# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# Copyright 2011 Justin Santa Barbara
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""Generic Node base class for all workers that run on hosts."""

import errno
import io
import logging
import os
import random
import signal
import sys
import time

import eventlet
from eventlet import event
from oslo_config import cfg

from designate.openstack.common import eventlet_backdoor
from designate.openstack.common._i18n import _LE, _LI, _LW
from designate.openstack.common import systemd
from designate.openstack.common import threadgroup


CONF = cfg.CONF
LOG = logging.getLogger(__name__)


def _sighup_supported():
    return hasattr(signal, 'SIGHUP')


def _is_daemon():
    # The process group for a foreground process will match the
    # process group of the controlling terminal. If those values do
    # not match, or ioctl() fails on the stdout file handle, we assume
    # the process is running in the background as a daemon.
    # http://www.gnu.org/software/bash/manual/bashref.html#Job-Control-Basics
    try:
        is_daemon = os.getpgrp() != os.tcgetpgrp(sys.stdout.fileno())
    except io.UnsupportedOperation:
        # Could not get the fileno for stdout, so we must be a daemon.
        is_daemon = True
    except OSError as err:
        if err.errno == errno.ENOTTY:
            # Assume we are a daemon because there is no terminal.
            is_daemon = True
        else:
            raise
    return is_daemon


def _is_sighup_and_daemon(signo):
    if not (_sighup_supported() and signo == signal.SIGHUP):
        # Avoid checking if we are a daemon, because the signal isn't
        # SIGHUP.
        return False
    return _is_daemon()


def _signo_to_signame(signo):
    signals = {signal.SIGTERM: 'SIGTERM',
               signal.SIGINT: 'SIGINT'}
    if _sighup_supported():
        signals[signal.SIGHUP] = 'SIGHUP'
    return signals[signo]


def _set_signals_handler(handler):
    signal.signal(signal.SIGTERM, handler)
    signal.signal(signal.SIGINT, handler)
    if _sighup_supported():
        signal.signal(signal.SIGHUP, handler)


class Launcher(object):
    """Launch one or more services and wait for them to complete."""

    def __init__(self):
        """Initialize the service launcher.

        :returns: None

        """
        self.services = Services()
        self.backdoor_port = eventlet_backdoor.initialize_if_enabled()

    def launch_service(self, service):
        """Load and start the given service.

        :param service: The service you would like to start.
        :returns: None

        """
        service.backdoor_port = self.backdoor_port
        self.services.add(service)

    def stop(self):
        """Stop all services which are currently running.

        :returns: None

        """
        self.services.stop()

    def wait(self):
        """Waits until all services have been stopped, and then returns.

        :returns: None

        """
        self.services.wait()

    def restart(self):
        """Reload config files and restart service.

        :returns: None

        """
        cfg.CONF.reload_config_files()
        self.services.restart()


class SignalExit(SystemExit):
    def __init__(self, signo, exccode=1):
        super(SignalExit, self).__init__(exccode)
        self.signo = signo


class ServiceLauncher(Launcher):
    def _handle_signal(self, signo, frame):
        # Allow the process to be killed again and die from natural causes
        _set_signals_handler(signal.SIG_DFL)
        raise SignalExit(signo)

    def handle_signal(self):
        _set_signals_handler(self._handle_signal)

    def _wait_for_exit_or_signal(self, ready_callback=None):
        status = None
        signo = 0

        LOG.debug('Full set of CONF:')
        CONF.log_opt_values(LOG, logging.DEBUG)

        try:
            if ready_callback:
                ready_callback()
            super(ServiceLauncher, self).wait()
        except SignalExit as exc:
            signame = _signo_to_signame(exc.signo)
            LOG.info(_LI('Caught %s, exiting'), signame)
            status = exc.code
            signo = exc.signo
        except SystemExit as exc:
            status = exc.code
        finally:
            self.stop()

        return status, signo

    def wait(self, ready_callback=None):
        systemd.notify_once()
        while True:
            self.handle_signal()
            status, signo = self._wait_for_exit_or_signal(ready_callback)
            if not _is_sighup_and_daemon(signo):
                return status
            self.restart()


class ServiceWrapper(object):
    def __init__(self, service, workers):
        self.service = service
        self.workers = workers
        self.children = set()
        self.forktimes = []


class ProcessLauncher(object):
    _signal_handlers_set = set()

    @classmethod
    def _handle_class_signals(cls, *args, **kwargs):
        for handler in cls._signal_handlers_set:
            handler(*args, **kwargs)

    def __init__(self, wait_interval=0.01):
        """Constructor.

