import logging

from peewee import SQL, IntegrityError
from cachetools import lru_cache
from collections import namedtuple

from data.model import (config, db_transaction, InvalidImageException, TorrentInfoDoesNotExist,
                        DataModelException, _basequery)
from data.database import (ImageStorage, Image, ImageStoragePlacement, ImageStorageLocation,
                           ImageStorageTransformation, ImageStorageSignature,
                           ImageStorageSignatureKind, Repository, Namespace, TorrentInfo)


logger = logging.getLogger(__name__)

_Location = namedtuple('location', ['id', 'name'])

@lru_cache(maxsize=1)
def get_image_locations():
  location_map = {}
  for location in ImageStorageLocation.select():
    location_tuple = _Location(location.id, location.name)
    location_map[location.id] = location_tuple
    location_map[location.name] = location_tuple

  return location_map


def get_image_location_for_name(location_name):
  locations = get_image_locations()
  return locations[location_name]


def get_image_location_for_id(location_id):
  locations = get_image_locations()
  return locations[location_id]


def add_storage_placement(storage, location_name):
  """ Adds a storage placement for the given storage at the given location. """
  location = get_image_location_for_name(location_name)
  try:
    ImageStoragePlacement.create(location=location.id, storage=storage)
  except IntegrityError:
    # Placement already exists. Nothing to do.
    pass


def _orphaned_storage_query(candidate_ids):
  """ Returns the subset of the candidate ImageStorage IDs representing storages that are no
      longer referenced by images.
  """
  # Issue a union query to find all storages that are still referenced by a candidate storage. This
  # is much faster than the group_by and having call we used to use here.
  nonorphaned_queries = []
  for counter, candidate_id in enumerate(candidate_ids):
    query_alias = 'q{0}'.format(counter)
    storage_subq = (ImageStorage
                    .select(ImageStorage.id)
                    .join(Image)
                    .where(ImageStorage.id == candidate_id)
                    .limit(1)
                    .alias(query_alias))

    nonorphaned_queries.append(ImageStorage
                               .select(SQL('*'))
                               .from_(storage_subq))

  # Build the set of storages that are missing. These storages are orphaned.
  nonorphaned_storage_ids = {storage.id for storage in _reduce_as_tree(nonorphaned_queries)}
  return list(candidate_ids - nonorphaned_storage_ids)


def garbage_collect_storage(storage_id_whitelist):
  """ Performs GC on a possible subset of the storage's with the IDs found in the
      whitelist. The storages in the whitelist will be checked, and any orphaned will
      be removed, with those IDs being returned.
  """
  if len(storage_id_whitelist) == 0:
    return []

  def placements_query_to_paths_set(placements_query):
    return {(get_image_location_for_id(placement.location_id).name,
             get_layer_path(placement.storage))
            for placement in placements_query}

  # Note: Both of these deletes must occur in the same transaction (unfortunately) because a
  # storage without any placement is invalid, and a placement cannot exist without a storage.
  # TODO(jake): We might want to allow for null storages on placements, which would allow us to
  # delete the storages, then delete the placements in a non-transaction.
  logger.debug('Garbage collecting storages from candidates: %s', storage_id_whitelist)
  with db_transaction():
    orphaned_storage_ids = _orphaned_storage_query(storage_id_whitelist)
    if len(orphaned_storage_ids) == 0:
      # Nothing to GC.
      return []

    placements_to_remove = list(ImageStoragePlacement
                                .select()
                                .join(ImageStorage)
                                .where(ImageStorage.id << orphaned_storage_ids))

    paths_to_remove = placements_query_to_paths_set(placements_to_remove)

    # Remove the placements for orphaned storages
    if len(placements_to_remove) > 0:
      placement_ids_to_remove = [placement.id for placement in placements_to_remove]
      placements_removed = (ImageStoragePlacement
                            .delete()
                            .where(ImageStoragePlacement.id << placement_ids_to_remove)
                            .execute())
      logger.debug('Removed %s image storage placements', placements_removed)

    # Remove all orphaned storages
    torrents_removed = (TorrentInfo
                        .delete()
                        .where(TorrentInfo.storage << orphaned_storage_ids)
                        .execute())
    logger.debug('Removed %s torrent info records', torrents_removed)

    signatures_removed = (ImageStorageSignature
                          .delete()
                          .where(ImageStorageSignature.storage << orphaned_storage_ids)
                          .execute())
    logger.debug('Removed %s image storage signatures', signatures_removed)

    storages_removed = (ImageStorage
                        .delete()
                        .where(ImageStorage.id << orphaned_storage_ids)
                        .execute())
    logger.debug('Removed %s image storage records', storages_removed)

