Make ETA

makeEtaState.ts

const makeEtaState = () => {
  type TimestampInSeconds = number
  const countBucketsForLast10Seconds: Map<TimestampInSeconds, number> = new Map()

  const countRun = (numberOfItems: number) => {
    const timestampInSeconds = Math.floor(Date.now() / 1000)

    const count = countBucketsForLast10Seconds.get(timestampInSeconds) ?? 0
    countBucketsForLast10Seconds.set(timestampInSeconds, count + numberOfItems)
  }

  const getEtaMs = (numberOfRemainingJobs: number) => {
    const currentTimestampInSeconds = Math.floor(Date.now() / 1000)

    let numberOfRunsInLast10Seconds = 0

    for (const [timestampInSeconds, count] of countBucketsForLast10Seconds.entries()) {
      if (currentTimestampInSeconds - timestampInSeconds > 10) {
        countBucketsForLast10Seconds.delete(timestampInSeconds)
      } else {
        numberOfRunsInLast10Seconds += count
      }
    }

    if (numberOfRunsInLast10Seconds === 0 || countBucketsForLast10Seconds.size < 5) {
      return null
    }

    const jobsPerMs = numberOfRunsInLast10Seconds / 10_000

    return Math.round(numberOfRemainingJobs / jobsPerMs)
  }

  return { countRun, getEtaMs }
}