#!/usr/bin/python
# SPDX-License-Identifier: MIT-0
#
# Implement the systemd notify protocol without external dependencies.
# Supports both readiness notification on startup and on reloading,
# according to the protocol defined at:
# https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html
# This protocol is guaranteed to be stable as per:
# https://systemd.io/PORTABILITY_AND_STABILITY/

import errno
import os
import signal
import socket
import sys
import time

reloading = False
terminating = False


def notify(message):
    if not message:
        raise ValueError('notify() requires a message')

    socket_path = os.environ.get('NOTIFY_SOCKET')
    if not socket_path:
        return

    if socket_path[0] not in ('/', '@'):
        raise OSError(errno.EAFNOSUPPORT, 'Unsupported socket type')

    # Handle abstract socket.
    if socket_path[0] == '@':
        socket_path = '\0' + socket_path[1:]

    with socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM | socket.SOCK_CLOEXEC) as sock:
        sock.connect(socket_path)
        sock.sendall(message)


def notify_ready():
    notify(b'READY=1')


def notify_reloading():
    microsecs = time.clock_gettime_ns(time.CLOCK_MONOTONIC) // 1000
    notify(f'RELOADING=1\nMONOTONIC_USEC={microsecs}'.encode())


def notify_stopping():
    notify(b'STOPPING=1')


def reload(signum, frame):
    global reloading
    reloading = True


def terminate(signum, frame):
    global terminating
    terminating = True


def main():
    print('Doing initial setup')
    global reloading, terminating

    # Set up signal handlers.
    print('Setting up signal handlers')
    signal.signal(signal.SIGHUP, reload)
    signal.signal(signal.SIGINT, terminate)
    signal.signal(signal.SIGTERM, terminate)

    # Do any other setup work here.

    # Once all setup is done, signal readiness.
    print('Done setting up')
    notify_ready()

    print('Starting loop')
    while not terminating:
        if reloading:
            print('Reloading')
            reloading = False

            # Support notifying the manager when reloading configuration.
            # This allows accurate state tracking as well as automatically
            # enabling 'systemctl reload' without needing to manually
            # specify an ExecReload= line in the unit file.

            notify_reloading()

            # Do some reconfiguration work here.

            print('Done reloading')
            notify_ready()

        # Do the real work here ...

        print('Sleeping for five seconds')
        time.sleep(5)

    print('Terminating')
    notify_stopping()


if __name__ == '__main__':
    sys.stdout.reconfigure(line_buffering=True)
    print('Starting app')
    main()
    print('Stopped app')