#!/bin/bash

### Mac OS X Desksaver Script
### by Michael Lee
### v1.00.00, 2009-01-22

###   About Desksaver
#
# This script is a wrapper for commands used to display a screensaver module on
# the desktop and restore the normal desktop wallpaper.
#
# You can specify an optional screensaver module name to override the default
# set in System Preferences.  For example, if you have the "RSS Visualizer" set
# as your screensaver but you want to have Flurry on your desktop, type:
#   desksaver on Flurry
# to override the system setting.  When specifying module names, use a name from
# the Screen Savers list in System Preferences, not a path or file name.
#
# Technical note: we can use nohup, but screen
# (1) doesn't leave nohup.out files everywhere and
# (2) can be killed with -HUP
#

###   License
#
#  Copyright (C) 2009  Michael Lee <kirbysdl@yahoo.com>
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU General Public License
#  as published by the Free Software Foundation; either version 2
#  of the License, or (at your option) any later version.
#
#  This program 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 General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
#

# "constant" definitions to make the code below nicer
DESKSAVER_ENGINE='/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background'
MY_NAME=`basename $0`

# Display usage info and exit
function display_usage () {
  echo "Usage: $MY_NAME on [module name]"
  echo '       '"$MY_NAME off"
  exit 1
}

# Return whether a ScreenSaverEngine is running in the background (on the Desktop)
function already_running () {
  ps aux | grep "ScreenSaverEngine -background" | grep -qv "grep"
}

# We only support Mac OS X
if [[ `uname -s` != "Darwin" ]]; then
  echo "This script only works on Mac OS X."
  exit 2
fi

# We need at least one commandline argument
if [[ $# == 0 ]]; then
  display_usage
fi

# See if the user wants to turn the desksaver on or off
if [[ "$1" == "on" ]]; then
  if already_running; then
    echo "A screensaver is already running on your desktop."
    echo "Use the following command to stop it:"
    echo '  '"$MY_NAME off"
    exit 3
  fi
  # Remove the "on" argument from the argument queue
  shift
  # See if the user specified a custom module name
  if [[ $# != 0 ]]; then
    echo "Using the screensaver module named '$*'"
    screen -d -m $DESKSAVER_ENGINE -module "$*"
    PID=$!
  else
    echo "Using the default screensaver module (set in System Preferences)"
    screen -d -m $DESKSAVER_ENGINE
    PID=$!
  fi
elif [[ "$1" == "off" ]]; then
  if already_running; then
    killall -HUP ScreenSaverEngine
    echo "Desktop screensaver stopped."
  else
    echo "No screensaver is currently running on your desktop."
    exit 4
  fi
else
  display_usage
fi