#!/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 $@ ]] && arg=reference || arg=date

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

    # Show full target date
    echo $(${date} --date="@$then")

    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