  # We are going to make the conscious decision to not delete image storage blobs inside
  # transactions.
  # This may end up producing garbage in s3, trading off for higher availability in the database.
  for location_name, image_path in paths_to_remove:
    logger.debug('Removing %s from %s', image_path, location_name)
    config.store.remove({location_name}, image_path)

  return orphaned_storage_ids


def create_v1_storage(location_name):
  storage = ImageStorage.create(cas_path=False)
  location = get_image_location_for_name(location_name)
  ImageStoragePlacement.create(location=location.id, storage=storage)
  storage.locations = {location_name}
  return storage


def find_or_create_storage_signature(storage, signature_kind_name):
  found = lookup_storage_signature(storage, signature_kind_name)
  if found is None:
    kind = ImageStorageSignatureKind.get(name=signature_kind_name)
    found = ImageStorageSignature.create(storage=storage, kind=kind)

  return found


def lookup_storage_signature(storage, signature_kind_name):
  kind = ImageStorageSignatureKind.get(name=signature_kind_name)
  try:
    return (ImageStorageSignature
            .select()
            .where(ImageStorageSignature.storage == storage, ImageStorageSignature.kind == kind)
            .get())
  except ImageStorageSignature.DoesNotExist:
    return None


def _get_storage(query_modifier):
  query = (ImageStoragePlacement
           .select(ImageStoragePlacement, ImageStorage)
           .switch(ImageStoragePlacement)
           .join(ImageStorage))

  placements = list(query_modifier(query))

  if not placements:
    raise InvalidImageException()

  found = placements[0].storage
  found.locations = {get_image_location_for_id(placement.location_id).name
                     for placement in placements}
  return found


def get_storage_by_subquery(subquery):
  """ Returns the storage (and its locations) for the storage id returned by the subquery. The
      subquery must return at most 1 result, which is a storage ID. """
  def filter_by_subquery(query):
    return query.where(ImageStorage.id == subquery)

  return _get_storage(filter_by_subquery)


def get_storage_by_uuid(storage_uuid):
  def filter_to_uuid(query):
    return query.where(ImageStorage.uuid == storage_uuid)

  try:
    return _get_storage(filter_to_uuid)
  except InvalidImageException:
    raise InvalidImageException('No storage found with uuid: %s', storage_uuid)


def get_layer_path(storage_record):
  """ Returns the path in the storage engine to the layer data referenced by the storage row. """
  store = config.store
  if not storage_record.cas_path:
    logger.debug('Serving layer from legacy v1 path')
    return store.v1_image_layer_path(storage_record.uuid)

  return store.blob_path(storage_record.content_checksum)


def lookup_repo_storages_by_content_checksum(repo, checksums):
  """ Looks up repository storages (without placements) matching the given repository
      and checksum. """
  # There may be many duplicates of the checksums, so for performance reasons we are going
  # to use a union to select just one storage with each checksum
  queries = []

  for counter, checksum in enumerate(set(checksums)):
    query_alias = 'q{0}'.format(counter)
    candidate_subq = (ImageStorage
                      .select(ImageStorage.id, ImageStorage.content_checksum,
                              ImageStorage.image_size, ImageStorage.uuid)
                      .join(Image)
                      .where(Image.repository == repo, ImageStorage.content_checksum == checksum)
                      .limit(1)
                      .alias(query_alias))
    queries.append(ImageStorage
                   .select(SQL('*'))
                   .from_(candidate_subq))

  return _reduce_as_tree(queries)


def _reduce_as_tree(queries_to_reduce):
  """ This method will split a list of queries into halves recursively until we reach individual
      queries, at which point it will start unioning the queries, or the already unioned subqueries.
      This works around a bug in peewee SQL generation where reducing linearly generates a chain
      of queries that will exceed the recursion depth limit when it has around 80 queries.
      """
  mid = len(queries_to_reduce)/2
  left = queries_to_reduce[:mid]
  right = queries_to_reduce[mid:]

  to_reduce_right = right[0]
  if len(right) > 1:
    to_reduce_right = _reduce_as_tree(right)

  if len(left) > 1:
    to_reduce_left = _reduce_as_tree(left)
  elif len(left) == 1:
    to_reduce_left = left[0]
  else:
    return to_reduce_right

  return to_reduce_left.union_all(to_reduce_right)


def set_image_storage_metadata(docker_image_id, namespace_name, repository_name, image_size,
                               uncompressed_size):
  """ Sets metadata that is specific to the binary storage of the data, irrespective of how it
      is used in the layer tree.
  """
  if image_size is None:
    raise DataModelException('Empty image size field')

  try:
    image = (Image
             .select(Image, ImageStorage)
             .join(Repository)
             .join(Namespace, on=(Repository.namespace_user == Namespace.id))
             .switch(Image)
             .join(ImageStorage)
             .where(Repository.name == repository_name, Namespace.username == namespace_name,
                    Image.docker_image_id == docker_image_id)
             .get())
  except ImageStorage.DoesNotExist:
    raise InvalidImageException('No image with specified id and repository')

  # We MUST do this here, it can't be done in the corresponding image call because the storage
  # has not yet been pushed
  image.aggregate_size = _basequery.calculate_image_aggregate_size(image.ancestors, image_size,
                                                                   image.parent)
  image.save()

  image.storage.image_size = image_size
  image.storage.uncompressed_size = uncompressed_size
  image.storage.save()
  return image.storage


def get_storage_locations(uuid):
  query = (ImageStoragePlacement
           .select()
           .join(ImageStorage)
           .where(ImageStorage.uuid == uuid))

  return [get_image_location_for_id(placement.location_id).name for placement in query]


def save_torrent_info(storage_object, piece_length, pieces):
  try:
    TorrentInfo.create(storage=storage_object, piece_length=piece_length, pieces=pieces)
  except IntegrityError:
    # TorrentInfo already exists for this storage.
    pass

def get_torrent_info(blob):
  try:
    return (TorrentInfo
            .select()
            .where(TorrentInfo.storage == blob)
            .get())
  except TorrentInfo.DoesNotExist:
    raise TorrentInfoDoesNotExist