# 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 collections
import errno
import functools
import gc
import inspect
import logging
import os
import random
import signal
import sys
import time

import eventlet
from eventlet import event
from eventlet import tpool

try:
    from eventlet.hubs import poll as poll_hub
except ImportError:
    poll_hub = None

from oslo_service._i18n import _
from oslo_service import _options
from oslo_service.backend._common.constants import \
    _LAUNCHER_RESTART_METHODS
from oslo_service.backend._common.service \
    import check_service_base as _check_service_base
from oslo_service.backend._common.service import get_signal_mappings
from oslo_service.backend._common.service import \
    is_sighup_and_daemon as _is_sighup_and_daemon
from oslo_service.backend._common.service import SignalExit
from oslo_service.backend._common.service import Singleton
from oslo_service.backend._eventlet import threadgroup
from oslo_service.backend.base import ServiceBase
from oslo_service import eventlet_backdoor
from oslo_service import systemd


LOG = logging.getLogger(__name__)


class SignalHandler(metaclass=Singleton):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.__setup_signal_interruption()

        # Map all signal names to signal integer values and create a
        # reverse mapping (for easier + quick lookup).
        self._signals_by_name, self.signals_to_name = get_signal_mappings()
        self._signal_handlers = collections.defaultdict(list)
        self.clear()

    def clear(self):
        for sig in self._signal_handlers:
            signal.signal(sig, signal.SIG_DFL)
        self._signal_handlers.clear()

    def add_handlers(self, signals, handler):
        for sig in signals:
            self.add_handler(sig, handler)

    def add_handler(self, sig, handler):
        if not self.is_signal_supported(sig):
            return
        signo = self._signals_by_name[sig]
        self._signal_handlers[signo].append(handler)
        signal.signal(signo, self._handle_signal)

    def _handle_signal(self, signo, frame):
        # This method can be called anytime, even between two Python
        # instructions. It's scheduled by the C signal handler of Python using
        # Py_AddPendingCall().
        #
        # We only do one thing: schedule a call to _handle_signal_cb() later.
        # eventlet.spawn() is not signal-safe: _handle_signal() can be called
        # during a call to eventlet.spawn(). This case is supported, it is
        # ok to schedule multiple calls to _handle_signal() with the same
        # signal number.
        #
        # To call to _handle_signal_cb() is delayed to avoid reentrant calls to
        # _handle_signal_cb(). It avoids race conditions like reentrant call to
        # clear(): clear() is not reentrant (bug #1538204).
        eventlet.spawn(self._handle_signal_cb, signo, frame)

        # On Python >= 3.5, ensure that eventlet's poll() or sleep() call is
        # interrupted by raising an exception. If the signal handler does not
        # raise an exception then due to PEP 475 the call will not return until
        # an event is detected on a file descriptor or the timeout is reached,
        # and thus eventlet will not wake up and notice that there has been a
        # new thread spawned.
        if self.__force_interrupt_on_signal:
            try:
                interrupted_frame = inspect.stack(context=0)[1]
            except IndexError:
                pass
            else:
                if ((interrupted_frame.function == 'do_poll' and
                     interrupted_frame.filename == self.__hub_module_file) or
                    (interrupted_frame.function == 'do_sleep' and
                     interrupted_frame.filename == __file__)):
                    raise OSError(errno.EINTR, 'Interrupted')

    def __setup_signal_interruption(self):
        """Set up to do the Right Thing with signals during poll() and sleep().

        Deal with the changes introduced in PEP 475 that prevent a
        signal from interrupting eventlet's call to poll() or sleep().
        """
        select_module = eventlet.patcher.original('select')
        self.__force_interrupt_on_signal = hasattr(select_module, 'poll')

        if self.__force_interrupt_on_signal and poll_hub is not None:
            # This is a function we can test for in the stack when handling
            # a signal - it's safe to raise an IOError with EINTR anywhere
            # in this function.
            def do_sleep(time_sleep_func, seconds):
                return time_sleep_func(seconds)

            time_sleep = eventlet.patcher.original('time').sleep

            # Wrap time.sleep to ignore the interruption error we're
            # injecting from the signal handler. This makes the behaviour
            # the same as sleep() in Python 2, where EINTR causes the
            # sleep to be interrupted (and not resumed), but no exception
            # is raised.
            @functools.wraps(time_sleep)
            def sleep_wrapper(seconds):
                try:
                    return do_sleep(time_sleep, seconds)
                except (OSError, InterruptedError) as err:
                    if err.errno != errno.EINTR:
                        raise

            poll_hub.sleep = sleep_wrapper

            hub = eventlet.hubs.get_hub()
            self.__hub_module_file = sys.modules[hub.__module__].__file__

    def _handle_signal_cb(self, signo, frame):
        for handler in reversed(self._signal_handlers[signo]):
            handler(signo, frame)

    def is_signal_supported(self, sig_name):
        return sig_name in self._signals_by_name


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

    def __init__(self, conf, restart_method='reload'):
        """Initialize the service launcher.

