import { assertNumber } from "../helpers/assertNumber"

export function toAvg() {
  const reducer = (
    sum: number,
    current: number,
    index: number,
    arr: number[],
  ): number => {
    assertNumber(current)

    const isLast = index === arr.length - 1

    const newSum = sum + current

    if (isLast) {
      return newSum / arr.length
    }

    return newSum
  }

  return [reducer, 0] as const
}