#!/usr/bin/env bash

# The variables are checked dynamically
# shellcheck disable=SC2034
seconds() {
  local day hour minute second span time
  (( day = $1 / 60 / 60 / 24 ))
  (( hour = $1 / 60 / 60 % 24 ))
  (( minute = $1 / 60 % 60 ))
  (( second = $1 % 60 ))

  for span in day hour minute second; do
    if (( ${!span} )); then
      if [[ $time ]]; then
        time+=", "
      fi

      time+="${!span} $span"

      if (( ${!span} > 1 )); then
        time+=s
      fi
    fi
  done

  printf %s "$time"

  if [[ -t 1 ]]; then
    printf '\n'
  fi
}

seconds "${1-3628800}"