# Copyright 2013 VMware, Inc.
# 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.

import collections
import uuid

from eventlet import event
from eventlet import greenthread
from neutron.common import exceptions
from oslo_log import log as logging
from oslo_service import loopingcall
import six

from neutron.i18n import _LE, _LI
from vmware_nsx.plugins.nsx_v.vshield.tasks import constants

DEFAULT_INTERVAL = 1000

LOG = logging.getLogger(__name__)


def nop(task):
    return constants.TaskStatus.COMPLETED


class TaskException(exceptions.NeutronException):

    def __init__(self, message=None, **kwargs):
        if message is not None:
            self.message = message

        super(TaskException, self).__init__(**kwargs)


class InvalidState(TaskException):
    message = _("Invalid state %(state)d")


class TaskStateSkipped(TaskException):
    message = _("State %(state)d skipped. Current state %(current)d")


class Task():
    def __init__(self, name, resource_id, execute_callback,
                 status_callback=nop, result_callback=nop, userdata=None):
        self.name = name
        self.resource_id = resource_id
        self._execute_callback = execute_callback
        self._status_callback = status_callback
        self._result_callback = result_callback
        self.userdata = userdata
        self.id = None
        self.status = None

        self._monitors = {
            constants.TaskState.START: [],
            constants.TaskState.EXECUTED: [],
            constants.TaskState.RESULT: []
        }
        self._states = [None, None, None, None]
        self._state = constants.TaskState.NONE

    def _add_monitor(self, action, func):
        self._monitors[action].append(func)
        return self

    def _move_state(self, state):
        self._state = state
        if self._states[state] is not None:
            e = self._states[state]
            self._states[state] = None
            e.send()

        for s in range(state):
            if self._states[s] is not None:
                e = self._states[s]
                self._states[s] = None
                e.send_exception(
                    TaskStateSkipped(state=s, current=self._state))

    def _invoke_monitor(self, state):
        for func in self._monitors[state]:
            try:
                func(self)
            except Exception:
                LOG.exception(_LE("Task %(task)s encountered exception in "
                                  "%(func)s at state %(state)s"),
                              {'task': str(self),
                               'func': str(func),
                               'state': state})

        self._move_state(state)

        return self

    def _start(self):
        return self._invoke_monitor(constants.TaskState.START)

    def _executed(self):
        return self._invoke_monitor(constants.TaskState.EXECUTED)

    def _update_status(self, status):
        if self.status == status:
            return self

        self.status = status

    def _finished(self):
        return self._invoke_monitor(constants.TaskState.RESULT)

    def add_start_monitor(self, func):
        return self._add_monitor(constants.TaskState.START, func)

    def add_executed_monitor(self, func):
        return self._add_monitor(constants.TaskState.EXECUTED, func)

    def add_result_monitor(self, func):
        return self._add_monitor(constants.TaskState.RESULT, func)

    def wait(self, state):
        if (state < constants.TaskState.START or
            state > constants.TaskState.RESULT or
            state == constants.TaskState.STATUS):
            raise InvalidState(state=state)

        if state <= self._state:
            # we already passed this current state, so no wait
            return

        e = event.Event()
        self._states[state] = e
        e.wait()

    def __repr__(self):
        return "Task-%s-%s-%s" % (
            self.name, self.resource_id, self.id)


class TaskManager():

    _instance = None
    _default_interval = DEFAULT_INTERVAL

    def __init__(self, interval=None):
        self._interval = interval or TaskManager._default_interval

        # A queue to pass tasks from other threads
        self._tasks_queue = collections.deque()

        # A dict to store resource -> resource's tasks
        self._tasks = {}

        # Current task being executed in main thread
        self._main_thread_exec_task = None

        # New request event
        self._req = event.Event()

        # TaskHandler stopped event
        self._stopped = False

        # Periodic function trigger
        self._monitor = None
        self._monitor_busy = False

        # Thread handling the task request
        self._thread = None

    def _execute(self, task):
        """Execute task."""
        LOG.debug("Start task %s", str(task))
        task._start()
        try:
            status = task._execute_callback(task)
        except Exception:
            LOG.exception(_LE("Task %(task)s encountered exception in "
                              "%(cb)s"),
                          {'task': str(task),
                           'cb': str(task._execute_callback)})
            status = constants.TaskStatus.ERROR

