#!/usr/bin/env python3
# -*-coding:utf-8-*-

# usage:
#   ./Watchdog.py <subfile> <commands>

# This script takes a <subfile> file and a list of <commands> which it immediately
# executes in a subprocess.
# It kills the subprocess and relaunches it whenever the file changes.
#
# If you accidentally introduce an error into the <subfile>, just fix that error
# and save the file again, and <commands> will be executed.
# Note that the subprocess shares the console with this process,
# therefore you will see its output.

import sys
import time
import subprocess
# import logging
import os
import watchdog
import watchdog.events
import watchdog.observers
import psutil
import signal

process = None
subfile = sys.argv[1]
command = ' '.join(sys.argv[2:])


def launch():
    global process
    process = subprocess.Popen(command, shell=True)
    print("process with pid of {0} created".format(process.pid))


def samefile(a, b):
    return os.stat(a) == os.stat(b)


def kill_or_do_nothing():
    global process
    try:  # Process might already have terminated
        process = psutil.Process(pid=process.pid)
        for proc in process.children(recursive=True):
            proc.kill()
        process.kill()
    except Exception as E:
        print("couldn't destroy process, reason:\n\t",
              str(E))


class Modified(watchdog.events.FileSystemEventHandler):
    def on_modified(self, event):
        if subfile not in event.src_path:
            return
        if not samefile(event.src_path, subfile):
            return

        print('<<', subfile, '>> modified, will restart\n')
        kill_or_do_nothing()
        launch()


class GracefulKiller():
    kill_now = False

    def __init__(self):
        signal.signal(signal.SIGINT, self.exit_gracefully)
        signal.signal(signal.SIGTERM, self.exit_gracefully)

    def __str__(self):
        print(self.kill_now)

    def exit_gracefully(self, signum, frame):
        self.kill_now = True


def main():
    global killer

    observer = watchdog.observers.Observer()
    observer.schedule(Modified(), '.')
    observer.start()

    launch()
    kill_or_do_nothing()

    # Idle forever, listening on Modified.on_modified
    while killer.kill_now is False:
        time.sleep(1)


if __name__ == '__main__':
    global killer
    killer = GracefulKiller()
    main()
    print("Watchdog exited successfully")