from datetime import timedelta, datetime
import platform
import time
import random

from django.db.models import Q
from django.utils.translation import ugettext as _

from celery.decorators import task, periodic_task

from ocr.api import do_document_ocr
from ocr.literals import QUEUEDOCUMENT_STATE_PENDING, \
    QUEUEDOCUMENT_STATE_PROCESSING, DOCUMENTQUEUE_STATE_ACTIVE, \
    QUEUEDOCUMENT_STATE_ERROR
from ocr.models import QueueDocument, DocumentQueue
from ocr.conf.settings import NODE_CONCURRENT_EXECUTION
from ocr.conf.settings import REPLICATION_DELAY
from ocr.conf.settings import QUEUE_PROCESSING_INTERVAL


@task
def task_process_queue_document(queue_document_id):
    queue_document = QueueDocument.objects.get(id=queue_document_id)
    if queue_document.state == QUEUEDOCUMENT_STATE_PROCESSING:
        #Recheck to avoid race condition
        return
    queue_document.state = QUEUEDOCUMENT_STATE_PROCESSING
    queue_document.node_name = platform.node()
    queue_document.result = task_process_queue_document.request.id
    queue_document.save()
    try:
        do_document_ocr(queue_document.document)
        queue_document.delete()
    except Exception, e:
        queue_document.state = QUEUEDOCUMENT_STATE_ERROR
        queue_document.result = e
        queue_document.save()


@periodic_task(run_every=timedelta(seconds=QUEUE_PROCESSING_INTERVAL))
def task_process_document_queues():
    #Introduce random 0 < t < 1 second delay to further reduce the
    #chance of a race condition
    time.sleep(random.random())
    q_pending = Q(state=QUEUEDOCUMENT_STATE_PENDING)
    q_delayed = Q(delay=True)
    q_delay_interval = Q(datetime_submitted__lt=datetime.now() - timedelta(seconds=REPLICATION_DELAY))
    for document_queue in DocumentQueue.objects.filter(state=DOCUMENTQUEUE_STATE_ACTIVE):
        if QueueDocument.objects.filter(
            state=QUEUEDOCUMENT_STATE_PROCESSING).filter(
            node_name=platform.node()).count() < NODE_CONCURRENT_EXECUTION:
            try:
                oldest_queued_document_qs = document_queue.queuedocument_set.filter(
                    (q_pending & ~q_delayed) | (q_pending & q_delayed & q_delay_interval))

                if oldest_queued_document_qs:
                    oldest_queued_document = oldest_queued_document_qs.order_by('datetime_submitted')[0]
                    task_process_queue_document.delay(oldest_queued_document.id)
            except Exception, e:
                print 'DocumentQueueWatcher exception: %s' % e