# -*- coding: utf-8 -*-

# (The MIT License)
#
# Copyright (c) 2013-2020 Kura
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the 'Software'), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# SOFTWARE.

"""Provides functionality to manage child processes from the supervisor."""


import asyncio
import logging
import os
import signal
import time

from . import protocols
from .child import Child
from .control import setgid, setuid
from .streams import StreamProtocol


try:
    import setproctitle
except ImportError:
    setproctitle = None


__all__ = ("Worker",)


logger = logging.getLogger("blackhole.worker")


class Worker:
    """
    A worker.

    Providers functionality to manage a single child process. The worker is
    responsible for communicating heartbeat information with it's child
    process and starting, stopping and restarting a child as required or
    instructed.
    """

    _started = False
    ping_count = 0

    def __init__(self, idx, socks, loop=None):
        """
        Initialise the worker.

        :param str idx: The number reference of the worker and child.
        :param list socks: Sockets to listen for connections on.
        :param loop: The event loop to use.
        :type loop: :py:class:`asyncio.unix_events._UnixSelectorEventLoop` or
                    :py:obj:`None` to get the current event loop using
                    :py:func:`asyncio.get_event_loop`.
        """
        self.loop = loop if loop is not None else asyncio.get_event_loop()
        self.socks = socks
        self.idx = idx
        self.start()

    def start(self):
        """Create and fork off a child process for the current worker."""
        assert not self._started
        self._started = True

        self.up_read, self.up_write = os.pipe()
        self.down_read, self.down_write = os.pipe()

        self.pid = os.fork()
        if self.pid > 0:  # Parent
            asyncio.ensure_future(self.connect())
        else:  # Child
            self.setup_child()

    def setup_child(self):
        """Basic setup for the child process and starting it."""
        setgid()
        setuid()
        asyncio.set_event_loop(None)
        if setproctitle:
            setproctitle.setproctitle("blackhole: worker")
        process = Child(self.up_read, self.down_write, self.socks, self.idx)
        process.start()

    def restart_child(self):
        """Restart the child process."""
        self.kill_child()
        self.pid = os.fork()
        if self.pid > 0:
            self.ping_count = 0
            self.ping = time.monotonic()
        else:
            self.setup_child()

    def kill_child(self):
        """Kill the child process."""
        try:
            os.kill(self.pid, signal.SIGTERM)
            os.wait()
        except ProcessLookupError:
            pass

    async def heartbeat(self, writer):
        """
        Handle heartbeat between a worker and child.

        If a child process stops communicating with it's worker, it will be
        killed, the worker managing it will also be removed and a new worker
        and child will be spawned.

        :param asyncio.StreamWriter writer: An object for writing data to the
                                            pipe.

        .. note::

           3 bytes are used in the communication channel.

           - b'x01' -- :const:`blackhole.protocols.PING`
           - b'x02' -- :const:`blackhole.protocols.PONG`

           The worker will sleep for 15 seconds, before requesting a ping from
           the child. If we go for over 30 seconds waiting for a ping, the
           worker will restart itself and the child bound to it.

           These message values are defined in the :mod:`blackhole.protocols`
           schema. Documentation is available at --
           https://kura.github.io/blackhole/api-protocols.html
        """
        while self._started:
            await asyncio.sleep(15)
            if (time.monotonic() - self.ping) < 30:
                writer.write(protocols.PING)
            else:
                if self._started:
                    logger.debug(
                        "worker.%s.heartbeat: Communication failed. "
                        "Restarting worker",
                        self.idx,
                    )
                    self.restart_child()

    async def chat(self, reader):
        """
        Communicate between a worker and child.

        If communication with the child fails the worker is shutdown and the
        child is killed.

        :param asyncio.StreamReader reader: An object for reading data from
                                            the pipe.

        .. note::

           3 bytes are used in the communication channel.

           - b'x01' -- :const:`blackhole.protocols.PING`
           - b'x02' -- :const:`blackhole.protocols.PONG`

           Read data coming in from the child. If a PONG is received, we'll
           update the worker, setting this PONG as a 'PING' from the child.

           These message values are defined in the :mod:`blackhole.protocols`
           schema. Documentation is available at --
           https://kura.github.io/blackhole/api-protocols.html
        """
        while self._started:
            try:
                msg = await reader.read(3)
                if msg == protocols.PONG:
                    logger.debug(
                        "worker.%s.chat: Pong received from child", self.idx
                    )
                    self.ping = time.monotonic()
                    self.ping_count += 1
            except:  # noqa
                self.stop()
            await asyncio.sleep(5)

    async def connect(self):
        """
        Connect the child and worker so they can communicate.

        :param int up_write: A file descriptor.
        :param int down_read: A file descriptor.
        """
        read_fd = os.fdopen(self.down_read, "rb")
        r_trans, r_proto = await self.loop.connect_read_pipe(
            StreamProtocol, read_fd
        )
        write_fd = os.fdopen(self.up_write, "wb")
        w_trans, w_proto = await self.loop.connect_write_pipe(
            StreamProtocol, write_fd
        )
        reader = r_proto.reader
        writer = asyncio.StreamWriter(w_trans, w_proto, reader, self.loop)
        self.ping = time.monotonic()
        self.rtransport = r_trans
        self.wtransport = w_trans
        self.chat_task = asyncio.ensure_future(self.chat(reader))
        self.heartbeat_task = asyncio.ensure_future(self.heartbeat(writer))

    def stop(self):
        """Terminate the worker and it's respective child process."""
        self.kill_child()
        self._started = False
        self.chat_task.cancel()
        self.heartbeat_task.cancel()
        self.rtransport.close()
        self.wtransport.close()
