#!/usr/bin/env python3

import argparse
import sys
import psutil
import subprocess
import os

screensavers = [
    # slock
    {'start': ['xautolock','-locker','slock'],
     'stop': ['xautolock','-exit'],
     'test': lambda : cmd_exists('xautolock') and cmd_exists('slock'),
     'running': 'xautolock',
    },
    # xscreensaver
    {'start' : ['XENVIRONMENT=~/.xscreensaver','/usr/bin/xscreensaver'],
     'stop' : ['xscreensaver-command','-exit'],
     'test' : lambda : cmd_exists('xscreensaver'),
     'running' : 'xscreensaver',
    },
    # xautolock
    {'start': ('xautolock','-notifier','true','-bell','0'),
     'stop': ('xautolock','-exit'),
     'test': lambda : cmd_exists('xautolock'),
     'running' : 'xautolock',
    },
]

#' Determine if named command exists on the path and is executable
def cmd_exists (cmd):
    return True

def cmd_running (cmd):
    user = os.getuid()
    for proc in psutil.process_iter():
        if proc.name() == cmd and proc.is_running() and proc.uids()[0] == user:
            return True
    return False

def parse_arguments():
    """Parses the arguments for the screensaver command
    """
    parser = argparse.ArgumentParser(
        description="A command to turn on/off screesavers"
        )
    parser.add_argument('command',choices=('sleep','off','stop','on','start'))
    return parser.parse_args()

def fork(cmd):
    try: 
        pid = os.fork() 
        if pid > 0:
            # parent process so return
            return
    except OSError as e:
        print >>sys.stderr, "fork failed: %d (%s)" % (e.errno, e.strerror) 
        sys.exit(1)

    os.setsid()
    try: 
        pid = os.fork() 
        if pid > 0:
            # parent process so return
            return
    except OSError as e:
        print >>sys.stderr, "fork failed: %d (%s)" % (e.errno, e.strerror) 
        sys.exit(1)
    subprocess.Popen(cmd)
    os._exit(os.EX_OK)

def fork_sleep_and_forget(delay,cmd):
    sleep(delay)
    fork(cmd)

    
def should_stop(args):
    if args.command == 'stop' or args.command == 'off':
        return True
    return False

def should_start(args):
    if args.command == 'start' or args.command == 'on':
        return True
    return False

def should_sleep(args):
    if args.command == 'sleep' or args.command == 'pause':
        return True
    return False

args = parse_arguments()

for screensaver in screensavers:
    if screensaver['test']():
        if should_stop(args):
            if cmd_running(screensaver['running']):
                fork(screensaver['stop'])
        elif should_start(args):
            if not cmd_running(screensaver['running']):
                fork(screensaver['start'])
        elif should_sleep(args):
            if cmd_running(screensaver['running']):
                fork(screensaver['stop'])
            fork_sleep_and_forget(args.sleep,screensaver['start'])
        else:
            print >>sys.stderr,"Unknown command"
        exit(0)
        
print >> sys.stderr,"No screensaver"