#!/bin/sh
# -*- tab-width:  4 -*- ;; Emacs
# vi: set tabstop=4     :: Vi/ViM
#
# Revision: 2.0
# Last Modified: June 28th, 2011
############################################################ COPYRIGHT
#
# (c)2011. Devin Teske. All Rights Reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
# SUCH DAMAGE.
#
############################################################ INFORMATION
#
# Displays a list of users that were on the system when it last went down.
#
# Command Usage:
#
#    lastdown [-h] [-f FILE] [-#]
#
#    OPTIONS:
#    	-h        Print this message to stderr and exit
#    	-f FILE   Optional path to wtmp log (default: /var/log/wtmp)
#    	-#        A number from 1-9 to subtract in minutes from the boot time.
#    	          A value of zero means ten. Can be passed multiple times.
#
# Dependencies (sorted alphabetically):
#
#    date(1)   last(1)   printf(1)*   sysctl(8)
#
# * Is a shell-builtin on some releases.
#
############################################################ GLOBALS

#
# Global exit status variables
#
SUCCESS=0
FAILURE=1

#
# Program name
#
progname="${0##*/}"

#
# Default location of the UTMP(5) log
#
WTMP=/var/log/wtmp

#
# Optional component to subtract time from the boot_epoch
#
TIMEWARP=0

############################################################ FUNCTIONS

# fprintf $fd $fmt [ $opts ... ]
#
# Like printf, except allows you to print to a specific file-descriptor. Useful
# for printing to stderr (fd=2) or some other known file-descriptor.
#
fprintf()
{
	local fd=$1
	[ $# -gt 1 ] || return $FAILURE
	shift 1
	printf "$@" >&$fd
}

# eprintf $fmt [ $opts ... ]
#
# Print a message to stderr (fd=2).
#
eprintf()
{
	fprintf 2 "$@"
}

# die [ $fmt [ $opts ... ]]
#
# Optionally print a message to stderr before exiting with failure status.
#
die()
{
	local fmt="$1"
	[ $# -gt 0 ] && shift 1
	[  "$fmt"  ] && eprintf "$fmt\n" "$@"

	exit $FAILURE
}

# usage
#
# Prints a short syntax statement and exits.
#
usage()
{
	local optfmt="\t%-11s%s\n"
	local envfmt="\t%-17s%s\n"

	eprintf "Usage: %s [-h] [-f FILE]" "$progname"

	eprintf "OPTIONS:\n"
	eprintf "$optfmt" "-h" \
	        "Print this message to stderr and exit"
	eprintf "$optfmt" "-f FILE" \
	        "Optioal path to UTMP(5) log (default: /var/log/wtmp)"
	eprintf "$optfmt" "-#" \
	        "A number from 1-9 to subtract in minutes from the boot time."
	eprintf "$optfmt" "" \
	        "A value of zero means ten. Can be passed multiple times."

	die
}

# eval2 $cmd ...
#
# Print a command to stdout before executing it.
#
eval2()
{
	echo "$*"
	eval "$@"
}

# boottime_sec
#
# Returns the "seconds" portion of the ``kern.boottime'' sysctl(8) MIB.
#
boottime_sec()
{
	set -- `sysctl -n kern.boottime`
	while [ "$1" != "sec" ]; do shift; done
	echo ${3%,}
}

############################################################ MAIN SOURCE

#
# Read optional script arguments
#
while getopts hf:1234567890 flag; do
	case "$flag" in
	h) usage;;
	f) [ "$OPTARG" ] || die \
		"%s: Missing or null argument to \`-f' flag" "$progname"
	   WTMP="$OPTARG";;
	1) TIMEWARP=$(( $TIMEWARP + 60*1 ));;
	2) TIMEWARP=$(( $TIMEWARP + 60*2 ));;
	3) TIMEWARP=$(( $TIMEWARP + 60*3 ));;
	4) TIMEWARP=$(( $TIMEWARP + 60*4 ));;
	5) TIMEWARP=$(( $TIMEWARP + 60*5 ));;
	6) TIMEWARP=$(( $TIMEWARP + 60*6 ));;
	7) TIMEWARP=$(( $TIMEWARP + 60*7 ));;
	8) TIMEWARP=$(( $TIMEWARP + 60*8 ));;
	9) TIMEWARP=$(( $TIMEWARP + 60*9 ));;
	0) TIMEWARP=$(( $TIMEWARP + 60*10 ));;
	\?) usage;;
	esac
done
shift $(( $OPTIND -1 ))

#
# What was the epoch when we booted?
#
boot_epoch=$( boottime_sec )

#
# ``Subtract one'' (make last(1) report on the time just prior to boot)
#
boot_epoch=$(( $boot_epoch - 1 )) # Pedantic really

#
# Go backwards in time (subtract TIMEWARP; which defaults to zero)
#
boot_epoch=$(( $boot_epoch - $TIMEWARP ))

#
# Convert boot_epoch into a format that last(1) accepts as an argument for
# determining who was logged on the system at the particular date/time.
# (resolution is 1-second)
#
start_time=$( date -r $boot_epoch +%Y%m%d%H%M.%S )

#
# Get the list of users that were on the system at that time
#
eval2 last -d $start_time -f "$WTMP"