#!/usr/bin/env bash
set -e
(( $# > 0 )) || exit

# Displays the time since $1 in a human readable format (e.g. 4h 25m 55s). If
# given a file, the modified time is used. If $1 == "--", then this script acts
# as a converter, converting $2 into human a readable format, e.g. since -- 72
# #=> 1m 12s

# TODO: A help fallback
# TODO: Options parsing?

# `date` on OSX does not have the --date parameter
date=date
if [[ $OSTYPE == darwin* ]]; then
  date=gdate
elif ! command -v $date >/dev/null; then
  echo "Unsupported system"
  exit 1
fi

# If given a file, give time since last modification
(( $# == 1 )) && [[ -f $1 ]] && arg=reference || arg=date

if [[ $1 == -- ]]; then
  t="$2"
else
  now=$($date +%s)
  then=$($date --$arg="$*" +%s)

  t=$(( now - then ))
fi

# Bash doesn't support floating point arithmetic like zsh does, therefore:
bc <<EOF
  define abs(i) {
    if (i < 0) return (-i)
    return (i)
  }

  t = abs($t)

  weeks = t / 60 / 60 / 24 / 7
  days = t / 60 / 60 / 24 % 7
  hours = t / 60 / 60 % 24
  minutes = t / 60 % 60
  seconds = t % 60

  if (weeks > 0) print weeks, "w "
  if (days > 0) print days, "d "
  if (hours > 0) print hours, "h "
  if (minutes > 0) print minutes, "m "
  print seconds, "s"
EOF