        :param wait_interval: The interval to sleep for between checks
                              of child process exit.
        """
        self.children = {}
        self.sigcaught = None
        self.running = True
        self.wait_interval = wait_interval
        rfd, self.writepipe = os.pipe()
        self.readpipe = eventlet.greenio.GreenPipe(rfd, 'r')
        self.handle_signal()

    def handle_signal(self):
        self._signal_handlers_set.add(self._handle_signal)
        _set_signals_handler(self._handle_class_signals)

    def _handle_signal(self, signo, frame):
        self.sigcaught = signo
        self.running = False

        # Allow the process to be killed again and die from natural causes
        _set_signals_handler(signal.SIG_DFL)

    def _pipe_watcher(self):
        # This will block until the write end is closed when the parent
        # dies unexpectedly
        self.readpipe.read(1)

        LOG.info(_LI('Parent process has died unexpectedly, exiting'))

        sys.exit(1)

    def _child_process_handle_signal(self):
        # Setup child signal handlers differently
        def _sighup(*args):
            signal.signal(signal.SIGHUP, signal.SIG_DFL)
            raise SignalExit(signal.SIGHUP)

        # Parent signals with SIGTERM when it wants us to go away.
        signal.signal(signal.SIGTERM, signal.SIG_DFL)
        if _sighup_supported():
            signal.signal(signal.SIGHUP, _sighup)
        # Block SIGINT and let the parent send us a SIGTERM
        signal.signal(signal.SIGINT, signal.SIG_IGN)

    def _child_wait_for_exit_or_signal(self, launcher):
        status = 0
        signo = 0

        # NOTE(johannes): All exceptions are caught to ensure this
        # doesn't fallback into the loop spawning children. It would
        # be bad for a child to spawn more children.
        try:
            launcher.wait()
        except SignalExit as exc:
            signame = _signo_to_signame(exc.signo)
            LOG.info(_LI('Child caught %s, exiting'), signame)
            status = exc.code
            signo = exc.signo
        except SystemExit as exc:
            status = exc.code
        except BaseException:
            LOG.exception(_LE('Unhandled exception'))
            status = 2
        finally:
            launcher.stop()

        return status, signo

    def _child_process(self, service):
        self._child_process_handle_signal()

        # Reopen the eventlet hub to make sure we don't share an epoll
        # fd with parent and/or siblings, which would be bad
        eventlet.hubs.use_hub()

        # Close write to ensure only parent has it open
        os.close(self.writepipe)
        # Create greenthread to watch for parent to close pipe
        eventlet.spawn_n(self._pipe_watcher)

        # Reseed random number generator
        random.seed()

        launcher = Launcher()
        launcher.launch_service(service)
        return launcher

    def _start_child(self, wrap):
        if len(wrap.forktimes) > wrap.workers:
            # Limit ourselves to one process a second (over the period of
            # number of workers * 1 second). This will allow workers to
            # start up quickly but ensure we don't fork off children that
            # die instantly too quickly.
            if time.time() - wrap.forktimes[0] < wrap.workers:
                LOG.info(_LI('Forking too fast, sleeping'))
                time.sleep(1)

            wrap.forktimes.pop(0)

        wrap.forktimes.append(time.time())

        pid = os.fork()
        if pid == 0:
            launcher = self._child_process(wrap.service)
            while True:
                self._child_process_handle_signal()
                status, signo = self._child_wait_for_exit_or_signal(launcher)
                if not _is_sighup_and_daemon(signo):
                    break
                launcher.restart()

            os._exit(status)

        LOG.info(_LI('Started child %d'), pid)

        wrap.children.add(pid)
        self.children[pid] = wrap

        return pid

    def launch_service(self, service, workers=1):
        wrap = ServiceWrapper(service, workers)

