const howManyMonthsBetween = (from, to) => {
  const fromDate = new Date(from)
  const toDate = new Date(to)
  const yearsBetween = toDate.getFullYear() - fromDate.getFullYear()

  return (yearsBetween * 12) + toDate.getMonth() - fromDate.getMonth()
}

const useCreateDataArray = (results) => {
  // sort array from earliest to latest
  const chronological = results.sort((a, b) => {
    return a.datetime > b.datetime
  })

  const earliestEntryDate = new Date(chronological[0].datetime)
  const latestEntryDate = new Date(chronological[chronological.length - 1].datetime)
  const monthsBetween = howManyMonthsBetween(earliestEntryDate, latestEntryDate)

  // create object where:
  //   keys: every possible month (in ms since 1970) from earliest to latest entries
  //   values: how many reports occurred in that month (initialized to 0)
  const initDataSeriesObj = Object.fromEntries(
      [...Array(monthsBetween)].map((_, idx) => {
        return [new Date(
          earliestEntryDate.getFullYear(),
          earliestEntryDate.getMonth() + idx,
          1
        ).getTime(), 0]
      })
  )

  const dataSeriesObj = chronological.reduce((acc, val) => {
    const valAsDate = new Date(val.datetime)
    const nearestMonth = new Date(valAsDate.getFullYear(), valAsDate.getMonth(), 1).getTime()
    acc[nearestMonth]++
    return acc
  }, initDataSeriesObj)

  // return Object.entries(dataSeriesObj)
  return Object.keys(dataSeriesObj).map((k) => [Number(k), dataSeriesObj[k]])
}

export default useCreateDataArray