        :param conf: Configuration object
        :param restart_method: If 'reload', calls reload_config_files on
            SIGHUP. If 'mutate', calls mutate_config_files on SIGHUP.
            Other values produce a ValueError.
        :returns: None
        """
        self.conf = conf
        conf.register_opts(_options.service_opts)
        self.services = Services(restart_method=restart_method)
        self.backdoor_port = (
            eventlet_backdoor.initialize_if_enabled(self.conf))
        self.restart_method = restart_method

    def launch_service(self, service, workers=1):
        """Load and start the given service.

        :param service: The service you would like to start, must be an
                        instance of :class:`oslo_service.service.ServiceBase`
        :param workers: This param makes this method compatible with
                        ProcessLauncher.launch_service. It must be None, 1 or
                        omitted.
        :returns: None
        """
        if workers is not None and workers != 1:
            raise ValueError(_("Launcher asked to start multiple workers"))
        _check_service_base(service)
        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):
        """Wait until all services have been stopped, and then return.

        :returns: None
        """
        self.services.wait()

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

        :returns: The return value from reload_config_files or
            mutate_config_files, according to the restart_method.
        """
        if self.restart_method == 'reload':
            self.conf.reload_config_files()
        else:  # self.restart_method == 'mutate'
            self.conf.mutate_config_files()
        self.services.restart()


class ServiceLauncher(Launcher):
    """Runs one or more service in a parent process."""

    def __init__(self, conf, restart_method='reload'):
        """Constructor.

        :param conf: an instance of ConfigOpts
        :param restart_method: passed to super
        """
        super().__init__(
            conf, restart_method=restart_method)
        self.signal_handler = SignalHandler()

    def _graceful_shutdown(self, *args):
        self.signal_handler.clear()
        if (self.conf.graceful_shutdown_timeout and
                self.signal_handler.is_signal_supported('SIGALRM')):
            signal.alarm(self.conf.graceful_shutdown_timeout)
        self.stop()

    def _reload_service(self, *args):
        self.signal_handler.clear()
        raise SignalExit(signal.SIGHUP)

    def _fast_exit(self, *args):
        LOG.info('Caught SIGINT signal, instantaneous exiting')
        os._exit(1)

    def _on_timeout_exit(self, *args):
        LOG.info('Graceful shutdown timeout exceeded, '
                 'instantaneous exiting')
        os._exit(1)

    def handle_signal(self):
        """Set self._handle_signal as a signal handler."""
        self.signal_handler.clear()
        self.signal_handler.add_handler('SIGTERM', self._graceful_shutdown)
        self.signal_handler.add_handler('SIGINT', self._fast_exit)
        self.signal_handler.add_handler('SIGHUP', self._reload_service)
        self.signal_handler.add_handler('SIGALRM', self._on_timeout_exit)

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

        if self.conf.log_options:
            LOG.debug('Full set of CONF:')
            self.conf.log_opt_values(LOG, logging.DEBUG)

        try:
            super().wait()
        except SignalExit as exc:
            signame = self.signal_handler.signals_to_name[exc.signo]
            LOG.info('Caught %s, handling', signame)
            status = exc.code
            signo = exc.signo
        except SystemExit as exc:
            self.stop()
            status = exc.code
        except Exception:
            self.stop()
        return status, signo

    def wait(self):
        """Wait for a service to terminate and restart it on SIGHUP.

        :returns: termination status
        """
        systemd.notify_once()
        self.signal_handler.clear()
        while True:
            self.handle_signal()
            status, signo = self._wait_for_exit_or_signal()
            if not _is_sighup_and_daemon(signo, SignalHandler()):
                break
            self.restart()

        super().wait()
        return status


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


class ProcessLauncher:
    """Launch a service with a given number of workers."""

    def __init__(self, conf, wait_interval=0.01, restart_method='reload'):
        """Constructor.