        LOG.info(_LI('Starting %d workers'), wrap.workers)
        while self.running and len(wrap.children) < wrap.workers:
            self._start_child(wrap)

    def _wait_child(self):
        try:
            # Don't block if no child processes have exited
            pid, status = os.waitpid(0, os.WNOHANG)
            if not pid:
                return None
        except OSError as exc:
            if exc.errno not in (errno.EINTR, errno.ECHILD):
                raise
            return None

        if os.WIFSIGNALED(status):
            sig = os.WTERMSIG(status)
            LOG.info(_LI('Child %(pid)d killed by signal %(sig)d'),
                     dict(pid=pid, sig=sig))
        else:
            code = os.WEXITSTATUS(status)
            LOG.info(_LI('Child %(pid)s exited with status %(code)d'),
                     dict(pid=pid, code=code))

        if pid not in self.children:
            LOG.warning(_LW('pid %d not in child list'), pid)
            return None

        wrap = self.children.pop(pid)
        wrap.children.remove(pid)
        return wrap

    def _respawn_children(self):
        while self.running:
            wrap = self._wait_child()
            if not wrap:
                # Yield to other threads if no children have exited
                # Sleep for a short time to avoid excessive CPU usage
                # (see bug #1095346)
                eventlet.greenthread.sleep(self.wait_interval)
                continue
            while self.running and len(wrap.children) < wrap.workers:
                self._start_child(wrap)

    def wait(self):
        """Loop waiting on children to die and respawning as necessary."""

        systemd.notify_once()
        LOG.debug('Full set of CONF:')
        CONF.log_opt_values(LOG, logging.DEBUG)

        try:
            while True:
                self.handle_signal()
                self._respawn_children()
                # No signal means that stop was called.  Don't clean up here.
                if not self.sigcaught:
                    return

                signame = _signo_to_signame(self.sigcaught)
                LOG.info(_LI('Caught %s, stopping children'), signame)
                if not _is_sighup_and_daemon(self.sigcaught):
                    break

                cfg.CONF.reload_config_files()
                for service in set(
                        [wrap.service for wrap in self.children.values()]):
                    service.reset()

                for pid in self.children:
                    os.kill(pid, signal.SIGHUP)

                self.running = True
                self.sigcaught = None
        except eventlet.greenlet.GreenletExit:
            LOG.info(_LI("Wait called after thread killed. Cleaning up."))

        self.stop()

    def stop(self):
        """Terminate child processes and wait on each."""
        self.running = False
        for pid in self.children:
            try:
                os.kill(pid, signal.SIGTERM)
            except OSError as exc:
                if exc.errno != errno.ESRCH:
                    raise

        # Wait for children to die
        if self.children:
            LOG.info(_LI('Waiting on %d children to exit'), len(self.children))
            while self.children:
                self._wait_child()


class Service(object):
    """Service object for binaries running on hosts."""

    def __init__(self, threads=1000):
        self.tg = threadgroup.ThreadGroup(threads)

        # signal that the service is done shutting itself down:
        self._done = event.Event()

    def reset(self):
        # NOTE(Fengqian): docs for Event.reset() recommend against using it
        self._done = event.Event()

    def start(self):
        pass

    def stop(self, graceful=False):
        self.tg.stop(graceful)
        self.tg.wait()
        # Signal that service cleanup is done:
        if not self._done.ready():
            self._done.send()

    def wait(self):
        self._done.wait()


class Services(object):

    def __init__(self):
        self.services = []
        self.tg = threadgroup.ThreadGroup()
        self.done = event.Event()

    def add(self, service):
        self.services.append(service)
        self.tg.add_thread(self.run_service, service, self.done)

    def stop(self):
        # wait for graceful shutdown of services:
        for service in self.services:
            service.stop()
            service.wait()

        # Each service has performed cleanup, now signal that the run_service
        # wrapper threads can now die:
        if not self.done.ready():
            self.done.send()

        # reap threads:
        self.tg.stop()

    def wait(self):
        self.tg.wait()

    def restart(self):
        self.stop()
        self.done = event.Event()
        for restart_service in self.services:
            restart_service.reset()
            self.tg.add_thread(self.run_service, restart_service, self.done)

    @staticmethod
    def run_service(service, done):
        """Service start wrapper.

        :param service: service to run
        :param done: event to wait on until a shutdown is triggered
        :returns: None

        """
        service.start()
        done.wait()


def launch(service, workers=1):
    if workers is None or workers == 1:
        launcher = ServiceLauncher()
        launcher.launch_service(service)
    else:
        launcher = ProcessLauncher()
        launcher.launch_service(service, workers=workers)

    return launcher