import logging
import traceback
from multiprocessing.dummy import Pool as ThreadPool
from threading import Lock

from apscheduler.schedulers import SchedulerAlreadyRunningError, SchedulerNotRunningError
from apscheduler.schedulers.background import BackgroundScheduler
from django import db
from django.db.models import Q, Count

from app.models import Task, Project
from nodeodm import status_codes
from nodeodm.models import ProcessingNode
from app.background import background

logger = logging.getLogger('app.logger')
scheduler = BackgroundScheduler({
    'apscheduler.job_defaults.coalesce': 'false',
    'apscheduler.job_defaults.max_instances': '3',
})

@background
def update_nodes_info():
    processing_nodes = ProcessingNode.objects.all()
    for processing_node in processing_nodes:
        processing_node.update_node_info()

tasks_mutex = Lock()

@background
def process_pending_tasks():
    tasks = []
    try:
        tasks_mutex.acquire()

        # All tasks that have a processing node assigned
        # but don't have a UUID
        # or tasks that have a pending action
        # and that are not locked (being processed by another thread)
        tasks = Task.objects.filter(Q(uuid='', last_error__isnull=True, processing_node__isnull=False) |
                                    Q(status__in=[status_codes.QUEUED, status_codes.RUNNING], processing_node__isnull=False) |
                                    Q(status=None, processing_node__isnull=False) |
                                    Q(pending_action__isnull=False)).exclude(Q(processing_lock=True))
        for task in tasks:
            logger.info("Acquiring lock: {}".format(task))
            task.processing_lock = True
            task.save()
    finally:
        tasks_mutex.release()

    def process(task):
        try:
            task.process()

            # Might have been deleted
            if task.pk is not None:
                task.processing_lock = False
                task.save()
        except Exception as e:
            logger.error("Uncaught error: {} {}".format(e, traceback.format_exc()))
        finally:
            db.connections.close_all()

    if tasks.count() > 0:
        pool = ThreadPool(tasks.count())
        pool.map(process, tasks, chunksize=1)
        pool.close()
        pool.join()


def cleanup_projects():
    # Delete all projects that are marked for deletion
    # and that have no tasks left
    total, count_dict = Project.objects.filter(deleting=True).annotate(
                    tasks_count=Count('task')
                ).filter(tasks_count=0).delete()
    if total > 0 and 'app.Project' in count_dict:
        logger.info("Deleted {} projects".format(count_dict['app.Project']))

def setup():
    logger.info("Starting background scheduler...")
    try:
        scheduler.start()
        scheduler.add_job(update_nodes_info, 'interval', seconds=30)
        scheduler.add_job(process_pending_tasks, 'interval', seconds=5)
        scheduler.add_job(cleanup_projects, 'interval', seconds=15)
    except SchedulerAlreadyRunningError:
        logger.warning("Scheduler already running (this is OK while testing)")

def teardown():
    logger.info("Stopping scheduler...")
    try:
        scheduler.shutdown()
        logger.info("Scheduler stopped")
    except SchedulerNotRunningError:
        logger.warning("Scheduler not running")