        :param conf: an instance of ConfigOpts
        :param wait_interval: The interval to sleep for between checks
            of child process exit.
        :param restart_method: If 'reload', calls reload_config_files on
            SIGHUP. If 'mutate', calls mutate_config_files on SIGHUP.
            Other values produce a ValueError.
        """
        self.conf = conf
        conf.register_opts(_options.service_opts)
        self.children = {}
        self.sigcaught = None
        self.running = True
        self.wait_interval = wait_interval
        self.launcher = None
        rfd, self.writepipe = os.pipe()
        self.readpipe = eventlet.greenio.GreenPipe(rfd, 'r')
        self.signal_handler = SignalHandler()
        self.handle_signal()
        self.restart_method = restart_method
        if restart_method not in _LAUNCHER_RESTART_METHODS:
            raise ValueError(_("Invalid restart_method: %s") % restart_method)

    def handle_signal(self):
        """Add instance's signal handlers to class handlers."""
        self.signal_handler.add_handler('SIGTERM', self._handle_term)
        self.signal_handler.add_handler('SIGHUP', self._handle_hup)
        self.signal_handler.add_handler('SIGINT', self._fast_exit)
        self.signal_handler.add_handler('SIGALRM', self._on_alarm_exit)

    def _handle_term(self, signo, frame):
        """Handle a TERM event.

        :param signo: signal number
        :param frame: current stack frame
        """
        self.sigcaught = signo
        self.running = False

        # Allow the process to be killed again and die from natural causes
        self.signal_handler.clear()

    def _handle_hup(self, signo, frame):
        """Handle a HUP event.

        :param signo: signal number
        :param frame: current stack frame
        """
        self.sigcaught = signo
        self.running = False

        # Do NOT clear the signal_handler, allowing multiple SIGHUPs to be
        # received swiftly. If a non-HUP is received before #wait loops, the
        # second event will "overwrite" the HUP. This is fine.

    def _fast_exit(self, signo, frame):
        LOG.info('Caught SIGINT signal, instantaneous exiting')
        os._exit(1)

    def _on_alarm_exit(self, signo, frame):
        LOG.info('Graceful shutdown timeout exceeded, '
                 'instantaneous exiting')
        os._exit(1)

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

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

        if self.launcher:
            self.launcher.stop()

        sys.exit(1)

    def _child_process_handle_signal(self):
        # Setup child signal handlers differently

        def _sigterm(*args):
            self.signal_handler.clear()
            self.launcher.stop()

        def _sighup(*args):
            self.signal_handler.clear()
            raise SignalExit(signal.SIGHUP)

        self.signal_handler.clear()

        # Parent signals with SIGTERM when it wants us to go away.
        self.signal_handler.add_handler('SIGTERM', _sigterm)
        self.signal_handler.add_handler('SIGHUP', _sighup)
        self.signal_handler.add_handler('SIGINT', self._fast_exit)

    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 = self.signal_handler.signals_to_name[exc.signo]
            LOG.info('Child caught %s, handling', signame)
            status = exc.code
            signo = exc.signo
        except SystemExit as exc:
            launcher.stop()
            status = exc.code
        except BaseException:
            launcher.stop()
            LOG.exception('Unhandled exception')
            status = 2

        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(self.conf, restart_method=self.restart_method)
        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('Forking too fast, sleeping')
                time.sleep(1)

            wrap.forktimes.pop(0)

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

        pid = os.fork()
        if pid == 0:
            # When parent used native threads the library on child needs to be
            # "reset", otherwise native threads won't work on the child.
            tpool.killall()
            self.launcher = self._child_process(wrap.service)
            while True:
                self._child_process_handle_signal()
                status, signo = self._child_wait_for_exit_or_signal(
                    self.launcher)
                if not _is_sighup_and_daemon(signo, SignalHandler()):
                    self.launcher.wait()
                    break
                self.launcher.restart()

            os._exit(status)

        LOG.debug('Started child %d', pid)

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

        return pid

    def launch_service(self, service, workers=1):
        """Launch a service with a given number of workers.