        LOG.debug("Task %(task)s return %(status)s",
                  {'task': str(task),
                   'status': status})
        task._update_status(status)
        task._executed()

        return status

    def _result(self, task):
        """Notify task execution result."""
        try:
            task._result_callback(task)
        except Exception:
            LOG.exception(_LE("Task %(task)s encountered exception in "
                              "%(cb)s"),
                          {'task': str(task),
                           'cb': str(task._result_callback)})
        LOG.debug("Task %(task)s return %(status)s",
                  {'task': str(task), 'status': task.status})

        task._finished()

    def _check_pending_tasks(self):
        """Check all pending tasks status."""
        for resource_id in self._tasks.keys():
            if self._stopped:
                # Task manager is stopped, return now
                return

            tasks = self._tasks[resource_id]
            # only the first task is executed and pending
            task = tasks[0]
            try:
                status = task._status_callback(task)
            except Exception:
                LOG.exception(_LE("Task %(task)s encountered exception in "
                                  "%(cb)s"),
                              {'task': str(task),
                               'cb': str(task._status_callback)})
                status = constants.TaskStatus.ERROR
            task._update_status(status)
            if status != constants.TaskStatus.PENDING:
                self._dequeue(task, True)

    def _enqueue(self, task):
        if task.resource_id in self._tasks:
            # append to existing resource queue for ordered processing
            self._tasks[task.resource_id].append(task)
        else:
            # put the task to a new resource queue
            tasks = collections.deque()
            tasks.append(task)
            self._tasks[task.resource_id] = tasks

    def _dequeue(self, task, run_next):
        self._result(task)
        tasks = self._tasks[task.resource_id]
        tasks.remove(task)
        if not tasks:
            # no more tasks for this resource
            del self._tasks[task.resource_id]
            return

        if run_next:
            # process next task for this resource
            while tasks:
                task = tasks[0]
                status = self._execute(task)
                if status == constants.TaskStatus.PENDING:
                    break
                self._dequeue(task, False)

    def _abort(self):
        """Abort all tasks."""
        # put all tasks haven't been received by main thread to queue
        # so the following abort handling can cover them
        for t in self._tasks_queue:
            self._enqueue(t)
        self._tasks_queue.clear()

        for resource_id in self._tasks.keys():
            tasks = list(self._tasks[resource_id])
            for task in tasks:
                task._update_status(constants.TaskStatus.ABORT)
                self._dequeue(task, False)

    def _get_task(self):
        """Get task request."""
        while True:
            for t in self._tasks_queue:
                return self._tasks_queue.popleft()
            self._req.wait()
            self._req.reset()

    def run(self):
        while True:
            try:
                if self._stopped:
                    # Gracefully terminate this thread if the _stopped
                    # attribute was set to true
                    LOG.info(_LI("Stopping TaskManager"))
                    break

                # get a task from queue, or timeout for periodic status check
                task = self._get_task()
                if task.resource_id in self._tasks:
                    # this resource already has some tasks under processing,
                    # append the task to same queue for ordered processing
                    self._enqueue(task)
                    continue

                try:
                    self._main_thread_exec_task = task
                    self._execute(task)
                finally:
                    self._main_thread_exec_task = None
                    if task.status is None:
                        # The thread is killed during _execute(). To guarantee
                        # the task been aborted correctly, put it to the queue.
                        self._enqueue(task)
                    elif task.status != constants.TaskStatus.PENDING:
                        self._result(task)
                    else:
                        self._enqueue(task)
            except Exception:
                LOG.exception(_LE("TaskManager terminating because "
                                  "of an exception"))
                break

    def add(self, task):
        task.id = uuid.uuid1()
        self._tasks_queue.append(task)
        if not self._req.ready():
            self._req.send()
        return task.id

    def stop(self):
        if self._thread is None:
            return
        self._stopped = True
        self._thread.kill()
        self._thread = None
        # Stop looping call and abort running tasks
        self._monitor.stop()
        if self._monitor_busy:
            self._monitor.wait()
        self._abort()
        LOG.info(_LI("TaskManager terminated"))

    def has_pending_task(self):
        if self._tasks_queue or self._tasks or self._main_thread_exec_task:
            return True
        else:
            return False

    def show_pending_tasks(self):
        for task in self._tasks_queue:
            LOG.info(str(task))
        for resource, tasks in six.iteritems(self._tasks):
            for task in tasks:
                LOG.info(str(task))
        if self._main_thread_exec_task:
            LOG.info(str(self._main_thread_exec_task))

    def count(self):
        count = 0
        for resource_id, tasks in six.iteritems(self._tasks):
            count += len(tasks)
        return count

    def start(self, interval=None):
        def _inner():
            self.run()

        def _loopingcall_callback():
            self._monitor_busy = True
            try:
                self._check_pending_tasks()
            except Exception:
                LOG.exception(_LE("Exception in _check_pending_tasks"))
            self._monitor_busy = False

        if self._thread is not None:
            return self

        if interval is None or interval == 0:
            interval = self._interval

        self._stopped = False
        self._thread = greenthread.spawn(_inner)
        self._monitor = loopingcall.FixedIntervalLoopingCall(
            _loopingcall_callback)
        self._monitor.start(interval / 1000.0,
                            interval / 1000.0)
        # To allow the created thread start running
        greenthread.sleep(0)

        return self

    @classmethod
    def set_default_interval(cls, interval):
        cls._default_interval = interval