from logging import getLogger
from queue import Queue, Empty
from threading import Thread, Event, RLock
from time import time
from typing import Iterable, List, Optional

from sqlalchemy import and_, or_
from sqlalchemy.orm import Session, make_transient

from platypush.context import get_bus
from platypush.message.event.entities import EntityUpdateEvent

from ._base import Entity


class EntitiesEngine(Thread):
    # Processing queue timeout in seconds
    _queue_timeout = 5.0

    def __init__(self):
        obj_name = self.__class__.__name__
        super().__init__(name=obj_name)
        self.logger = getLogger(name=obj_name)
        self._queue = Queue()
        self._should_stop = Event()
        self._entities_cache_lock = RLock()
        self._entities_cache = {
            'by_id': {},
            'by_external_id_and_plugin': {},
            'by_name_and_plugin': {},
        }

    def _get_db(self):
        from platypush.context import get_plugin

        db = get_plugin('db')
        assert db
        return db

    def _get_cached_entity(self, entity: Entity) -> Optional[dict]:
        if entity.id:
            e = self._entities_cache['by_id'].get(entity.id)
            if e:
                return e

        if entity.external_id and entity.plugin:
            e = self._entities_cache['by_external_id_and_plugin'].get(
                (entity.external_id, entity.plugin)
            )
            if e:
                return e

        if entity.name and entity.plugin:
            e = self._entities_cache['by_name_and_plugin'].get(
                (entity.name, entity.plugin)
            )
            if e:
                return e

    @staticmethod
    def _cache_repr(entity: Entity) -> dict:
        repr_ = entity.to_json()
        repr_.pop('data', None)
        repr_.pop('meta', None)
        repr_.pop('created_at', None)
        repr_.pop('updated_at', None)
        return repr_

    def _cache_entities(self, *entities: Entity, overwrite_cache=False):
        for entity in entities:
            e = self._cache_repr(entity)
            if not overwrite_cache:
                existing_entity = self._entities_cache['by_id'].get(entity.id)
                if existing_entity:
                    for k, v in existing_entity.items():
                        if e.get(k) is None:
                            e[k] = v

            if entity.id:
                self._entities_cache['by_id'][entity.id] = e
            if entity.external_id and entity.plugin:
                self._entities_cache['by_external_id_and_plugin'][
                    (entity.external_id, entity.plugin)
                ] = e
            if entity.name and entity.plugin:
                self._entities_cache['by_name_and_plugin'][
                    (entity.name, entity.plugin)
                ] = e

    def _entity_has_changes(self, new_entity: Entity) -> bool:
        with self._entities_cache_lock:
            cached_entity = self._get_cached_entity(new_entity)
            if cached_entity:
                if cached_entity.get('id'):
                    new_entity.id = cached_entity['id']
                if cached_entity == self._cache_repr(new_entity):
                    return False

            if new_entity.id:
                self._cache_entities(new_entity)

            return True

    def _init_entities_cache(self):
        with self._get_db().get_session() as session:
            entities = session.query(Entity).all()
            for entity in entities:
                make_transient(entity)

        with self._entities_cache_lock:
            self._cache_entities(*entities, overwrite_cache=True)

        self.logger.info('Entities cache initialized')

    def _process_event(self, entity: Entity):
        if self._entity_has_changes(entity) and entity.id:
            get_bus().post(EntityUpdateEvent(entity=entity))

    def post(self, *entities: Entity):
        for entity in entities:
            self._queue.put(entity)

    @property
    def should_stop(self) -> bool:
        return self._should_stop.is_set()

    def stop(self):
        self._should_stop.set()

    def run(self):
        super().run()
        self.logger.info('Started entities engine')
        self._init_entities_cache()

        while not self.should_stop:
            msgs = []
            last_poll_time = time()

            while not self.should_stop and (
                time() - last_poll_time < self._queue_timeout
            ):
                try:
                    msg = self._queue.get(block=True, timeout=0.5)
                except Empty:
                    continue

                if msg:
                    msgs.append(msg)
                    # Trigger an EntityUpdateEvent if there has
                    # been a change on the entity state
                    self._process_event(msg)

            if not msgs or self.should_stop:
                continue

            try:
                self._process_entities(*msgs)
            except Exception as e:
                self.logger.error('Error while processing entity updates: ' + str(e))
                self.logger.exception(e)

        self.logger.info('Stopped entities engine')

    def _get_if_exist(
        self, session: Session, entities: Iterable[Entity]
    ) -> Iterable[Entity]:
        existing_entities = {
            (entity.external_id or entity.name, entity.plugin): entity
            for entity in session.query(Entity)
            .filter(
                or_(
                    *[
                        and_(
                            Entity.external_id == entity.external_id,
                            Entity.plugin == entity.plugin,
                        )
                        if entity.external_id is not None
                        else and_(
                            Entity.name == entity.name, Entity.plugin == entity.plugin
                        )
                        for entity in entities
                    ]
                )
            )
            .all()
        }

        return [
            existing_entities.get(
                (entity.external_id or entity.name, entity.plugin), None
            )
            for entity in entities
        ]

    def _merge_entities(
        self, entities: List[Entity], existing_entities: List[Entity]
    ) -> List[Entity]:
        def merge(entity: Entity, existing_entity: Entity) -> Entity:
            columns = [col.key for col in entity.columns]
            for col in columns:
                if col not in ('id', 'created_at'):
                    setattr(existing_entity, col, getattr(entity, col))

            return existing_entity

        new_entities = []
        entities_map = {}

        # Get the latest update for each ((id|name), plugin) record
        for e in entities:
            key = ((e.external_id or e.name), e.plugin)
            entities_map[key] = e

        # Retrieve existing records and merge them
        for i, entity in enumerate(entities):
            existing_entity = existing_entities[i]
            if existing_entity:
                entity = merge(entity, existing_entity)

            new_entities.append(entity)

        return new_entities

    def _process_entities(self, *entities: Entity):
        with self._get_db().get_session() as session:
            existing_entities = self._get_if_exist(session, entities)
            entities = self._merge_entities(entities, existing_entities)  # type: ignore
            session.add_all(entities)
            session.commit()

        with self._entities_cache_lock:
            for entity in entities:
                self._cache_entities(entity, overwrite_cache=True)