#!/usr/bin/python
# -*- coding: utf-8 -*-
#
# Copyright 2012 The Plaso Project Authors.
# Please see the AUTHORS file for details on individual authors.
#
# 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.
"""Queue management implementation for Plaso.

This file contains an implementation of a queue used by plaso for
queue management.

The queue has been abstracted in order to provide support for different
implementations of the queueing mechanism, to support multi processing and
scalability.
"""

import abc

from plaso.lib import errors


class QueueEndOfInput(object):
  """Class that implements a queue end of input."""


class Queue(object):
  """Class that implements the queue interface."""

  @abc.abstractmethod
  def __len__(self):
    """Returns the estimated current number of items in the queue."""

  @abc.abstractmethod
  def IsEmpty(self):
    """Determines if the queue is empty."""

  @abc.abstractmethod
  def PushItem(self, item):
    """Pushes an item onto the queue."""

  @abc.abstractmethod
  def PopItem(self):
    """Pops an item off the queue."""

  def SignalEndOfInput(self):
    """Signals the queue no input remains."""
    self.PushItem(QueueEndOfInput())


class QueueConsumer(object):
  """Class that implements the queue consumer interface.

     The consumer subscribes to updates on the queue.
  """

  def __init__(self, queue_object):
    """Initializes the queue consumer.

    Args:
      queue_object: the queue object (instance of Queue).
    """
    super(QueueConsumer, self).__init__()
    self._abort = False
    self._queue = queue_object

  def SignalAbort(self):
    """Signals the consumer to abort."""
    self._abort = True


class QueueProducer(object):
  """Class that implements the queue producer interface.

     The producer generates updates on the queue.
  """

  def __init__(self, queue_object):
    """Initializes the queue producer.

    Args:
      queue_object: the queue object (instance of Queue).
    """
    super(QueueProducer, self).__init__()
    self._abort = False
    self._queue = queue_object

  def SignalAbort(self):
    """Signals the producer to abort."""
    self._abort = True

  def SignalEndOfInput(self):
    """Signals the queue no input remains."""
    self._queue.SignalEndOfInput()


class EventObjectQueueConsumer(QueueConsumer):
  """Class that implements the event object queue consumer.

     The consumer subscribes to updates on the queue.
  """

  @abc.abstractmethod
  def _ConsumeEventObject(self, event_object, **kwargs):
    """Consumes an event object callback for ConsumeEventObjects."""

  def ConsumeEventObjects(self, **kwargs):
    """Consumes the event object that are pushed on the queue.

       This function will issue a callback to _ConsumeEventObject for every
       event object (instance of EventObject) consumed from the queue.

    Args:
      kwargs: keyword arguments to pass to the _ConsumeEventObject callback.
    """
    while not self._abort:
      try:
        item = self._queue.PopItem()
      except errors.QueueEmpty:
        break

      if isinstance(item, QueueEndOfInput):
        # Push the item back onto the queue to make sure all
        # queue consumers are stopped.
        self._queue.PushItem(item)
        break

      self._ConsumeEventObject(item, **kwargs)

    self._abort = False


class ItemQueueConsumer(QueueConsumer):
  """Class that implements an item queue consumer.

     The consumer subscribes to updates on the queue.
  """

  @abc.abstractmethod
  def _ConsumeItem(self, item):
    """Consumes an item callback for ConsumeItems.

    Args:
      item: the item object.
    """

  def ConsumeItems(self):
    """Consumes the items that are pushed on the queue."""
    while not self._abort:
      try:
        item = self._queue.PopItem()
      except errors.QueueEmpty:
        break

      if isinstance(item, QueueEndOfInput):
        # Push the item back onto the queue to make sure all
        # queue consumers are stopped.
        self._queue.PushItem(item)
        break

      self._ConsumeItem(item)

    self._abort = False


class ItemQueueProducer(QueueProducer):
  """Class that implements an item queue producer.

     The producer generates updates on the queue.
  """

  def _FlushQueue(self):
    """Flushes the queue callback for the QueueFull exception."""
    return

  def ProduceItem(self, item):
    """Produces an item onto the queue.

    Args:
      item: the item object.
    """
    try:
      self._queue.PushItem(item)
    except errors.QueueFull:
      self._FlushQueue()

  def ProduceItems(self, items):
    """Produces items onto the queue.

    Args:
      items: a list or generator of item objects.
    """
    for item in items:
      self.ProduceItem(item)