#!/usr/bin/python3
#
# Since this is meant to be run as a daemon, do not use #!/usr/bin/env python3,
# because the process name would then be python3, not based on __FILE__.
#
# [filename] -d 3 192.168.1.1 192.168.1.12 &
# disown [jobid]
import os
import sys
import subprocess
import time
from argparse import ArgumentParser
import threading
import queue
import signal


def log_exit(_signal, frame):
    _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())}'
                      f' PID={os.getpid()} signal={signal.Signals(_signal).name} Exiting.'])
    _print_queue.join()
    sys.exit(0)


def pinger(host, delay):
    """Independent worker thread: repeatedly ping, check, print and sleep."""
    last_results = None
    while True:
        now = time.localtime()
        success = ping(host)
        if success != last_results:
            status = "UP" if success else "DOWN"
            _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", now)} {host} {status}'])
            last_results = success
        time.sleep(delay)


def ping(host):
    """Returns True if host (str) responds to a ping request."""
    return subprocess.call([*_ping_cmd, host], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL) == 0


def print_manager():
    """The only thread allowed to write output."""
    while True:
        job = _print_queue.get()
        for line in job:
            log(line)
        _print_queue.task_done()


def log(*args, **kwargs):
    """Opens the logfile, writes the log, and closes the logfile."""
    # I don't leave the log file open for writing because another process needs access too.
    with open(_logname, 'a') as fp:
        return print(*args, **kwargs, file=fp)


if __name__ == '__main__':
    parser = ArgumentParser(description="Repeatedly ping sites. Ex: %(prog)s -d 3 192.168.1.1 192.168.1.12")
    parser.add_argument('-d', '--delay', type=float, default=3.0, help='Delay between pings')
    parser.add_argument('addresses', nargs='+', help='Addresses to ping')
    parser_args = parser.parse_args()

    _logname = os.path.join(os.path.expanduser('~'), 'log', os.path.basename(sys.argv[0]).replace('py', 'txt'))

    # Choose the ping parameters appropriate for the platform
    if sys.platform == 'cygwin' or sys.platform == 'win32':
        _ping_cmd = ('ping', '-n', '1', '-w', '2000')
    else:
        _ping_cmd = ('ping', '-c', '1', '-W', '2', '-q')

    _print_queue = queue.Queue()
    print_thread = threading.Thread(target=print_manager, daemon=True)
    print_thread.start()

    _print_queue.put([f'{time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())} PID={os.getpid()}'
        f' repeat={parser_args.delay}s addresses={",".join(parser_args.addresses)} Starting'])

    signal.signal(signal.SIGINT, log_exit)
    signal.signal(signal.SIGTERM, log_exit)

    # Create worker threads for all but one host address. (Saving one address for this thread.)
    for address in parser_args.addresses[:-1]:
        t = threading.Thread(target=pinger, args=(address, parser_args.delay), daemon=True)
        t.start()
        del t

    # Main thread becomes a worker pinger, too.
    pinger(parser_args.addresses[-1], parser_args.delay)