#!/bin/bash

# The Qubes OS Project, http://www.qubes-os.org
#
# Copyright (C) 2016 Patrick Schleizer <adrelanos@riseup.net>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, see <https://www.gnu.org/licenses/>.

## Similar code as Boot Clock Randomization.
## https://www.whonix.org/wiki/Boot_Clock_Randomization

set -e

## Get a random 0 or 1.
## Will use this to decide to use plus or minus.
ZERO_OR_ONE="$(shuf -i0-1 -n1 --random-source=/dev/random)"

## Create a random number between 0 and 180.
DELAY="$(shuf -i0-180 -n1 --random-source=/dev/random)"

## Create a random number between 0 and 999999999.
##
## Thanks to
## https://stackoverflow.com/questions/22887891/how-can-i-get-a-random-dev-random-number-between-0-and-999999999-in-bash
NANOSECONDS="$(shuf -i0-999999999 -n1 --random-source=/dev/random)"

## Examples NANOSECONDS:
## 117752805
## 38653957

## Add leading zeros, because `date` expects 9 digits.
NANOSECONDS="$(printf '%0*d\n' 9 "$NANOSECONDS")"

## Using
## printf '%0*d\n' 9 "38653957"
##  38653957
## becomes
## 038653957

## Examples NANOSECONDS:
## 117752805
## 038653957

if [ "$ZERO_OR_ONE" = "0" ]; then
  PLUS_OR_MINUS="-"
elif [ "$ZERO_OR_ONE" = "1" ]; then
  PLUS_OR_MINUS="+"
else
  exit 2
fi

#OLD_TIME="$(date)"
#OLD_TIME_NANOSECONDS="$(date +%s.%N)"

OLD_UNIXTIME="$(date +%s)"

NEW_TIME="$(( $OLD_UNIXTIME $PLUS_OR_MINUS $DELAY ))"

NEW_TIME_NANOSECONDS="$NEW_TIME.$NANOSECONDS"

echo "$NEW_TIME_NANOSECONDS"

## Testing the `date` syntax:
## date --date @1396733199.112834496
## date --date "@$NEW_TIME_NANOSECONDS"