new Date()

function main () {
  let sum = 0

  async function sumWithRangeQuery () {
    const c = client()

    /**
     * https://redis.io/commands/xrange
     * Returns the stream entries matching a given range of IDs.
     *
     * Arguments:
     * key - The name of our stream.
     * '-' - Special ID meaning the minimum ID possible.
     * '+' - Special ID meaning the maximum ID possible.
     *
     * Explanation:
     * '-' is effectively the same as declaring 0-0 while '+' is the same as
     * declaring 18446744073709551615-18446744073709551615 just easier to
     * type. Autogenerated messages follow the format of timestamp-index,
     * therefore multiple messages can be written with the same timestamp if
     * need be but ordering _in which they were written_ will be guaranteed
     * because of indexing. The significance of 18446744073709551615 is that
     * the timestamp and the index can each be at most a 64-bit integer.
     **/
    const msgs = await c.xrangeAsync(key, '-', '+')

    if (!msgs) {
      console.log(`${date.getTime()}: Stream "${key}" has no messages.`)
      process.exit()
    }

    msgs.forEach(msg => {
      sum += parseInt(msg[1][1])
    })

    console.log(`${date.getTime()}: Sum of stream "${key}" is ${sum}.`)
    process.exit()
  }

  sumWithRangeQuery()
}

main()