        :param service: a service to launch, must be an instance of
               :class:`oslo_service.service.ServiceBase`
        :param workers: a number of processes in which a service
               will be running
        """
        _check_service_base(service)
        wrap = ServiceWrapper(service, workers)

        # Hide existing objects from the garbage collector, so that most
        # existing pages will remain in shared memory rather than being
        # duplicated between subprocesses in the GC mark-and-sweep. (Requires
        # Python 3.7 or later.)
        if hasattr(gc, 'freeze'):
            gc.freeze()

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

        if pid not in self.children:
            LOG.warning('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()
        if self.conf.log_options:
            LOG.debug('Full set of CONF:')
            self.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 = self.signal_handler.signals_to_name[self.sigcaught]
                LOG.info('Caught %s, stopping children', signame)
                if not _is_sighup_and_daemon(self.sigcaught, SignalHandler()):
                    break

                child_signal = signal.SIGTERM
                if self.restart_method == 'reload':
                    self.conf.reload_config_files()
                elif self.restart_method == 'mutate':
                    self.conf.mutate_config_files()
                    child_signal = signal.SIGHUP
                for service in {
                        wrap.service for wrap in self.children.values()}:
                    service.reset()

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

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

        # if we are here it means that we are trying to do graceful shutdown.
        # add alarm watching that graceful_shutdown_timeout is not exceeded
        if (self.conf.graceful_shutdown_timeout and
                self.signal_handler.is_signal_supported('SIGALRM')):
            signal.alarm(self.conf.graceful_shutdown_timeout)

        self.stop()

    def stop(self):
        """Terminate child processes and wait on each."""
        self.running = False

        LOG.debug("Stop services.")
        for service in {
                wrap.service for wrap in self.children.values()}:
            service.stop()

        LOG.debug("Killing children.")
        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('Waiting on %d children to exit', len(self.children))
            while self.children:
                self._wait_child()


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

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

    def reset(self):
        """Reset a service in case it received a SIGHUP."""

    def start(self):
        """Start a service."""

    def stop(self, graceful=False):
        """Stop a service.

        :param graceful: indicates whether to wait for all threads to
            finish or terminate them instantly
        """
        self.tg.stop(graceful)

    def wait(self):
        """Wait for a service to shut down."""
        self.tg.wait()


class Services:

    def __init__(self, restart_method='reload'):
        if restart_method not in _LAUNCHER_RESTART_METHODS:
            raise ValueError(_("Invalid restart_method: %s") % restart_method)
        self.restart_method = restart_method
        self.services = []
        self.tg = threadgroup.ThreadGroup()
        self.done = event.Event()

    def add(self, service):
        """Add a service to a list and create a thread to run it.

        :param service: service to run
        """
        self.services.append(service)
        self.tg.add_thread(self.run_service, service, self.done)

    def stop(self):
        """Wait for graceful shutdown of services and kill the threads."""
        for service in self.services:
            service.stop()

        # 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):
        """Wait for services to shut down."""
        for service in self.services:
            service.wait()
        self.tg.wait()

    def restart(self):
        """Reset services.

        The behavior of this function varies depending on the value of the
        restart_method member. If the restart_method is `reload`, then it
        will stop the services, reset them, and start them in new threads.
        If the restart_method is `mutate`, then it will just reset the
        services without restarting them.
        """
        if self.restart_method == 'reload':
            self.stop()
            self.done = event.Event()
        for restart_service in self.services:
            restart_service.reset()
            if self.restart_method == 'reload':
                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
        """
        try:
            service.start()
        except Exception:
            LOG.exception('Error starting thread.')
            raise SystemExit(1)
        else:
            done.wait()


def launch(conf, service, workers=1, restart_method='reload', no_fork=False):
    """Launch a service with a given number of workers.

    :param conf: an instance of ConfigOpts
    :param service: a service to launch, must be an instance of
           :class:`oslo_service.service.ServiceBase`
    :param workers: a number of processes in which a service will be running,
        type should be int.
    :param restart_method: Passed to the constructed launcher. If 'reload', the
        launcher will call reload_config_files on SIGHUP. If 'mutate', it will
        call mutate_config_files on SIGHUP. Other values produce a ValueError.
    :param no_fork: Ignored for this backend.
    :returns: An instance of a launcher that was used to launch the service
    """
    if workers is not None and not isinstance(workers, int):
        raise TypeError(_("Type of workers should be int!"))

    if workers is not None and workers <= 0:
        raise ValueError(_("Number of workers should be positive!"))

    if workers is None or workers == 1:
        launcher = ServiceLauncher(conf, restart_method=restart_method)
    else:
        launcher = ProcessLauncher(conf, restart_method=restart_method)

    launcher.launch_service(service, workers=workers)

    return launcher
