import logging
import os
import pickle
from contextlib import contextmanager, suppress
from sqlite3 import DatabaseError

from django.conf import settings
from django.core.cache import cache
from django.db import models, transaction
from django.utils.http import int_to_base36
from django.utils.timezone import make_naive
from django.utils.translation import ugettext_lazy as _

from c3nav.mapdata.tasks import process_map_updates


class MapUpdate(models.Model):
    """
    A map update. created whenever mapdata is changed.
    """
    TYPES = (
        ('changeset', _('changeset applied')),
        ('direct_edit', _('direct edit')),
        ('control_panel', _('via control panel')),
        ('management', 'manage.py clearmapcache'),
    )
    datetime = models.DateTimeField(auto_now_add=True, db_index=True)
    user = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, on_delete=models.PROTECT)
    type = models.CharField(max_length=32, choices=TYPES)
    processed = models.BooleanField(default=False)
    geometries_changed = models.BooleanField()

    class Meta:
        verbose_name = _('Map update')
        verbose_name_plural = _('Map updates')
        default_related_name = 'mapupdates'
        get_latest_by = 'datetime'

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

    @classmethod
    def last_update(cls, force=False):
        if not force:
            last_update = cache.get('mapdata:last_update', None)
            if last_update is not None:
                return last_update
        try:
            with cls.lock():
                last_update = cls.objects.latest().to_tuple
                cache.set('mapdata:last_update', last_update, None)
        except cls.DoesNotExist:
            last_update = (0, 0)
            cache.set('mapdata:last_update', last_update, None)
        return last_update

    @classmethod
    def last_processed_update(cls, force=False):
        if not force:
            last_processed_update = cache.get('mapdata:last_processed_update', None)
            if last_processed_update is not None:
                return last_processed_update
        try:
            with cls.lock():
                last_processed_update = cls.objects.filter(processed=True).latest().to_tuple
                cache.set('mapdata:last_processed_update', last_processed_update, None)
        except cls.DoesNotExist:
            last_processed_update = (0, 0)
            cache.set('mapdata:last_processed_update', last_processed_update, None)
        return last_processed_update

    @property
    def to_tuple(self):
        return self.pk, int(make_naive(self.datetime).timestamp())

    @property
    def cache_key(self):
        return self.build_cache_key(self.pk, int(make_naive(self.datetime).timestamp()))

    @classmethod
    def current_cache_key(cls, request=None):
        return cls.build_cache_key(*cls.last_update())

    @classmethod
    def current_processed_cache_key(cls, request=None):
        return cls.build_cache_key(*cls.last_processed_update())

    @staticmethod
    def build_cache_key(pk, timestamp):
        return int_to_base36(pk)+'_'+int_to_base36(timestamp)

    @classmethod
    @contextmanager
    def lock(cls):
        with transaction.atomic():
            yield cls.objects.select_for_update().get(pk=cls.objects.earliest().pk)

    def _changed_geometries_filename(self):
        return os.path.join(settings.CACHE_ROOT, 'changed_geometries', 'update_%d.pickle' % self.pk)

    class ProcessUpdatesAlreadyRunning(Exception):
        pass

    @classmethod
    @contextmanager
    def get_updates_to_process(cls):
        queryset = cls.objects.filter(processed=False)
        with transaction.atomic():
            if settings.HAS_REDIS:
                import redis
                lock_aquired = None
                lock = redis.Redis().lock('mapupdate:process_updates:lock')
                try:
                    lock_aquired = lock.acquire(blocking=False, blocking_timeout=1800)
                    if not lock_aquired:
                        raise cls.ProcessUpdatesAlreadyRunning
                    yield tuple(queryset)
                finally:
                    if lock_aquired:
                        lock.release()
            else:
                try:
                    yield tuple(queryset.select_for_update(nowait=True))
                except DatabaseError:
                    raise cls.ProcessUpdatesAlreadyRunning

    @classmethod
    def process_updates(cls):
        logger = logging.getLogger('c3nav')

        with cls.get_updates_to_process() as new_updates:
            if not new_updates:
                return ()

            if any(update.geometries_changed for update in new_updates):
                from c3nav.mapdata.utils.cache.changes import changed_geometries
                changed_geometries.reset()

                logger.info('Recalculating altitude areas...')

                from c3nav.mapdata.models import AltitudeArea
                AltitudeArea.recalculate()

                logger.info('%.3f m² of altitude areas affected.' % changed_geometries.area)

                last_processed_update = cls.last_processed_update(force=True)

                for new_update in new_updates:
                    logger.info('Applying changed geometries from MapUpdate #%(id)s (%(type)s)...' %
                                {'id': new_update.pk, 'type': new_update.type})
                    try:
                        new_changes = pickle.load(open(new_update._changed_geometries_filename(), 'rb'))
                    except FileNotFoundError:
                        logger.warning('changed_geometries pickle file not found.')
                    else:
                        logger.info('%.3f m² affected by this update.' % new_changes.area)
                        changed_geometries.combine(new_changes)

                logger.info('%.3f m² of geometries affected in total.' % changed_geometries.area)

                changed_geometries.save(last_processed_update, new_updates[-1].to_tuple)

                logger.info('Rebuilding level render data...')

                from c3nav.mapdata.render.renderdata import LevelRenderData
                LevelRenderData.rebuild()
            else:
                logger.info('No geometries affected.')

            logger.info('Rebuilding router...')
            from c3nav.routing.router import Router
            Router.rebuild(new_updates[-1].to_tuple)

            logger.info('Rebuilding locator...')
            from c3nav.routing.locator import Locator
            Locator.rebuild(new_updates[-1].to_tuple)

            for new_update in new_updates:
                new_update.processed = True
                new_update.save()

            transaction.on_commit(
                lambda: cache.set('mapdata:last_processed_update', new_updates[-1].to_tuple, None)
            )

            return new_updates

    def save(self, **kwargs):
        new = self.pk is None
        if not new and (self.was_processed or not self.processed):
            raise TypeError

        from c3nav.mapdata.utils.cache.changes import changed_geometries

        if self.geometries_changed is None:
            self.geometries_changed = not changed_geometries.is_empty

        super().save(**kwargs)

        with suppress(FileExistsError):
            os.mkdir(os.path.dirname(self._changed_geometries_filename()))

        if self.geometries_changed:
            pickle.dump(changed_geometries, open(self._changed_geometries_filename(), 'wb'))

        if new:
            transaction.on_commit(
                lambda: cache.set('mapdata:last_update', self.to_tuple, None)
            )
            if settings.HAS_CELERY and settings.AUTO_PROCESS_UPDATES:
                transaction.on_commit(
                    lambda: process_map_updates.delay()
                )